6, ,7,0,1,2 2 7, 0, 1, 2, 3 Multiple Access By checking the detector output patterns we see that the sequence 6, 7, 0, 1,2 corresponding to X = 6 had the greatest number of entries. This is the circled chip energy detector output sequence shown. Under this hard quantized detector output with the above pattern deci- sion rule, errors will occur when noise and other users combine to form allowed sequences with more entries than the sequence that was actually transmitted. The multiple access scheme just described assumes that, given the output pattern of m chip sequence of M hard decision bits, the receiver first checks for the possible sequences of the 1st radio and makes a data symbol deci- sion for it. Then it independently checks the same output pattern for possi- ble sequences of the 2nd radio and makes a data symbol decision for it. It does this L times for the L radios that are transmitting. Here each data sym- bol decision is independent of each other even though the output pattern of the m chip sequence of M quantized bits for making decisions is the same. This is illustrated in Figure 2.26. Goodman et al. [117] has shown that for M = 625 and m = 19 with per- fect transmission where the only degradation is mutual interference, an error rate of less than 10-3 can be maintained with up to 209 simultaneous trans- mitting radios. Transmission impairments, consisting of white Gaussian noise and frequency-selective Rayleigh fading with an average signal-to-noise ratio of 25 dB, reduced the number of simultaneous users to about 170. This exceeded the capacity of the original frequency-hopped, phase-shift-keying, spread-spectrum system proposed by Cooper and Nettleton [119]-[121]. Haskell [122] did computer simulations to compare the performance of ran- domly chosen address sequences with chirp sequences and those found by Einarsson [123]. His results show that the chirp and Einarsson address sequences were equivalent and somewhat better than random address sequences but the differences diminish as the number of sy