Error probabilities for DS/SSMA communications using random sequences

A simple evaluation of the probability of error for direct sequence spread spectrum multiple access (DS/SSMA) communications based on a series expansion method is presented. When the processing gain is large, it is shown that the Gaussian approximation for the matched filter output becomes valid independently from the number of users on the system. It is concluded that a DS/SSMA system can be designed to accommodate approximately as many users as the processing gain. When a CW interferer is assumed present, the interferer is reduced by approximately the processing gain depending on its location with respect to the carrier frequency