Abstract: CDMA is an interference limited system. Of which, the multicarrier CDMA integrate orthogonal frequency division modulation (OFDM) into CDMA,the interference including ISI and ACI is one of the main performance affected issue for multicarrier CDMA. We establish some important conclusions. 1).The noise average power of the receiver signal is independent of the modulation and demodulation scheme. 2).The sum of the required signal and intersymbol interference has no relative with the scheme,but the required signal and intersymbol interference are individually dependent on the scheme.Furthermore,if we change the scheme,an optimum scheme can be found to make the signal to intersymbol interference's ratio maximum.A fast searching optimal wavelet packet bases algorithm is presented to find optimal modulation and demodulation scheme,simulations have been made to prove the above conclusions.

Key words: CDMA, wavelet packet, multicarrier, optimum bases