Satellite System Parameters

Transcription

1 Satellite System Parameters Lecture 3 MUHAMAD ASVIAL Center for Information and Communication Engineering Research (CICER) Electrical Engineering Department, University of Indonesia Kampus UI Depok, 16424, Indonesia asvial@ee.ui.ac.id

2 Objectives Satellite System Parameters Transmit Power and Bit Energy Effective Isotropic Radiated Power Equivalent Noise Temperature Carrier-to-Noise Density Ratio Bit Energy to Noise Density Ratio G/Te Ratio Illumination Level and Power Flux Density C/Ts Ratio 1

3 Satellite System Figure Satellite mobile communications system configuration 2

4 Noise in Earth Station G/T Ref rf if Ta Tf T LNA LNA T IPA IPA T D/L Lo DEMOD BASEBAND QoS (BER) DOWN CONV Ts C/N OD Noise comes from: Ta= picked up by antenna from outside ( =effective noise) Tf= lossy feeder T LNA, T IPA = amplifiers in receiver chain T D/C = down converter Refer all noise to a reference plane into the LNA Pa kb 3

5 Noise in Payload G/T Ref Cu C D D/C C/N eirps 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. 4

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7 Noise Characterization 6

8 Noise Characterization 7

9 Noise contribution of an attenuator 8

10 Noise Thermal Noise Sources Thermal Noise Power 9

11 Noise Noise Measurements in a Receiver Figure Noise Ratios at Receiver 10

12 Transmitter Power and Bit Energy Transmitter Power and Bit Energy E b = P t x T b or P t / f b where P t is Tx Power in Watts or Jo ules per Sec, T b is Bit duration in Sec, f b is bps and E b is Bit Energy in Joules per Sec Figure HPA input/output characteristic curve 11

13 EIRP Effective Isotropic Radiated Power (EIRP) EIRP = P T x G T / L T where G T is Tx Antenna Gain and L T is trans mission line losses including back-off loss, feeder loss, and b ranching loss etc. EIRP (dbw) = P t (db) L bo (db)- L bf (db)+ G T (db) Where P T = actual power output of the transmitter (dbw) L bo = back-off losses of HPA (db) L bf = total branching and feeder loss (db) G T = transmit antenna gain (db) 12

14 Equivalent Noise Temperature Equivalent Noise Temperature N = KTB where K (1.39 x joules per Kelvin) is Boltzmann s constant, T (degree Kelvin) is environment temperature, and B (Hz) is System BW F = 1+T e /T where F (unitless) is noise factor and T e is Equivale nt Noise Temperature (degree Kelvin) T e = T (F-1) Example 5-3: Convert noise figures 4 and 4.01 to equivalent tem peratures. Use 300 K for the environmental temperature. Solution 5-3: For F = 4 For F = 4.01 Te = T(F-1) Te = 300(4-1) = 900 K Te = 300 (4.01 1) = 903 K Noise Density N o = N/B or N o = KT e B/B = KT e 13

15 Carrier to Noise Density Ratio Carrier to Noise Density Ratio C/N o = C/KT e E b /N o = P t /f b x B/N or C/N x B/f b where f b is bit rate R (bits per sec) and P t is replaced with C This E b /N o is a very good measure to compare digital systems employing different modulation or encoding schemes and data rates Example 5-5: Comparison of Two Digital Systems: Compare the performance characteristics of the two digital systems listed below, and determine which system has the lower probability of error. QPSK 8PSK Bit rate 40 Mbps 60 Mbps Bandwidth 1.5 X minimum 2 X minimum C/N db db 14

16 G/T e Gain to Equivalent Noise Temperature Ratio G/T e : G/T e = G-10 log (T s ) = G- 10 log (T a +T r ) where Ts is equivale nt system noise temperature. Ta is antenna noise temp. and Tr is receiv er effective noise temp. As LNA is placed so closed (at feed point) to antenna, so, G/Te is chan ged as under: G/T e = [G r +G LNA ]/T e Expressed in log, G/T e (dbk -1 ) = G r (db) + G LNA (db) T e (dbk -1 ) 15

17 Illumination Level Illumination Level W = EIRP L + G* (dbw/m 2 ) Or, W = EIRP 20 log 10 S 71 (dbw/m 2 ) Where S= Link distance in km Figure Illumination level for geostationary satellite Power Flux Density (PFD)- EIRP/4πd 2 * Gain of a theoretical antenna with one m 2 area D=1.13m 16

18 C/T s Carrier-to-Thermal Noise Ratio-C/T s C/T S = EIRP L L ADD + G R /T S Where EIRP: Equivalent isotropic power of transmitter (dbw) L: Path loss (db) L ADD : Additional transmission losses (db) G R /T S : Receiving system figure of merit (dbi/k) C/T S = w+ G R /T S G 1m 2 17

19 BER BER (Pe) Vs C/N and Eb/No 18

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