Blind multi-user detection using CMA in a multicarrier CDMA receiver

Abstract

In this paper we develop a blind adaptive multiuser detector for muticarrier (MC) codedivision multiple access (CDMA) based on constant modulus algorithm (CMA). The proposed system results in a modification of a blind multicarrier CDMA receiver proposed before. We introduce a dedsion- feedback blind adaptive multiuser detector structure at the end of the receiver, which is adapted without knowing of system parameters such as the channel or transmitted signal. Simulations indicate that the performance of the DFBD is acceptable while conserve a reasonable computational cast. I. INTRODUCTION As the radio fiequency spectrum is a scarce resource, future wireless radio networks need to make efficient use of the frequency spectrum by providing high capacity in terms of the number of users allowed in the system. As a consequence, modulation and multiple access techniques designed specifically for wireless channels play an important role in achieving this goal. For mobile communication systems, diversity reception is essential to counteract the effects of fading radio channels. Direct-sequence (DS) code division multiple access (CDMA) is a multiplexing technique where several independent users share a common channel by modulating preassigned signature waveforms. The receiver then observes the sum of the transmitted signals over an additive white Gaussian noise (AWGN) channel. The major limitation on the performance and channel capacity of DS-CDMA system is the multiple-access interference (MAI) due to simultaneous transmissions. The conventional matched filter (MF) detector cannot suppress MA1 efectively, and it suffers from the near-far problem. Since CDMA is not fundamentally MAI limited, multiuser detection (MUD) techniques can substantially improve the performance of a CDMA system. While the optima1 multiuser detector, which is essentially a maximum-likelihood (ML) sequence detector, has prohibitive complexity, many other multiuser detectors with relatively low complexity such as decision feedback detector, successive or parallel interference canceller, and linear multiuser detectors have been developed. The linear decorrelator removes all cross-correlations between active users and thereby eliminates MA1 at the price of enhancing noise (2).