Multistage RLS Subcarrier-Combining Method for Uplink Quasi-Synchronous MC-CDMA

In order to improve the performance of multicarrier code division multiple access (MC-CDMA) in the uplink channel, quasi-synchronous MC-CDMA with minimum-mean-square-error (MMSE)-based subcarrier-combining method is effective. However, conventional MMSE methods require a lot of pilot symbols for derivation of optimal weights. In this paper, in order to reduce the number of pilot symbols for uplink MC-CDMA systems, we propose a multistage recursive-least-square (MS-RLS) method for the derivation of the weights for the MMSE subcarrier combining. In the MS-RLS, the received symbols are stored in the buffer memory, and the RLS algorithm is repeatedly performed with a multistage structure by using the same pilot symbols. In this method, the weights and the inverse matrices of correlation matrices of the adjacent subcarriers are utilized for the initial values of the next-stage weight updating. Through computer simulation, we confirm that the performance of MC-CDMA in the uplink channel is improved by using the proposed MS-RLS method, even with short pilot symbols.