Adaptive Reduced Complexity Multicarrier CDMA (MC‐CDMA) Structure for Downlink PCS

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Abstract
Conventional multiuser code division multiple access (CDMA) suffers from the well‐known near‐far problem. Both the conventional decorrelator and an adaptive separator termed bootstrap algorithm were used to mitigate this problem and obtain near‐far resistant receivers. These approaches still require the knowledge of which users are active and their respective codes. Eliminating this requirement is advantageous for downlink communication as only the desired user is of interest. Furthermore, in a multipath environment the use of the RAKE receiver adds to the complexity. A transmission method called multicarrier CDMA (MC‐CDMA) uses multiple narrowband subcarriers and, as a result, the channel is flat‐fading at each subcarrier. In this paper, a receiver for downlink MC‐CDMA is proposed that does not require the knowledge of which users are active. This is achieved by replacing the bank of matched filters of the full dimensional multiuser detector by 2 matched filters; one for the desired user and one representing all the interfering users combined in a specific way. Additionally, this significantly reduces the number of adaptively controlled weights. The performance of this system is analyzed and simulation results are obtained for the Rayleigh fading channel with and without correlation between the subcarriers.

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