A constant amplitude transmission scheme for multicode wideband CDMA systems is proposed. Multicode wideband CDMA systems result in large amplitude fluctuation because the multicode signal is the sum of constituent code channel signals. This large amplitude fluctuation brings out large non-linear distortion and then, if unaccounted, can significantly degrade the bit error rate (BER) performance. Constant amplitude transmission, achieved by using a Walsh code and parity generator, is proposed to combat the large amplitude fluctuation and reduce the peak-to-average power ratio (PAPR). Unlike other constant amplitude transmission scheme, the proposed scheme does not use a redundant code channel. Computer simulation results show that the proposed scheme improves BER performance significantly and that the proposed scheme is extremely effective to the non-linear distortion of high power amplifier (HPA).

This paper presents a performance analysis of the standard non-coherent delay-locked loop in asynchronous direct-sequence code division multiple access (DS-CDMA) environments. In particular, the effects of multiple access interference on the loop performance are addressed. We work out an expression for the steady-state tracking-error variance and provide performance curves in terms of mean time to lose lock as a function of the number of interfering users and Eb/No.