Interference control and chip waveform design in multirate DS-CDMAcommunication systems

摘要

We study the interference effects in a multirate DS-code-divisionnmultiple-access (CDMA) system. Optimum chip waveform selection withnarbitrary shapes is analyzed using a time domain approach. The problemnis posed as an interference minimization problem under energy andntime-bandwidth constraints and prolate spheroidal wave functions arenused to arrive at a solution. Various factors affecting the interferencenare identified and the trade-off between competing factors is analyzed.nThe effect of the interchip interference on the optimum chip waveformndesign is also quantified under a practical bandwidth constraint. Wenstudy the benefits of employing two different chip waveforms for twonclasses of users. We compare the performance of systems employing twondifferent chip waveforms with that of a single-chip waveform system suchnas IS-95. We show that when the power imbalance is large, it isnadvantageous to employ two different chip waveforms for differentnclasses of users