1. 8.5 SATELLITE COMMUNICATIONS
Antenna Coverage

2. Figure 8-29. (a) Satellite repeater link
Figure (a) Satellite repeater link. (b) Frequency-translation satellite communications relay. (c) Demod/remod satellite communications relay.

3. Figure 8-30 Polar representation of a general antenna gain function.

4. Example 8.4

5. Earth Station and Transmission Methods
Figure Satellite ground station receiver/transmitter configuration The command transmitter and telemetry receivers are not shown.

6. Figure 8-32 Illustration of multiple-access techniques. (a) FDMA
Figure Illustration of multiple-access techniques. (a) FDMA. (b) TDMA. (c) CDMA using frequency-hop modulation (numbers denote hopping sequences for channels 1, 2, and 3.

8. Figure 8-33 Details of a TDMA frame format.

11. Figure Signal and noise powers in the uplink and downlink portions of a bent-pipe satellite relay system.

12. Link Analysis: Bent-Pipe Relay

14. Example 8.5

15. Figure Transition probability diagram for uplink and downlink errors on a demod/remod satellite relay.
Figure Transition probability diagram for uplink and downlink errors on a demod/remod satellite relay.

16. Link Analysis:OBP Digital Transponder

17. Example 8.6

18. Figure 8-36 Comparison of bent-pipe and OBP relay characteristics.

19. Figure Hexagonal grid system representing cells in a cellular radio system; a reuse pattern of seven is illustrated.

22. Link Budget Analysis

23. From performance analysis to physical transceiver specs
Link budget analysis connects performance analysis to physical transceiver specs
Transmit power
Antenna directivities at Tx and Rx
Quality of receiver circuitry (how much noise do we incur)
Desired link range

24. Taking stock of what we know
Given bit rate and signal constellation (including any error correction code that is used), we know the required modulation degrees of freedom per unit time (the symbol rate)
This gives minimum Nyquist bandwidth
Now factor in excess bandwidth
Given the constellation and desired BER, can find Eb/N0 required, and hence the required SNR
SNR=(energy/bit * bits/sec)/(noise PSD*bandwidth)
Given receiver noise figure and bandwidth, can find noise power
We can now specify the receiver sensitivity (min required received power):
Receiver sensitivity
(typically quoted in dBm)

25. Friis’ Formula (free space propagation)
Carrier
wavelength
Range
Transmit
power
antenna
directivity
Receive
Antenna directivity (gain with respect
to isotropic antenna) is often
expressed in dB scale
Friis’ Formula in dB scale

26. Link Budget Equations More generally, the received power is given by
for free space propagation
Add on a link margin (to compensate for unforseen
or unmodeled performance losses) to get the link budget:

27. Example: link budget for a WLAN
WLAN link at 5 GHz
20 MHz bandwidth, QPSK, excess bandwidth 33%,
receiver noise figure 6 dB
BIT RATE
Symbol rate
Bit rate
REQUIRED SNR
10-6 BER for QPSK requires Eb/N0 of 10.2 dB (use BER formula ) )
In dB,

28. Link budget for WLAN (contd.)
Receiver
sensitivity
(transmit power of 100 mW, or 20 dBm, and antenna directivities of 2 dBi
at Tx and Rx)
Find the max allowable path loss for the desired receiver sensitivity:
Invert path loss formula for free space propagation
Range is 107 meters
Of the order of advertised WiFi ranges
Max. allowable path loss
Noise power
Try variants: redo for other constellations; carrier frequency of 60 GHz
with antenna directivities of 20 dBi.