Outage probability for the uplink of a DS-CDMA system operating over a LEO mobile satellite channel

A DS CDMA satellite uplink with power control error is considered. CDMA system performance is normally interference limited, and individual users typically experience the average performance over all users. This is particularly true in a Gaussian, additive white noise channel, with many users, sufficient processing gain, and effective power control. In this case, the other users appear as Gaussian noise and each user experiences the same environment. Under fading channel conditions however, the average behavior notion is flawed, since the fade conditions for each user are different, even if the fading statistics are identical. An alternative measure of performance under these conditions is the probability of outage. For coded signals, the fading must be averaged over all the symbols in the codeword. For properly interleaved signals and i.i.d. Rayleigh fade statistics, the average must be performed over a chi-squared variate. The probability of outage, defined as the probability that the decoded bit error rate exceeds a specified threshold, is monotonic with the probability that the chi-squared variate is less than a specified threshold. The authors derive upper and lower bounds on the outage probability for soft decision decoding