Interference from Radars into Adjacent Band UMTS ... - … · ERA Business Unit: ERA Technology...

ERA Business Unit: ERA Technology

Report Title: Interference from Radars into Adjacent Band

UMTS and WiMAX Systems

Author(s): Z Wang, M Ganley, Bal Randhawa, I Parker.

Client: Ofcom

Client Reference: Kamlesh Masrani

ERA Report Number: 2007-0554

ERA Project Number: 7G0403803

Report Version: Final Report

Document Control: Commercial-in-Confidence

ERA Report Checked by:

Approved by:

Stephen Munday

Ofcom Resource Project Manager

Martin Ganley

Head of RF & EMC

September 07

Ref. C:\ERA\Ofcom 2.6GHz radar\Final Report.doc

ERA Report 2007-0554

Ref: C:\ERA\Ofcom 2.6GHz radar\Final Report.doc

© ERA Technology Ltd

2

© Copyright ERA Technology Limited 2007 All Rights Reserved

No part of this document may be copied or otherwise reproduced without the prior written permission of ERA Technology Limited. If received electronically, recipient is permitted to make such copies as are necessary to: view the document on a computer system; comply with a reasonable corporate computer data protection and back-up policy and produce one paper copy for personal use.

Disclaimer

This report ("report") has been prepared by ERA Technology Ltd for Ofcom, in connection with the award of wireless

telegraphy licences to use the three spectrum bands at 2500-2690 MHz and 2010MHz -2025MHz (the “Spectrum Bands”).

This report is intended for information purposes only. This report is not intended to form any part of the basis of any

investment decision or other evaluation or any decision to participate in the award process for the Spectrum Bands, and

should not be considered as a recommendation by Ofcom or its advisers to any recipient of this report to participate in the

award process for the Spectrum Bands. Each recipient of this report must make its own independent assessment of the

potential value of a licence after making such investigation as it may deem necessary in order to determine whether to

participate in the award process for the Spectrum Bands. All information contained in this report is subject to updating and

amendment.

The content of the report, or any other communication by or on behalf of Ofcom or any of its advisers, should not be

construed as technical, financial, legal, tax or any other advice or recommendation. Accordingly, any person considering

participating in the award process for the Spectrum Bands (either directly or by investing in another enterprise) should

consult its own advisers as to these and other matters or in respect of any other assignment of any radio spectrum.

Limitations

The results detailed in this report apply only to the tests made at that time, using the test equipment detailed and are

indicative. They do not indicate that on another date an identical set of results may be achieved, due to changes in the local

environmental conditions, characteristics of different receivers, test equipments or other factor which may or may not have

an effect on the measurement results obtained at that future time.

DOCUMENT CONTROL

If no restrictive markings are shown, the document may be distributed freely in whole, without alteration, subject to Copyright.

ERA Technology Ltd Cleeve Road Leatherhead Surrey KT22 7SA UK Tel : +44 (0) 1372 367000 Fax: +44 (0) 1372 367099 E-mail: [email protected]

Read more about ERA Technology on our Internet page at: http://www.era.co.uk/




3

Summary

Ofcom has recently commissioned a series of technical studies in support of the award of

spectrum in the band 2500 to 2690 MHz [1], [2] which could possibly be occupied in the

future by systems such as UMTS or WiMAX. This band is very near to the band 2700 to

3100 MHz used by aeronautical and military radars and there is the potential for adjacent

channel interference from radars into the 2.6GHz band due to the nature of radar out-of-

band (OOB) and spurious emissions. Ofcom commissioned ERA Technology Ltd to

undertake a measurement programme to identify the potential for interference to UMTS and

WiMAX systems operating in adjacent bands to aeronautical and military radars. This report

details the measurements that were undertaken and the conclusion drawn by ERA on the

findings.

Measurements were undertaken at four airports characterising the emissions arising from

solid-state, Travelling Wave Tube (TWT) and magnetron technologies. In addition, laboratory

measurements have been performed using simulated radar signals generated by a

Frequency Agile Signal Simulator and a signal generator (using pulse building software).

The conducted laboratory based measurements have been used to gain a deeper

understanding of the interference mechanism from radar emissions into UMTS(mobile

modelled according to specifications ETSI 3GPP TS 25.101) and WiMAX systems(fixed user

unit modelled according to specifications IEEE 802.16-2004).

It was determined in the laboratory that the degradation of the UMTS and WiMAX systems

was dominated by the average power experienced, as a result of the radar side-lobe

emissions, as opposed to the intermittent peak experienced from the radar antenna main

beam. It is therefore found to be important to be precise in the methodology used for the

calculation of any C/I protection criteria (whether peak or average interference) and how

these are used in subsequent interference simulations. Protection criteria based on both

peak and average interference levels are given within the report for comparison. Also

provided for comparison are the level of Carrier Wave (CW) and Additive White Gaussian

Noise (AWGN) emission required to cause co-frequency interference to the UMTS or

WiMAX system.

ERA’s analysis of the results from the airport measurements indicate that the bit error rate

(BER) in the presence of the measured radar interference was less than 10e-3 (0.1%) to

either the UMTS or WiMAX systems at a separation distance of 600m from the radar and

with a set minimum usable carrier signal for the wanted system. These results were based

on the measurement of BER within a reference UMTS channel having a user data-rate of

12.2 kbps, and into a reference WiMAX channel having a user data rate of 1.5mbps. It

should be noted the study did not consider the effect of radar interference to other system

parameters such as quality of service or the impact radar interference has on particular

types of communication applications (e.g., voice, video, and different types of data

transmissions).




4

All the results were established on the basis of the radar interference being co-channel with

the communications receiver. In practice, the communications systems operating in the

2.6GHz band may well be separated greater than about 18 MHz away from a radar centre

frequency and, as such, may be expected to experience radar powers at least 20 to 30dB

below the co-frequency radar power level.

The measurements could not be used to determine the exact Carrier-to-Interference (C/I)

protection ratios, as no significant interference was experienced. However, they can be used

to specify the maximum value of C/I likely to be experienced. This was determined by

comparing the minimum carrier signals used with the maximum radar interference level

measured at each of the four Airports, when the radar and the UMTS/WiMAX receiver were

operating in the same channel.

The calculated maximum C/Is that could be experienced are shown in the following tables:

UMTS TWT/Airport A TWT/Airport B SS/Airport C Magnetron/Airport D

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

Max peak,

Max hold

-92 -21 -71 -92 -20 -72 -92 -32 -60 -92 -22 -70

Max Peak,

Average

-92 -62 -30 -92 -44 -48 -92 -64 -28 -92 -55 -37

WiMAX TWT/Airport A TWT/Airport B SS/Airport C Magnetron/Airport D

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

Max peak,

Max hold

-60 -12 -48 -60 -11 -49 -60 -19 -41 -60 -13 -47

Max Peak,

Average

-60 -42 -18 -60 -35 -25 -60 -58 -2 -60 -42 -18




5

Contents

Page No.

1 Introduction 14

2 Objectives 15

3 Test Methodology 16

3.1 Introduction 16

3.2 Identification of radars 17

3.3 Radar interference into UMTS 20

3.4 Radar interference into WIMAX 23

3.5 Measurement Procedure 25

4 Results 26

4.1 Measured Radar Emissions 26

4.1.1 TWT/airport [A] 26

4.1.2 TWT/airport [B] 30

4.1.3 Solid State/Airport [C] 33

4.1.4 Magnetron/Airport [D] 37

4.2 Interference from Radar into Communications Equipment 39

4.2.1 Interference from Radar into UMTS DL 40

4.2.2 Interference from Radar into WiMAX 43

4.3 Conducted measurements of simulated radar emissions 44

4.3.1 Conducted measurements of C/W and AWGN 44

4.3.2 Simulated radar emissions using FASS 45




6

4.3.3 Simulated radar emissions using a Signal Generator 45

5 Conclusions 46

6 References 48

APPENDIX A 49

APPENDIX B 54

APPENDIX C 57




7

Tables List

Page No.

Table 1: Typical ATC radar parameters ..................................................................................18

Table 2: UMTS downlink signal parameters ...........................................................................20

Table 3: DL reference measurement channel physical parameters (12.2 kps)......................21

Table 4: UL reference measurement channel physical parameters (12.2 kps)......................21

Table 5: Out of band blocking and Spurious Response .........................................................21

Table 6: Frequency offsets for concerned UMTS and radar frequencies...............................22

Table 7: Wanted WiMAX signal parameters ...........................................................................23

Table 8: Frequency offsets for concerned WiMAX and radar frequencies.............................24

Table 9 Calculation of received maximum signal levels .........................................................41

Table 10: Maximum C/I values for radar to UMTS interference .............................................43

Table 11: Maximum C/I values for radar to WiMAX interference ...........................................44

Table 12: Measured C/I using AWGN and CW interference sources ....................................44

Table 13 Statistics Distribution of interference level ...............................................................59




8

Figures List

Page No.

Figure 1: Example of radar emission mask and out-of-band and spurious emissions falling

into potentially new UMTS/WiMAX bands .......................................................................15

Figure 2: 2.6 GHz award band adjacencies ............................................................................16

Figure 3: Example of measured harmonics from a magnetron radar.....................................18

Figure 4: Radar interference zones.........................................................................................19

Figure 5: Illustrative radar pulse train as seen by a stationary receiver .................................19

Figure 6 Radar emission measurement setup ........................................................................20

Figure 7: Conducted measurement setup for radar interference into UMTS .........................22

Figure 8: Conducted measurement setup for WiMAX 802.16-2004.......................................25

Figure 9: Measurement location of TWT/airport [A] ................................................................27

Figure 10: Measured emissions at TWT/airport [A] showing a large number of consecutive

radar sweeps individually, using a peak detector, and max-hold for the length of one

radar rotation. ...................................................................................................................28

Figure 11: Measured emissions at TWT/airport [A] using a peak detector, and showing the

“max hold” and average result over a long time period. ..................................................28

Figure 12: Measured emissions at TWT/airport [A] using a peak detector, and showing the

emissions in the band 2.5 to 2.69 GHz. ...........................................................................29

Figure 13: Measured emissions at TWT/airport [A] in the frequency band 2.5 to 2.69 GHz,

showing the probability of any given received power level..............................................30

Figure 14: Measurement location of TWT/airport [B] ..............................................................31

Figure 15: Measured emissions at TWT/airport [B] showing a large number of consecutive

radar sweeps individually, using a peak detector, and max-hold for the length of one

radar rotation. ...................................................................................................................32

Figure 16: Measured emissions at TWT/airport [B] using a peak detector, and showing the

“max hold” and average result over a long time period. ..................................................32




9

Figure 17: Measured emissions at TWT/airport [B] in the frequency band 2.5 to 2.69GHz,

showing the probability of any given received power level..............................................33

Figure 18: Measurement location of Solid State/Airport [C]....................................................34

Figure 19: Measured emissions at solid state/Airport [C] showing a large number of

consecutive radar sweeps individually, using a peak detector, and max-hold for the

length of one radar rotation. .............................................................................................35

Figure 20: Measured emissions at solid state/Airport [C] using a peak detector, and showing

the “max hold” and average result over a long time period. ............................................35

Figure 21: Measured emissions at solid state/Airport [C] using a peak detector, and showing

the emissions in the band 2.5 to 2.69 GHz......................................................................36

Figure 22: Measured emissions at solid state/Airport [C] in the frequency band 2.5 to 2.69

GHz, showing the probability of any given received power level. ...................................36

Figure 23: Measurement location of Magnetron/Airport [D]....................................................37

Figure 24: Measured emissions at magnetron/Airport [D] showing a large number of


length of one radar rotation. .............................................................................................38

Figure 25: Measured emissions at magnetron/airport [D] using a peak detector, and showing

the “max hold” and average result over a long time period. ............................................38

Figure 26: Measured emissions at magnetron/Airport [D] in the frequency band 2.5 to 2.69

GHz, showing the probability of any given received power level ....................................39

Figure 27 Emission Limits at the measurement locations with maximum EIRP at Airports A,

predicted with freespace path loss...................................................................................41

Figure 28 Emission Limits at the measurement locations with maximum EIRP at Airports B,


Figure 29 Emission Limits at the measurement locations with maximum EIRP at Airports C,


Figure 30 Emission Limits at the measurement locations with maximum EIRP at Airports D,


Figure 31 Validation of Radar spectra from FASS, against measurement at Airport [A] airport

and data from AMS report [6] ...........................................................................................49

Figure 32: Effect of pulse width on the TWT radar signal.......................................................50




10

Figure 33: Measured and simulated antenna pattern and rotation.........................................51

Figure 34: OOB emissions falling within the UMTS and WiMAX bandwidths ........................52

Figure 35: FASS RF output .....................................................................................................53

Figure 36: TWT Radar Spectrum from Signal Generator .......................................................54

Figure 37 Simulated antenna pattern/rotation compared with measured emissions .............55

Figure 38: Bandwidth of simulated signal using signal generator ..........................................55

Figure 39: Comparison of OOB emissions using the signal generator ..................................56

Figure 40 a) Spectra of Max hold and Clear/Write b) Probability distribution of interference

levels.................................................................................................................................58




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Abbreviations List

ACI

Adjacent Channel Interference

ATPC

Automatic Transmit Power Control

ATC

Air Traffic Control

AWGN

Additive White Gaussian Noise

BER

Bit Error Ratio

CAA

Civil Aviation Authority

CDMA

Code Division Multiple Access

DFS

Dynamic Frequency Selection

DL

Downlink

DPCH

Dedicated Physical Channel

DPCCH

Dedicated Physical Control Channel

DPDCH

Dedicated Physical Data Channel

DTCH

Dedicated Traffic Channel

DTX

Discontinuous Transmission

FASS

Frequency Agile Signal Simulator

FDD

Frequency Division Duplex

FEC

Forward Error Correction

IF

Intermediate Frequency

LNA

Low Noise Amplifier

MoD

Ministry of Defence




12

MCA

Maritime & Coastguard Agency

OOB

Out of band

PER

Packet Error Ratio

PHY

Physical Layer

QAM

Quadrature Amplitude Modulation

RF

Radio Frequency

RLC

Radio Link Control

RMC

Reference Measurement Channel

RSA

Recognised Spectrum Access

SDU

Service Data Unit

SE

Spurious Emissions

SS

Solid State

SUR

Spectrum User Rights

TDD

Time Division Duplex

TFCI

Transport Format Combination Indicator

TM

Telecomm Management

TWT

Travelling Wave Tube

UE

User Equipment

UL

Uplink

UMTS

Universal Mobile Telecommunications System




13

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14

1 Introduction

Ofcom has recently commissioned a series of technical studies in support of the award of

spectrum in the band 2500 to 2690 MHz [1], [2] which could possibly be occupied in the

future by systems such as UMTS or WiMAX. This band is very near to the band 2700 to

3100 MHz used by aeronautical and military radars and there is the potential for adjacent

channel interference due to the nature of radar out-of-band (OOB) and spurious emissions.

Ofcom commissioned ERA Technology Ltd to undertake a measurement programme to

identify the potential for interference to UMTS and WiMAX systems operating in adjacent

bands to aeronautical and military radars. This report details the measurements that were

undertaken and the conclusion drawn by ERA on the findings.

Measurements have been performed using real radar emissions around four airports A, B,

C, D along with conducted laboratory measurements. The laboratory measurements have

been performed using simulated radar signals generated by a Frequency Agile Signal

Simulator (FASS) and a signal generator (using pulse building software). The conducted

laboratory based measurements have been used to gain a deeper understanding of the

interference mechanism from radar emissions into UMTS and WiMAX systems.

Spectrum quality is an increasingly important issue for Ofcom, particularly with the recent

developments in technology neutrality and spectrum liberalisation, spectrum user rights

(SUR), recognised spectrum access (RSA), spectrum pricing and Cave-related band sharing

with radar.

Radar emissions may produce significant out-of-band emissions, particularly older

magnetron radars. In recent times, there has been considerable effort in terms of the design

of radar pulse generation and filtering to reduce the bandwidth occupied by radar signals

and the amount of out-of-band emissions that are generated. However, the ITU

recommendations allow a significant percentage of radar output power to spill over into

adjacent bands.

The figure below shows the ITU mask for radar spurious emissions (SE) and out-of-band

(OOB) emissions [3] and how they can fall into the 2500 to 2690 MHz band.




15

Figure 1: Example of radar emission mask and out-of-band and spurious emissions

falling into potentially new UMTS/WiMAX bands

The main interference mechanism is from a number of harmonics which only appear each

time the radar rotates to face the victim receiver, and whose levels vary on each sweep. This

would have a very different effect on a voice-based application compared to a data-based

application such as broadband wireless for example.

2 Objectives

The objectives of the work were as follows:

• To determine the effect that adjacent channel interference from radar systems

operating in the 2700 – 3100 MHz band has on a range of possible mobile systems

operating in the band 2500 – 2690 MHz.

• To simulate different types of radar pulses, taking into account the result of the radar

antenna radiation pattern (e.g., through differences in main-beam and side-lobe

gains) and antenna rotation. The time-domain and emissions spectra of the radar

pulses are to be representative of the different types of radar systems deployed in

the band for air traffic control.

• To set up an end-to-end UMTS and WiMAX communications test bed of: “transmitter

-> unfaded propagation channel -> receiver” chain and then introduce known radar

interference impairments within the mobile radio channel arising from adjacent

channel radar usage.




16

• To quantify the effect that different levels of radar interference has on the mobile

system receiver performance in terms of the degradation in the data throughput and

packet error rate.

• Mobile standards to be considered are WCDMA/UMTS, OFDM/WiMAX – 802.16-

2004 (representative of fixed WiMAX systems) and, if available, OFDMA/WiMAX –

802.16e (representative of mobile WiMAX systems).

• The test equipment should be able to simulate the full FEC coding of the mobile

standard under investigation, to enable packet error ratio and throughput

measurements to be made.

• The interference mechanisms to be assessed will be out-of-band and spurious

emissions from the radar based on the proposed adjacent award bands for UMTS

and WiMAX as shown in the figure below.

2690

MoD and civil radars

2500 MHz

Radio Astronomy, Earth Exploration Satellite (Passive) and Space Research (Passive) Award spectrum - Channels 1 to 38

31002700

C3

8

C3

7

C3

6

C1

C2

RA

DA

R

Figure 2: 2.6 GHz award band adjacencies

3 Test Methodology

3.1 Introduction

Conducted measurements were initially undertaken in a laboratory environment to quantify

the interference effects from radars into adjacent band UMTS and WiMAX systems.

The radar signals were simulated using a Frequency Agile Signal Simulator (FASS) and also

with a complex signal generator running pulse building studio software. The WiMAX system

under test was representative of a 2-way fixed 802.16-2004 WiMAX system. It was not

possible to obtain any mobile 802.16e WiMAX equipment in the short timeframe of the

project. The UMTS User Equipment (UE) under test was a standard 3G handset from an

established manufacturer.




17

The laboratory measurements were then compared with results obtained from operational

radars at four airport sites referred to as A, B, C and D in this report.

3.2 Identification of radars

The 2700 – 3100 MHz radiolocation band is used by the Civil Aviation Authority (CAA) and

Ministry of Defence (MoD) for air traffic control (ATC) services, by the MoD for other radar

services such as air defence and naval radar for example, by the Maritime and Coastguard

Agency (MCA) for ship borne radar from 2900 – 3100 MHz, and by port authorities for

Vessel Traffic Services (VTS) radars from 2900 – 3100 MHz. The radars in the maritime

band 2900 – 3100 MHz were not included in the study as they are at least 200 MHz from the

2690 MHz band edge.

It was determined that the closest adjacency of the different types of radar systems to the

band 2500 – 2690 band is with ATC radars. The MoD ATC radars are located at about 20 to

30 bases in the UK; there are approximately 40 civil ATC radars operating in the band of

interest.

There are three main amplifier technologies used to generate radar transmissions:

magnetron, travelling wave tube (TWT) and solid state, all of which have different spectral

properties and other emission characteristics.

Some radars, particularly older magnetron or TWT types, may have significant out of band or

spurious emissions that can extend for 10’s of MHz beyond their operating frequencies. If

these radars have been designed to operate on frequencies close to the 2700 MHz band

edge, their emissions may extend into the top channels of the award band (2500 – 2690

MHz).

Ofcom have identified 22 civil radars that operate within 100 MHz of the expansion band’s

topmost channel 38 (C38, 2685 – 2690 MHz). Of these:

• Eleven are magnetron radars operating at peak EIRP power levels up to 92 dBW

• Six are TWT radars operating at peak EIRP power levels up to 82 dBW

• Five are solid state radars operating at peak EIRP power levels up to 80 dBW

Typical UK ATC radar parameters used in a previous study for Ofcom [4] are detailed in

Table 1. Watchman radars are the most commonly used ATC radars and use TWT

technology.




18

Table 1: Typical ATC radar parameters

These parameters were used to programme the FASS/SigGen, giving the required OOB

emissions. An example of the OOB emissions measured from a magnetron ATC radar in the

previous Ofcom study [4] is shown below. This shows a 10 MHz span around 2.5 GHz,

indicating the number of harmonics that appear in a typical receiver bandwidth.

Figure 3: Example of measured harmonics from a magnetron radar

An important consideration in the study was the effect of radar rotation and the antenna

characteristics. These were programmed into the FASS and observed on a spectrum

analyser using a zero-span at the radar centre frequency and a CW signal source. An

example antenna horizontal beam pattern is shown in Figure 4, and it can be seen that the

antenna typically has a narrow main beam and side lobes which are typically about 30dB

below the main beam gain. The FASS/SigGen was programmed with various beam widths

representing the different antenna patterns used by different radars.




19

Figure 4: Radar interference zones

An example of the radar emissions, combining the effect of the radar pulsed interference

with the antenna beam pattern and rotation, is shown in Figure 5. This shows the type of

interference that would be experienced by any nearby communications receiver, including a

swept beam zone and side-lobe zone.

4s antenna rotation

1/60s

main beam seen t

side lobes seen

Figure 5: Illustrative radar pulse train as seen by a stationary receiver

The radar emission measurements setup is shown in Figure 6




20

Figure 6 Radar emission measurement setup

3.3 Radar interference into UMTS

For measurements of radar interference into UMTS UE, the received UMTS downlink signal

parameters shown in Table 2 were used.

Table 2: UMTS downlink signal parameters

3GPP downlink Value

Multiple access method CDMA

Channel modulation QPSK

Number of carriers 1

Chip rate 3.84 Mcps

Modulation filter A=0.22

Channel raster 5 MHz

Loopback Bit Error Ratio (BER) measurements were performed on a standard reference

measurement channel (RMC) with a data rate of 12.2 kbps as defined in ETSI 3GPP TS

25.101 [7].

When measuring the BER using frequency division duplex (FDD), the DL and UL reference

measurement channel operating at 12.2 kbps should be configured to:

• DL and UL transport block = 244 bits (RLC, TM).

• UE test loop mode 1 parameter UL RLC SDU size = 244 bits.

Attenuator Spectrum Analyser

Antenna

Mast

ATC

radar




21

The physical parameters of DL and UL RMC (12.2 kps) from Annex C of ETSI 3GPP TS

34.121 [8] are given in Table 3 and Table 4 respectively.

Table 3: DL reference measurement channel physical parameters (12.2 kps)

Table 4: UL reference measurement channel physical parameters (12.2 kps)

A 15-bit pseudo-random bit sequence was sent on the downlink dedicated traffic channel

(DTCH) to the UE configured to loopback mode 1.

The re-transmitted data on the uplink DTCH from the UE was tested to see how closely it

matched the data bits originally sent on the downlink in terms of BER.

Note the test set compares the downlink and uplink data one transport block at a time and

reports the BER. Also, the uplink dedicated physical data channel (DPDCH) includes both

the DTCH and the DCCH; however, only the DTCH information is used for the loopback

BER measurement.

The interference criterion was assumed to be the BER not to exceed 0.1% for the

parameters specified in the table below for the out of band and spurious response emissions

from the intefering radar.

Table 5: Out of band blocking and Spurious Response

Parameter Unit Level

DPCH_Ec dBm/3.84 MHz -114 Îor dBm/3.84 MHz -103.7




22

Where Ior is the received downlink spectral power density in a 3.84 MHz bandwidth.

Measurements were undertaken for the frequencies given in the table below. The power of

the radar was increased until a given BER measured by the signal simulator using the

loopback function was measured.

Table 6: Frequency offsets for concerned UMTS and radar frequencies

Radar centre frequencies

UMTS Wanted

channel numbers

UMTS Wanted

centre frequencies 2706.0 MHz 2720.0 MHz 2740.0 MHz

C38 2687.5 MHz 18.5MHz 32.5MHz 52.5MHz C34 2667.5 MHz 38.5MHz 52.5MHz 72.5MHz C30 2647.5 MHz 58.5MHz 72.5MHz 92.5MHz

C25 2622.5 MHz 83.5MHz 97.5MHz 117.5MHz

The test setup for the conducted measurements is shown in the figure below.

Figure 7: Conducted measurement setup for radar interference into UMTS

Simulated

/Radiated

Radar

Emissions

Signal

Simulator

UE

Downlink

Combiner

Splitter Spectrum

Analyser

Band Pass

Filter

Uplink

Pre-amp Mixer

Sig

Gen




23

3.4 Radar interference into WIMAX

ERA has two fully operational WiMAX 802.16-2004 systems. The first system comprises a

base station and subscriber station designed to meet the IEEE 802.16-2004 [9] MAC and

physical layer (PHY) specifications. However, this system has a fixed bandwidth of 3.5 MHz

and so was not considered representative of WiMAX equipment required for this project.

The second system is designed to provide broadband wireless infrastructure and can be

deployed for fixed and mobile wireless access and backhaul applications. It provides the

following features: Up to 72 Mbps raw and 49 Mbps data throughput; dynamic time division

duplex transmission; bi-directional dynamic adaptive modulation; point-to-point and point-to-

multipoint; dynamic frequency selection (DFS) and automatic transmit power control (ATPC)

options. The system has a fixed bandwidth of 20 MHz, which was considered more

representative of a wide-band system required for the project.

It should be noted that the available WiMAX system was designed to operate at 5.5 GHz.

Therefore, the WiMAX signals were down converted to the 2.5 – 2.69 GHz band for use in

this study.

The WiMAX signal parameters shown in Table 7 below were used for the wanted system.

Table 7: Wanted WiMAX signal parameters

WiMAX parameter Value

Multiple access method OFDM

Modulation QPSK,

FEC ½

FFT points 256

Guard interval 1/16

Frame duration 5 ms

Channel raster 20MHz

Duplex TDD




24

Table 8: Frequency offsets for concerned WiMAX and radar frequencies

Radar wanted frequencies

WiMAX Wanted centre

frequencies

2706MHz 2720MHz 2740MHz

2685.0 MHz 21MHz 35MHz 55MHz 2665.0 MHz 41MHz 55MHz 75MHz 2645.0 MHz 61MHz 75MHz 95MHz 2610.0 MHz 96MHz 110MHz 130MHz 2560.0 MHz 146MHz 160MHz 180MHz

The test setup is shown in the figure below. The FTP applications were set up to transfer

data between the WiMAX master and slave stations. The WiMax equipment uses TDD

multiplexing and therefore it was not possible to undertake separate measurements on the

uplink and downlink. Instead, any interference resulted in an overall drop in data throughput

on the WiMax link. The WiMax system was down converted from 5.5 GHz to the 2.6GHz

frequency band with frequency offsets shown in Table 8, and the out of band and spurious

emissions from the interfering radar were measured as a function of throughput.




25

Figure 8: Conducted measurement setup for WiMAX 802.16-2004

3.5 Measurement Procedure

The measurement procedure for measuring the BER/throughput with interference from radar

to UMTS and WiMAX respectively is presented below.

1. The wanted UMTS frequency was fixed at the operational frequency. The radar

interfering signal simulated by the FASS/SigGen was set to the centre frequencies

with the frequency offsets , the radar interfering signal at airports was down

converted the frequencies offset to the operational UMTS DL frequency, the offset

values were given in Table 6. For The WiMax system, the radar frequency at

Master Station Slave Station

Tx/Rx

Mixer

Filter

Simulated/ Radiated

Radar Emissions

Tx/Rx

Mixer

IF IF

LO

RF

Signal Generator

Splitter

RF

LO

Spectrum

Analyser

Laptop

A

Laptop

B

Co

mb

iner

Pre-amp

Attenuator




26

airport/FASS/SigGen was the operational frequencies observed at airports, the

wanted WiMax centre frequency was down converted to the concerned frequency

with frequency offsets given in Table 8.

2. The wanted signal for either the UMTS or WiMAX system was configured according

to the parameters shown in Table 2 or Table 7.

3. The interfering radar signal level was increased until the desired BER for UMTS UE

or the degradation of throughput for the WiMAX slave was attained.

4. The level of interference was recorded in a 1 MHz resolution bandwidth using peak

detection. The sweep time of spectrum analyser was 1 second.

5. The above steps were then repeated for the various wanted and unwanted centre

frequency combinations.

4 Results

4.1 Measured Radar Emissions

ERA undertook a measurement campaign at 4 airports (A, B, C and D) to measure the radar

emissions from operational TWT, solid-state, and magnetron radars. All of the

measurements presented in the following sections have the relevant correction factors

applied (for antenna gain, cable losses etc) so that they specify the power that would be

received at the base of a 0dBi antenna, and therefore what would be incident at the port of a

typical communications receiver. For all the emission measurements, the setting of

Spectrum analyser was resolution bandwidth of 1MHz, sweep time of 1 second.

4.1.1 TWT/airport [A]

The TWT/Watchman radar at airport [A] operates on two frequencies, 2.845 and 2.908 GHz.

Measurements were carried out at 700m away from the radar site, with a receiving horn

antenna situated at a height of 16m, as shown in the figures below.




27

Figure 9: Measurement location of TWT/airport [A]

The measured emissions are shown in Figure 10 to 13, as the power that would be received

at the base of a 0dBi antenna at a height of 16m. The level experienced at ground level will

typically be some 6 to 10dB lower. Figure 10 shows individual radar sweeps captured by

setting the spectrum analyser to max hold for the duration of one radar rotation. Figure 11

shows the peak levels compared to the average levels (average of each peak

measurement).




28

Figure 10: Measured emissions at TWT/airport [A] showing a large number of


length of one radar rotation.

Maximum and Average level of Emissions - TWT/Airport[A]

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2640 2690 2740 2790 2840 2890 2940 2990 3040

Frequency (MHz)

dB

m/M

Hz

Max Peak, Max hold

Max Peak, Average

Figure 11: Measured emissions at TWT/airport [A] using a peak detector, and showing

the “max hold” and average result over a long time period.




29

Figure 12 shows the levels experienced in the frequency band under consideration, 2.5 to

2.69 GHz

Emissions at the frequency band of 2.5-2.69GHz

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2500 2520 2540 2560 2580 2600 2620 2640 2660 2680

Frequency (MHz)

dB

m/M

Hz

Figure 12: Measured emissions at TWT/airport [A] using a peak detector, and showing

the emissions in the band 2.5 to 2.69 GHz.

Figure 13 shows the probability of receiving any given emission level. The averaged results

in Figure 11 and the statistical results in Figure 13 demonstrate the combined effects of the

radar pulsing, antenna rotation and narrow beam antenna, showing that instantaneous levels

have a high probability of being considerably below the peak levels.




30

Probability of the emissions at the 2.5-2.69GHz frequency band

0%

20%

40%

60%

80%

100%

120%

-96 -91 -86 -81 -76 -71 -66 -61 -56

Signal Level (dBm/MHz)

Perc

en

tag

e

Figure 13: Measured emissions at TWT/airport [A] in the frequency band 2.5 to

2.69 GHz, showing the probability of any given received power level.

The measurements show that in the frequency band 2.5 to 2.69 GHz, the recorded

maximum radar emission were -54dBm/MHz and the statistics show that the probability of

this level occurring is about 0.004% of the time. In this band, the probability of the received

level being above the noise floor of -89dBm/MHz was only about 0.98% of time.

4.1.2 TWT/airport [B]

Measurements on the TWT radar at airport [B] were carried out at 600m away from the radar

site with the receiving antenna at a height of 16m, as shown in the figure below.




31

Figure 14: Measurement location of TWT/airport [B]






measurement).



radar pulsing, antenna rotation and narrow beam antenna, showing that the instantaneous

levels have a high probability of being considerably below the peak levels.




32

Figure 15: Measured emissions at TWT/airport [B] showing a large number of



Maximum and Average level of Emissions - TWT/Airport [B]

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2665 2685 2705 2725 2745 2765 2785 2805 2825 2845 2865

Frequency (MHz)

dB

m/M

Hz

Max Peak, Max Hold

Max Peak, Average

Figure 16: Measured emissions at TWT/airport [B] using a peak detector, and showing

the “max hold” and average result over a long time period.




33

Probability of the emissions at the concerned frequency band

0%

20%

40%

60%

80%

100%

120%

-83 -82 -81 -80 -79 -78 -77 -76 -75 -74 -73 -72 -71 -70 -69


Pe

rce

nta

ge

Figure 17: Measured emissions at TWT/airport [B] in the frequency band 2.5 to

2.69GHz, showing the probability of any given received power level.

In the frequency band 2.5 to 2.69 GHz, the recorded maximum radar emission were -

69dBm/MHz and the statistics show that the probability of this level occurring is about 0.08%

of the time (for data between 2.665 GHz and 2.69 GHz, as no emissions above noise floor

observed between 2.5 GHz and 2.665 GHz). In this band, the probability of the received

level being above the noise floor of -79dBm/MHz was only about 0.67% of time. (The noise

floor for this measurement was above that in the other airport measurements due to the

spectrum analyser reference level setting.)

4.1.3 Solid State/Airport [C]

4.1.3.1 Radar location and emissions

The Solid State/ASR10 radar at airport [C] operates on two frequencies, 2.785 GHz and

2.8105 GHz. Measurements were carried out at 840m away from the radar site, with a

receiving horn antenna situated at a height of 16m, as shown in Figure 18.




34

Figure 18: Measurement location of Solid State/Airport [C]






measurement).

Figure 21 shows the levels experienced in the frequency band under consideration, 2.5 to

2.69 GHz. Figure 22 shows the probability of receiving any given emission level. The

averaged results in Figure 20 and the statistical results in Figure 22 demonstrate the

combined effects of the radar pulsing, antenna rotation and narrow beam antenna, showing

that the instantaneous levels have a high probability of being considerably below the peak

levels.




35

Figure 19: Measured emissions at solid state/Airport [C] showing a large number of



Maximum and Average level of Emissions - SS/Airport [C]

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2586 2636 2686 2736 2786 2836 2886 2936 2986

Frequency (MHz)

dB

m/M

Hz

Max Peak, Max Hold

Max Peak, Average

Figure 20: Measured emissions at solid state/Airport [C] using a peak detector, and

showing the “max hold” and average result over a long time period.




36

Figure 21: Measured emissions at solid state/Airport [C] using a peak detector, and

showing the emissions in the band 2.5 to 2.69 GHz.

Probability of the emissions at the concerned frequency band

0%

20%

40%

60%

80%

100%

120%

-93 -88 -83 -78 -73 -68 -63 -58 -53 -48 -43 -38


Perc

en

tag

e

Figure 22: Measured emissions at solid state/Airport [C] in the frequency band 2.5 to

2.69 GHz, showing the probability of any given received power level.




37

The measurements show that in the frequency band 2.5 GHz to 2.69 GHz, the recorded

maximum radar emission was -39dBm/MHz and the statistics show that the probability of

this level occurring is about 0.002% of the time. In this band, the probability of the received


4.1.4 Magnetron/Airport [D]

4.1.4.1 Radar location and emissions

Measurements on the magnetron radar at airport [D] were carried out at 650m away from the

radar site with the receiving antenna at a height of 16m, as shown in the figure below.

Figure 23: Measurement location of Magnetron/Airport [D]






measurement).



radar pulsing, antenna rotation and narrow beam antenna, showing that the instantaneous

levels have a high probability of being considerably below the peak levels.




38

Figure 24: Measured emissions at magnetron/Airport [D] showing a large number of



Maximum and Average level of Emissions - Magnetron/Airport[D]

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2530 2580 2630 2680 2730 2780 2830 2880 2930

Frequency (MHz)

dB

m/M

Hz

Max Peak, Max Hold

Max Peak, Average

Figure 25: Measured emissions at magnetron/airport [D] using a peak detector, and

showing the “max hold” and average result over a long time period.




39

Probability of the emissions at the Concerned frequency band

0%

20%

40%

60%

80%

100%

120%

-93 -88 -83 -78 -73 -68


Perc

en

tag

e

Figure 26: Measured emissions at magnetron/Airport [D] in the frequency band 2.5 to

2.69 GHz, showing the probability of any given received power level

In the frequency band 2.5 GHz to 2.69 GHz, the recorded maximum radar emission was

-68dBm/MHz and the statistics show that the probability of this level occurring is about

0.002% of the time (for data between 2.53 GHz and 2.69 GHz, as no emissions above noise

floor observed between 2.5 GHz and 2.53 GHz). In this band, the probability of the received


4.2 Interference from Radar into Communications Equipment

Measurements were performed at the four airports (A, B, C and D) of interference into a

UMTS handset and a WiMAX terminal. This was done for a range of frequency offsets, from

the centre radar frequency to a frequency offset of 180 MHz.

The test method of introduced an extra 6dB of loss of radar signal, which can be considered

as having the receiving antenna at a height of 2m. (As noted above, the difference in

received signal level between an antenna height of 16m and 2m was found to be between 6

and 10 dB.)

It was determined in the laboratory that the degradation of UMTS and WiMAX systems was

dominated by the average power experienced, as a result of the radar side-lobe emissions,

as opposed to the intermittent peak experienced from the radar antenna main beam. It is

therefore important to be precise in the methodology used for the calculation of any C/I

protection criteria and how these are used in subsequent interference simulations.




40

The radar emissions, and hence the incident interference levels are specified using a

spectrum analyser resolution bandwidth of 1MHz. The C/I is specified with ‘I ‘as the

interference due to the peak (max hold) power in a 1MHz bandwidth. It is important that in

any calculations, the same specification of radar emissions is used. It might have been more

representative to specify the average power in the C/I calculations as this is the dominant

mechanism, however, this is not how radar emissions are usually presented and could

therefore be misleading. Both value are given for comparison.

4.2.1 Interference from Radar into UMTS DL

The interference measurements to the UMTS handset showed that, between 600 meters to

800 meters away from the radar, there was no measurable interference observed from the

radar into the UMTS system during the time interval of a complete radar antenna rotation.

This was true even for the radar centre frequency being co-channel with the UMTS channel

being used, and with the UMTS handset receiving its minimum usable carrier signal of -

92dBm/MHz (Max Peak). Frequency offsets used were from 0 to 112 MHz.

This measurement could therefore not be used to determine the exact C/I protection ratios,

as no significant interference was experienced. However, it can be used to specify the

maximum value of C/I that could be experienced. This was determined by comparing the

minimum wanted carrier signal used with the maximum radar interference level at the four

Airports, assuming the radar is co-channel with the UMTS handset. The radar interference

level is the measured downconverted radar signal at the UMTS DL frequency, which is

slightly different than the direct measured radar signal due to probability of the maximum

emissions, measurement dwell time and environment variations.

The interference level at the receiver with 0dBi gain antenna is given by:

Ireceived = Prad – Pathloss– Bandwidth Factor

Where:

Ireceived is the predicted maximum emission limits (maximum EIRP power from Radar

antenna is assumed) at the receiver with 0dBi antenna.

Prad is the power radiated from the radar antenna

Pathloss= 92.4 = 20*log(Freq GHz) + 20*log(Path dist km)

Bandwidth Factor = 20*Log(Necessary Bandwidth MHz)

In the following figures the mask indicates the maximum EIRP limits allowed at the

measurement location, calculation according to Document NTIA 5-420 [10] are shown in

Table 9.




41

Table 9 Calculation of received maximum signal levels

TWT/

Airport[A]

TWT/

Airport[B]

Solid State/

Airport[C]

Magnetron/

Airport[D]

Max EIRP(dBm) 108 108 103 122

Frequency (MHz) 2840 2765 2785 2730

Necessary bandwidth

(MHz) 10 10 2.5 5.6

Bandwidth factor (dB) 20 20 8 15

Distance (km) 0.7 0.6 0.84 0.65

Path Loss (dB) 98.4 96.8 99.8 97.4

Estimated received

maximum signal

(dBm/MHz)

-10.4 -8.8 -4.8 9.6

Maximum and Average level of Emissions - TWT/Airport[A]

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2640 2690 2740 2790 2840 2890 2940 2990 3040

Frequency (MHz)

dB

m/M

Hz

MASK1

Max Peak, Max hold

Max Peak, Average

Figure 27 Emission Limits at the measurement locations with maximum EIRP at

Airports A, predicted with freespace path loss




42

Maximum and Average level of Emissions - TWT/Airport [B]

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2665 2685 2705 2725 2745 2765 2785 2805 2825 2845 2865

Frequency (MHz)

dB

m/M

Hz

Max peak, Max Hold

Max Peak, Average

MASK1


Airports B, predicted with freespace path loss

Maximum and Average level of Emissions - SS/Airport [C]

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2586 2636 2686 2736 2786 2836 2886 2936 2986

Frequency (MHz)

dB

m/M

Hz

MASK1

Max Peak, Max Hold

Max Peak, Average


Airports C, predicted with freespace path loss




43

Maximum and Average level of Emissions - Magnetron/Airport[D]

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

2530 2580 2630 2680 2730 2780 2830 2880 2930

Frequency (MHz)

dB

m/M

Hz

MASK1

Max Peak, Max Hold

Max Peak, Average


Airports D, predicted with freespace path loss

The resulting maximum C/I levels experienced are presented in Table 10.

Table 10: Maximum C/I values for radar to UMTS interference


C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

Max peak,

Max hold

-92 -21 -71 -92 -20 -72 -92 -32 -60 -92 -22 -70

Max Peak,

Average

-92 -62 -30 -92 -44 -48 -92 -64 -28 -92 -55 -37

4.2.2 Interference from Radar into WiMAX

The interference measurements to the WiMAX subscriber unit showed that, between 600

meters to 800 meters away from the radar, there was no measurable interference observed

from the radar into the WiMAX system during the time interval of a complete radar antenna

rotation. This was true even for the radar centre frequency being co-channel with the WiMAX




44

channel being used, and with the WiMAX subscriber receiving its minimum usable carrier

signal -60dBm/MHz (Max Peak). Frequency offsets used were from 0 to 180 MHz.

This measurement could therefore not be used to determine the exact C/I protection ratio

values, as no significant interference was experienced. However, it can be used to specify

the maximum value of C/I that could be experienced. As for the UMTS case, this was

determined by comparing the minimum wanted carrier signal used with the maximum radar

interference level at the four Airports, assuming the radar is co-channel with the WiMAX

system. The results are presented in Table 11.

Table 11: Maximum C/I values for radar to WiMAX interference


C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

Max peak,

Max hold

-60 -12 -48 -60 -11 -49 -60 -19 -41 -60 -13 -47

Max Peak,

Average

-60 -42 -18 -60 -35 -25 -60 -58 -2 -60 -42 -18

4.3 Conducted measurements of simulated radar emissions

Conducted measurements were made using radar simulators and a number of reference

interference sources to help determine the interference mechanisms occurring.

4.3.1 Conducted measurements of C/W and AWGN

When CW or AWGN was applied as the interference source into the UMTS or WiMAX

system, the C/I values shown in Table 12 were obtained.

Table 12: Measured C/I using AWGN and CW interference sources

AWGN C/I (dB) CW C/I (dB)

UMTS -12 -26

WiMAX -2 -16




45

4.3.2 Simulated radar emissions using FASS

The FASS was used to simulate the radar interference source for laboratory conducted

interference tests. Comparing with the radar measurements at the airports, it was found that

the RF output of FASS had a fairly significant component of noise at frequency offsets

greater than around 60MHz from the radar centre frequency in addition to the radar

emissions. The measurement results are shown in the Appendix A. It can be seen that the

results are very close to those using the AWGN interferer, due to the noise-like nature. Thus,

we considered the out-of-band radar signal emissions simulated using the FASS was not

accurate enough for the purpose of this project. An improved radar simulator was used as

described in Section 4.3.3.

4.3.3 Simulated radar emissions using a Signal Generator

The interfering radar signals were replicated using a high performance Signal Generator

(Agilent 8267D-M2) and pulse building studio software. The generator is capable of

producing narrow radar pulses and has the advantage of having a wide bandwidth, as

shown in Appendix B.

The conducted measurements with the signal generator did not cause any measurable

interference to the UMTS or WiMAX receivers with the simulated TWT, solid state or

magnetron radar signals at the output levels that could be achieved. This result compared

well with the measurements at the airports and it is considered that the signal generator

gave a more accurate representation of the radar signals than the FASS.




46

5 Conclusions

Measurements have been undertaken to quantify the interference effects from aeronautical

radars operating in the 2.7 – 3.1 GHz band into representative communications systems that

could be used in future in the 2.5 to 2.69 GHz band. The representative communications

systems used in this case were UMTS and WiMAX.

Measurements were undertaken at four airports, characterising the emissions arising from

solid-state, TWT and magnetron technologies. In addition, laboratory measurements have

been performed using simulated radar signals generated by a Frequency Agile Signal

Simulator and a signal generator (using complex pulse building software). The conducted

laboratory based measurements have been used to gain a deeper understanding of the

interference mechanism from radar emissions into UMTS and WiMAX systems.

It was determined in the laboratory that the degradation of the UMTS and WiMAX systems

was dominated by the average power experienced, as a result of the radar side-lobe

emissions, as opposed to the intermittent peak experienced from the radar antenna main

beam. It is therefore found to be important to be precise in the methodology used for the

calculation of any C/I protection criteria (whether peak or average interference) and how

these are used in subsequent interference simulations. Protection criteria based on both

peak and average interference levels are given within the report for comparison. Also

provided for comparison are the level of Carrier Wave and Additive White Gaussian Noise

(AWGN) emission required to cause interference to the UMTS or WiMAX system.

ERA’s analysis of the results from the airport measurements indicate that the bit error rate

(BER) in the presence of the measured radar interference was less than 10e-3 (0.1%) to

either the UMTS or WiMAX systems at a separation distance of 600m from the radar and

with a set minimum usable carrier signal for the wanted system. These results were based

on the measurement of BER within a reference UMTS channel having a user data-rate of

12.2 kbps, and into a reference WiMAX channel having a user data rate of 1.5mbps. It

should be noted the study did not consider the effect of radar interference to other system

parameters such as quality of service or the impact radar interference has on particular

types of communication applications (e.g., voice, video, and different types of data

transmissions).

The results were established on the basis of the radar interference being co-channel with the

communications receiver. In practice, the communications systems operating in the 2.6GHz

band may well be separated greater than about 18 MHz away from a radar centre frequency

and, as such, may be expected to experience radar powers at least 20 to 30dB below the

co-frequency radar power level.




47

The measurements could not be used to determine the exact Carrier-to-Interference (C/I)

protection ratios, as no significant interference was experienced. However, they can be used

to specify the maximum value of C/I likely to be experienced. This was determined by

comparing the minimum carrier signals used with the maximum converted radar interference

level measured at each of the four Airports, with the radar co-channel with the

UMTS/WiMAX receiver.

The calculated maximum C/Is that could be experienced are shown in the following tables:


C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

Max peak,

Max hold

-92 -21 -71 -92 -20 -72 -92 -32 -60 -92 -22 -70

Max Peak,

Average

-92 -62 -30 -92 -44 -48 -92 -64 -28 -92 -55 -37


C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

C

(dBm/

MHz)

I

(dBm/

MHz)

C/I

(dB)

Max peak,

Max hold

-60 -12 -48 -60 -11 -49 -60 -19 -41 -60 -13 -47

Max Peak,

Average

-60 -42 -18 -60 -35 -25 -60 -58 -2 -60 -42 -18




48

6 References

[1] Adjacent and In-Band Compatibility Assessment for 2500-2690MHz, Ofcom

Technical Study, 11 Dec 06

[2] 2500-2690MHz, 2010-2025MHz and 2290-2302MHz Spectrum Awards –

Engineering Study (Phase 2), Mason Communications Ltd, November 2006

[3] ITU-R Recommendation SM.1541 “Unwanted emissions in the out-of-band domain”

[4] CAA radar out of band emissions, Radio Technology & Compatibility Group, March

2001.

[5] Radar Unwanted Emissions, J Holloway, ITU WP8B Radar Seminar, Geneva,

September 2005.

[6] The report of an investigation into the characteristics, operation and protection

requirements of civil aeronautical and civil maritime radar system, Alenia Marconi Systems

Ltd, October 2002.

[7] 3GPP TS 25.101 v7.8.0, 3rd Generation Partnership Project; Technical Specification

Group Radio Access Network; UE Radio Transmission and Reception (FDD) (Release 7),

Giugno 2001.

[8] 3GPP TS 34.121 V6.0.0, 3rd Generation Partnership Project; Technical Specification

Group Terminals; Terminal conformance specification; Radio transmission and reception

(FDD) (Release 6), 2005.

[9] IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for

Fixed Broadband Wireless Access Systems

[10] NTIA Document 5-420, Measurement Procedures for the Radar Spectrum

Engineering Criteria (RSEC), March 2005




49

APPENDIX A

Calibration of Radar Emissions from FASS

Emission profile of TWT Radar

The unwanted emissions from the radar include both OOB and spurious emissions. OOB

emissions occur at frequencies immediately outside the necessary bandwidth resulting from

the modulation process, but excluding spurious emissions. Spurious emissions are

emissions on frequencies which are outside the necessary bandwidth and the level of which

maybe reduced without affecting the corresponding transmission of information. Spurious

emissions include harmonics emissions, ‘parasitic’ emissions, intermodulation products and

frequency conversion products, but exclude OOB emissions [5].

The output from the FASS was assessed to determine if the OOB and spurious emissions

are comparable to the emissions from real radar transmissions.

As shown in Figure 31, the emission characteristics of a TWT radar simulated by the FASS

are very similar to the spectra measured in a study by Alenia Marconi Systems Ltd (the AMS

report) [6] and radar measurements carried out by ERA at airport [A], especially for the in

band and OOB emissions.

Spectrum of FASS, Measurement at airport[A] and from AMS report

-120

-100

-80

-60

-40

-20

0

-2.5E+08 -2.0E+08 -1.5E+08 -1.0E+08 -5.0E+07 0.0E+00 5.0E+07 1.0E+08 1.5E+08 2.0E+08 2.5E+08 3.0E+08

Frequency (Hz)

dB

m/M

Hz

AMS

FASS

Airport[A]

Figure 31 Validation of Radar spectra from FASS, against measurement at Airport [A]

airport and data from AMS report [6]




50

The TWT radar has two operating frequencies and two pulse widths of 0.4µs and 20 µs. At

the lower operating frequency the radar transmits 9 short pulses, followed by 9 long pulses

while at the upper operating frequency 9 long pulses are transmitted followed by 9 short

pulses. The unwanted emissions are therefore components from both short pulse and long

pulse. The spectra of short pulse, long pulse and the short+ long pulse are shown in Figure

32. It can be seen that the short pulse gives less in-band peak power but gives the worst

case of OOB/spurious emission levels, as also noted in the Ofcom consultation document.

For this study both the short and long pulse series was applied to simulate the situation

which is more close to the real radar signal.

TWT radar with different pulse width

-80

-70

-60

-50

-40

-30

-20

-10

0

1.94E+09 1.96E+09 1.98E+09 2.00E+09 2.02E+09 2.04E+09 2.06E+09

Frequency (Hz)

dB

m/M

Hz

Long pulse 20us

short pulse 0.4us

Short + Long Pulse

Figure 32: Effect of pulse width on the TWT radar signal

Radar antenna rotation and antenna pattern

The effect of radar antenna pattern and rotation is shown in Figure 33. The plot on the left is

measured at airport [A], and on the right is simulated by the FASS. The FASS gives the

same antenna rotation rate of 4 second per rotation and simulates the same 1.5° beamwidth

as the real radar, with a fast roll-off. The radar antenna has a -20 to -25dBc back lobe, while

the antenna pattern of FASS gives null up to -50dBc.




51

Ref 10 dBm Att 20 dB*

*

A

3DB

RBW 1 MHz

VBW 1 MHz

Center 2.8452 GHz 1 s/

SWT 10 s

*

PRN

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

1

Marker 1 [T1 ]

-16.70 dBm

1.000000 s

Ref 0 dBm Att 10 dB*

3

RBW 100 kHz

VBW 300 kHz

S

WR

*K

Center 2 GHz 800 ms/

*

SWT 8 s

P

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

1

Marker 1 [T1 ]

-40.97 dBm

1.000000 s

Figure 33: Measured and simulated antenna pattern and rotation

Emission Bandwidth

For this project, the unwanted emissions are the main interference source to either the

UMTS or WiMAX system. The bandwidth of a normal UMTS link is 5MHz and 10MHz for

WiMAX links, and the spectral characteristics of the unwanted radar emissions falling into

these bandwidths are shown in Figure 34.

From a previous Ofcom study [4]




52

A

3DB

*

*

RBW 1 MHz

VBW 1 MHz

SWT 1 s*Ref -10 dBm Att 0 dB*

Center 2.7 GHz Span 10 MHz1 MHz/

1 PK

VIEW

PRN

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

1

Marker 1 [T1 ]

-57.53 dBm

2.705000000 GHz

Date: 27.JUN.2007 13:33:39

Measured at airport [A]


Ref -20 dBm Att 0 dB **

A

* RBW 1 MHz

VBW 3 MHz

SWT 1 s*

1 PK

VIEW

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

1

Marker 1 [T1 ]

-44.01 dBm

2.144423077 GHz

Simulated by the FASS

Figure 34: OOB emissions falling within the UMTS and WiMAX bandwidths

With a 10MHz span, one frequency component appears during each radar antenna rotation.

It can be seen from Figure 34 that the emissions simulated by the FASS closely mimic the

emissions measured at Airport [A] and the measurements presented in the previous Ofcom

report on CAA radar OOB emissions [4]. The shape of each emission indicates the energy

distribution from the emission, and the shape reproduced from the FASS gives the same

energy distribution as the emissions from the real radar.

However, it should be noted that the FASS is designed to simulate in-band radar signals and

as such the RF output is limited to a 60 MHz bandwidth. Beyond 60 MHz the FASS spectra

is dominated by noise, as shown in Figure 35, and it was found that the transmit power of

the simulated signal was not high enough to cause interference before this broadband noise

started to affect the UMTS/WiMAX system. For this reason it was concluded that the radar

signal simulated by the FASS was not accurate enough for this project.




53

Output of FASS Max Pk, Max Hold

-100

-80

-60

-40

-20

0

20

2.00E+09 2.05E+09 2.10E+09 2.15E+09 2.20E+09 2.25E+09 2.30E+09

Frequency (Hz)

dB

m

20dBm

10dBm

0dBm

-10dBm

-20dBm

-30dBm

-40dBm

Output of FASS - Average

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

2.00E+09 2.05E+09 2.10E+09 2.15E+09 2.20E+09 2.25E+09 2.30E+09

Frequency (Hz)

dB

m

20dBm

10dBm

0dBm

-10dBm

-20dBm

-30dBm

-40dBm

Figure 35: FASS RF output




54

Appendix B

Calibration of Emissions from Signal Generator

The radar signals were also simulated with a modern Agilent Signal Generator running pulse

building studio software.

Emission profile of TWT Radar

As shown in Figure 36, the emission characteristics of the simulated signal are similar to

those measured by ERA at airport [A].

TWT Radar Spectra

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-2.0E+08 -1.5E+08 -1.0E+08 -5.0E+07 0.0E+00 5.0E+07 1.0E+08 1.5E+08 2.0E+08

Frequency (Hz)

dB

Airport[A]

SiG Gen

Figure 36: TWT Radar Spectrum from Signal Generator

Radar antenna rotation and antenna pattern

The signal generator was programmed with the actual radar antenna rotation/pattern, and is

shown in Figure 37 compared with the emissions measured at airport [A]. It can be seen that

the simulated signal matches closely with the measured emissions.




55

Antenna Pattern/Rotation

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

0 0.5 1 1.5 2 2.5 3 3.5 4

Time (second)

dB

SiG Gen

TWT/Airport[A]

Figure 37 Simulated antenna pattern/rotation compared with measured emissions

Emission Bandwidth

The signal generator has a wide bandwidth, which is more than 800 MHz, and the OOB/SE

emissions are quite similar to those measured from a real radar, using peak detector and

max hold, as shown in the Figures below.

noise floor of SiG Gen E8267D

-80

-70

-60

-50

-40

-30

-20

-10

0

10

2.21E+09 2.31E+09 2.41E+09 2.51E+09 2.61E+09 2.71E+09 2.81E+09 2.91E+09 3.01E+09 3.11E+09

Freq

dB

Series1

Series2

Figure 38: Bandwidth of simulated signal using signal generator




56

From a previous Ofcom study [4]

A

3DB

*

*

RBW 1 MHz

VBW 1 MHz

SWT 1 s*Ref -10 dBm Att 0 dB*


1 PK

VIEW

PRN

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

1

Marker 1 [T1 ]

-57.53 dBm

2.705000000 GHz

Date: 27.JUN.2007 13:33:39

Measured at Airport [A]

Simulated by the SiG Gen

Figure 39: Comparison of OOB emissions using the signal generator




57

Appendix C

Definition of Radar interference

The Out-Of-Band and Spurious Emissions of the radar signal are quite complex; the

measured spectra are a combination of the radar transmission spectrum, factors of radar

antenna rotation, and other factors such as non-linear effects from the radar components

etc. The components of the radar emissions include essentially two types of emissions,

narrow peaks and broadband-like emissions. The narrow peaks tend to be higher but do not

occur as often statistically as the broadband interference. They are both limited by the

antenna rotation, but the narrow peaks are even less statistically likely. For example, on a

typical spectrum analyser setting, 1s sweep time, it may take up to about 10 seconds for

most of the narrowband peaks to appear, whereas the broadband noise appears fairly

instantaneously.

The radar emissions can then be presented and interpreted differently with different

measuring methods. The radar emissions are defined in the spurious emissions standards to

be measured using peak detector, 1 MHz RBW and max hold. However, an average

measurement (with peak detector) instead of a max hold measurement shows that the

narrowband peaks disappear and you essentially have the average of the broadband noise.

For this reason, specifying C/I is completely dependent on how to specify the measurement

of the value of I. If an average measurement is used then a relative constant value C/I to

cause problems of other comm kits is observed for all frequency offsets. If a max hold

measurement, the level of the narrowband peaks is measured, although these are not

actually causing the interference. Therefore higher C/Is is observed for small frequency

offsets, approaching same C/I as broadband emissions for offsets tending towards large

frequency offset. This is because with increasing frequency offset, the ratio of the

narrowband peaks to the level of the broadband emissions reduces.




58

-75

-70

-65

-60

-55

-50

-45

-40

-6.00 -5.00 -4.00 -3.00 -2.00 -1.00 0.00 1.00 2.00 3.00 4.00

Freqency (MHz)

dB

m

Max Peak, Max hold

Max Peak,clear/write

(a)

Probability Distribution Function of Emissions

0%

20%

40%

60%

80%

100%

120%

-75 -74 -73 -72 -71 -70 -69 -68 -67 -66 -65 -64 -63 -62 -61 -60 -59 -58 -57 -56 -55 -54

Emission level (dBm)

Pe

rcen

tag

e

Max Peak, Clear/Write

Max peak, Max Hold

(b)

Figure 40 a) Spectra of Max hold and Clear/Write b) Probability distribution of

interference levels




59

Comparing with the Max hold measurement and “snapshots”, the statistics analysis clearly

showed that the chance of narrowband emissions is much lower at any time step/

“snapshot”, the chance of having a peak emission of -55dBm/MHz is 0.004%, rather than

0.4% with Max hold method.

Table 13 Statistics Distribution of interference level

dBm/MHz Snapshots Max-hold

-73 100.000% 100.000%

-72 99.655% 100.000%

-71 81.550% 100.000%

-70 27.307% 100.000%

-69 4.545% 96.200%

-68 1.632% 82.200%

-67 1.299% 74.400%

-66 1.107% 67.800%

-65 0.980% 63.800%

-64 0.859% 58.200%

-63 0.650% 46.600%

-62 0.414% 34.000%

-61 0.176% 16.000%

-60 0.069% 6.800%

-59 0.051% 5.200%

-58 0.036% 3.600%

-57 0.020% 2.000%

-56 0.012% 1.200%

-55 0.004% 0.400%

-54 0.000% 0.000%

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