Numerical optimization for CDMA spreading sequences

Abstract

The performance of a direct sequence spread spectrum (DS-SS) code division multiple access (CDMA) communications systems is highly dependent upon the set of spreading sequences used in these systems. The multiple access interference could become very large if the spreading sequences are not carefully selected. A new numerical optimization procedure is proposed for the selection of spreading sequences based on minimizing the interference parameter among the sequences. The improvement in the average output signal-to-noise ratio or CDMA capacity improvement is used to compare the performance of the optimized code set with that of the set of Gold codes of the same length. An improvement of about 26% in the system capacity is obtained. Also, construction of different optimized code sets suitable for use in cellular systems applications is considered.