News from Rohde & Schwarz · 2019-10-13 · 2 News from Rohde & Schwarz Number 155 (1997/III)...

News from Rohde & Schwarz

DECT signalling testsindispensable in development and service

Standard-conforming fading simulationin mobile-radio measurements

Operational and test equipmentfor digital audio broadcasting

1551997/III

DECTDECT

2 News from Rohde & Schwarz Number 155 (1997/III)

Number 155 1997/III Volume 37

DECTDECTDECT Signalling Test Unit PTW15 met with greatinterest at CeBIT 97. This unit launched by Rohde& Schwarz is a signalling tester of unrivalledprice/performance ratio for development ofDECT equipment as well as for installation andservicing of DECT networks. PTW15 impressesnot only with its price, but also with its compactsize, multitude of functions and convenient oper-ation in the lab or in mobile use (page 4).

Holger Jauch; Peter Riedel DECT Signalling Test Unit PTW15Support in installation and maintenance of DECT networks . . . . . . . . . . . . . . . . . . . .4

Werner Mittermaier Digital Radiocommunication Testers CMD65 and CMD80Multiband and multimode testers for mobile-radio telephones. . . . . . . . . . . . . . . . . .6

Franz Lüttich Signal Generator SMIQ + SMIQ-B14Fading simulator and signal generator in one unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Peter H. Frank DAB componentsDigital audio broadcasting – all from a single source . . . . . . . . . . . . . . . . . . . . . . . .12

Dr Klaus Rieskamp Morse Radio Decoder GM094New dimensions in Morse decoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Franz Demmel; Ulrich Unselt Single-station location with HF direction finders of DDF01x family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Günter Wicker; Erich Schippan International ALE (automatic link establishment) standard for HF Transceiver XK2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Sigmar Grunwald Analysis of compressed MPEG2 data stream for digital TV . . . . . . . . . . . . . . . . . .22

Michael Lehmann; DAB monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24Christian Christiansen

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Application notes

Günther Klenner ESMC-RAMON – entry into computer-aided radiomonitoring. . . . . . . . . . . . . . . .26

Software

ESMC-RAMON – a versatile operating softwarefor VHF-UHF Radiomonitoring Receiver ESMC –takes the chore out of tasks connected with recep-tion of emissions, display of frequency spectraand monitoring of frequencies (page 26).

3News from Rohde & Schwarz Number 155 (1997/III)

Imprint

Refresher topic

Peter Hatzold Digital modulation and mobile radio (VI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Panorama

Frank Körber; Roland Steffen Digital Radiocommunication Test Set CRTC02 growing with GSM standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Dr Jürgen Lauterjung DVB-T, the new terrestrial TV standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

Gottfried Holzmann New measurement functions in Digital Radio Tester CTS55 . . . . . . . . . . . . . . . . . .33

Michael Borgmann T&M technology from Rohde & Schwarz for EMC mobile of TÜV Rheinland Japan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Helmar Scherpe New from Cologne: telescopic masts with universal control unit . . . . . . . . . . . . . .36

Regular features

Dr Olaf Ostwald Test hint: Fast S-parameter measurements on four-port devices . . . . . . . . . . . . . . .16

Otmar Wanierke Patent: Power measurement in mobile-radio channel . . . . . . . . . . . . . . . . . . . . . . . . .27

Information in print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Newsgrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Press comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Dr Günter Greiner Final article: Fast and secure data transmission on shortwave – result of intensive research. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

Digital Radiocommunication Testers CMD can befound in every mobile-phone production line.And the new models CMD65 and CMD80 makesure that this continues to be true in the future aswell. Their multimode and multiband capabilitiestake into account the breath-taking speed of de-velopment on the mobile radio market (page 6).

Supplement

Index of publications 1995/96 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Published by ROHDE & SCHWARZ GmbH & Co. KG Mühldorfstraße 15 D -81671 MunichTelephone (0 89) 41 29-0 · international (+49 89) 41 29-0 · Editors: H. Wegener and G. Sönnichsen(German) · English translation: Dept. 5CL4 · Photos: S. Huber · Artwork: N. Hofmann · Circulation100 000 four times a year · ISSN 0028-9108 · Supply free of charge · State company or position ·Printed in the Federal Republic of Germany by peschke druck, Munich · Reproduction of extracts permitted if source is stated and copy sent to R & S Munich


The powerful DECT Protocol TesterTS1220 [1] from Rohde & Schwarz is now seconded by the extremely favourably priced DECT Signalling TestUnit PTW15 (FIG 1). This unit can beused wherever the full functionality of

TS1220 is not required: in installationand maintenance of DECT WLL andPABX systems, in DECT audio tests toTBR10 and in the field of DECT soft-ware development.

In the installation of DECT WLL net-works [2] or test networks, PTW15 produces data about the occupancy of the DECT frequency band includingrelevant statistics to support antennapositioning and assessment of various

parameters of the DECT equipment (egdynamic channel selection algorithm).Since most tests are carried out on sitedirectly in the network, the unit was designed for mobile use through itscompact size and optional batterypowering. For DECT audio tests toTBR10, PTW15 can be used as a DECTsignalling unit that supports call setup toportable and fixed DECT radio termina-tions both in normal operation (genericaccess profile GAP to ETS 300 444)and in test standby mode by providingvoice data at an analog and a digitalinterface. The required DECT referenceimplementations can also be used forDECT software development.

The DECT Signalling Test Unit comeswith channel-occupancy software cov-ering all DECT activities at the air inter-face as well as with a monitor mode for recording and analyzing selectedDECT activities between user-definedfixed radio terminations (FT) and the associated portable terminations (PT).

System architecture

The unit is based on a 133 MHz AMDK5 processor with 32 Mbyte DRAM, an8.4-inch colour display and furthercomputer peripherals. The DECT-specificpart is accommodated on a separatemodule, which in addition to the RF section contains the DECT basebandprocessor and the ADPCM coder/de-coder as well as an additional chip de-veloped by Rohde & Schwarz. It is thischip that enables channel-occupancymeasurement and operation as a DECTmonitor. The entire module is controlledby its own microprocessor.

In addition to two RF connectors, whichalso allow antenna diversity if PTW15is operated as a fixed DECT termi-nation, the following data interfaces(eg for audio tests) are available forconnection to external equipment:• analog input/output (may also be

used to connect an external tele-phone receiver when simulating aportable termination),

• 64 kbit/s PCM input/output (V.11).

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DECT Signalling Test Unit PTW15

Support in installation andmaintenance of DECT networksDECT Signalling Test Unit PTW15 provides all test functions required for the installation and maintenance of DECT WLL networks and DECT PABX systems atan unrivalled price. Compact design, front-panel keypad and optional built-inbattery modules make this unit suitable for use in the laboratory as well as formobile applications.

FIG 1 DECT Signalling Test Unit PTW15, compact signalling tester for use in installation ofDigital Enhanced Cordless Telecommunicationsnetworks and in software development

Photo 42 891


The unit can be AC- or DC-poweredfrom built-in or external batteries.

The implemented DECT protocol stackis mapped on the hardware as follows:the time-critical physical layer (PHL) andmedium access control layer (MAC) are implemented in the DECT-specificmodule. The data received betweenPHL and MAC at the point of obser-vation are imaged in the processor kernel and displayed. The data linkcontrol layer and network layer, usedfor reference implementations, run asindependent processes in the processorkernel. All layers communicate viapoints of control and observation. Theexchanged data are displayed in win-dows on the graphic user interface.

The processor kernel uses the realtimeUnix operating system LynxOS, whichensures smooth running of the variousprocesses (DECT layers, display func-tions, user interface, etc). LynxOS is fully compatible with System V and Posix. The graphic user interface allowsconvenient operation of the unit via the front-panel keypad supplied as standard or via the external keyboardplus mouse included in the comfortpackage. All test functions of PTW15can be activated by hotkey or a mouseclick on the matching symbol of the display (FIG 1).

Measurement examples

Channel-occupancy measurement pro-vides a quick and comprehensive over-view of all signals received in the DECTfrequency band (FIG 2). In addition tothe radio signal strength levels for eachDECT slot, other information such asidentity, signal drift (referred to a user-defined fixed DECT termination) and bit position (referred to the same fixedtermination) is displayed. All results canbe stored for subsequent evaluation.

In monitor mode the unit synchronizesto a user-defined fixed DECT termi-nation and records all data packets exchanged with portable terminations

via the air interface, without activelyparticipating in signalling. From the collected data, failed or successfulhandover and call-setup attempts or thenumber of actually occupied channelscan be determined for instance. Alldata are available both as visualizationof the points of (control and) observa-tion and in a message-sequence chartor as an ASCII file.

Simulation of fixed and portable ter-minations is implemented in line withETS 300 444 (GAP) and provides thefunctionality of a fixed or portableDECT termination. The user can set allidentities. Each activity after startingsimulation is stored in an easy-to-readtrace file. The user can also take thepoints of (control and) observation andthe message-sequence chart for analy-sis and troubleshooting.

Holger Jauch; Peter Riedel

REFERENCES

[1] Gloger, M.; Riedel, P.: DECT Protocol TesterTS1220 – Type approval measurements onDECT fixed parts (FP) and portable parts (PP)to TBR22. News from Rohde & Schwarz(1995) No. 148, pp 9–11

[2] Gloger, M.; Riedel, P.: Optimizing wirelesslocal loop systems. News from Rohde &Schwarz (1996) No. 152, p 35

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Condensed data of DECT Signalling Test Unit PTW15Frequency range 1881.792 to 1897.344 MHz

Transmitter power 22 dBm ±2 dBm (typ.)

Modulation 288 kHz

Carrier frequency DECT carrier ±30 kHz

Receiver sensitivity –89 dBm (BER <0.001)

CPU AMD K5, 133 MHz

RAM 32 Mbytes

Interfaces 2 x RS-232-C, 1 x Centronics, 1 x external keyboard

Weight 8 kg

Reader service card 155/01

FIG 2Channel-occupancymeasurement providing all essen-tial information at a glance


Digital RadiocommunicationTester CMD65

CMD65 (FIG 1) is a specialist for thefollowing network standards and theassociated frequency bands:• GSM900: Global System for Mobile

Communications (900 MHz band),used in Europe, Australia, etc,

• R-GSM: Railway GSM, ie use ofGSM in trains (channels below GSMfrequency band),

• PCN (DCS1800): Personal Commu-nications Network in Germany andEngland in 1800 MHz band (othercountries to follow),

• PCS/DCS1900: Personal Commu-nications Service in 1900 MHzband in North America (GSMNorth America),

• DECT Europe: Digital EnhancedCordless Telecommunications (chan-nels between 1880 and 1900 MHz),

• DECT Latin America: digital cordlesstelephones in frequency range aboveEuropean DECT band.

A modern digital radiocommunicationtester is expected to handle several network standards all in one unit, sinceservice centers for instance in Germanymust be able to test GSM and PCN mo-bile phones as well as cordless phonesto DECT standard. To save costs andspace, it is expedient to use a singletester for all the different kinds of DUTs. On modern production lines, not only GSM mobile phones are manufactured, but usually also mobilephones of the related PCN and PCSstandards (GSM with several channelsand in a different frequency band). To compensate fluctuating sales figures for different networks, it is anadvantage if the manufacturer can use testers on his production lines that are able to measure any type of mobile phone.

Some manufacturers are working atpresent on multimode mobile phones,a combination of GSM mobile andcordless phone. Such a GSM/DECTmultimode mobile phone can be usedat home to make favourably priced

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Digital Radiocommunication Testers CMD65 and CMD80

Multiband and multimode testersfor mobile-radio telephonesFuture multimode mobile phones as well as service centers’ and manufacturers’demands for cost-effective testing of mobile phones to different network stan-dards call for radio testers supporting several standards all in one unit. Rohde &Schwarz is ready with the solution: Digital Radiocommunication Tester CMD65measures GSM, PCN, PCS as well as DECT mobile phones, and Digital Radio-communication Tester CMD80 supports CDMA in several frequency bands as wellas analog AMPS.

FIG 1 Digital Radiocommunication Tester CMD65 for GSM, PCN, PCS and DECT mobile phones Photo 42 875/2


calls via the fixed DECT terminationconnected to the public switched tele-phone network, and beyond DECTcoverage via the GSM network. A radiocommunication tester supportingboth standards is ideally suited in termsof flexibility, economy, space andspeed for checking and measuring the performance features of suchphones in production.

PCN (DCS1800) mobile-radio net-works are used in Germany and England within Europe so far. Othercountries are to follow, but PCN net-works will not be available through-out Europe. To ensure European-widecoverage with PCN mobile phones, itis intended – in countries exclusivelysupporting GSM900 networks – to introduce roaming in the GSM900network of a foreign operator. Thiskind of phone is called a dual-bandmobile phone since it combinesGSM900 and DCS1800 (same net-work technology in different frequencybands) in a single unit. For the pro-duction of such dual-band mobiles aGSM radiocommunication tester willbe required that also supports theDCS1800 band.

All the above applications fall withinthe domain of CMD65. It provides the following essential features for use in production: all measurementsare performed exactly in line with net-work specifications. Signalling andmeasurements as well as remote control of the tester are optimized

for high speed. Following switchoverto a different network standard, CMD is ready to measure again in less than a second. This is particularlyimportant for use of the tester in theproduction of multimode and multi-band mobile phones to avoid loss ofvaluable process time.

In addition to performing RF measure-ments to different mobile-phone stan-dards, CMD65 also checks the audiocharacteristics of mobiles for all select-ed networks and operating states. Forthis purpose CMD65 comes with an AFgenerator, AF voltmeter with counter,distortion meter and multitone audioanalyzer. Up to 14 audio tones can begenerated and selectively measured ata time. Frequency response for instancecan be measured within two seconds.CMD is able to check the more de-manding audio quality of cordless tele-phones without any further measuringequipment.

Digital Radiocommunication TesterCMD65 basically supports GSM, PCNand DECT standards. R-GSM, PCS andDECT Latin America are optionallyavailable. All GSM and DECT modelsof the CMD family [1; 2] can be enhanced for further network stan-dards. The possibility of subsequent upgrading ensures maximum versatilityand future-proofness as well as low investment for units already available.TABLE 1 gives an overview of the various CMD models and network standards supported by basic equip-

ment or options. Models CMD50/53are intended for use in qualified servicecenters, models CMD52/55/60/65for production lines.

Digital RadiocommunicationTester CMD80CMD80 (FIG 2) serves for testing mo-bile phones operating according to theUS mobile-radio system CDMA (codedivision multiple access). Mobiles of theanalog AMPS standard (AdvancedMobile Phone System) can be testedoptionally [3]. These mobile-radiosystems evolved in the US in recentyears as follows. In the North-Americancountries cellular phones were first operated in the analog AMPS network.Although this network is widespread, ithas reached the limits of its subscribercapacity. The successor system CDMAwith higher spectral efficiency is usedtoday in the 800 MHz band to supple-ment and relieve the analog AMPS net-work. CDMA mobile phones for the800 MHz band therefore also containanalog AMPS signalling, ie the mobilesoperate in dual CDMA and AMPSmode. Even handover between CDMAand AMPS has been defined, iechange of network during a setup call.American operators have also installednetworks to CDMA standard in the1900 MHz band: PCS mobile phonesfor CDMA. CDMA mobiles supportingboth frequency bands (800 and 1900 MHz) are referred to as dual-band CDMA mobiles. Apart from theUS, South Korea also uses the CDMAstandard, where CDMA mobiles oper-ate in the 1700 MHz band.

CMD80 supports all three CDMA fre-quency bands mentioned as well as analog AMPS in one unit. Its RF conceptprovides a continuous frequency rangefrom 800 to 2200 MHz. Transmit andreceive frequencies are independent ofone another. Signalling and measure-ment use ultramodern digital signal processing.

All these features make CMD80 idealfor use in service shops in the US.

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GSM R-GSM PCN GSM North America DECT DECT(Railway) (DCS1800) PCS/DCS1900 Europe Latin America

CMD50

CMD53

CMD52

CMD55

CMD60

CMD65

TABLE 1: Overview of CMD models and network standards supported ( standard, optional)


As an all-in-one unit it allows testing of CDMA800 and CDMA1900 mo-biles, mobiles of different network operators and multiband mobiles alike. Plus it can be used to check theanalog AMPS functions of a dual-modemobile.

CMD80 features the following benefitsfor use in modern production:• Large mobile-phone manufacturers

produce CDMA mobiles for all fre-quency bands. A multiband testerprovides the necessary versatility incase of fluctuating sales figures forsingle-band mobiles.

• A radiocommunication tester cov-ering both frequency bands pro-

vides the most economical solutionfor the production of dual-bandmobiles.

• A radiocommunication tester sup-porting CDMA and AMPS is themost cost-effective, compact and, interms of measurement, fastest solu-tion for the production of dual-modephones.

• Only a multimode tester allows simple testing of CDMA/AMPShandover.

TABLE 2 shows the network standardsand frequency bands supported byDigital Radiocommunication TesterCMD80.

Werner Mittermaier

REFERENCES

[1] Mittermaier, W.: Digital Radiocommunica-tion Tester CMD55 with new measurementfunctions. News from Rohde & Schwarz(1996) No. 152, pp 48–49

[2] Maucksch, T.: Digital RadiocommunicationTester CMD60 – A favourably priced com-pact test set for series production of DECTmobiles. News from Rohde & Schwarz(1995) No. 149, pp 13 –15

[3] Maucksch, T.: CMD80: measurements forCDMA and AMPS mobiles. News from Rohde & Schwarz (1997) No. 154, pp 22–23

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Network standard Specification Country/name Frequency band

CDMA IS95 US Cellular 800 MHz

CDMA J-STD-008 US PCS 1900 MHz(Upbanded IS95)

CDMA J-STD-008 Korea PCS 1700 MHz

AMPS IS55 US Cellular 800 MHz

TABLE 2:Network standards

and frequency bandscovered by Digital

RadiocommunicationTester CMD80

Key features of Digital Radiocommunication Testers CMD65 and CMD80

Measurements to relevant standards

Large graphic LCD

Ease of operation

Extremely fast remote control

DSP technology

Full-featured configuration

Compact design


FIG 2 Digital Radiocommunication TesterCMD80 incorporating measurement functionalityfor both digital standard CDMA (800, 1700 and1900 MHz) and analog AMPS

Photo 42 816/3


Signal Generator SMIQ (FIG 1) is a universal RF signal source for use in research, development and productionin the field of digital mobile radio [1].The fading-simulator option makesSMIQ even more attractive.

Degradation during transmissionPropagation conditions between a sta-tionary transmitter and a mobile re-ceiver undergo constant changes. Thecharacteristics of a radio channel varywith time and frequency, which leads totime- and frequency-selective fading.The receive signal is mainly affected by multipath fading, local scattering,Doppler shift and slow signal varia-tions.

Multipath fading. The emitted electro-magnetic wave is reflected, diffractedand attenuated by obstacles (buildings,terrain, vegetation, clouds) in manyways, so the signal arriving at the receiver is the sum of several single signals. Since these signals travel ondifferent propagation paths, they arrivewith different amplitude and delay andconsequently with different phase,which may lead to cancellation of signals. The mobile-radio channel thuscontains several paths (M paths, M inmodels up to 12), with great differencesin path length. This results in delay

differences that are significant referredto the symbol period Ts of digital trans-missions (τ ≥ Ts, τ = delay difference of two signals).

One effect of multipath reception,which also occurs in the case of stationary receivers, is narrowband,frequency-selective fading showing

notches in the bandwidth of the radiochannel. The spacing of the notches is 1/τ (FIG 2).

Another effect of multipath reception is the delay spread of the received signal, consisting of several compo-nents that arrive at different times. Withdelay differences exceeding one sym-bol period Ts, the signal components of the symbol present at the receiver in-put may be impaired by components of previously sent symbols. This effect is called intersymbol interference. In the GSM system delay differences offour times the symbol period are ex-pected (FIG 3).

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Signal Generator SMIQ + SMIQ-B14

Fading simulator and signal generator in one unitSignal transmission between a transmitter and a receiver, in particular a mobilereceiver, is strongly affected by the characteristics of the radio channel. So test signals reflecting the real conditions of mobile-radio reception are used in the development and type approval of receivers. Fading simulators are employed forsuch tasks. Up to now three instruments were required to generate real-life testsignals: signal generator, local oscillator and fading simulator. But when SignalGenerator SMIQ and its fading-simulator option are used, the required test signals can be produced in a single unit.

FIG 2 Simulation of multipath propagation:SMIQ set for 2-path simulation, delay differenceof active paths being 5 µs. Frequency-dependentnotches spaced 200 kHz apart are displayed.

FIG 1 Signal Generator SMIQ with optionalFading Simulator SMIQ-B14 produces real-lifesignals for testing mobile-radio and sound-broad-cast receivers of practically all present-day andfuture communication systems. Photo 42 890


Local scattering. Because of diffuse re-flection of the signal in the immediatevicinity of the receiver, a large numberof waves are produced. Thus a clusterof signals for each path of the multipathpropagation scenario will arrive at thereceiver. The delay differences of thesesignals are irrelevant with respect to thesymbol period (τ << Ts), but significantwith respect to the carrier-frequency period. As the receiver moves, the am-plitude and phase of the various echoeschange arbitrarily causing time-selec-tive fading. This effect, also known asfast fading, produces stochastic signalvariations that give rise to notches at aspacing of about one wavelength andat an interval of a few milliseconds –depending on the speed at which thereceiver is moving (FIG 4).

Doppler shift. As a consequence of receiver movement, shifts of the receivefrequency are produced. Due to echoesarriving from different directions withdifferent Doppler shifts, the frequency

of the receive signal is spread. This iscalled Doppler spread. The Dopplerspectrum is spread around the transmitfrequency within the limits ±fDmax.

Long-term fading, slow fading. Thiseffect covers slow field-strength varia-tions as may be caused by shadowingin hilly terrain. In slow fading, varia-tions of path losses extend over dis-tances that correspond to a multiple ofthe wavelength.

Fading simulator

Mobile-radio systems are designed sothat they are to a large extent not im-paired by the anomalies of the radiochannel. The techniques developed tocompensate for the effects of multipathpropagation comprise error-correctionmethods (FEC), equalization algorithms,data interleaving and frequency-match-ing circuits. To be able to perform reproducible tests of these techniques,fading simulators are used for the realistic simulation of transmission con-ditions in the radio channel [2]. Thescenarios to be simulated and the mathematical-statistical models used tosimulate sporadic fading are laid downin the test specifications of mobile-radiostandards.

Up to now fading simulators were available as separate and rather ex-pensive units. With SMIQ and optionSMIQ-B14, a signal generator and afull-featured fading simulator are inte-

grated in a single unit. Full-featuredmeans that all requirements for fadingsimulation prescribed by the test spec-ifications of various mobile-radio stan-dards, eg GSM, IS54/IS136, IS95,are met. The SMIQ fading simulatorpermits the radio channels of allpresent-day and future communicationsystems to be simulated irrespective ofwhether mobile radio, sound broad-casting, flight telephone services, WLLor WLAN systems are concerned.

The fading option for SMIQ may beused in two configurations. With oneoption fitted, SMIQ is able to simulate6-path fading, whereas with two op-tions 12-path fading can be performed.The different types of fading, ie Ray-leigh, Rice or pure Doppler, may be as-signed individually to any signal path.

In the case of pure Doppler fading atransmission path with only one directsignal between transmitter and movingreceiver is simulated. The signal con-sists of one component shifted by theDoppler frequency.

With Rayleigh fading a radio field issimulated like that produced by localscattering. A great number of waves of different strength arrive evenly distributed from all directions. The received amplitude varies with time.The random variations of a signal as received under real transmission con-ditions are reproduced realistically in away that the probability distribution

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FIG 5 SMIQ output level (left) and spectrum of Rayleigh distribution. Path with Doppler frequency off Dmax = 250 Hz is active for displayed signal.

FIG 4 Typical variations of receive signal levelcaused by time-selective fading

FIG 3 Intersymbol interference in multipath reception caused by delay differences of pathsexceeding symbol period

1 2

1 2

1

Symbols sent

Symbols received

t


function of the magnitude of the re-ceived signal (corresponding to the amplitude produced by the signal gen-erator) follows the Rayleigh distribution.With an unmodulated radio signal the classic Doppler spectrum typical ofRayleigh fading is obtained (FIG 5).

With Rice fading a radio field is simulated where a strong direct signaldominates the great number of scat-tered signals received. The probabilitydistribution function of the magnitude of the received signal is characterizedby the Rice distribution. In the fadingspectrum of an unmodulated signal adiscrete line is superimposed on theclassic Doppler spectrum.

In addition to the described types offading, other parameters may be specified for each path: loss, delay,Doppler frequency or speed, correla-tion of two paths for 2-channel fadingas well as parameters characterizinglong-term fading. Long-term fading, also called log normal fading, has amultiplicative effect on path loss. In thiscase the signals are modelled in addi-tion by a log-normally distributed, slowvariation of the mean field strength.When log normal fading and Rayleighfading appear simultaneously, Suzukifading is the result.

With SMIQ plus fading option the useris able to set almost any fading condi-tions and to call up preprogrammedchannel models by a few keystrokes,eg GSM rural area, typical urban orhilly terrain.

Integration of fading option

The SMIQ fading simulator is integratedinto the I/Q baseband of Signal Gen-erator SMIQ (FIG 6). The input and out-put signals of the simulator are analogI/Q signals. Fading simulation can beperformed with internal digital modula-tion signals (the modulation coder pro-duces I/Q signals from the data signalsat its input) or with externally appliedI/Q signals. One or two fading simula-tors for 6-path or 12-path fading maybe used.

Two Signal Generators SMIQ are re-quired to simulate 2-channel fading asmay be required for instance to test frequency-diversity characteristics. Oneof the two signal generators is fittedwith two fading-simulator options, thesecond one does not require an option.This permits 6-path fading to be simu-lated for each channel.

The superiority of this combination ofsignal generator and fading simulatoris obvious when compared to the pre-viously used solutions. Signal Gen-erator SMIQ with integrated fadingsimulator produces faded signals in the complete frequency range 300 kHzto 3.3 GHz and with any modulation.Previously three instruments were re-quired for the purpose: a signal sourceto generate the RF signal, a fading sim-ulator and a signal generator used as a local oscillator for frequency conver-sion. Apart from the price and size ofthe SMIQ combination, the technicalaspects are also convincing: wide levelrange (–137 to –5 dBm), high level accuracy and spectral purity with re-gard to spuriae, one user interface and one IEC/IEEE-bus interface for signalgenerator and fading simulator.

Franz Lüttich

REFERENCES

[1] Klier, J.: Signal Generator SMIQ – High-quality digital modulation up to 3.3 GHz.News from Rohde & Schwarz (1997) No. 154, pp 4 – 6

[2] Zumkeller, M.; Saalfrank, W.: Fadingkanal-Simulator FADICS. Rundfunktechnische Mit-teilungen 35 (1991) No. 4, pp 153–158

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Condensed data of Fading Simulator SMIQ-B14RF bandwidth (3 dB) 14 MHz

Channels 1 or 2 (with second SMIQ)

Paths per channel 12 (1 channel), 6 (2 channels)

Path loss 0 to 50 dB, resolution 0.1 dB

Path delay 0 to 1600 µs, resolution 50 ns

Doppler shift 0 to 1600 Hz

Fading profile Rayleigh, Rice, pure Doppler, log normal

Preprogammed channel models GSM (GSM05.05/GSM11.10), IS54,IS136 (IS55/IS56), IS95 (IS97/IS98)


FIG 6 Fading simulator in I/Q signal path of Signal Generator SMIQ, one simulator for 6-path fading,two for 12-path fading

OptionalFading

SimulatorSMIQ-B14

Modula-tion coder

Data signal

∑

cos (ωt)

sin (ωt)

I/Q modulator RF converter

0.3 to 3300 MHz

Outputlevel

RF

IExternal

One or twooptions fitted

Q


Besides terrestrial transmitters, a complete DAB system encompasses MUSICAM coders for instance, multi-plexers and COFDM modulators aswell as special measurement facilitiesfor network planning and operationalmonitoring. Rohde & Schwarz can supply the entire spectrum (FIG 1).

Components for signal processing

MUSICAM Codec MUSIC [1] serves forsource coding of audio data and datacompression depending on the set datarate in line with ISO-MPEG-11172-3standard, layer II. Data compression

utilizes psychoacoustic effects relatedto the human ear. Program-associateddata (PAD) can also be added. The resulting output signal (including PAD)is fed to the DAB multiplexer (FIG 2).

DAB Multiplexer DM001 combines allsource-coded audio data as well asnon-audio data to form a multiplex DABsignal, ie the ensemble transport inter-face (ETI). This ETI signal is divided up into two layers – ETI(NI = network independent) and ETI(NA = networkadapted) – and is taken to the trans-mitter in one of various ways (via satel-lite, microwaves or telecommunicationlines). There it functions as a control sig-nal for the COFDM (coded orthogonalfrequency-division multiplex) modula-tors. The multiplexer can be convenient-ly configured on a PC by Windows-based software.

The ETI(NA) output signal of the DABmultiplexer contains additional errorcontrol (Reed-Solomon coding) and enables automatic delay compen-sation. Signal conversion fromETI(NA) to ETI(NI) – the input signal for the COFDM modulators – and dynamic delay compensation up to 1 s are performed by DAB NetworkAdapter DY001 located at the trans-mitter site.

The analog DAB signal is generatedfrom the incoming ETI signal byCOFDM Modulator MCM01 [2] usingthe COFDM method (ETS 300 401).Depending on the transmission modeused, this signal consists of a multi-tude of carriers (eg 1536 carriers for VHF band III or 384 carriers for theL-band), each of which is 4PSK-mod-ulated. The output bandwidth of thisanalog multicarrier signal is 1.5 MHz.Static delay compensation of up to0.5 s can be set for each input di-rectly at the modulator.

DAB transmitters

Applied to the terrestrial TransmittersNA5... (band III) and NL5... (L-band),the analog DAB signal from the

Articles

DAB components

Digital audio broadcasting – all from a single sourceSince 1992 Rohde & Schwarz has taken part in the EUREKA 147 project for thedevelopment, testing and specification of digital audio broadcasting. The com-pany is also a member of several working groups of the German DAB platform.These activities laid the foundations for the development of DAB products at Rohde & Schwarz – and today the company is the only supplier worldwide ableto offer all essential system components from a single source.

FIG 1 Rohde & Schwarz has a complete product range for digital audio broadcasting.Photo 42 897


COFDM modulator undergoes pre-correction in the exciter and is con-verted to the transmission frequency[3]. Several power ranges are avail-able for the various frequency bands:250 W to 1 kW transmitters for the VHF band (174 MHz to 230 MHz) and 100 W to 400 Wtransmitters for the L-band (1452 MHzto 1492 MHz).

The highly linear amplifiers are fullytransistorized and air-cooled. The trans-mitters are also suitable for single-fre-quency networks, in which transmittersuse a common frequency and are synchronized in time.

Broadcasting the DAB signal withoutdisturbance is made possible by usingan RF power bandpass filter followingintermodulation attenuation, depend-ing on the requirements to be met. Thisfilter may be installed either in the trans-mitter rack (L-band) or a separate one.Various filters are available for the different frequency bands.

Additional system components such asGPS receivers for synchronizing DABtransmitters within a single-frequencynetwork, but also DAB transmitting antennas for band III and L-band, are tobe found among the products offeredby Rohde & Schwarz.

DAB measurements

For measuring field strength – the mostimportant parameter in the planning ofa DAB network – Test Receiver ESVB [4]is used. Its bandwidth matches the DABchannel, so it can monitor the entireCOFDM spectrum. Monitoring systems[5] are available to supervise ongoingbroadcasts.

Rohde & Schwarz fully utilized its DABsystem know-how for the first time in theBavarian pilot project, in the course ofwhich a turnkey project comprisingtwelve transmitter stations was imple-mented in less than eight months. Thisnetwork, currently the largest worldwideoperating with a common frequency,has been on the air since autumn 1995.

Peter H. Frank

REFERENCES

[1] Stark, A.; Krawinkel, C.: MUSICAM CodecMUSIC – Compression of audio data withoutany loss in quality. News from Rohde &Schwarz (1994) No. 144, pp 20–23

[2] Heinemann, C.: COFDM ModulatorMCM01 – Channel coding and modulationfor digital audio broadcasting. News from Rohde & Schwarz (1995) No. 148, pp 26 –28

[3] Steen, R.; Steffens, J.: 100/200 W Solid-State DAB Transmitter NL5010/5020 – Terrestrial broadcasting of digital audio in L band. News from Rohde & Schwarz(1996) No. 152, pp 24–26

[4] Weber, D.: New test receiver models forpresent-day and future transmission methods.News from Rohde & Schwarz (1995) No. 148, pp 37– 38

[5] Lehmann, M.; Christiansen, C.: DAB monitor-ing. In this issue, pp 24–25

Articles

DAB system componentsTransmitters

Band III NA5025 (250 W), NA5050 (500 W),NA5100 (1 kW)

L-band NL5010 (100 W), NL5020 (200 W),NL5040 (400 W)

Source coding MUSICAM Codec MUSIC

Multiplexing DAB Multiplexer DM001

Signal conversion DAB Network Adapter DY001

Modulation COFDM Modulator MCM01

Measurements Test Receiver ESVB, monitoring systems


FIG 2 Signal path and equipment used in digital audio broadcasting (options yellow)

MUSIC DM001

Audio dataAudio ETI(NI)/

ETI(NA)converter

DY001 NA5… orNL5…

ETI(NI) ETI(NA) ETI(NI)MCM01

MUSICAMcoder

DABmultiplexer

DABnetwork adapter

COFDMmodulator

DABtransmitter

Band IIIorL-band

GPSreceiver

Transmissionby

telecommunicationline

GPSreceiver

PAD

Non-audio data

Configuration

ETI(NI)Transmission via satellite or

microwave radio link

Morse has a long tradition as a reliableshortwave transmission technique andstill remains an important mediumalong with more advanced techniques.This is primarily due to two factors:

1. Compared to other kinds of signal,Morse signals using robust amplitudemodulation are affected relatively littleby the various types of interferencepresent on the transmission path.

2. Neither transmitter nor receiver areoperated automatically but by trainedoperators. Routine and experience enable them to compensate for inter-ference on the transmission path as wellas for any shortcomings by the personthey are communicating with.

Morse profits from human capability toadapt to very different transmission errors occurring in a message guided

by its context and thus to tolerate errored transmissions. Because Morsecontinues to be widely used, its monitor-ing is an important focus. The nature ofMorse, however, makes monitoring thesignals highly labour-intensive. MorseRadio Decoder GM094 is aimed inparticular at cutting down on personnelespecially for routine tasks and at extending the range of channels covered, even in unmanned operation.It is implemented as a software modulethat can be run on the supplied DSPcard in a PC and it can be connected toalmost any shortwave receiver (FIG 1).

GM094 also achieves excellent decod-ing results in real operating condi-tions, ie • if keying is performed with a vari-

able touch-break ratio and is there-fore not ideal, as is the case withsemiautomatic or manual keying forinstance,

• if keying devices and radio equip-ment are not optimal in terms of frequency stability, AM/FM conver-sion, level, switch-on/off transients,etc,

• if the transmission path betweensignals is disturbed by a host ofsuperimposed signals,

• or if the received Morse signal is af-fected by considerable interference.

Decoder GM094 was designed for tolerance to different types of keying.Varying dot-dash ratios from letter to letter or fluctuations in keying speed areaccepted. Frequency and level fluctua-tions are compensated for by a discreteIF receive unit with matched filters. Thereal achievement of this new develop-ment is its capability to run a continuousclassification process during reception,setting the Morse signal apart from

Articles

FIG 1 Powerful team: digital VLF-HF ReceiverEK895 and Morse Radio Decoder GM094

Photo 42 876/1

Morse Radio Decoder GM094

New dimensions in Morse decodingMorse Radio Decoder GM094 serves for automatic detection of Morse messagesunder the particular conditions of shortwave propagation and manual keying. It relieves personnel from tedious routine tasks. Its particular advantages are that it can work around the clock without fatigue and that it runs a classificationprocedure distinguishing Morse from other signals.

GM091/094 Dongle

HF receiver

HF antenna

IF filtermatchedtracking



IF filtermatched


IF filter De-modulator

De-modulator

De-modulator

De-modulator

De-modulator

De-modulator

Decisionlogic

A/Dconverter


other signals. The potential of digitalsignal processing is fully utilized inGM094 with the aid of modern signalprocessors. In this way characteristicscould be implemented in the decoderthat were not available in the past andare combined here in a unique way:• automatic signal search with adjust-

able capture range,• frequency-accurate display of signal

offset from the receiver center fre-quency,

• adjustable signal hold time,• decoding of both manually and

automatically keyed signals,• decoding of short-time signals,• decoding of duplex traffic.

GM094 also integrates further fea-tures that proved to be helpful duringnumerous trials performed by varioususers. Among these are:• registration of receive time,• editable and selectable Morse code,• editable and selectable radio traffic

abbreviations,• structuring of Morse text,• marking of call sequences and call

signals,• automatic saving of Morse text,• fast and easy-to-use text editor.

These features allow optimal adapta-tion of the decoder to different types oftraffic as well as easy editing of decod-ed text.

Morse Radio Decoder GM094 may beused as a simplex or duplex device.The duplex version consists of two sim-plex versions requiring two DSP cardsGM091 and two software packages

GM094 (FIG 2). Up to six simplex orthree duplex channels may be integrat-ed into a PC. A number of PCs provid-ing several channels each can be con-nected via a LAN interface to a centralmonitoring and process controller run-ning under UNIX software.

To obtain uncorrupted input signalsthe decoder is connected to the IF of the HF receiver (2 kHz to 18 kHz and 22 kHz to 38 kHz), which also allows direct connection to a tape recorder. Frequency control is alsoavailable for common receivers. Thecapture range is adjustable between±5 Hz and ±500 Hz. A certain se-lectable frequency range is defined as the capture range, within which thedecoder periodically searches for thesignal with the strongest level at inter-vals of 0.8 s. The signal is then decod-ed if it is classified as Morse. The holdtime may be selected between 0 and60 s or as infinite. Once the decoderhas detected a Morse signal, it remainsat the detected frequency in the pausesbetween two signals for the hold time

selected. If the hold time is 0 s, the decoder again starts searching for thestrongest signal within the capturerange after maximally 0.8 s. If the holdtime set is infinity however, the decoderremains at a Morse signal once it is detected.

Operation of the decoder is extremelyconvenient and user-friendly. The Morsecode to be used and radio traffic ab-breviations can be freely defined bymeans of the supplied editor. The signalspectrum received can be displayed toallow checking of receiver settings andsignal quality. The maximum error rateis typically less than 0.5 % of charac-ters transmitted at an S/N ratio of 6 dB, receiver bandwidth of 600 Hzand keying speed of 20 Bd. The maxi-mum baud rate is around 60 Bd, whichrepresents approximately 150 lettersper minute. If frequency changes byless than 10 Hz/s, the signal is trackedwithin the set capture range. Keyingspeeds may vary from one letter to thenext by a factor of 3. The dot-dash ratiomay change from one letter to the nextwithin the range 1:2 to 1:5. The signal-level variation within one letter may bemore than 20 dB.

Once the decoder stops, the decodedtext is saved on harddisk as a text file.A special text editor is available to pro-cess, print or delete all saved files.Characters that cannot be decoded are logged as dot-dash combinations.The text being decoded is displayed unstructured in a single moving line (FIG 3). The structured text appears in

Articles

GM091/094 Dongle

HF receivereg EK895

HF antenna

FIG 2 Configuration forsimplex (green) and duplex (green plus blue)

FIG 3 Display of decoded

text in simplex operation during

reception


18 lines on the screen with time of day and signal offset from IF center fre-quency given in each line. Structuringof the log can be switched on or off.Identified call sequences are markedline by line with ADDR. Single call signals are marked line by line with R (these must have been identified before-hand in call sequences). Duplex trafficis decoded and logged in a special format. The decoded texts of the two transmitting ends are allocated to different lines and identified byupper- and lower-case letters. In addi-tion a symbol before each line of text indicates which transmitter was the origin.

A modern workstation for HF monitor-ing can be composed of Morse RadioDecoder GM094, VLF-HF ReceiverEK895/896 [1] and Digital IF Spec-trum Display EP090 [2].

Dr Klaus Rieskamp

REFERENCES

[1] Rohde & Schwarz: Digital VLF-HF ReceiversEK895/EK896 (data sheet PD 757.1225.22)

[2] Rieskamp, K.: Analyzing radio signals withDigital IF Spectrum Display EP090. Newsfrom Rohde & Schwarz (1997) No. 153, p 32

Articles

Condensed data of Morse Radio Decoder GM094Signal Processor Card GM091 AT (long)A/D converter 16 bitsAnalog input bandwidth 80 kHz

Decoder input signal receiver IF (2 kHz to 18 kHz, 22 kHz to 38 kHz)

PC requirements MS-DOS 5.0 or later, 80486 CPU minimum,harddisk drive ≥30 Mbytes, 1 serial interface forsimplex, 2 for duplex


Fast S-parameter measurementson four-port devicesTest hint

A two-port device can be connected to test ports 1 and 2 of Vector Network Analyzer ZVR formeasurement of its S-parameters. If the device has more than two ports however (eg an antennadiplexer with three ports or directional coupler with four ports), it is necessary to change the cabling by hand to be able to measure all the scattering parameters. With the 3-Port Adapterand new 4-Port Adapters available as accessories(ZVR-B8 and -B14) this time-consuming procedurecan be avoided. Switchover between the differentports is then made with the aid of fast electronicswitches.

The 3-port adapter has an electronic switch atport 1, thus extending it to two ports, while port 2is directly connected through without switchover.The new 4-port adapters contain two electronicswitches and come in two versions: model .02 hasa switch each for extending port 1 and port 2 of the analyzer. It can be used for measurements on4-port DUTs such as directional couplers. All reflec-tion coefficients as well as most of the transmissionparameters of a 4-port DUT can thus be measuredwithout having to reconnect it. Due to the design ofthe adapter the transmission between ports 1 and3 and between ports 2 and 4 cannot be measured.If this is required, eg for antenna junction boxes,where the transmission between one input andthree outputs has to be measured, use of model .03is recommended. It has a different internal structureand was specially designed for the above type of4-port devices under test.

In all cases, the ports that are not through-connect-ed are terminated for low reflection by internal 50 Ω thin-film resistors. The adapters are drivenwith the aid of an optional rear-panel connector ofthe analyzer, via which the electronic switches areactuated according to the active display channel ofthe network analyzer. System-error calibration canbe made for each independent display channel to

achieve high measurement accuracy. Switchoverbetween channels is so fast that the traditionallyhigh measurement and display speed of the ana-lyzers of the ZVR family is fully maintained.

Dr Olaf Ostwald


4-port adapter

DUT (4-port)

Port 1 Port 2

1 23 4

ZVR

1 43 24-port adapter (model .02)

1 3 23-port adapter

1 43 24-port adapter (model .03)


Digital Scanning Direction FindersDDF0xS and Digital Monitoring Direc-tion Finders DDF0xM [1] can make useof the special characteristics of short-wave propagation to locate emitters in a particularly effective way with asingle station (FIG 1). The algorithms required for bearing determination bythe Watson-Watt or correlative inter-ferometer method are standard in thesedirection finders. The method used willdepend on the specific application andin particular on the available DF anten-

na system. Adcock or crossed-loop an-tennas are required for evaluation bythe Watson-Watt method. In this config-uration the direction finder provides azimuth values only (angles in the hori-zontal plane). With correlative inter-ferometry the elevation (vertical angleof incidence) is determined in addition.In shortwave direction finding the elevation angle is displayed and outputat the data interface.

Direction finding only determines theangle of incidence, so the signal sourcemay be anywhere along a line withinthe area covered. Emitter location inthe shortwave range can be performedin two ways, the classic and most accu-rate method being triangulation. Here

two or more direction finders are connected via data lines to a locationcenter, where the position of the signalsource is computed from the receivedbearings and normally marked on anelectronic map. The second methodmakes use of the physical characteris-tics of ionospheric wave propagation:over long distances (> 100 km) short-waves are propagated as skywaves.On its way to the receiver (directionfinder) the emitted wave is reflectedonce or several times on the iono-sphere, the vertical angle of incidenceat the receiver being equal to the vertical angle of emission. During theday this reflecting ionospheric layer (E layer) is at an altitude of about 100 km. But at nightfall it disappears

Application notes

Single-station location with HF direction finders of DDF01x family

FIG 1 Digital Monitoring Direction FinderDDF01M with circular array interferometerADD011 Photo 42 880/2


and waves are reflected by the F layer,the altitude of which varies between250 and 400 km. These propagationcharacteristics can be applied to locatean emitter by means of direction findersthat yield azimuth and elevation anglesby using the virtual layer height Hvirtderived from ionospheric parameters (FIG 2). The prerequisite here is that the wave be reflected only once on the ionosphere. This permits fixing oftargets up to a distance of 1200 km.Position location with only one short-wave direction finder is called single-station location (SSL). SSL is usedwherever it is not possible to set up a triangulation system with two or moredirection finders, or if the orientation ofthe involved stations to the target trans-mitter is so unfavourable that a reliablepoint of intersection cannot be ob-tained (direction finder and transmitteron or near the bearing line). With anoptimum site selected, triangulationmostly yields more accurate results because with SSL the elevation anglesrequired to determine the distance ofthe target may greatly vary as a result

SSL software for HF Doppler DirectionFinder PA010 [2]. Tried and tested operating features were retained andnew ones added. So the requiredionospheric data need not necessarilybe determined each time but may becalled up from an ionosphere modelwith database integrated in the SSLsoftware.

One condition for position location withSSL is accurate measurement of ele-vation, independent of the azimuth and frequency of the incident wave. DF Antenna ADD011 used as a correl-ative interferometer is an optimum solu-tion here in spite of partly contradictoryrequirements like• wide aperture for high accuracy,• good isotropic characteristics for

determining elevation angle inde-pendent of azimuth,

• widely spaced crossed-loop anten-nas for low mutual coupling,

• minimum number of crossed-loop antennas affording simple infra-structure.

The whole frequency range from 0.3 to30 MHz is covered with only nine antennas arranged on a circle of 50 min diameter. These crossed-loop an-tennas guarantee high sensitivity andbearing accuracy even for steep-angled skywaves and are virtually unaffected by inhomogeneities of theterrain around the antenna array.

HF Antenna ADD010 is available forsemi-mobile applications and for wavesarriving at a less steep angle (up to anelevation angle of 50°). It consists ofnine active monopoles, each 2 m high.The elements can be set up and dismantled in a very short time and require extremely little stowage fortransportation.

After installation the optional single-station locator from Rohde & Schwarzis an integral part of the directionfinder’s user interface and can becalled up via the menu bar in fixed-frequency mode. Only a few settingsare required to operate the option: position of direction finder and iono-spheric data such as critical frequency(MUF) of E layer, virtual height of E layer, critical frequency of F2 layerand M3000 factor. If no relevant iono-spheric data (eg from chirp sounders)are available, the single-station locatoruses average values to CCIR Rep. 340 [3] from its database, which canbe adapted to the actual situation givensome additional information, eg thesun-spot number. Adapting data fromthe database to the actual ionosphericconditions to improve location accura-cy is also possible by taking bearingsof known transmitters and using the cal-ibration function. It is however essentialfor the transmitters to be as close aspossible to the area of interest at smallfrequency spacing.

Application notes

of frequent instabilities of the iono-sphere. So only average values bymeans of a histogram can be expected.

Rohde & Schwarz developed the SSLprogram for Digital Direction FindersDDF01S and DDF01M based on the

FIG 2 Determination of emitter distance D fromsignal propagation path via ionosphere

Emitter Direction finderD

Hvirt

Ionosphere

ε ε

FIG 3 SSL window with

histogram and waterfall display


To perform a measurement, histogramand waterfall diagrams for azimuthand elevation are displayed in the SSL window of the controller (FIG 3).Two modes are available for result evaluation:

1) Manual selection of bearings withthe aid of marker lines in the azimuthand elevation histogram and transfer ofthese values for position calculation bymeans of the Calculate key.

2) Automatic assignment of bearingvalues by pressing the Calculate key inthe quick-shot mode.

Location accuracy depends on systemaccuracy, the reliability of ionosphericdata and on the integrity of the iono-spheric model. Theoretical considera-tions [4] and measurements haveshown that distance determination istypically less accurate by one order ofmagnitude than azimuth measurement.Furthermore the accuracy of elevationmeasurement and knowledge of the virtual layer height are of particular importance and a fixing error of 5 to15 % (rms) of the distance is to be expected under known propagationconditions.

Franz Demmel; Ulrich Unselt

REFERENCES

[1] Demmel, F.; Unselt, U.; Schmengler, E.: Digi-tal Monitoring Direction Finders DDF0xM –State-of-the-art monitoring direction findingfrom HF to UHF. News from Rohde &Schwarz (1996) No. 150, pp 22–25

[2] Georgi, S.: Single-station location with HFDoppler Direction Finder PA010. News from Rohde & Schwarz (1990) No. 129, pp 16 –19

[3] CCIR: Atlas of ionospheric characteristics,Report 340

[4] Höring, H.-C.: Comparison of the fixing accuracy of single-station locators and trian-gulation systems assuming ideal shortwavepropagation in the ionosphere. IEE Proceed-ings 137 (1990) No. 3, pp 173–176


Application notes

International ALE (automatic link establishment)standard for HF Transceiver XK2000Because of the dynamic propagationconditions in the shortwave range, set-ting up a reliable link for this type ofcommunication is anything but a simpletask, which in the past could only beperformed successfully and within rela-

tively short time by experienced opera-tors. Today this job has been taken overand perfected by automatic-link-estab-lishment techniques. Besides company-specific procedures such as ALIS (automatic link setup) from Rohde &

Schwarz [1; 2], which were speciallydeveloped and optimized for fast

FIG 1 Modern HF transceiver of XK2000 familywith integrated communication processor

Photo 41 251


data transmission via critical HF paths (adaptive response), internationalstandards like FED-STD-1045 and MIL-STD-188-141 have been workedout and widely accepted.

For reasons of interoperability thesestandardized ALE (automatic link estab-lishment) techniques along with R&S-specific ALIS are supported by theXK2000 HF transceiver family [3] fromRohde & Schwarz and their integratedData Link Processor GS2200 (FIG 1).

ALE specifies solely the shortwave link setup; subsequent communication (speech, data) is not defined by thestandard and may take place in accor-dance with any other protocol desired.However, brief messages may be con-veyed by the setup protocol. Besidesthe actual link setup protocol, the ALEstandard provides several addressingmodes for operation in a network as well as means of protection of the link setup against eavesdroppingand deception through encrypting theprotocol.

link setup are also specified. Standard1045 is supplemented by standards1046 to 1052. An 8FSK signal with discrete frequencies from 750 Hz to2500 Hz is used for link setup. This signal type is suitable for transmissionvia HF transceivers as an SSB (single-sideband) signal with bandwidth of 3 kHz. The tones are transmitted at a symbol rate of 125 per second. AnALE word consists of 24 data bits (3 bitsfor the preamble and 3 x 7 data bits).To enhance the transmission reliabilityof ALE words on the HF channel, each one is extended by a 24-bit Golay FEC code (forward error correc-tion), then interleaved and emitted with threefold redundancy. The entireALE word including error correctionconsists of 49 tones and is 392 ms long(FIG 2).

Each ALE network is assigned a num-ber of frequencies for establishing links.A station switched to receive modescans all assigned frequencies at a rateof two or five channels per second,waiting for calls to come in on any

When a link is being set up, ALE wordsare combined to form an ALE frame.This frame is divided into individual sections, the transitions between whichare indicated by preambles containedin the ALE words. A complete ALE linksetup is made up of three such frames.First the calling station emits a callframe, which is answered by the called station (response frame). Thecalling station acknowledges receipt of the response frame by transmittingan appropriate frame to the called station. At this juncture the link setup is completed.

An ALE station is identified by an address with a maximum length of 15 characters consisting of upper-case letters A to Z and numbers 0 to 9.Besides this unequivocal addressing ofan individual station (individual call,point-to-point link), further addressingmethods for contacting all stations orgroups of stations in a network are alsopossible. All Call serves for addressingall stations of a network (broadcast)and is not acknowledged by the calledstations (FIG 3). Selective All Call isused to call stations with the same finalcharacter. With Group Call, severalstations of a network respond to a callaccording to a predefined responseprotocol. Net Call addresses all sta-tions of a network assigned to a net-work address. Again the called stationsrespond according to a predefined protocol. Further types of addresses are Any Call for emergencies, which isresponded to by all stations receivingthis call, and Wild Card addressing, inwhich case only certain characters ofthe address are to conform.

ALE allows the link quality of the trans-mission path to be checked in order to minimize link establishment times.The sequence in which frequencies arecalled will then be made dependent on actual link quality. This is possible by storing and administering the linkquality to each subscriber. The informa-tion on link quality is provided by asounding process that involves calls being emitted at programmable inter-

Application notes

Technical featuresof ALE standard

FED-STD-1045 specifies the parametersinvolved in automatic link setup with HFtransceivers. Besides basic parameterslike modulation type and transceiverbandwidth, signal type, coding methodsand protocol sequence for automatic

of those frequencies. A calling stationemits a call whose length is matched to the number of channels available, so the call can be captured by the scanning receive station. If a call is not successful, another call will be per-formed on the next channel. Severalsuch frequency lists (scan groups) maybe stored in an ALE station.

49-bit ALE word interleaved

24-bit ALE wordwith 24-bit Golay FEC

24-bit ALE word3 bitsPreamble

7 bitsParameter 1

7 bitsParameter 2

7 bitsParameter 3

12 bitsData

12 bitsGolay FEC

12 bitsData

12 bitsGolay FEC

0

Bit 0 Bit 48 = stuffing bit

FIG 2ALE word

coding andinterleaving


vals and determination of their receivequality (link quality analysis, LQA).

Brief messages may already be trans-mitted during link setup. AMD (auto-matic message display) enables thecalling station to transmit, while calling,a predefined message up to 90 char-acters long, which is displayed at thecalled receive station. This feature ofthe standard is utilized by TransceiverXK2000, among other things for trans-mitting a phone number to the receivestation to allow a telephone networklink to be set up via an APP (automaticphone patch). UUF (user-unique func-tion) enables transmission of a manu-facturer-specific 14-bit value during linksetup, which may for example be usedfor controlling the subsequent datatransmission protocol (in Data Link Processor GS2200). With the aid ofDTM (data text message) mode, briefmessages can be transmitted without requiring an additional data modemand protocol.

Encryptionof link setupLinking protection (FED-STD-1049) isone of the ALE functions. It serves toprotect the information contained in theprotocol such as address and networkrelation against eavesdropping. Thismethod is also resistant to deception(spoofing) by the enemy through re-cording and retransmitting the emittedinformation. This function protects thelink setup only. For the protection of subsequent speech and data messag-

es, additional cryptographic measureshave to be taken at the transmit and receive ends.

The Rohde & Schwarz implementationsupports three of five protection levelsdefined in FED-STD-1049 (AL-0, AL-1and AL-2). Level AL-2 offers the greatestsecurity (protection interval 2 s), but also means more stringent requirementsfor network synchronization, while LevelAL-1 offers somewhat less security (protection interval 60 s), but networksynchronization requirements are notas high either. The protection interval isthe time interval within which the inputvariables of the encryption algorithmare constant.

The 24-bit ALE words for link setup areencrypted with the aid of the Johnsonalgorithm [4]. Input variables for this algorithm are the crypto key defined bythe user, frequency, date and time. Thekey may be a word up to 63 bits long,which results in a maximum number ofkeys of 263. Because this technique istime-referenced, a time-synchronizednetwork is required. Different proce-dures are provided to first establish and then maintain synchronization.One station in the network serves as the time master station, supplying theother stations with the exact time viaprotocols. Time may also be manuallyentered at each station. For maintain-ing synchronization, a time-acquisitionprotocol polling the exact time from thetime reference station is started when-ever a certain degree of inaccuracy is detected in the system. This protocol

is also protected as long as the time deviations are found to be within toler-ance by the linking protection process.For stations without any information ondate and time or with insufficient timeaccuracy, an acquisition protocol hasbeen implemented, which however isnot protected because of the absenceof time information. This option is pri-marily intended for stations entering thenetwork at a later date.

Günter Wicker; Erich Schippan

REFERENCES

[1] Greiner, G.: Reliable shortwave with ALIS.News from Rohde & Schwarz (1987) No. 116, pp 47– 50

[2] Greiner, G.: Fast and secure data trans-mission on shortwave – result of intensive research. In this issue, pp 41– 43

[3] Helmke, B.; Wachter, G.: HF TransceiverXK2100 – Digital shortwave for future-proof,long-haul communication. News from Rohde& Schwarz (1994) No. 144, pp 47

[4] Johnson, E.: A 24 bit Encryption Algorithmfor Linking Protection. Technical ReportASQB-OSI-S-TR-92-04, March 1992


Application notes

Scanning section

COMMANDTX-

DATASON

THISWASSAM

DATAE66

REPEATSAG

DATAMES

TO6?6

ALE word392 ms

TO6?6

TO6?6

TO6?6

TO6?6

Preamble

Parameter

Leading section Message section Conclusion section

FIG 3 Example of frame for All Call from SAMSON station in automatic message display function withTx message


Even if TV signals are digitized, com-pressed according to MPEG2 specifi-cations and transmitted in line with DVBspecifications, they are not free of er-rors and therefore need to be measuredin any case. Rohde & Schwarz is world-wide the sole company to supply acomplete range of measuring instru-ments meeting MPEG2 and DVB stan-dards.

The first parameter in the transmissionchain to be analyzed is the digitizedand compressed MPEG2 data stream.To obtain reproducible results, exactlydefined test sequences are required in the form of elementary streams forvideo, audio and data as well as the relevant tables. With MPEG2 thismeans generation and multiplexing ofmoving picture sequences and accom-panying audio signals – eg excerptsfrom concerts – that have been data-compressed according to the conven-tions (MUSICAM). The data channelcontains teletext and other data for any other applications. Tables for PSI(program-specific information) and SI(service information) complete the datastream.

The elementary streams for video, audioand data are organized in packets, the

PES (packetized elementary streams),each up to 64 kbytes long. They con-tain synchronization and identificationinformation. They are subdivided inturn into packets of 188 bytes (transportpackets) that contain further informa-tion for synchronization and identifica-tion. Several programs in the form oftransport packets, which may containvideo, several audio and data PES, are combined to a transport stream thatcan be modulated in line with DVB.Since the packing, synchronization andidentification procedures are rathercomplex, reference transport streamsare needed for measurements. MPEG2Generator DVG [1; 2] is the solution of-fered by Rohde & Schwarz. It providesall the conditions required for reprodu-cible measurements in realtime analysis

of the MPEG2 transport stream withMPEG2 Measurement Decoder DVMD(FIG 1).

The transport-stream multiplex signalcontaining several programs can bemeasured on line. No error, howeverslight, may go unnoticed. First thedata rate of the whole transportstream, which is decisive for utiliza-tion of the DVB transmission channel,is determined. Once the number ofprograms in the data stream is known,the data rate of the individual pro-grams and then the data rate of the program elements – PES for video,audio, data, etc – are measured to obtain the volume of data transmittedfor each program (FIG 2). The volumeof data transmitted per PES determinesthe picture and sound quality of the compressed programs. Continuousevaluation of data rates is therefore essential when signal quality is moni-tored.

With the aid of the MPEG2 decodingprocess in MPEG2 Measurement Decoder DVMD all other items of the(protocol) analysis can be checked:• The decoder searches for the begin-

ning of the transport-stream packets,which is identified by the sync byte.A sync byte is sent every 188 bytes.The analyzer checks the length andcontent of these bytes.

• When the sync byte is found, the decoder stores and checks the data content of the transport-streampackets. In a next step it searches for the transport-stream tables, themost important of which is the PAT(program-association table). It is assigned the identification number00hex (packet identification, PID)and describes all programs in thetransport stream. If DVMD does notfind a PID with the value 00hex, itsignals this error but neverthelesssearches for decodable data.

Application notes

Analysis of compressed MPEG2 data stream for digital TV

FIG 1 MPEG2 GeneratorDVG and MPEG2Measurement De-coder DVMD, expertduo for generatingand analyzingMPEG2 referencetransport streamsPhoto 42 498/2

FIG 2 Evaluation of data rates of MPEG2 trans-port stream


• PAT is the list of programs. The indi-vidual programs are described insubdirectories, the PMTs (programmap tables). The program to be decoded is specified by selecting aPMT, the PIDs of which must all belisted in the PAT. The specificationsexactly define the minimum andmaximum repetition rate of the tables. For data protection, PAT andPMTs are transmitted together withthe CRC sum (cyclic redundancycheck). Both the repetition rate andCRC are continuously monitored byDVMD.

• The decoder selects a program, ie aPMT in the PAT, to check whether thePAT really contains the PID of thePMT or, vice versa, whether all PMTsidentified by the PAT are containedin the transport stream.

• Not only the program but also theprogram content is selected. To thisend all files with their PIDs for video,audio and data elementary streamsare listed in the PMT subdirectories.PIDs are again analyzed, and missing or unreferenced PIDs are indicated.

• If applicable, the program is next descrambled. Scrambled programsand their PIDs are listed in a separate table, the CAT (conditionalaccess table) with PID 01hex.MPEG2 Measurement DecoderDVMD compares the information onscrambling with the information inthe CAT, measures the repetition rateand compares the CRC sum calcu-lated in the decoder with the CRCtransmitted in the transport stream.

• The decoder is at this stage not synchronous with the video and audio data in the transport stream.The system clock of the transport-stream demultiplexer is to be syn-chronized. To achieve this the decoder searches for the PCR (program-clock reference) in thespecially marked transport-streampackets. DVMD also measures therepetition rate of all PCRs, which isat least 10 Hz. To allow jitter-freedecoding, the PCRs of the programselected via the PMT must be

transmitted in a time window withan accuracy of ±500 ns.

• To enable the decoder to detect at alltimes whether all transport streamsare available in the right order fordecoding, the status of the continuitycounter is monitored. Counter dataare transmitted in the transport-stream packets so that the correct order of the video and audio datapackets can be checked. A disconti-nuity in the count shows that elemen-tary stream data are missing, whichwould cause the reproduced visionand sound signals to flicker. DVMDsignals an error when discontinuitiesare detected in the count.

• Transport-stream data for video andaudio arrive at the decoder in timemultiplex. The decoder is informedby DTS (decoding time stamps) atwhat time it should provide particu-lar data in decoded form. PTS (presentation time stamps) decidewhen the decoded data are to be forwarded to the display or theloudspeaker. The decoder deter-mines the frequency of the two timestamps and indicates deviationsfrom the standard.

• For transmitting the transport-streampackets via cable, satellite or terres-trial links, an error-correction code isadded to the transport-stream packet(Reed and Solomon, named after its creators). If this forward error correction is not able to correct the errors incurred, a bit is set in the header of the transport stream. The decoder evaluates this bit and

signals a transport error. The respec-tive packet is then no longer used forerror analysis.

Errors in the PAT and PMT tables con-taining program-specific information, in the associated PIDs as well as thesync bytes and the continuity counterare put in the highest category in theDVB measurement guidelines (FIG 3).Transport errors, CRC, PTS and the twoPCR errors as well as errors in the CATare assigned to the second category.This latter contains events which lead to incorrect reproduction of the signalbut still allow data to be processed. The third group contains errors in theservice information tables. These tablesare read from the transport stream at the end of the described decoding process and then analyzed in DVMD.The repetition rate of the tables is usedas a measurement criterion. Althoughthese errors do not impair reproductionof audio and video data, the service in-formation tables are important becausethey convey all important informationon the transmission media (eg channelbandwidth, transponder, network infor-mation table or a complete programjournal) to the TV set or measurementdecoder.

Sigmar Grunwald

REFERENCES

[1] Fischbacher, M.; Weigold, H.: MPEG2 Generator DVG and MPEG2 MeasurementDecoder DVMD – Test equipment for digitalTV in line with MPEG2. News from Rohde &Schwarz (1996) No. 152, pp 20–23

[2] Fischbacher, M.; Rohde, W.: PC software for MPEG2 dream team DVG/DVMD. News from Rohde & Schwarz (1997) No. 154, p 29

Reader service card 155/09 for further informa-tion on DVG and DVMD

Application notes

FIG 3 Evaluation of events of first, second andthird error class to DVB measurement guidelines


The world’s largest digital audio broad-casting (DAB) pilot project has been onthe air in Bavaria since the autumn of1995, providing the whole region witha wide selection of stereophonic soundprograms in CD quality [1]. Rohde &Schwarz is the principal DAB equip-ment supplier, from modulation feed topower transmitters including associatedantennas [2]. The project has yielded a wealth of experience with DAB. Toguarantee high availability of the transmitter network, Rohde & Schwarzdeveloped a DAB monitoring conceptto detect and prevent failures in thetransmission chain [3]. Monitoringsystems of this type are already beingused at a number of selected terrestrialsites within the Bavarian pilot projectand during the current phase serve toprovide information about satellitetransmission quality (FIG 1). A study byBayerischer Rundfunk (Bavarian broad-casting corporation) showed that anytransmitter in a single-frequency net-work that is not exactly synchronized to the other transmitters, be it because itgives off a wrong type of modulation ordoes not operate at exactly the samefrequency or does not emit simulta-neously with the other transmitters, willinterfere with other DAB transmittersthroughout the network. The interferingtransmitter generally cannot be identi-fied by touring the coverage area andconducting measurements. It is there-fore essential that the operator shouldhave information on the state of all DAB transmitters in the network at alltimes [4].

Monitoring concept

Various types of disturbance may occur in the DAB transmission chain,anything from light interference tocomplete transmission breakdown.The newly developed monitoring con-cept from Rohde & Schwarz enablesthe operator to choose to what extentmonitoring for the DAB network is necessary (FIG 2).

The uplink of the satellite transmissionpath (including the multiplexer) is themost critical point in the DAB chain because here several programs arecombined in a multiplexer to form aDAB ensemble, which is then transmit-ted to the satellite (eg DFS Kopernikus).If the multiplexer fails or an error occursin the ETI (ensemble transport interface)signal of the multiplexer, the whole net-work will be affected and possibly evenbreak down. To avoid such failures,which may result in considerable costsfor the operator, a DAB transport-framedecoder is used to continuously monitorthe ETI signal output by the multiplexerand to switch to a second multiplexerwhenever necessary. This guaranteesan errorfree ETI signal at the output of the uplink to the satellite. In addition,a spectrum analyzer may be used tomonitor the RF signal on the uplink.

Located at the downlink stations are theDAB transmitters, which serve for terres-trial broadcasting to DAB receivers.Here the satellite signal received via thedownlink and the terrestrial signalbroadcast by the DAB power transmit-ter are to be monitored. The transmis-sion quality of the satellite link can bedetermined through a variety of param-eters provided by the satellite receiverused for demodulating and decodingthe incoming signal. The signal output

by the terrestrial transmitter is continu-ously monitored by a DAB monitoringreceiver, which enables comprehensiveanalysis of the DAB signal. Any erroroccurring within the DAB transmissionchain will be detected by the monitor-ing receiver and localized with the aidof further monitoring components. Themonitoring receiver is suited for mobileuse as well as for use directly at thetransmitter site. A further component formonitoring the transmission chain is theCOFDM (code orthogonal frequency-division multiplex) modulator, whichprovides status information. The terres-trial DAB transmitter may also be con-trolled and polled from a PC connectedvia a remote-control interface.

The DAB monitoring components canbe used as stand-alone units or inte-grated into a monitoring system at thetransmitter site. The monitoring system (slave) can be connected to a controlcenter (master), which makes automaticmonitoring and control of unattendedstations possible.

Monitoring components

DAB Transport Frame Decoder DAB-FDserves for monitoring ETI signals suchas the output signal of the DAB trans-port multiplexer as well as the signaltransmission components between

Application notes

DAB monitoring

FIG 1 Example showing

availability of DABtransmitter sites in %


multiplexer and COFDM modulator.The decoder is also capable of demulti-plexing a channel of a transport frameand displaying selected parameters.The following functions can be moni-tored by the decoder:• correct change of frame sync sym-

bol,• incrementing of frame counter and

frame phase,• cyclic redundancy check of header,

mainstream and individual informa-tion channels,

• consistency of frame length with individual stream lengths and ofstream start addresses,

• presence of signalled audio streams,• audio bit rate.

The DAB transport-frame decoder is a PC card and runs using a Windowsapplication program. It may be usedwith portable and stationary PCs alike.

DAB Monitoring Receiver DAB-TR isfor the continuous checking of DAB programs and allows easy and intuitiveoperation (hypertext markup language,HTML). DAB data services are alsotransmitted as HTML pages, so the re-ceiver can check them for correctness.The receiver’s DAB test screen displaysinformation such as ensemble desig-nation and identification number, des-ignation of audio and data service including their identification as well assignal strength and frequency of occur-rence of errors. Signal strength and error rate are continuously monitoredand compared with an adjustable tolerance threshold. If the threshold is exceeded, an acoustic alarm may be generated. The opening screen ofthe DAB monitoring receiver shows thename of the audio service, the desig-nation of the program received, the en-sembles available and the HTML pages

transmitted. Switching back and forthbetween various ensembles or audioservices is possible. The DAB monitor-ing receiver has an RF input for band IIIand L-band, outputs for the connectionof audio analyzers and loudspeakersand an RS-232-C data interface withover 30 commands allowing connec-tion to a PC for integration into a moni-toring system.

Besides the equipment explicitly de-signed for monitoring purposes, thecomponents involved in data trans-mission also provide important infor-mation. Satellite Receiver CM701, forinstance, reveals information on S/Nratio, clock and offset at its input andon automatic gain control. COFDMModulator MCM01 signals whenevera clock is missing at its input or if the signal frame structure is invalid or the input signal or the modulator itself is faulty. Seen together, all theseparameters give a clear view of the cur-rent status of the whole DAB network.

Michael Lehmann;Christian Christiansen

REFERENCES

[1] Kalthoff, W.: Bavaria has started into DAB future. News from Rohde & Schwarz (1995)No. 149, pp 48–49

[2] Frank, P. H.: DAB components – Digital audio broadcasting – all from a singlesource. In this issue, pp 12–13

[3] Schukat, M.: Distribution of the multiplexedsignal via satellite. 3rd Int. Symp. on DigitalAudio Broadcasting, Montreux, June 1996

[4] Lau, A.; Pausch, M.; Selle, A.; Wütschner,W.: Erste Ergebnisse aus den Untersuchun-gen mit dem DAB-Gleichwellennetz inBayern. DAB-Plattform e. V. c/o BayerischerRundfunk, Munich


Application notes

R

L

R

L

Uplink

32 to 384 kbit/s 2.048 Mbit/s 70 MHz 14 GHz

Spectrumanalyzer

Downlink

226.5 MHz or1.5 GHz 70 MHz 1.3 GHz 12 GHz

Spectrumanalyzer

2

Low-noiseconverter

QPSKdemodulator

COFDMmodulator

DAB trans-mitter

band III,L-band

DAB testreceiver

MUSICAM

MUSICAM

DABmultiplexer

QPSKmodulator

High-poweramplifier

f2f1

f1f2

31

4567

FIG 2 Principle of DAB network monitoring.Following functions are monitored: multiplexerconfiguration (1), ETI signal (2), RF signal onuplink (3) and downlink (4), S/N ratio Eb/N0 (5),DAB transmitter data (6) and broadcast DAB signal (7).


The ESMC-RAMON program packageoffers an attractively priced entry intocomputer-aided radiomonitoring. Theuniversal operating software is a newoption for Compact Receiver ESMC [1; 2]. Derived from RadiomonitoringSystem RAMON® [3; 4], it combinesthe two names to ESMC-RAMON thusindicating its origin. This programpackage is the solution for newcomersto computer-aided radiomonitoring. Itsgraphics interface and the standard-ized Windows operating conceptmake the user feel familiar right fromthe startup of the program. The scope of functions is reduced to the essential,operation is simple and the benefits ofESMC-RAMON will show after a veryshort period of use.

The favourable price is not only easy onthe budget but also a spur to try andtest, particularly when customized solutions are to be developed. This especially applies to the complex fieldof instrument control, where the outlayrequired for software development rapidly exceeds the price of ESMC-RAMON. This software is proof that instrument control too is a Rohde &Schwarz domain. Despite data ex-change with the receiver, other pro-grams may also be active. The user

can monitor signals with ESMC andprepare reports at the same time (FIG 1). Another example of optimizedinstrument control are the two possibil-ities for operation. ESMC can be setfrom the controller, or settings can bemade on the receiver without anyswitchover being required. Settingsmade on the one are automatically up-dated on the other. The user thus bene-fits from direct instrument control andfrom computer control at the same time.

Resolution, colours and the memory ofthe controller open up new dimensionsfor radiomonitoring with ESMC. This isemphasized by the integrated over-

view window (FIG 2), where all signallevels of a search run are displayed.Discrete signals can be selected bymeans of colour markers and lines andtheir parameters measured. Search parameters are taken from files on theharddisk. These capabilities and theuse of ESMC-RAMON give access tocomputer-aided radiomonitoring.

ESMC-RAMON is not only capable ofcontrolling a single ESMC. With the aidof the “Transfer” software option it canalso allocate signal parameters to otherunits (FIG 3). Since not only otherESMCs but even VHF-UHF ReceiversESM500 can be set, users of ESM500

Software

ESMC-RAMON – entry into computer-aided radiomonitoring

IEC/IE

EE bu

s

ESMC

ESM 500

FIG 1 ESMC-RAMON for simultaneous receiver operation and preparationof reports

FIG 2 Overview window of ESMC-RAMON in search mode

FIG 3 ESMC-RAMON software combining VHF-UHF Receivers ESMC and ESM500 into one system


will also be able to enhance the effec-tiveness of their units. Signals from theESMC overview window can be directlytransferred to the receivers for monitor-ing and evaluation. The time betweensignal detection and monitoring is thusreduced to a mouse click.

Search data can be recorded using the“Evaluate” software option. Recordedresults may be recalled and then analyzed. ESMC-RAMON makes step-ping up to Radiomonitoring System

RAMON® easy. ESMC setups can be transferred to RAMON without anymodifications, reducing the outlay forthe change to a minimum. Operation ofthe two systems is identical, so know-how acquired with ESMC-RAMON canimmediately be put to use on RAMON.

Günther Klenner

REFERENCES

[1] Boguslawski, R.; Egert, H.-J.: VHF-UHF Com-pact Receiver ESMC – Easy radio detectionin VHF-UHF range. News from Rohde &Schwarz (1993) No. 143, pp 11–13

[2] Gottlob, C.; Demmel, F.: Fit for future radio-monitoring and radiolocation up to 3 GHz.News from Rohde & Schwarz (1997) No. 153, pp 24 –25

[3] Ehrichs, R.; Holland, C.; Klenner, G.: Radio-monitoring System RAMON – Customizedradiomonitoring from VLF through SHF.News from Rohde & Schwarz (1996) No. 151, pp 19–21

[4] Holland, C.; Reimann, R.: RAMON basicsoftware for Digital Direction FindersDDF0xM and DDF0xS. News from Rohde &Schwarz (1997) No. 153, pp 30–31


Software

PatentPower measurement in mobile-radio channel

In mobile-radio networks where carrier signals aretransmitted from several transmitters to different receivers, interfering signals may be present at thereceiver input that are superimposed on the carriersignal intended for the specific receiver. Such sig-nals come from transmitters in the network or fromother signal sources. Measuring the power of inter-fering signals is vitally important for network oper-ation. The technique described in the patent utilizesthe fact that if the carrier signals are transmittedwith unused time slots between the time slots occu-pied by the signal, the power of a superimposedsignal can be measured by selecting the time slotsnot containing a carrier signal from the sum signalin the receiver. This can be done by means of pulse compression and the patented technique. Ina GSM signal, for instance, pulse compression canbe performed on the training sequence of the sig-nal. In the case of an indoor DECT network the syncsequence of the signal can be used for compres-sion. The average power of the successive timeslots of the sum signal may be measured over thetotal width of the time slot or in part of it. Likewisethe average power of the compressed signal section can be measured or calculated in a sectionof the pulse obtained by compression, in the totalpulse or over a predefined width of the compressedsignal. This depends on signal bandwidth, syncquality and, if any, on propagation delays in theradio channel. The interfering signal power in theselected carrier-free time slot can be calculatedfrom the digital data of the time slot as an averagevalue measured either over the whole time slot orin a section of it. Spectral power evaluation is alsopossible.

The diagram illustrates the relationship betweenthe carrier signal C consisting of occupied timeslots ZS and empty time slots Z0 in between, the

sections of the time slot, is subjected to pulse compression and the average power of the pulseobtained by compression in the compressed signalK is calculated. The ratio of these two averagepowers is then compared with a preset limit. If the power is below the limit, the time slot does notcontain a carrier signal but an interfering signal tobe evaluated. The stored digital data of this timeslot may then be used to measure the interferingsignal power (average interference power, maxi-mum interference power or interference power ver-sus time). In the simplest case the power calculatedfor the time slots Z0 may be taken as the averageinterference power. Another useful method forevaluating the interfering signal power is calcula-tion of spectral power density.

interfering signal I, resulting sum signal S at the receiver input, signal sections Sk used for pulsecompression and signal section K compressed foreach time slot, the GSM network being used as anexample. The sum signal arriving at the receiver isdigitized, and the sequence of the samples of timeslots Z1 to Zn of the sum signal are stored. Whenan IF signal is scanned, a sequence of real num-bers is obtained, and for the I/Q signal a sequenceof complex numbers. Time synchronization canthen be derived from the stored signal databetween the frame structure of the carrier signaland the values of the sum signal already scannedor still to be scanned. Then the average RF poweris first calculated from the digital samples of thesuccessive time slots. At the same time a selected,network-specific section of the carrier signal, whichis in a time slot between the signalling or data

C

ZS Z0 Z0 ZS

Z1 Z2 Z3 Z4

Sk

Z1 Z2 Z3 Z4

Z1 Z2 Z3 Z4t

I

S

K

Extract from patent specification DE 44 30 349 C2Patent applied for by Rohde & Schwarz on 26 Aug 1994Issue of patent published on 28 Nov 1996Inventor: Otmar Wanierke

Used in Digital Radio Analyzer PCSD

Reader service card 155/12 for further infor-mation on PCSD


3.2.3 Bandwidth reduction by baseband filtering

The power-density spectrum of unfil-tered MSK can be described analyti-cally by the function

modulating signals cI(t) and cQ(t) arecalculated from it by means of a non-linear operation.

For the time being it will be convenientto think of the I/Q modulator as a fre-quency modulator (VCO) as far as theprocessing of the modulating signals is

or by its transfer functionln 2 ln 2– —–—– f2 – ——––—–—– (Tbit f )22 B2 2(B·Tbit)2H(f) = e = e (29)

where and B = 3 dB

bandwidth of filter. These expressionscontain the new term B·Tbit, which nor-

Refresher topic

In FIG 14 it is compared with the QPSKpower-density spectrum function. Thediagrams show that the main lobe of the MSK spectrum is considerably wider and that there are no spectrumzeroes at fc+/– fbit . On the other hand,the MSK spectrum’s tail-off, which isproportional to f –4, is considerablysteeper than that of the QPSK spectrum.In both cases the spectrum can be improved by baseband filtering, butwith one big difference – in the case ofQPSK it is the modulating signals cI(t)and cQ(t) that are filtered, but with MSKthe data function is filtered before the

concerned, because this simplifies thedescription of filtering. Simply imaginethe filter connected to the input of thefrequency modulator (FIG 15). GSMspecifications stipulate that the data signal should be passed through aGaussian filter, hence the designationGaussian minimum-shift keying (GMSK)for this type of bandlimited modulation.This filter can be described in terms ofits impulse response

1t2

h(t) = ——————e—–––———

(28)σTbit √——2 π

2(σTbit)2

malizes the filter bandwidth to the bit frequency fbit and which is used instead of the actual bandwidth of the Gaussian filter to describe the efficiency of the filtering process. B·Tbit = ∞ means that MSK is being implemented, while smaller values ofB·Tbit indicate GMSK with a corre-spondingly smaller bandwidth. FIG 16shows the effect on the RF spectrum.

GSM networks use B ·Tbit = 0.3. Thismeans that the 3 dB bandwidth of the baseband signal is 81.25 kHz (TABLE 4).

Apart from the wanted effect of band-limiting that is obtained by filtering thedata function, there is also an unwant-ed effect referred to as intersymbolinterference. Theoretically, when a rectangular pulse pc(t) = rect(t/Tbit) ofduration Tbit is filtered, its duration t satisfies the inequality –` < t < +`. To estimate the interference, the ap-

Digital modulation and mobile radio (VI)

FIG 14 Spectra for QPSK and MSK FIG 16 GMSK spectra for various values of bandwidth · bit duration

FIG 15Generation of GMSK

Baseband signal(unfiltered)

u(t)

t

Phase position ofGMSK signal

ϕ(t)

t

Output frequency

f(t)

t

Baseband signal(filtered)

ufil(t)

t

Modulator(VCO)Filter

16 A2 Tbit cos 2 π f Tbit2

Φvv(MSK)= —————3————————4π2 1–16 f2 Tbit2 (27)

√—–—ln 2σ = —––——B · Tbit


proximate response of the filter to this pulse can be obtained from con-volution with the impulse response ofthe filter. The convolution of pc(t) * h(t)gives rise to integrals of the form

which do not have

closed-form solutions but can be calcu-lated from the Gaussian error function

erf(x) using the methods of numericalanalysis (FIG 17).

In practice, when B·Tbit = 0.3, only aninterval from t = –3Tbit to t = +3Tbit, theduration of 6 bits, needs be consid-ered; outside this time interval the filterresponse can be assumed to be zero. A delay of at least 3Tbit must be intro-duced to prevent causality from being

violated. Due to pulse spreading andthe conservation of energy, the maxi-mum value of the filtered pulse drops toabout 0.7 times the amplitude of thestimulus.

The responses of the Gaussian filter to neighbouring rectangular pulses re-inforce and cancel each other out. Re-inforcement occurs if neighbouringpulses have the same polarity (FIG 18)and cancellation, ie the maximum ampli-tude of the current pulse is reduced evenfurther to about 0.5 times the value of theoriginal pulse, if neighbouring pulseshave opposite polarities (FIG 19).

Because of filtering, the function cfil(t),which is proportional to the instanta-neous output frequency, is continuous at the modulator input and the phasefunction ϕ fil(t) loses its breakpoints. Thisin turn smooths the modulating func-tions cI(t) and cQ(t) and, as a result,there is an improvement in the spectrumthat is a function of B ·T; this is shown in FIG 16.

However, because of intersymbol inter-ference, the improvement in the spec-trum has to be traded off against an er-ror rate that increases as B ·T decrea-ses, the ratio Ebit/N0 remaining con-stant (FIG 20).

To be concluded. Peter Hatzold

Refresher topic

+1

0

-1

Response

+1

0

-1

Stimulus

TC TC

+1

0

-1

Response

+1

0

-1

Stimulus

TC TC TC TC

+1

0

-1

Response

+1

0

-1

Stimulus

TC TC

TCTC

4 6 8 10 12 14 dB 16

BER

10-1

10-2

10-3

10-4

10-5

10-6

Ebit/No

Ideal antipodal modulation

(BPSK)

B·T=

∝(M

SK)B·T

=0.25

B·T=

0.2

FIG 17Shaping

rectangular pulsewith Gaussian filter

FIG 19Cancellation of

two neighbouringrectangular pulses

with opposite polarity (resulting

output functionshown by dashes)

FIG 18Reinforcement of

two neighbouringrectangular pulseswith same polarity

(resulting output function shown by

dashes)

FIG 20 Bit error rate, BER, as function ofEbit/N0 with B · T as parameter

Bit duration Bit frequency Bandwidth · bit duration3 dB bandwidth

Tbit fbit B · Tbit

3.69 µs 270.833 kHz 0.3 81.25 kHz

B1

x2

e—–—— e–—–

dx,A √——

2 π2

TABLE 4 GMSK parameters for GSM


The high innovation rate on the mobile-radio market with new products ap-pearing year after year forces manu-facturers to make considerable effortsin development. The GSM standard isin a state of flux, with new functionsand improvements continually beingadded. The resulting necessary modifi-cations in the complex mobile-phonesoftware may lead to unexpected de-lays in type approval if a manufacturerfails to test his mobiles to sufficientdepth.

Digital Radiocommunication Test SetCRTC02 (FIG 1) and the associatedsoftware products can make a decisivecontribution towards avoiding such undesired delays and ensuring theproduct’s market introduction in time*.

Through continuous further develop-ment CRTC is always able to check thelatest GSM features. It is one of the twostand-alone testers approved in Europeand is used for type-approval measure-ments in test houses. The validated software used is now available as anoption for CRTC and allows optimumpreparation for the type-approval test.CRTC is at present worldwide the onlymeasuring instrument for which vali-dated tests for all three networks (GSM900, DCS1800 and GSM NorthAmerica) are available. The unrivalleddiagnostic functions of CRTC – down tobit level of a burst – not only permitcareful documentation of the test resultsbut also minimize troubleshooting timesshould the mobile phone not pass a testright away.

The new test software was configuredso that only minor modifications are re-quired for a fully automatic regressiontest. In this case the device under test is no longer manually operated but remotely controlled by manufacturer-specific commands via an RS-232-Cinterface. A sequencer controlling test-program selection and providing forstorage of results and signalling logscomes with the software (FIG 2). New

software releases can thus be testedwith little effort at short notice and un-expected side effects of software mod-ifications detected at an early stage.

In addition to the main application of aGSM mobile phone, ie voice transmis-sion, data and short message servicesare being used more and more. Due tothe increasing use of E-mail and Internetin wire-line networks, these functionsare now also called for in mobile radio.Therefore, manufacturers already sup-ply special PCMCIA modules designedfor radio data transmission for use withlaptops or small organizers with inte-grated mobile phone. This is the reasonwhy, in addition to the basic data ser-vice functions available for some time,appropriate test suites in line withGSM 11.10 are now offered forCRTC02. These ready-to-run test pro-grams not only check the basic functionunder ideal conditions but also the response of the mobile if part of the in-formation is lost by interference in theradio channel or if mobile and base station have first to “agree” on trans-mission parameters and protocols.

The increasing number of mobile-radiosubscribers causes bottlenecks during

Panorama

Digital Radiocommunication Test Set CRTC02 growing with GSM standard

* Steffen, R.: Digital Radiocommunication TestSet CRTC02 – Universal tester for GSM and DCSmobile phones. News from Rohde & Schwarz(1995) No. 149, pp 10 –12

FIG 1 Digital Radiocommunication Test SetCRTC02, specialist for development and type-ap-proval testing of GSM, DCS1800 and DCS1900mobile phones Photo 42 777


peak periods. Apart from the usual remedies like installation of microcellsand allocation of additional frequen-cies, the use of half-rate speech codingis another efficient means of increasingcapacity. Here two mobiles share atime slot and use the individual burstsalternately. Powerful hardware in themobile phone in conjunction with anelaborate algorithm ensures approxi-mately the same speech quality al-though only half the number of bits aretransmitted. In addition to the requiredbasic functions such as half-rate speechand channel coding, the signalling soft-ware must be considerably enhancedso that the network is informed that the mobile phone supports the half-rate mode and wants to make use of the benefits of a half-rate connection,which include lower charges for in-stance. Thanks to new software op-tions, also available for testers alreadysupplied, CRTC02 is able to perform allthe necessary tests.

Through further development of speechcoders, speech quality can be im-proved in full-rate mode using thesame number of bits. CRTC02 is nowable to test these new enhanced full-rate speech coders with the associatedsignalling.

CRTC02 also has functionality forchecking multiband mobile phones.These phones can be operated both in the GSM900 and the DCS1800band. DCS1800 mobiles can thus usethe 900 MHz band for roaming incountries where no DCS1800 networkyet exists. This means that DCS1800network subscribers can now be calledworldwide.

In some countries a network operatormay use both bands – GSM900 andDCS1800. In these cases long-rangeGSM frequencies can be used to coverlarge areas while the short-rangeDCS1800 frequencies are more suit-able in cities where, for reasons of capacity, microcells are employed

anyway. The required handover func-tions between GSM900 and DCS1800are defined in GSM specifications.CRTC02 provides two RF carriers thatcan be operated independently of eachother both in the GSM900 and theDCS1800 band. The tester is thus able to perform even these extremelyelaborate and complex tests.

Frank Körber; Roland Steffen


Panorama

FIG 2Automatic test run

with sequencer

DVB-T, the new terrestrial TV standardIn February 1997 the voting procedurefor the new terrestrial European Telecom-munications Standard ETS 300 744 (inshort DVB-T) ended with a unanimousvote*. Thus, within about two years, abasis has been created for the terres-trial television of the future. This newstandard will be applied in Europe

first, and is expected to be taken up inother parts of the world too.

The basic technical specificationswere prepared by the European DVBProject and in particular by its Tech-nical Module, in which Rohde &Schwarz is taking an active part. Like

all other DVB specifications, the terres-trial broadcasting standard is basedon the requirements of potential users.

* ETS 300 744: Digital broadcasting systems fortelevision, sound and data services; Framingstructure, channel coding and modulation for digital terrestrial television. March 1997


The DVB-T standard contains elementsof the standards for satellite and cabletransmission. The input signal, for in-stance, is defined in all cases as anMPEG2 transport stream. For error protection too, well-proven techniqueshave been resorted to. In contrast toother systems, a multicarrier transmis-sion method was chosen for adaptationto the terrestrial transmission channelwith its multipath propagation. Chan-nel coder and modulator contain thefollowing functional blocks (FIG):

• Inner interleaver: combination of bit interleaving and symbol inter-leaving.

• Mapper: allocation of information tothe individual carriers and constella-tion points; permissible modes areQPSK (quadrature phase-shift key-ing), 16QAM and 64QAM (quad-rature amplitude modulation), Graymapping.

• Frame adaptation: providing syn-chronization to frame structure of thesignal.

For the socalled hierarchical modula-tion, two sets of the forward error-correction blocks are required and the MPEG2 transport stream is split upaccordingly.

Rohde & Schwarz pre-series DVB-Tmodulators successfully passed theirfirst interoperability tests and are at present being used in laboratory and field tests in cooperation with customers.

Dr Jürgen Lauterjung

Panorama

The DVB-T standard is envisaged tofulfill the following requirements:• Trade-off between transmission ca-

pacity and coverage range shouldbe possible.

• The implementation of large-areaand local single-frequency networksshould be possible.

• The system should allow transmis-sion of data containers irrespectiveof their actual contents (eg com-pressed video or audio data).

• The system should be robust and allow adjacent-channel operation ofanalog and digital TV signals in adensely occupied frequency band.

• The transmission standard shouldbe available well in time to enablenetwork operators wishing to adoptthe standard to start operation stillin 1997.

• Multiplex adaptation and energy dis-persal: multiplex adaptation throughappropriately standardized inter--faces, inversion of every eighth sync byte, energy dispersal for even power distribution in the trans-mission channel.

• Outer coder: coder with shortenedReed-Solomon code (204,188, t= 8),capable of correcting up to eight errored bytes in an MPEG2 trans-port-stream packet.

• Outer interleaver: interleaver with a depth of I = 12 for dispersal of burst errors to different packets so that higher probability of suc-cessful error correction is achieved.

• Inner coder: punctured convolu-tional code with code rates of 1/2, 2/3, 3/4, 5/6 and 7/8.

• Pilot and TPS signals (transmissionparameter signalling): insertion ofpilot carriers, some of which carrythe transmission parameters in cod-ed form as modulation signals.

• OFDM (orthogonal frequency-divi-sion multiplex): calculation of IFFTwith 2048 or 8192 carriers, with1705 or 6817 of which containingdata or transmission parameters,1512 or 6048 being exclusively re-served for payload data.

• Guard interval insertion: insertion of a guard interval for the OFDM signal, permissible intervals are1/4, 1/8, 1/16 or 1/32 of symbolduration.

• Digital/analog conversion: conver-sion of digital into an analog signal.

• Front end: conversion to outputchannel, usually in UHF range.

Guardintervalinsertion

MUXadaptation,

energydispersal

Outercoder

Outerinter-leaver

Innercoder

Innerinter-leaver

MapperFrame

adapta-tion

OFDM D/A Front end

To antenna

MUXadaptation,

energydispersal

Outercoder

Outerinter-leaver

Innercoder

Pilots &TPS

signals

Splitter

Videocoder

Audiocoder

Datacoder

ProgramMUX

TransportMUX

1

2

n

Functional block diagram of system (terrestrial channel adapter)


Digital Radio Tester CTS55 is a compactunit for testing GSM, DCS1800 andPCS1900 mobile phones in qualifiedservice [1]. Rohde & Schwarz has nowenhanced measurement and controlfunctions, making this successful testersuitable for new fields of applications.

The BER search routine offers an inter-esting application. Here CTS55 per-forms successive bit-error-rate measure-ments in the course of which the signallevel is continuously reduced relative to a selectable start value until the BERlimit, which can also be adjusted, isreached. With this function the sensi-tivity of a mobile phone can be deter-mined in an extremely easy way andwith high accuracy.

Another function of modern mobilephones – the short message service –can also be tested conveniently withCTS55. Without explicit call setup, either a text message is sent from thetester to the mobile phone or a messagereceived from the mobile phone. If anerror occurs in transmission, eg if thetext memory of the mobile is full, thetester will output a corresponding errormessage.

The module test mode (option CTS-B7)allows measurements and adjustments

of individual modules of mobile phonesor operation in the service mode. Forthis purpose CTS55 contains an RFsynthesizer that, in addition to GSM,DCS1800 and PCS1900 bands, alsocovers the 900 to 995 MHz and 1800to 1990 MHz bands. The level can beadjusted at two outputs in the range–10 to –110 dBm with or without burstshaping. Available modulation modesare “dummy burst modulation” with se-lectable midamble (training sequence)and “unmodulated”. After entry of the expected frequency, ie channelnumber, and power, the RF signal generator can synchronize to GSM sig-nals (FIG 1). Measurement is triggeredby pulsed signals on the received burstand by CW signals on a midamble.CTS55 then measures peak power, average power, power ramp versus timeas well as frequency and phase error.

The I/Q spectrum measurement func-tion allows simple checking or adjust-ment of an I/Q modulator module.Graphical display of the spectrum closeto the carrier provides a quick overviewof carrier and sideband suppression,while the delta marker functions allowqualitative assessment (FIG 2).

The remote-control function of CTS55(option CTS-K6) opens up further

possibilities. The tester can be fully controlled via an RS-232-C interface forsetting parameters, conducting measure-ments and reading out results. With fewexceptions, the remote-control com-mands are identical to those for theGSM testers of the CMD series [2]. Soautomatic test routines, as used for CMDtesters on repair lines in production forinstance, can also be implemented with CTS55. This means an interestingvariety of applications for the customer,such as automatic product-specific testroutines, test-result documentation, cen-tral evaluation or statistical analyses.

Gottfried Holzmann

REFERENCES

[1] Vohrer, M.: Digital Radio Tester CTS55 – All-in-one service tester for GSM, PCN andPCS mobile telephones. News from Rohde &Schwarz (1996) No. 152, pp 4–6

[2] Mittermaier, W.: Module test with Digital Radiocommunication Tester CMD52/55.News from Rohde & Schwarz (1995) No. 149, pp 36–37


Panorama

New measurement functions in Digital Radio Tester CTS55

FIG 1 Result of signal analysis in module test FIG 2 I/Q spectrum analysis with Digital Radio Tester CTS55


TÜV Rheinland (Technical InspectorateRhineland) is based in Germany andhas more than 50 overseas offices inover 30 countries. It is a private organi-zation with international activities thatcan look back on 125 years of experi-ence in the field of testing and certifyingtechnical installations and products. Theorganization also acts as an advisor togovernment and industry on technologyand safety matters. Of all the Germansafety standards authorities, TÜV Rhein-land is one of the largest and interna-tionally most widely known. The spec-trum of items tested and inspected byTÜV Rheinland is striking: everythingfrom an electric hair drier to a power sta-tion, from a toy train to a chemical plant.

TÜV Rheinland has been active in Asiasince 1978 and after a period of re-markable growth now employs over170 specialists from Germany and other European countries plus a host

of local professionals, currently totallingover 400 staff at 21 locations. TÜVRheinland Group Asia covers the entireFar East from fully fledged offices in Japan, Hong Kong, China, Taiwan,South Korea, Singapore, Indonesia,Thailand, the Philippines and India.

TÜV Rheinland in Asia offers the following services:• quality control and consulting,• safety and EMC testing for all kinds

of products from household appli-ances to industrial equipment andmedical apparatus,

• testing in TÜV’s own laboratories,• certification of quality and environ-

mental management systems ac-cording to ISO9000, QS9000 andISO14000 by TÜV-CERT,

• testing of vehicles, their parts andaccessories as well as certification oftheir compliance with internationalstandards,

• testing of children’s toys,• educational services by the TÜV

Academy,• support for companies who wish to

enter Asian markets through FEMAC(Far East Market Access GmbH).

Because of the mandatory implementa-tion of a European EMC directive earlyin 1996, industry in Japan like in othercountries has undertaken great effortsto comply with the new legislation. Thegeneral scarcity of EMC test facilitiesmeant serious problems in particular formanufacturers of large equipment suchas industrial or medical goods. EMC inspection is usually carried out at a test house, requiring the manufacturerto pack the product and transport it tothe test site. For large machinery, how-ever, this means disassembling, load-ing, transporting and reassembling themachine at the test house – a time-con-suming and expensive process. And

Panorama

T&M technology from Rohde & Schwarz for EMC mobile of TÜV Rheinland Japan

FIG 1EMC mobile of TÜV Rheinland Japan in the field


once testing is completed, the wholeprocess has to be reversed to return themachine to the factory.

To meet testing needs for large machin-ery or machinery requiring a specialoperating environment, the TÜV Rhein-land Japan office in Osaka devised anEMC mobile, a custom-built MercedesBenz van equipped with a miniature office and the latest in EMC test equip-ment (FIG 1). The van drives to thecustomer’s site, so time delays and ex-penses normally associated with trans-porting a machine to and from a testhouse are eliminated. And becausetesting is performed at the customer’sfactory, many resources like construc-tion plans, special tools and equipmentas well as personnel are readily avail-able. Customers also appreciate thefact that they can continue machine testing and assembly at their factorywhile EMC testing is in progress. Together these benefits add up to majorsavings in time and increased flexibilityfor the manufacturer.

When confronted with the difficult taskof choosing equipment for the EMCmobile, TÜV Rheinland defined the following key criteria, in addition to requiring full compliance with relevanttest standards:• After-sales service: the equipment

manufacturer was to have local Japanese facilities offering instantand reliable service in case of trouble. The provider of such servicemust be aware that any equipmentdowntime makes the customer dis-satisfied because he may not beable to keep to schedule.

• When used for testing at factories or being transported throughout thecountry, the measurement equip-ment is subject to an unusual amountof stress and strain. Extreme temper-ature changes, vibration, frequentsetting up and disassembly are just some of the factors to consider.The manufacturer was therefore tohave a reputation for high-qualityproducts.

• To ensure testing efficiency, themeasurement equipment should beeasy to use, but still flexible enoughto adapt to testing situations that candiffer from day to day.

As a result of these considerations, the following tests and products werechosen for the initial phase:

• measurement of radiated and con-ducted emission by LISNs, high-im-pedance probes and Receiver ESS,all from Rohde & Schwarz (FIG 2),as well as a bi-log antenna fromSchwarzbeck,

• measurement of electrostatic dis-charge, fast transient noise andsurge by generators and networksfrom Schaffner,

• measurement of conducted sus-ceptibility, again by equipmentfrom Rohde & Schwarz, in thiscase signal generators and powermeters.

After more than a year of service, thesechoices have proven to be right. Al-though the equipment has been sub-jected to a great deal of stress, no problems occurred. Neither repairs noradjustments were needed after calibra-tions, frequently performed to evaluatethe impact of environmental factors.The services offered by TÜV Rheinlandhave met with an extremely positive response from Japanese companies.The list of big-name firms already uti-lizing the services includes Shimadzu,Mori Seiki, Nissin High Voltage, Sumi-tomo Precision Products, Meiki, Ube Industries, Yutani Heavy Industries andKubota.

Michael Borgmann(TÜV Rheinland Japan)

Reader service card 155/15 for further informa-tion on EMC T&M technology

Panorama

FIG 2 EMC Test Receiver ESS from Rohde &Schwarz in action at TÜV Rheinland Japan

Photos: TÜV Rheinland Japan


Panorama

New from Cologne:telescopic masts with universal control unit

For many years Rohde & Schwarz Cologne has been fitting out vehiclesfor radiated emission testing, field-strength or coverage measurements,and not only with the required instru-mentation but also with telescopicmasts for the antenna systems. The Cologne plant has now developed Rotor Control Unit HSRG (FIG) for telescopic masts. HSRG features highreliability, simple manual operation via the front-panel keypad as well as effective remote control via an RS-232-Cinterface. Of course it can be adaptedto different types of rotors.

The desired extension height can be adjusted manually or automatically. Forrotating the antenna, an azimuth andan elevation rotator can be controlledindependently of each other (1° reso-lution of rotation angle). To ensuresmooth startup of the rotors, the rotatingspeed is kept low at first. The controlunit shows its strengths particularly incomputer-controlled use in test vehicles:automatic extension and retraction ofthe mast with monitoring of the pro-grammable mast configuration and in-dication of height and rotating angleon separate displays. Thanks to the integrated monitoring functions anyfaults are immediately detected and automatically signalled to the user, soincorrect handling that may cause an-tenna damage is excluded. All essentialparameters such as minimum and max-

imum extended height, minimum work-ing and transport height and the park-ing position required by the antennadesign are stored in an EEPROM.

The control unit comes as a bench model or 19-inch rackmount. Plug-in PC cards are provided for different conditions of use. The basic model isequipped for control of an azimuth rotor. Retrofittable optional PC cardsare available for polarization rotor (elevation) and mast control. Depend-ing on the application, power modulesfor 230 V AC and 12 or 24 V DC areavailable. The rotors can be driven with 12 or 24 V DC or 230 V AC. Theconnectors are rated for startup currentsof up to 50 A.

The electrically extendible telescopicmasts of the MxEA series are an idealmatch for Rotor Control Unit HSRG.They meet the stringent requirements in terms of reliability, stability and freedom from maintenance. The mainmechanical features such as little wearand tear, high carrying capacity andhorizontal top load show their benefitsespecially in mobile use. The mast sections are made of ALU F22, otherparts of stainless steel. The mast is driven by a 12/24 V DC motor in aweatherproof enclosure. Masts areavailable with extension heights of4600 up to 9150 mm, as well as suitable rotors and accessories such asroof feedthroughs for different types ofvehicles and special mast feet. Rohde &Schwarz Cologne also offers completeintegration as a service package:everything from a single source.

Helmar Scherpe


Rotor Control Unit HSRG for local or remote control of telescopic masts of MxEA seriesPhoto: R&S Cologne


Information in print

Software SME-K2 runs under Windows and setsSignal Generator SME to signals to GSM, DCS1800,DCS1900, IS136 DECT or PDC standards.

Data sheet PD 757.3092.21 enter 155/17

Spectrum Analyzers FSE (20 Hz to 40 GHz) 40 GHz models FSEK20 and FSEK30 are now covered by the data sheet.


Security System ComSaveBox from SIT (Gesell-schaft für Systeme der Informationstechnik mbH)encrypts serial data transmission (also available inform of a PCB as Security System ComSave).


LaserVision TS-LV1, TS-LV2 for optical componenttesting are available as a complementary system(LV1) for parameters not covered by electrical tests and as a complete stand-alone system (LV2); numerous options.


EMI Test Receiver ESCS30 (9 kHz to 2.75 GHz) iscompact, compliant to standard (CISPR 16-1) andhas a 6.5-inch colour screen; level measurementrange from –38 to +137 dBµV, measurement error<0.5 dB (typ.), integrated preselection, macrofunctions; IF spectrum analysis, tracking generatorand OCXO reference oscillator available as op-tions, internal/external battery operation.


TV Test Transmitter SFQ (0.3 MHz to 3.3 GHz)provides standardized and also variable digital (4PSK, DVB-S, QAM, DVB-C) and analog satellitesignals (depending on model used); FM or ADRsound subcarriers as well as noise signals (op-tions); optional ASI input.


MPEG2 Measurement Generator DVG providesdigital TV test signals to 525- and 625-line standard (moving/still video, audio, data) at akeystroke; infinite sequence length, selectable PID;various interfaces.


MPEG2 Measurement Decoder DVMD monitors,analyzes and decodes 19 DVB signals at a time;two-line LC display, OSD on external screen; various interfaces.


Radiomonitoring System RAMON (10 kHz to 40 GHz) is a modular system that can be anythingfrom a portable receiver to a nationwide networkfor monitoring, location and analysis, dependingon the individual application.

Info PD 757.3234.21 enter 155/27

Message Handling Software PostMan serves forthe integration of shortwave and VHF-UHF radiolinks into international communications networksunder WindowsNT.


VHF Manpack Radio XV3088 (30 MHz to89.975 MHz; 0.2 W or 5 W) Modular transceiv-er system for mobile/stationary use; simplex/half-duplex, selective/group call, voice scrambler, sub-audio squelch; numerous options (among othersfor 25 and 50 W).


VHF/UHF Airborne Transceiver Family 610 Thedata sheet has been revised and now appears inthe new design (new order number).


Digital IF Spectrum Display EP090 Besides somemodifications, the frequency specifications for theAF input (30 Hz to 20 kHz), IF input (30 kHz andabove 50 kHz) and sweep (to 1 MHz/s) have beennewly defined.


New application notes

Limit Checking with Audio Analyzers UPL or UPDAppl. 1GA33_1E enter 155/32

Measurements on Frequency-Converting DUTs using Vector Network Analyzer ZVRAppl. 1EZ31_E enter 155/33

Schz

This CD, which will be available free of chargefrom all Rohde & Schwarz representatives as ofAugust this year, gives an overview of productsand services provided by Rohde & Schwarz in thefields of T&M, sound and TV broadcasting. The CDcomprises the contents of the printed catalog plusthe new equipment from Rohde & Schwarzlaunched before May 97. It can be run on any 486 or higher standard PC. Finding any product is made easy by comprehensive instructions, navi-gation aids and a full-text search function.

In addition, the completely revised Sound and TVBroadcasting Catalog is now available in print. Itpresents, among other equipment, new DVB andDAB transmitters including all equipment neededfor building up DVB/DAB systems, the TV Test andMonitoring System Family TS6100, Audio DataTransmission System ADAS/AMON, Program In-put Rack PI6200, new broadband-communicationsystem components and signal generators for digital signals as well as Receiver Family EFA andAudio Analyzer UPL.

Catalog PD 756.7294.23 enter 155/23

Catalogs “Test & Measurement Products” and “Sound and TV Broadcasting”now for the first time on CD-ROM

Is your data as secure as the rest of your com-pany? asks SIT (Gesellschaft für Systeme der In-formationstechnik mbH) in its new brochure, thusoffering the services of Rohde & Schwarz also inmatters of security.

Info PD 757.3328.21 enter 155/22

Catalogs

Test & Measurement Products

Cata

log

Sound and TV Broadcastinganalog/digital

Cata

log


Newsgrams

Fully automated EMC test facilityopens at Panasonic in Wales

One of the biggest and most up-to-date EMC test facilities in the UK hasbeen opened at Panasonic’s Euro-pean Television Division in SouthWales. It enables the company to reduce their testing time by a factorof ten. The recent inauguration cere-mony (photo above) marked thecompletion of two years of work involving Rohde & Schwarz, whosupplied the fully automated turnkeysolution, and Hemford Communica-tions, supplier of the anechoic cham-ber. Together Charles Toda (frontcenter), Managing Director of Pana-sonic European Television Division,and Dr Wolfgang Winter (frontright), Managing Director of Rohde& Schwarz UK, cut the ribbon at theentrance to the anechoic chamber.Rohde & Schwarz has been supply-ing transmission and test equipmentto Panasonic for more than 17 years,so it came as no surprise when thecompany was awarded the contractfor designing the EMC test facility.The facility includes two TS9980systems for immunity testing, two ESBI receivers for emission measure-ments up to 5 GHz, and a completeset of products for the anechoicchamber. Testing is conducted toEN55013 and EN55020.

This new completely automated facility will be used almost entirelyfor batch testing, enabling Pana-sonic to conform to the 80/80 rule(80% of units pass the test with aconfidence level of 80%). Thepresent production rate of more than4000 TV sets per day makes that absolutely essential. According toPhil Josty, responsible for the projectat the Panasonic end: “With ascheme as huge as this we had to

award the contract to a capable and well established organization.Rohde & Schwarz was the only com-pany who could meet our criteria”.This latest delivery brings the totalvalue of Rohde & Schwarz EMC test equipment in use at Panasonic to around one million pounds. Thisincludes equipment used purely for design and development.

T. Stephens

Reference test engineering from Munich for booming US mobile-radio market

Type testing of mobile stations to PCS(Personal Communications Service)standard for the North-Americanmarket has been obligatory as of thebeginning of June 1997 as part ofCTIA (Cordless Telephone IndustryAssociation) type certification. By

agreement with the PCS network op-erators represented in the PCS1900Type Certification Review Board (PTCRB), the internationally knownGerman test house and service enterprise CETECOM was selectedfor the type-certification tests. CETECOM will be using Rohde &Schwarz equipment throughout forits tests on the air interface. ThusRohde & Schwarz extends its world-wide leadership in test engineeringfor type certification.

In the general-purpose Test SystemTS8915B (photo below), based on Radiocommunication Test SetCRTC02 (see page 30 in this issue),Rohde & Schwarz has already im-plemented more than 200 test cases– of 283 – for the PCS1900 band. To guarantee conformance of thetests with standards, CETECOM andRohde & Schwarz have decided to cooperate with the objective of ensuring timely test-case validation.So, for example, all RF tests fromphase II of European GSM type testing are already available forPCS1900 certification. Virtually allthe signalling procedures needed –some 150 – can be performed withboth the CRTC02 tester and theTS8915B system. PI

Rohde & Schwarz and Tektronix extend their marketing cooperation

Rohde & Schwarz and Tektronix Inc. of Wilsonville, Oregon/US, an-nounced extension of their globalmarketing agreement at the begin-

ning of April this year, with the aimof providing customers worldwidewith a complete range of test andmeasurement equipment for digitaltelevision. Under the terms of theagreement Tektronix will marketRohde & Schwarz developed MPEGand DVB test and measurementequipment in North and SouthAmerica, Pacific Rim and Asia,while Rohde & Schwarz will be responsible for marketing in Europeand Japan as well as the MiddleEast. The two companies are thus intensifying their successful coop-eration, begun in August 1993, and which has already seen joint de-velopment projects like test andmeasurement equipment for theNorth-American mobile-radio net-work (CDMA) and achievement ofan excellent position on the market.

“This agreement builds on the suc-cessful partnership we have estab-lished over the past several yearsand significantly leverages the resources both companies bring toour customers in the television and broadcast markets”, explainedDan Terpack, President of Tektronix’Measurement Business Division. “With this new chapter in our rela-tionship we will be working togetherclosely to bring an even stronger setof tools and solutions to a market-place undergoing dramatic changesas it moves to digital”. According toReinhard Bruckner, President andCOO of Rohde & Schwarz, this expansion of relationships gives customers worldwide ready accessto the broadest and most capablefamily of digital television test andmeasurement equipment currentlyavailable on the market. PI


Newsgrams

Rohde & Schwarz faculty prizein Jena

The faculty prize for outstanding scientific achievement, donated byRohde & Schwarz, was awarded at the beginning of the year during a special colloquium convened bythe dean of the physics and astrono-my faculty, Professor Dr RolandSauerbrey, of Friedrich Schiller University in Jena. The prize for thebest dissertation in 1996 was pre-sented by engineer Karl-Otto Müller,responsible for university contacts at Rohde & Schwarz, to Dr JörgGehler of Fraunhofer Institute for applied optics and precision mechanics. The prize for the bestgraduate thesis went to physicistSandor Nietzsche.

Dr Gehler’s work “Experimental in-vestigation of new kinds of photoncomponents based on resonantwaveguides in SiON and KTiOPO4”attracted a lot of international inter-est and resulted in an invitation toJapan. There he is continuing his research at Kanagawa University forScience and Technology in Kawasa-ki. In his lecture Dr Gehler (left in thephoto above, right Prof. Sauerbrey)explained and illustrated the newprinciple. Its economic significancestems from the possible multiple useof optical fibers in wavelength multi-plexing. The thesis submitted by Sandor Nietzsche “Design and testing of basic configurations forposition detectors with SQID ” is ofimportance for basic research inphysics, allowing the space betweentwo closely adjacent bodies to bemeasured more precisely by severalorders of magnitude than was pre-viously possible. This means that examination of the equivalence prin-ciple of the equality of gravitationaland inert mass can be performedmuch more accurately.

In the awarding of the prize for1996 Rohde & Schwarz continued atradition that goes back six years.The recipients of the prizes are chosen by the university. In this way Rohde & Schwarz demonstratesits interest in excellence in scienceeducation. AS

Security for modem linkswith ComSaveBox

SIT, an affiliate of Rohde & Schwarzengaged in systems for informationsecurity, is offering ComSaveBox (large photo below) for online encryption of a modem link. Thecompact unit with its RS-232-C inter-face is connected between PC andmodem and encrypts data up to 115 kbaud. Transmission rates up to 110 kbaud are achieved in the useof ISDN modems with B-channeltrunking. Applications for ComSave-Box are secure data transmission intelejobs, mailboxes, remote mainte-nance and network linking. Initial-ization of ComSaveBox and codeentry are possible by PC software. Asecure, symmetrical block algorithm

is used for encryption. It has a codelength of 128 bits and is an insuper-able barrier even for the latest methods of cryptoanalysis. SIT is also offering the ComSave plug-incard for PCs (small photo), com-patible with ComSaveBox and pro-viding the same functionality (readerservice card 155/19).

F. Bergmann

Shortwave experts from Rohde & Schwarz help stage course by Carl Cranz Society

Although today’s telecommunicationlinks are cable, fiber optic or by satellite for the most part, the short-wave band – 1.5 through 30 MHz –is enjoying increased popularity. It isespecially interesting for administra-tions, embassies, armed forces andin amateur radio. Data transmissionby shortwave has also taken ongreater significance in recent years.Data rates of 4.8 kbit/s or even 5.4 kbit/s can be achieved throughthe use of modern digital trans-mitting and receiving techniques.

The Carl Cranz Society showed itsinterest in this development by including a course “Radio transmis-sion by shortwave” in its 1997 pro-gram. The course was held inOberpfaffenhofen in April, stagedby Prof. Dr Friedrich Jondral ofKarlsruhe University and a team ofshortwave experts from Rohde &Schwarz – Dr Günter Greiner, Johann Hackl, Peter Iselt, Dr ChristofRohner and Bernhard Wolf. Thecourse began with an introduction tothe fundamentals (physical featuresof shortwave, modulation and trans-mission security, transmission andreception techniques, MIL-STD-188-110A) and moved on in the secondpart to equipment and systems engineering (shortwave antennas,transceivers, modems and radioprocessors, interfaces with the user, network structures and stationdesign). To round off the course therewere demonstrations of modernshortwave transmission systems atRohde & Schwarz in Munich. Thecourse was attended by 28 personsfrom industry, administrations andthe armed forces, and the consensuswas that the event had been a success worth repeating. PI/CC

Phot

o: M

ülle

r


Press comments

The RF and microwave magazine “hf-praxis” putEMI Test Receiver ESCS30 from Rohde & Schwarzinto just the right perspective on the cover of its5/97 edition. But it is not only attractiveness thatcounts – the instrument also excels through its6.5-inch VGA TFT colour display, sophisticatedspecifications, lean dimensions and favourableprice.

The Austrian electronics magazine “ Elektronik-schau” showed a composition as the title spreadof its 1-2/97 edition on the subject of electro-magnetic compatibility, centering on SoftwarePackage EMS-K1 from Rohde & Schwarz.

The editors of the British magazine “ What’s newin Electronics” awarded TV Test Receiver EFAfrom Rohde & Schwarz a preferred positioningon the cover of their April 1997 issue.

To mark the launch of the European issue of theAmerican electronics magazine “EDN”, the Euro-pean editor Brian Kerridge (photo) introducedhimself to readers in an informative brochure. As his platform he chose a photo from Rohde &Schwarz, showing Digital Radio Tester CTS55.

Edition 1-2/97 of “productronic” showed a part view of the LaserVision II optical test systemfrom Rohde & Schwarz on its title page and wenton inside to tell of the benefits of this modernsystem for optical testing of populated boards.

Module test systems fromRohde & Schwarz for automobile industryThe monthly “Automobil Industrie”, published inWürzburg, which looks at every kind of automo-bile topic, described in its 4/97 issue the prob-lems of sensitivity to an electromagnetic environ-ment resulting from the increased use of differentkinds of controllers in car design. But it alsoshowed the solution – the new Automotive Pro-duction Test System APTS from Rohde & Schwarz:

At the end of 1996 Rohde & Schwarz presentedthe new Automotive Production Test System APTSfrom the family of TSUx systems. It is primarily in-tended for performance testing of all kinds of auto-motive electronic circuitry. What is special about itis a modular plug-in called the automotive loadsystem (ALS). This can hold up to 24 modules forsimulating the special loads and signal sources inautomotive electronics. … A number of modulesfor the major applications like ABS, airbag, motormanagement and chassis control are alreadyavailable.

The world’s first, compactmultimode radiocom testerfor GSM, DCS1800,DCS1900 and DECTis how the British electronics magazine “Compli-ance Engineering” presented Digital Radio-communication Tester CMD65 in edition 3-4/97:

In Digital Radiocommunication Tester CMD65 Rohde & Schwarz has brought out the only instru-ment uniting GSM, DCS1800/1900 and DECT testing capability in a single unit. CMD65 is the latest model from the successful CMD platform, supporting GSM, DCS, DECT, PCD and CDMA testson mobiles and base stations. In both volume andweight it is the smallest and lightest tester of its kind.(See also article on page 6 in this issue.)

PostMan knocks on e:mail door“CommsMEA”, a magazine appearing in theMiddle East and Africa, reported in its 3/97 issueon Rohde & Schwarz’s PostMan software:

The PostMan message-handling software is one ofthe first solutions for the proven and cost-attractiveshortwave medium that offers access to worldwidecommunication networks. PostMan opens up thewhole world of international communication – formerly the reserve of cable networks – coveringislands, deserts and the polar regions.


Final article

Fast and secure data transmission on shortwave –result of intensive research

The sophistication of Rohde & Schwarz’sALIS processor for automatic link setupand shortwave-link adaptability is theresult of technical advances and con-tinuous experimentation and trials [1].By variation of the system parametersframe length, redundancy, type of modulation and frequency, the HF trans-ceivers of the XK2000 family (FIG 1)[2] show high capability in adapting to time-variant channel quality and can achieve data rates up to 3.6 kbit/susing Modem GM2100 (max. 5.4 kbit/s)and the RSX.25 protocol.

Measuring quality ofshortwave channels

To obtain typical values for variations of channel quality with time and for the availability of shortwave channels,Rohde & Schwarz carried out trials withprototypes of the ALIS processor on aradio link between Hamburg and Munich at the beginning of 1985 [3].After link setup, data blocks were sentcontinuously for periods of one hour at a rate of 100 bit/s, with transmitteroutput of 100 W, 2FSK modulation deviation of ±42.5 Hz and filter band-width of 150 Hz. BER (bit error rate)was continuously determined and recorded. FIG 2 shows typical BER over

a period of one hour on a channel ofgood quality. For the most part it is be-low 1%. FIG 3 illustrates deteriorationof the originally good channel qualityafter about 20 min and an increase ofBER from less then 1% to figuresbetween 10 and 50%.

Relative outages of the tested channelsare presented in FIG 4 (mean valuesover two weeks). BER above 10% was considered a channel failure. Four outage spans were defined: 0 to 12.5 s/12.5 to 30 s/30 to 60 s/60 sto 1 h. The following results were obtained. Failures in the three groupsbelow 60 s occur with approximatelythe same frequency, but this is consider-

ably less than that for failures between60 s and 1 h. In other words, if BER exceeds a threshold of 10%, the prob-ability of the failure lasting longer than1 min is significantly higher than thechannel recovering after a short period.This leads to the conclusion that achange of channel is the best reactionfor restoring quality once outage hasreached 1 min.

FIG 1 HF Transceiver XK2100 with integratedALIS Processor GP2000 and HF Modem GM2100

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FIG 4 Relative outage of shortwave channels(FSK, 150 Hz bandwidth, 100 bit/s, 100 W)

FIG 2 BER for shortwave channel between9:00 and 10:00 h (7.512 MHz, FSK, 150 Hzbandwidth, 100 bit/s, 100 W)

FIG 3 BER for channel between 15:00 and16:00 h (8.165 MHz, FSK, 150 Hz bandwidth,100 bit/s, 100 W)


Final article

Automatic adaptation of system parameters to channel quality

The above trials showed that channelquality in Europe varies strongly and rapidly. For this reason the ALIS con-cept attaches great importance toadaptive matching of radio parametersto momentary channel quality. Based

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FIG 5 Throughput and frame length on goodshortwave channels; low variation of channelquality and thus frame length

FIG 6 Throughput and frame length on medium-quality shortwave channels. Two adaptive fre-quency changes can be seen in center. In firstcase suitable frequency was found after five tries,in second case one try was sufficient.

FIG 7 Mean throughput on channel during day-time (RSX.25, 8PSK); at about 16:00 h through-put starts to fall off.

on measurements of current channelquality, the system is provided with allthe information needed for selecting orchanging frequency when a link is setup and during data transmission.When a suitable frequency for link set-up is selected, the levels last measuredin the channels (passive channel analy-sis) plus a forecast analysis are taken ascriteria for channel availability. Variousparameters can be used to measurechannel quality during transmission, ieactive channel analysis. The efficiencyof the data-transmission method is ahighly indicative parameter, easy to obtain and adequate for deciding what measures to take. The followingparameters can be varied to maintainan established link: transmitter outputpower, (frame) length of data packets,redundancy for detecting and correct-ing transmission errors, bandwidth,type of modulation (parameters directlyaffecting data rate) and frequency.

When the ALIS system was first im-plemented with a conventional FSK modem, the transmission channel was changed in the presence of per-sistent interference. With HF ModemsGM857C4 and GM2000 [4] and the RSX.25 protocol, specially createdfor this purpose, it became possible to adapt several parameters – framelength, number of frames per packetand frequency – to channel quality. Plusthere was the use of narrowband 2FSKmodulation. RF power is not adaptedbecause transmission is usually at full level and this would produce no im-provement. The RSX.25 protocol usedwith the new modem generation is amodified AX.25 packet radio protocol.The advantages compared to earliershortwave communication protocolsare: use of a common channel in a network, routing and relay function, bi-directional communication and greaterflexibility of frame structure due to asynchronous transmission. With 8PSK the net data rate of the serial modemwith adaptive echo cancellation is5400 bit/s. Errors are at first correctedby FEC (forward error correction, con-volutional code, 1/2 code rate, Viterbi

decoding), which reduces net data rateto 2700 bit/s. Errors escaping FEC areeliminated by the ARQ (automatic re-peat request) procedure of the RSX.25protocol.

FIGs 5 and 6 show the results from fieldtrials with HF Transceivers XK2000 onchannels of good and medium quality.These trials were carried out in early1993 on a link between Bonn and Munich. The upper trace represents theefficiency of the RSX.25 transmissionprotocol, while the lower one showshow frame length varies between 16and 250 bytes. FIG 7 illustrates aver-age throughput between 10:00 and21:00 h on a particular day.

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FIG 9 Adaptability of frame length (bytes/frame), throughput versus S/N ratio


Final article

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FIG 10 Comparison of STC and RSX.25 proto-cols, throughput versus S/N ratio

FIG 11 Comparison of RSop2 (RSX.25 + selec-tive repeat ARQ + adaptive modem speed) andRSX.25 protocols

Further improvement of RSX.25 transmission protocol

To investigate possibilities for improv-ing the RSX.25 protocol, Rohde &Schwarz compared it by computer sim-ulation with the STC protocol devel-oped by and named after the ShapeTechnical Centre [5]. Major features ofthis STC protocol are the adaptive datarate of the modem, which matches typeof modulation (8-, 4-, 2PSK) and redun-dancy, and selective repeat ARQ. Themaximum data rate of the modem is2.4 kbit/s, yielding a maximum datarate of the ARQ protocol of around 2 kbit/s. The RSX.25 protocol adaptsframe length in the memory-go-back N-ARQ. The modem, otherwise identi-cal, achieves a data rate of 2.7 kbit/sbecause of a different ratio of test todata bits. Thus a maximum data rate of2.5 kbit/s is obtained for the RSX.25protocol. However, even in the dia-gram normalized to the same modemrate and at higher S/N ratios, the trans-mission rate of the RSX.25 protocol issomewhat higher than that of the STCprotocol because of the slightly loweroverhead.

The advantages of an adaptive modemrate can be seen from FIG 8, those ofthe adaptive frame length from FIG 9,where the data-rate improvement isshown as a function of S/N ratio(ES/N0). The greater robustness of the modulation at lower modem rates isattained by increasing the phase angleof the mPSK modulation and the re-dundancy in the coder of the modem,while shortening frame length reducesthe probability of bit errors in the frameand thus the need for data repetition.

The two protocols are compared in FIG 10. At low S/N ratios the adap-tation of modulation method and re-dundancy has a greater effect, andhere the STC protocol produces higherthroughput. Above an S/N ratio of 17 dB, the throughput of the RSX.25protocol is higher even in the normal-ized display because of the lower over-head, particularly when long frames

are transmitted. FIG 11 compares theRSX.25 protocol and an optimizedform of it called RSop2. The latter usesan adaptive modem data rate, adap-tive frame length and selective repeatARQ. Throughput improves in thewhole S/N range.

As a result of what was learnt from the comparative simulation, Rohde &Schwarz developed HF ModemGM2100 [6] for HF TransceiversXK2000. This offers different types ofmodulation (2-, 4-, 8PSK) and redun-dancy (1/2, 1/3, 5/6, 1/1 coderates) and features maximum data rate of 5400 bit/s. The modem was integrated in an optimized RSX.25 pro-tocol that controls modulation and re-dundancy adaptation. With the aid ofthis protocol, data rates of 3600 bit/scan be achieved on undisturbed links,ie considerably more than the 2 to 3 kbit/s of conventional shortwavelinks.

Dr Günter Greiner

REFERENCES

[1] Greiner, G.: Reliable shortwave with ALIS.News from Rohde & Schwarz (1987) No. 116, pp 47– 50

[2] Helmke, B.; Wachter, G.: HF TransceiverXK2100 – Digital shortwave for future-proof,long-haul communication. News from Rohde& Schwarz (1994) No. 144, pp 4 –7

[3] Greiner, G.: Kurzwellenkommunikation: Historischer Überblick über die Entwicklungund Diskussion moderner Verfahren. telekompraxis, Schiele & Schön GmbH, Berlin,23–24 (1989), 1–2 (1990)

[4] Hackl, H.: Secure data transmission with2700 bit/s on shortwave links. News from Rohde & Schwarz (1994) No. 146, pp 29–31

[5] Eken, F.; Clark, D.; Voordouw, H.: High-Fre-quency Open Systems Interconnection DataLink Protocol, Technical Memorandum ShapeTechnical Centre TM-930 (1993)

[6] Wicker, G.; Greubel, G.: Fast adaptive data transmission on shortwave at up to5400 bit/s with HF Modem GM2100. Newsfrom Rohde & Schwarz (1996) No. 152, pp 42 –43


ROHDE& SCHWARZ GmbH & Co. KG · Mühldorfstraße 15 · D-81671 MünchenP. O. B. 8014 69 · D-81614 München · Tel. (+49 89) 41 29-0 · Fax (+49 89) 41 29-21 64

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