Problems. FER-Zagreb, Satellite communication systems 2011/12

Transcription

1 Problems FER-Zagreb, Satellite communication systems 011/1

2 Problem list Problem 1 Satellite speed Problem Orbit period Problem 3 Propagation delay in satellite links (GEO) Problem 4 Data transfer speed Problem 5 Received uplink power Problem 6 Received downlink power Problem 7 - DVB-S Problem 8 Coverage area Problem 9 Effective receiver temperature noise Problem 10 Intermodulation products of 3rd order FER-Zagreb, Satellite communication systems 011/1 1

3 Problem 1 Satellite speed Geosynchronous transfer orbit (GTO) from LEO to GEO orbit h A is the apogee height and h P is the perigee height V A and V P are satellite speeds at apogee and perigee of GTO orbit, respectively. FER-Zagreb, Satellite communication systems 011/1

4 Problem 1 Satellite speed (continued) Expression for determining satellite speeds at perigee and apogee is a is half of main ellipse axis µ is gravitational Earth parameter (3.986x10 m 3 /s ). It is actually GxM or product of gravitational constant (6.674x10-11 m 3 kg- 1 s - ) and Earth mass (5.97x10 4 kg). r is the distance from Earth center to the point at ellipse moving at speed V. For Ariane 5 (perigee height is 560 km), the value of a is obtained from a hp + h ( ) Accordingly, perigee and apogee speeds are + A RE V P V 4551km 9933m/s µ µ r a V A m/s FER-Zagreb, Satellite communication systems 011/1 3

5 Problem Orbit period Expression for determining satellite speeds at perigee and apogee is µ µ V If the orbit is circular, r a, and the speed is r a µ V a 3 T π a (s) Period time is calculated from µ What is the speed and period of satellite in circular LEO orbit at 500 km height? Satellite speed is equal to V 7613m/s Orbit period is obtained from ( ) T π 5674s Height (km) Diameter (km) Period (s) Speed (m/s) FER-Zagreb, Satellite communication systems 011/1 4

6 Problem 3 Propagation delay in satellite links (GEO) Signal delay on uplink or downlink dependent on frequency is determined from where d is distance between transmitter and receiver equipment and c is the speed of light (3x10 8 m/s). Total delay on link is the sum of individual delay from first to second earth satellite station. Minimum delay is when both earth satellite stations are placed in sub-satellite point. Sub satellite point is a point on Earth surface which connects the center of Earth and satellite. t t SV d c km km/s SV c d ms Thus, total delay on satellite link is x t SV or 38.6 ms. For smaller elevation angle, delay is higher. FER-Zagreb, Satellite communication systems 011/1 5

7 Problem 4 Data transfer speed Satellite transponder has frequency bandwidth of 36 MHz. If QPSK modulation is used, what is the possible data transfer speed if α 0.3 (raised cosine)? Symbol speed bit speed/number of bits send per every symbol. For raised cosine filter, frequency bandwidth symbol speed x (1+α). If ideal impulse (α 0) is used, speed is If impulse is shape with α 0.3, bandwidth will be It follows that RS B 36Msps R S B ( α ) R S 1+ B 1+ α ( ) 7.7 Ms/s QPSK demands bits per 1 symbol so the data transfer speed is equal to Modulation Theoretical border of frequency bandwidth MSK 1 bit/s/hz BPSK 1 bit/s/hz QPSK bit/s/hz 8PSK 3 bit/s/hz 16 QAM 4 bit/s/hz 3 QAM 5 bit/s/hz 64 QAM 6 bit/s/hz 56 QAM 8 bit/s/hz 7.7 Ms/s 55.4 Mb/s FER-Zagreb, Satellite communication systems 011/1 6

8 Problem 5 Received uplink power Transmitting antenna of earth satellite station has diameter D 4m. Antenna is fed with power P t 100 W (0 dbw) at frequency f U GHz. Geostationary satellite is at a distance d km from the earth satellite station. Receiving antenna gain is 38. dbi. Efficiency of earth antenna is η 0.6. What is the uplink received signal level? PG Φ max t t 4πd 9 πd πdfu π 4 10 G η O η 8 U 3 10 λ c Power flux at satellite is calculated from Antenna gain is calculated from EIRP, or effectively isotropic radiated power of earth satellite station is Power flux is then Φ max EIRP P t G 53.1dBi + 0dBW t P t G t 73.1dBW -10log 4πd 73.1 dbw ( W/m ) 53.1dBi ( ( ) ) 7 4π dBW/m FER-Zagreb, Satellite communication systems 011/1 7

9 Problem 5 Received uplink power (continued) Received power (in dbw) from satellite antenna is obtained from P EIRP + r Lfs G r where G r is receiving antenna gain and L fs is the free space attenuation: L Received power is equal to fs 4πd λu 4πdfU c 06.5dB. P r dbw Converted into W, P r 0.30 nw 30 pw. FER-Zagreb, Satellite communication systems 011/1 8

10 Problem 6 Received downlink power Transmitting antenna on geostationary satellite is fed with P t 10 W, or 10dBW at frequency f S 1 GHz, and antenna gain G t 38. dbi. Earth antenna with diameter d 4m is at a distance of. The efficiency of earth antenna is η 0.6. What is the received downlink power? Flux density at receiving earth station is calculated from: EIRP, or effective isotropic radiated power of satellite station is Flux density is then Φ Φ max PG 4 d t t π The received power (in dbw) from satellite antenna is obtained from P + ( W/m ) EIRP P t G 38. dbi + 10dBW max t P t G t 48. dbw -10log 4πd dbw/m r EIRP Lfs G r 48. dbw ( ( ) ) 7 4π FER-Zagreb, Satellite communication systems 011/1 9

11 Problem 6 Received downlink power (continued) Free space loss L fs is calculated from: L fs 4πd λu Receiving antenna gain G r is obtained from G r πd η λs The received power is equal to P r πdfu η c 4πdfU c Converted into W, P r 30.5 pw dB. π dBW dB FER-Zagreb, Satellite communication systems 011/1 10

12 Problem 7 - DVB-S Satellite channel bandwidth is usually 7 MHz r 36 MHz. DVB-S uses QPSK modulation and convolution coding with code rate ρ and Reed-Solomon coding (04,188). Spectral efficiency of QPSK modulation is 1.56 bit/s/hz. Data rate R c (with bandwidth B 7 MHz) is equal to To determine the speed of information R b, the code rate ρ and RS code (code rate 188/04) must be taken into consideration: For ρ 7/8, and for ρ 1/ R c R b R b MHz R 188 ρ 04 b R c Mbit/s bit/s 4.1Mbit/s 34Mbit/s 4.1Mbit/s 19.4Mbit/s FER-Zagreb, Satellite communication systems 011/1 11

13 Problem 8 Coverage area Calculate coverage area of a LEO satellite at height of 800 km. Earth radius R E is 6378 km. S π RE 1 h E R + E R E Surface of the Earth is 5.1x10 m. S ( ) ( ) m 6 FER-Zagreb, Satellite communication systems 011/1 1

14 Problem 9 Effective receiver temperature noise Calculate receiver noise factor shown in figure if low noise amplifier temperature is T LNA 150 K and gain G LNA 50 db. Mixer has temperature T MX 850 K and loss L MX -10 db, while MF amplifier has temperature T MF 400 K and gain G MF 30 db. Surrounding temperature is T 0 90 K. T T (K) MX MF T er TLNA + + GLNA GLNA G F( db) MX 10log 1 T K 150K T er F ( db) FER-Zagreb, Satellite communication systems 011/1 + 10log dB T

15 Problem 10 Intermodulation products of 3rd order Earth satellite station operates with two antennas and with uplink frequency f u 055 MHz and downlink frequency f d 3 MHz. Local oscillator of receiving converter works at frequency f LO 37 MHz. MF frequency is 0 MHz. If there is a transmitter in the vicinity of earth station operating at frequency f x 1598 MHz, is it possible that intermodulation products of third order could interfere? f f ( 37 ± 3) MHz 4604MHz; LO ± r Intermodulation products of third order are: ( 3196 ± 055) 0MHz f X ± f u MHz 11MHz; 551MHz fo ± fx ( 4110 ± 1598) MHz 5708MHz; 51MHz ( 51 37) MHz 0MHz no effect no effect possible effect Intermodulation products of 3rd order in combination with local oscillator frequency results at the mixer output frequency of 0 MHz. FER-Zagreb, Satellite communication systems 011/1