OFDM and CDMA, unified approach and channel-matched spreading codes generation algorithm

摘要

In this paper TDMA, CDMA, MC-CDMA and OFDM are presented through an unified formalism. The cyclic prefixudinsertion is extended to all approaches presented and not only restricted to OFDM. Many fundamental results areudhighlighted. It is for example shown that if we are looking for a family of orthogonal spreading sequences being yetudorthogonal after a one chip delay then we have not another choice than OFDM.udDifferent kind of receivers, involving a same « channel » matrix, are presented : OFDM receiver, Rake receiver and MMSEudreceiver. All these receivers involve a same channel matrix representing the effect of the propagation channel, the cyclic prefix insertion and its suppression. Finally an algorithm for generating spreading sequences matched to a givenudpropagation channel is introduced. Spreading sequences generated having unequal transmission properties, a powerudand modulation allocation algorithm is introduced for them. Performances obtained are then very close to thoseudobtained through the OFDM approach.