Performance improvement of correlation-flattened binary CDMA

In this paper, we present an improvement of the performance of binary CDMA communication system by flattening the correlation values. A binary CDMA system, in which multi-level transmission signal of multi-code CDMA is truncated into a binary value, is cost-efficient. The strict linearity of the power amplifier is relieved since the transmission signal level is binary. The overall performance of binary CDMA is comparable to DS-CDMA when appropriate spreading codes are used. However, the orthogonality between each spreading pattern of a channel is lost in the truncation process and this causes the magnitude of the correlation value at the correlation receiver to have a random distribution. If the correlation value for even a single channel goes too low, then we get an inherent bit error and the average BER drops. We developed a method of correlation flattening, where the transmission binary chip pattern is adjusted so that the correlation values of all channels have similar average magnitude and the average BER performance is improved. Results from experiments on several spreading codes show that the correlation flattening method is very effective.