On the design of comb spectrum code for multiple access scheme

Abstract

A new methodology that applies frequency orthogonality to the spreading code design has been presented. The main purpose is to reduce the receiver complexity of the cyclic prefix code division multiple access (CP-CDMA) over the downlink channel and to enable parallel transmission over the uplink channel. The receiver complexity has been found for requiring full-band FFT and IFFT calculations in the channel equalizer. To handle this problem, we developed the comb spectrum codes organized in frequency orthogonal groups, in each of which the codes have time correlation orthogonality. For the downlink channel, the reduction of complexity in signal processing of a CSCDMA receiver is due to that the separation of groups is simple and each separated group is in the form of a narrower bandwidth CP-CDMA. Thus, the full-band FFT and IFFT can be replaced by the partial FFT and partial IFFT as shown in this proposed approach. For the uplink channel, we assign the code groups to different users to form a group division multiple access (GDMA) for enabling an independent channel equalization of each user at base station. The theoretical analysis and the simulation results agree well with each other and both confirm the effectiveness of this approach.