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Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.1
Satellite Communications APart 3
Link planning / budgetting-Professor Barry G Evans-
EEM.scmA
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.2
Link budget & system planning
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.3
Mobile System
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.4
Performance
• (i) QoS – b.e.r.– 10-4 if speech– 10-6 – 10-8 data (extra coding)
• (ii) Availability– 95%– Channel conditions
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.5
Basic Transmission
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.6
Carrier Transmission Budget-Antenna Gain-
The antenna gain is defined as the ratio of the power per unit solid angle received/radiated by the antenna in a given direction to the power per unit solid angle received/radiated by an isotropic antenna supplied with the same power.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.7
Basic Transmission
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.8
Basic Transmission
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.9
Antenna radiation pattern
Antenna radiation pattern = gain variations as a function of the angle relative to boresight
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.10
Transmitted power in a given direction
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.11
Predicted coverage areas for the HOTBIRD satellites
(a) Superbeam(b) Widebeam(courtesy of EUTELSAT)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.12
Effective isotropically radiated power (EIRP)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.13
Exercise (1) - Carrier Transmission Budget
• Given– Power fed to antenna: PT = 10W– Antenna gain (at boresight): GTmax = 40dB– Distance: R = 36000km (earth to geostationary satellite
• Calculate– Transmitter EIRP in dB(W)– Flux density at receiver in dB(W/m2)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.14
Down Path
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.15
GEO - Geometry
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.16
Earth station from the geostationary orbit
• Satellite– Height h above the equator
– Sub-satellite point, longitude ΦS
• Earth station– Latitude E, longitude ΦE
– Relative longitude satellite = (ΦE – ΦS) = ΦES
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.17
Exercise (2) – Carrier Transmission Budget
• Given– Uplink frequency = 14GHz– Eart station
• Power fed to the antenna: PT=100W• Antenna diameter: D=4 (efficiency =0.6)• Location: Bercenay (France)
Latitude = 48º13’07”N Longitude = 03º53’13”E
– Satellite• Receiving antenna gain at boresight: GRmax=40dB• Location: 7ºE (EUTELSAT 1-F2)
• Calculate– EIRP of earth station– Free space loss– Received power
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.18
Noise in an Earth Station
– Noise comes from:• Ta= picked up by antenna from outside ( =effective noise)• Tf= lossy feeder• TLNA, TIPA= amplifiers in receiver chain• TD/C= down converter
– Refer all noise to a reference plane into the LNA
kB
Pa
DEMODBASEBAND
QoS(BER)
LNA IPA
rf if
G/T Ref
Lo
DOWN CONVC/NOD
Ta Tf
Ts
TLNA TIPA
TD/L
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.19
Noise in a Payload
G/T Ref
Cu
D/C
C/Nou
• Noise comes from:– Antenna received noise –earth + galaxy– Feeder lossy noise (nb.290K)– Equipment noise –amps / D/C etc. added in same way as for earth
station.
CD
eirps
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.20
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.21
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.22
Noise Characterisation (1)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.23
Noise Characterisation (2)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.24
Noise contribution of an attenuator
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.25
B/K10Log(Ts)dL)(GaTG
L)dB - (G referenceat antenna ofGain
10log(g)GdB
α10log(l),LdB
...g x g
T
g
T T )Tf-(1 TaTs
a
IPALNA
CD
LNA
IPALNA
l1
D/CLNA IPA
Ref
Ta Tf TLNA TIPA TD/C
LD/C
LdB
xTal
1
)Tfl
(1
1
IPALNA
D/Cxgg
T
LNA
IPAg
TTLNA
GLNA GIPA
Earth-station system G/Tand noise temp.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.26
Earth station antenna noise temperatureExamples (clear sky conditions)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.27
Exercise (3) - Noise Contribution Budget
• Operating frequency = 12 GHz• LNA: TLNA = 150K, GLNA = 50dB• MIXER: TMX = 850K, GMX = -10dB• IF AMP: TIF = 400K, GIF = 30dB
• Calculate– Receiver effective input noise temperature TR
– Receiver noise figure
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.28
Exercise (4) - G/T of C-band earth station
• Dish=15m, n=70%• Ta=30K• Tf=290K• Loss f=0.5dB• TLNA=35K• GLNA=30dB• FIPA=3dB• GIPA=20dB• TD/C=1000K• Loss D/C=-10dB
• Calculate the earth station G/T– What are the advantages of trading off dish size and LNA
temp.?
D/CLNA IPA
Feeder if
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.29
Propagation-Effects to be considered-
• Radio noise• Ionospheric effects
– Absorption– Total electron content effects (group delay, refraction,
polarisation rotation)– Scintillation
• Tropospheric effects– Attenuation by rain– Depolarisation– Refraction effects
• Shadowing and multipath effects
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.30
• Any ATTENUATION process which involves energy absorption is associated with THERMAL NOISE GENERATION from the medium
• Absorption by atmospheric gases is frequency dependent, hence clear sky noise temperature exhibits similar variations with frequency
Clear Sky Noise Temperature
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.31
• See CCIR Rep.719 for a detailed description of practical techniques of calculation for LAG. The following curve displays AAG(E) versus frequency; E is the elevation angle.
Attenuation by atmospheric gases
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.32
Noise temperature of the sun
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.33
Ionospheric effects
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.34
Attenuation due to rain, etc.
• Mist
• Clouds
• Snow
• Ice
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.35
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.36
References for calculation methodology
• Course notes or chapter 8 of the book
• ITU-R PN 618-3 splant path rain induced attenuation and depolarisation and scintillatin
(available from lending libraries or ITU, Geneva)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.37
Attenuation due to precipitation and cloudsRelevant techniques described in CCIR (see rep.563, 564, 721, 723)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.38
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.39
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.40
Contours of RAINFALL RATE
R₀․₀₁ (mm/h) exceeded for 0.01% OF AN AVERAGE YEAR:
Maps of rainfall contours (1/3)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.41
Contours of RAINFALL RATE
R₀․₀₁ (mm/h) exceeded for 0.01% OF AN AVERAGE YEAR:
Maps of rainfall contours (2/3)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.42
Contours of RAINFALL RATE
R₀․₀₁ (mm/h) exceeded for 0.01% OF AN AVERAGE YEAR:
Maps of rainfall contours (3/3)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.43
with circular polarization use the arithmetic mean of attenuation with horizontal and vertical polarization
Nomogram for determination of specific attenuation
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.44
Comments:30/20 GHz systems face a problem, especially in tropical regions where rainfall rate is very high during small percentage of time.Performance objective must be achieved when rain occurs. The link will probably be over dimensioned during most of the time (margin).
Typical values of rain attenuation
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.45
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.46
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.47
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.48
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.49
DEPOLARISATION
• Rain and ice cause this due to shape of particles– Need to know shape and orientation of particles– Linear and circular POLN different– Circular POLN is worst case– Can form a model linking depolarisation (XPD)
and attenuation
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.50
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.51
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.52
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.53
XPD STATISTICS
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.54
Raininduced XPD circular polarisation(for 1% worsth month)
CO-POLAR ATTENUATIONdB
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.55
Other tropospheric effects
• Snow– Dry snow –ok (little effect)
– Wet snow –as bad as rain
– Problem if snow builds up on antenna
• Atmospheric absorption– Gas and particle absorption (worse at low
elevation angles)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.56
Noise Contribution Budget-Satellite Antenna Noise Temperature-(1)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.57
Noise Contribution Budget-Satellite Antenna Noise Temperature-(2)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.58
Influence of Rain
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.59
Noise
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.60
Exercise (5.a) - Carrier Transmission Budget
• Ta=50K, =0.9, Tf=290k• Pointing loss = 0.7dB• Atmospheric loss = 0.3dB• Rain loss = 3dB for 99% lime• Rain temp = 275K
• Calculate the G/T of the earth station under worst weather conditions
• Calculate the down link C/No• Calculate the down link C/N if the link bandwidth is 100KHz• Complete the link budget sheet
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.61
Exercise (5.b) – Link budget sheet
• Link budget sheet – Downlink
Satellite EIRP dBW
Pointing loss dB
Atmospheric loss dB
Rain loss (99%) dB
Free space loss dB
Gain E/S dB
Downlink carrier dBW
E/S noise temp. dB-K
E/S G/T dB/K
Boltzmann constant -228.6 dBW/Hz/K
Downlink noise density (NOD)
dBW/Hz
C/NOD dB-Hz
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.62
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.63
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.64
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.65
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.66
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.67
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.68
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.69
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.70
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.71
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.72
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.73
DOWNLINK
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.74
UPLINK
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.75
Up Path
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.76
Exercise (6) – Up-link
• Ku-band uplink 14GHz
• Dish size=5m, =0.65
• Distance to satellite=38,000km
• Uplink atmospheric loss=0.3dB
• Uplink pointing loss=0.7dB
• Uplink rain loss=3dB
• Tx e/s w.g. feed loss=3dB
• Satellite Rx antenna gain=26dBi (from Tx e/s)
• Satellite Tx antenna gain=25dBi (at boresight)
• Rx earth station AR=-2dB
• Satellite Tpdr gain=120dB
• The satellite transponder has a single carrier saturation condition PFDi=-76dBW/m2, eirp sut=50dBW
• The transponder’s is operated at 8dB input and 5dB output back off
Calculate1. The uplink HPA rating if this has to operate at 6dB back off
2. The uplink carrier at the satellite Cu
3. The downlink carrier eirp from the satellite
SAT
120dBCu
eirps
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.77
• The order of any intermodulation product is defined as ‘(n+m) where the IMP’s are:
where n, m= 1,2,3,…
• When the center frequency of the amplifier is large compared to its bandwidth, odd-order intermodulation products are the only ones falling within the useful frequency band
• Intermodulation product power decreases with the order of the product. So only third and fifth order intermodulation products are concerned
Characteristics of intermodulation products
)21( fmfn
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.78
Link Performance-Intermodulation noise
Intermodulation products may appear at:- the output of the transmitting earth station non linear power amplifier- the output of the satellite repeaterThese intermodulation products can interfere with the desired carriers, and hence be considered as noise called “intermodulation noise”.With modulated carriers, the intermodulation noise is distributed over the entire frequency band.
Example: Intermodulation noise spectrum for a typical TWT with 10 carriers. (6 central carriers modulated by a multiplex of 24 telephone channels, two 64 channels carriers and two 132 channels carriers)
Intermodulation products can be considered as filtered white noise with constant spectral density (No)IM
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.79
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.80
Intermodulation
• (nf1 mf2), order = (n+m)
• IMP’s vary (order-1)dB/dB with carrier.
– E.g. 3rd – 2dB/dB 5th – 4dB/dB
• Payloads –linearisers to reduce IMP’s
• Ku-band transponders– TV– 3rd order important
• L/S-band transponder –1000’s small mobile carriers. 5th and 7th important
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.81
Total Link Operation(link from earth station to earth station)
1 – LINEAR OPERATION: PT‹(PT)max’ (NO)IM = O
Repeater power gain GS is constant. Satellite transmitter output power is shared between:- amplified carriers- amplified input noise
2 – SATURATION REGION OPERATION:
Available power from satellite repeater is limited.
Output power is shared between:- amplified carriers- amplified input noise- intermodulation products
Power gain value depends on operating point.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.82
Total Link Budget-Non linear operation-
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.83
Interference
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.84
Interference Management (1)
• Between Satellite and Terrestrial systems –limit PFD’s satellites and terrestrial Tx’s
• Radio Reg’s –Appendix S7• 1st stage
– Calculate coordination contour– Calculate all Tx’s inside contour
• 2nd stage– If needed– Detailed calc’s using all parameters– Site shielding– Energy dispersal etc.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.85
EARTH STATION: MADLEYSAT: INTELSAT 5 LONGITUDE 3415RX FREQUENCY: 4.18 GHZ
- CO-ORDINATION CONTOUR- MODE 1 CONTOUR
Radio regulations(Appendix S7)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.86
Interference
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.87
Interference Management (2)
• Between satellite networks• Radio Reg’s –Appendix S8• Analyse noise increase ΔT6% (otherwise go to second
detailed stage)
S1 S2
I
C
E1 E2
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.88
Total Link Budget-Non Linear Operation-
Total noise at receiver input = uplink retransmitted noise + intermodulation noise + downlink noise:
1 – Assuming that all incoming carriers at repeater input have SAME POWER(as with controlled uplink power FDMA for instance):
(C/N0)T-1 = (C/N0)U
-1 + (C/N0)D-1 + (C/N0)IM
-1+ (C/I0)U/D-1
2 – If incoming carriers at repeater input DO NOT HAVE SAME POWER:
There is a CARRIER SUPPRESSION EFFECT: large power carriers tend to suppress small power carriers.
Generally speaking:
- for SMALL POWER carriers:(C/N0)T is smaller than in the case of equal power carriers.
- for LARGE POWER carriers:(C/N0)T is larger than in the case of equal power carriers.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.89
Exercise (7) – Link Performance
• Given– Uplink carrier power-to-noise power spectral density: (C/No)U=85dB(Hz)
– Downlink carrier power-to-noise power spectral density: (C/No)D=83dB(Hz)
– Carrier power-to-intermodulation noise power spectral density: (C/No)IM=87dB(Hz)
– Uplink carrier power-to-interference power spectral density: (C/No)I,U=90dB(Hz)
– Downlink carrier power-to-interference power spectral density: (C/No)I,D=90dB(Hz)
– Noise equivalent bandwidth of earth station receiver: BN=5MHz
• Calculate– Overall link carrier power-to-noise power spectral density: (C/No)T
– Overall link carrier power-to-noise power ratio: (C/N)T
SATUplink interference
Downlink interference
Uplink path Downlink path
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.90
Total Link Budget-Non linear operation with interference
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.91
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.92
Figure 6.11 Gains and losses in power of signals being relayed by satellite. The signal falls to about one hundred billion billionth of its strength (10-34) on each of its 25,000-mile journeys through space. This great loss is balanced by the grains of the antennas and amplifier
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.93
UplinkEIRP
C/NouSatellite
C/IM oC/IU
C/ID
C/ND
Sat. Link Performance
C/NTOT
Requirements for QoS
C/No.Req
Margin =C/NTOT – C/NoReq
If Not 2-3 dB
Increase EIRPAnd Repeat
Setting out Link budgets
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.94
Types of Objectives
• SIGNAL QUALITY OBJECTIVES:
In terms of thresholds which must not be exceeded for more than a given percentage of time.
• SYSTEM AVAILABILITY OBJECTIVES:
Asys = (required time – down time) / required time
Required time = period of time during which the user requires the link to be in condition to perform a required functionDown time = cumulative time of link interruption within the required time
Interruption is a period in which there is a complete or partial loss of signal, excessive noise, or a discontinuity or severe distortion of the signal.
• PROPAGATION TIME:
The overall link propagation time should not overstep a maximum value depending on the user’s requirement.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.95
System Availability
SYSTEM AVAILABILITY ASYS implies that the quality objectives be met during a given percentage of time (typically between 99 and 99.9%).
This requires the link C/N0 ratio to be larger or equal to a given value for the considered percentage of time.
C/N0 varies according to:- propagation effects (mainly influence of rain)- implementation losses (mainly antenna depointing or equipment failure)
ASYS = ATX Asat Alink ARX
where:ATX = transmitting earth station availabilityAsat = satellite availabilityAlink = link availabilityARX = receiving earth station availability
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.96
RAIN INDUCED attenuation and depolarization can reduce the C/N0 value, and cause link outage.
A LARGER MARGIN value leads to a HIGHER LINK AVAILABILITY, as C/N0 will understep the required value during a shorter time interval.
Link Availability
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.97
System cost increases rapidly with system availability:
CUSTOMER SHOULD NOT ASK FOR TIGHT SPECIFICATIONS, UNLESS STRICTLY NEEDED.
Cost of System Availability
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.98
PERFORMANCE: - BIT ERROR RATE- BANDWIDTH
Digital Transmission Techniques-System Model-
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.99
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.100
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.101
Time Division Multiplexing
Digital signals are organized in bursts by means of buffers where bits are stored and then read at a higher clock rate.
Bursts are transmitted sequentially within time slots according to a time frame structure.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.102
Time Division Multiplex Standards
(CCITT,Rec. G702, G732, G733):
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.103
Two types of encryption techniques:- stream cipher: each bit of the plain text is combined bit per bit with the keystream,- block ciphering: the plain text is modified block per block.
Data Encryption
DATA ENCRYPTION entails two aspects:- confidentiality: avoid access to message by an unauthorized party.- authentication: protection against someone changing the message content.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.104
Scrambling
• At receiver side CLOCK TIMING for bit detection is extracted from DATA SYMBOL TRANSITIONS. Long data streams of 0’s and 1’s can result in the loss of data synchronization.DIGITAL DATA CSRAMBLING at transmitter side provides a data symbol transition probability close to 0.5. At receiver side DESCRAMBLING is performed to restore original data.
• SCRAMBLING also removes any periodic pattern in the baseband pulse train. Hence it CANCELS any DISCRETE LINE COMPONENT in the modulated RF spectrum. This offers better protection against overstepping the permissible level of radiated power flux density: scrambling is an ENERGY DISPERSAL technique.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.105
Channel encoding
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.106
Decoding gain
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.107
Digital Speech Interpolation (DSI)
• A talker has an activity factor which is less than 1. By INSERTING BITS from another channel INTO PAUSES of a given channel, DSI compresses a number m of voice channels into a SMALLER number n of satellite channels.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.108
Performance objectives
• Quality objectives for telephony (CCIR Rec.522)DIGITAL TRANSMISSION
– The BIT ERROR RATE (BER) should not exceed:a) 10-6, 10-minute mean value, for more than 20% of any monthb) 10-4, 1-minute mean value, for more than 0.3% of any monthc) c) 10-3, 1-second mean value, for more than 0.01% of any year
• Quality objectives for data transfer (CCIR Rec.614)– for 64 kbit/s channels as part of ISDN:
The BIT ERROR RATE (BER) should NOT EXCEED:a) 10-7, for more than 10% of any monthb) 10-6, for more than 2% of any monthc) 10-3, for more than 0.03% of any month
• No standard yet for bit rates in excess of 64 kbit/s. Likely 10-9 to 10-12.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.109
Noise performance
• Problems– Additive white Gaussian noise– Co-channel interference
• Frequency re-use
– Adjacent channel interference• From other signals
– Intersymbol interference• Due to band limiting
– Phase noise• From carrier recovery
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.110
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.111
Which modulation?
• Power limited satellite use B/QPSK• Mobiles need OQPSK/MSK to avoid non linear amp problems• Bandwidth limited satellite –16 QAM etc.
PSK
FSKASK
BER
Eb/Nominimum power from satellite
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.112
Digital transmission techniquesM-PSK modulation
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.113
Carrier-to-noise power ratio at demodulator input
The noise equivalent bandwidth BN of their receiver is assumed to be matched to the modulated carrier bandwidth B
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.114
BPSK QPSK
• QPSK is half bandwidth of BPSK• PSD in QPSK is 3dB higher
Rs= Rb/2Rs= Rb
1
0
DECN
ERROR
Prob(Error) = BER
NoEberfcBER
AWGNSIGNAL
2
1
+/2
Vn=AWGN
VR
VR
-/2
2 x errorsBw=1/2 BPSKResult same
11
10 00
01
ERROR
NoEberfcBER
2
1
ERROR
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.115
Theoretical Bit Error Probability (BEP)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.116
Bit Error Probability (BEP)
Useful values
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.117
Theoretical Bit Error Probability(BEP)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.118
Carrier & Bit Error Probability (cont’d)
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.119
Demodulation of digital signalsCONCLUSION
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.120
M-PSK modulation Power spectral density
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.121
Matched filtering
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.122
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.123
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.124
Bit Rates and Bandwidth
• Example
– What is Rb, Rc and Rs?– If filtering is Rc, =0.5, what is the bandwidth?
PCMcoder
=1/2FEC coder
QPSKMODRb Rc Rs
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.125
Spectral efficiency
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.126
Exercise (8) – Digital Transmission Techniques
• Given– Type of modulation: coherent QPSK (spectral efficiency r = 1.5 bits/s.Hz)
– Received information bit rate: Rb = 36 Mbit/s
– Required BER = 10-5
• Calculate required value of C/No and bandwidth:– 1. Without coding– 2. With coding (code rate = 3/4)– Could you use a smaller code rate (for instance 2/3 or 1/2)?
satellite transponder bandwidth B=36MHz
Free space loss L=200dB
G/T=14dB(K-1)receiver bandwidth BIF
PT=10W
GT=30dBEIRP=40dB(W)
C/No = EIRP x 1/L x G/T x 1/k
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.127
Power/Bandwidthtrade off and coding
• Power and bandwidth limitations are complimentary
• A transponder has finite bandwidth BT and hence traffic limit = BT/BC (BC = channel spacing)
Bandwidth limit case
• A transponder has fixed power so can only support ‘n’ channels at a given QoS (ber)
– Traffic limit (PTPD-Pc)=10log(n) (Pc=power per channel)
Power limit case
• Coding allows trade-off between bandwidth and power to optimise throughput
cnc No
Eb
No
EbPower
1RbB
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.128
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.129
Exercise (9) – Overall Link Budget
• The attached link budget has been calculated for a 9.6 kb/s email service for a VSAT into a hub. The modulation used is BPSK and the coding gives a coding gain of 4dB. The desired quality of service is a BER of 10-6.
• The hub available has the following parameters:– Antenna diameter = 4m– Efficiency = 65%– Feeder loss = 0.5dB– Skynoise = 50K– LNA temp = 75K– Rain temp = 275K
• Fill in the missing components of the budget.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.130
Exercise (9) cont’d
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.131
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.132
Exercise A – Earth Station
• An INTELSAT-A (4/6 GHz) earth-station is required to transmit two IDR carriers (eirp = 65 dBW/carrier). The specification of the station is:– G/T >35 dB/K at 5° elevation– 2 carrier IDR, intermodulation eirp is not to exceed 10dBW/4kHz.
• A list of major available equipment is shown in Table next page.• The earth-station waveguide feed loss is 0.5dB on receive and 3dB on
transmit. All components beyond the LNA can be neglected for noise calculation purposes and all antennas have a 70% efficiency. The output back-offs of HPAs can be taken as 10dB for multicarrier operation and the IMP eirp is given by;
• E12 = 2E1 + E2 – 2(GTX – LTX) + D - SF• Where:
– (GTX – LTX) is the effective atenna gain at the HPA flange.
– D = (-2.PSAT – 28 + 2 x BOo)dBW2.– SF (Spreading Factor) = 20 dBW/4kHz.
• Calculate the minimum cost earth-station configuration to meet the specification.
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.133
Exercise A – Earth Station (cont.)
• List of equipmentEquipment Cost (£k)
Antenna
13.0 m
15.5 m
18.0 m
Noise Temp
30 K
25 K
20 K
160
200
300
HPA
125 W
400 W
700 W
50
60
80
LNA
33 K
55 K
80 K
30
6
3
Autumn2004 © University of Surrey SatComms A - part 3 - B G Evans 3.134
Exercise B – Payload
• Figure A shows a 20/30 GHz payload with specification– G/T 16.5 dB/K– eirp 50 dBW– C/I3 20 dB
• The input power at the antenna receive terminals is –111 dBW. There is an input feeder loss of 1dB at a temperature of 75K.
i. Determine the noise specification for the payload.ii. 20 GHz LNAs of gain 10, 13 and 20 dB with noise figure of 3, 4 and 5 dB
respectively are available. Determine the LNA configuration to be used.iii. Estimate whether the noise specification is achievable.iv. Describe how you would check the linearity specification.