Performance evaluation of new multi level spreading codes for DS CDMA communication over Rayleigh fading channel

Code Division Multiple Access system allows multiple users to communicate with each other by sharing common resources and distinguishes each user by assigning a unique spreading code. Spreading codes are also called as user codes as they are used to discriminate multiple users of the system. Walsh, Gold and Kasami codes are the popularly used Binary (2-level) spreading codes. There are orthogonal and non-orthogonal spreading codes. Walsh codes are perfectly orthogonal whereas Gold codes and Kasami codes are nearly orthogonal. In the recent years, researchers are concentrating on the design of multiple level spreading codes. This paper proposes new multi level orthogonal spreading codes constructed using ternary and quaternary Gray and Inverse Gray codes for Direct Sequence Code Division Multiple Access systems. The methodology explained in this paper allows generating r-level user codes of length- 2n. It also allows generation of codes whose lengths are even multiples of the basic code sets. Multi level spreading codes discussed in this paper are non-zero mean, varying power codes. Bit error rate performance of the proposed codes over Rayleigh fading channel and their comparison with those of Walsh and Gold codes is presented in this paper.