Approximation of bit-error-rate distributions for asynchronous multicarrier CDMA and direct-sequence CDMA systems

This paper presents a method for the approximation of the Bit-Error-Rate (BER) probability density function (pdf) of asynchronous Multicarrier Code Division Multiple Access (MC-CDMA) and Direct-Sequence Code Division Multiple Access (DS-CDMA) systems. This method is applicable for any given set of spreading codes, but in this paper only Walsh Hadamard (WH) and Gold codes are analyzed. The Multiple Access Interference (MAI) powers produced at every possible asynchronous timing misalginment of each interferer are estimated. ne final BER distribution is generated from the pdf of the total MAI power inccurred by the reference user. System performances are compared for both types of spreading codes with different spreading factors. The mean BER results show that the MC-CDMA scheme considered outperforms the DS-CDMA in the mean case for the use of both Walsh Hadamard and Gold codes. It is therefore concluded that the MC-CDMA scheme considered offers higher MAI resistance than conventional DS-CDMA in an asynchronous environment for the considered codes.