Multi-stage RLS subcarrier combining method for up-link quasi-synchronous MC- CDMA

In order to improve the performance of multi-carrier code division multiple access (MC-CDMA) in the up-link channel, quasi-synchronous MC-CDMA with a minimum mean square error (MMSE) based subcarrier combining method is effective. However, the MMSE method requires many reference pilot symbols to derive the optimal weights with realistic computational complexity. In order to reduce the number of pilot symbols for up-link MC-CDMA systems, we propose a multi-stage RLS (MS-RLS) method for deriving the weights of MMSE subcarrier combining. In the MS-RLS, the received symbols are stored in the buffer memory and the RLS algorithm is performed repeatedly using the same pilot symbols. The weights and the inverse matrices of the correlation matrices of the adjacent subcarriers are utilized for the initial values of the next stage weight updating. By computer simulation, we can confirm that the performance of MC-CDMA in the up-link channel is improved using the proposed MS-RLS method with short pilot symbols.