Performance analysis of DS/CDMA communication system considering the nonlinear HPA

We propose analytic chip waveforms minimizing MAI (multiple access interference) in band-limited DS/CDMA (direct sequence-code division multiple access) system and analyze the nonlinear effects from the HPA. Proposed chip waveforms are classified into 2 types: uniform chip waveforms with uniform envelope and non-uniform chip waveforms with non-uniform envelope. Also, we find BER (bit error rate) performance when these chip waveforms are used for the DS/CDMA including the nonlinear HPA (high power amplifier). For the linear case, to meet BER = 10^-4, non-uniform chip waveforms have 0.5 dB power gain than uniform chip waveforms and have 1.5 dB power gain than raised cosine which is the best performance among the conventional chip waveforms. For the nonlinear case, BERs of non-uniform chip waveforms are worse than those of uniform chip waveforms and conventional chip waveforms because of high PAPR when IBO=0 dB. But, BER performances of non-uniform chip waveforms are improved by IBO (input back-off) than the others. That is, the nonlinear DS/CDMA system using non-uniform chip waveforms has nearly same performance as linear system if IBO is 15 dB. When IBO=15 dB, BER performance of non-uniform chip waveform is the best. Therefore, we propose that non-uniform chip waveforms are appropriate chip waveforms considering nonlinear and MAI effects.