to Eb/No with the following formula: Eb/No=C/N0-10 log(bit = rate) (9.25) The Eb/No value can now be applied to the typical curves found in Figure 9.10 to derive the BER. As we have mentioned previously, satellite communication is downlink-limited because downlink EIRP is strictly restricted. Still we want to receive sufficient power to meet error performance objectives. One way to achieve this goal is use forward error correction on the links where the lower Eb/No ratios will still meet error objectives. Thus INTELSAT requires coding on their digital accesses. Some typical INTELSAT digital link parameters 9.3 SATELLITE COMMUNICATIONS Table 9.6 QPSK Characteristics and Transmission Parameters for IDR Carriers Parameter Requirement 1. Information rate (IR) 64 kbps to 44.736 Mbit/s 2. Overhead data rate for carriers with IR 1.544 Mbps 96 kbps 3. Forward error correction encoding Rate 3/4 convolutional encoding/Viterbi decoding 4. Energy dispersal (scrambling) As per ITU-R5.524-4 5. Modulation Four-phase coherent PSK 6. Ambiguity resolution Combination of differential encoding (180°) and FEC (90°) 7. Clock recovery Clock timing must be recovered from the received data stream 8. Minimum carrier bandwidth (allocated) 0.7 R Hz of [0.933 (IR + Overhead)] 9. Noise bandwidth (and occupied bandwidth) 0.6 R Hz or [0.8 (IR + Overhead)] 10. Eb/No at BER (Rate 3/4 FEC) a. Modems back-to-back 5.3 dB 8.3 dB 8.8 dB b. Through satellite channel 5.7 dB 8.7 dB 9.2 dB 11. C/T at nominal operating point -219.9 + 10 log 10 (IR + OH), dBW/K 12. C/N in noise bandwidth at nominal operating point 9.7 dB (BER < 10-7) 13. Nominal bit error rate at operating point 1 X 10-7 14. C/T at threshold (BER = 1 X 10-3 -222.9 + 10 log10 (IR + OH), dBW/K 15. C/N in noise bandwidth at threshold 6.7 dB (BER = 1 X 10-3 16. Threshold bit error rate Notes: IR is the information rate in bits per second. R is the transmission rate in bits per second and equals (IR + OH) times 4/3 for carriers employing rate 3/4 FEC. The allocated bandwidth will be equal to 0.7