Improving direct sequence code division multiple access performance in frequency selective fading channels

In this paper we present the results for both fixed and floating point operation of a single-input-single-output (SISO) direct spreading code-division multiple-access (DS-CDMA) communication system. Conventional Walsh codes DS-CDMA systems suffer from high levels of interference in frequency selective fading channels due to the loss of their mutual orthogonality which limits the maximum error-free data rates achieved. The CDMA system proposed uses complete complementary (CC) codes due to their robust orthogonality in frequency selective fading environment and is termed CC-CDMA, which together with Walsh-CDMA systems are simulated for an equivalent data rate equal to 3.84 Mbps. Results obtained for CC-CDMA reveal significant improvement in bit-error-rate (BER) performance and data rates when compared to a conventional SISO-CDMA system using orthogonal Walsh spreading codes. Finally to reduce complexity and power consumption of CC-CDMA system a fixed point digital signal processing (DSP) implementation is presented and a comparison with the original floating point system is shown.