 to determine Y, the required bit energy-to-noise ratio for a given bit error probability, would be obtained from analysis assuming Rayleigh fading (see Chapter 1 in Part 2). Otherwise, Figure 2.9 can still be applied. As with pulse jamming, because the real time bit energy-to-noise ratio varies in time, with the use of coding, care must be taken to distinguish between using side information to obtain the maximum-likelihood metric or a simpler non-optimum metric. With suboptimum metrics (no side infor- mation about real time bit energy-to-noise ratio) hard decision channel quantization can outperform soft decision channel quantization [90]. 2.3.2 Conventional Multipoint-to-Point Consider the possibility of two or more radios transmitting simultaneously to a single radio terminal in a network. For a conventional FDMA system this would be possible if the transmitting radios use different frequencies and the receiving radio terminal has separate receivers each tuned to one of the transmitting freuencies. For DS/BPSK waveforms the analogous system is where the transmitting radios use different keys and the receiving radio ter- minal has separate receivers each using a key with a pseudorandom sequence synchronized to the corresponding transmitting radio. Here a key in the SSMA system is similar to a frequency in the FDMA system. This is illus- trated in Figure 2.10. A radio terminal capable of receiving several signals of different fre- quencies in an FDMA system or DS/BPSK waveforms of different pseudo- random sequences in an SSMA system is often too complex and costly. This is because the receiving radio terminal essentially consists of several sepa- rate receivers. Conventional TDMA systems get around this problem since Multiple Access DETECTOR MATCHED FILTER QUANTIZER/ DECODER DETECTOR MATCHED FILTER QUANTIZER/ DECODER MATCHED DETECTOR FILTER QUANTIZER/ DECODER Figure 2.10. Transmissions with different keys. a single radio receiver can sequentially receive each of the transmitted radio signals that occupy non-over