Suppression of Multiple Access Interference (MAI) in Wideband Code Division Multiple Access (WCDMA)

Recent advances in communications are driven by the requirements of next-generation wireless systems to provide high-data-rate and high quality services anywhere at anytime. However, the spectrum continues to be scarce and expensive, which creates new challenges in the developments of telecommunications systems. Wireless cellular systems are known to suffer from fading and intersymbol interference (ISI) caused by multipath propagation, which may degrade the system performance significantly. Therefore, the effective and efficient interference mitigation is required for a high quality signal reception. The air interface of the third generation mobile radio systems UMTS (Universal Mobile telecommunications system) is based on wideband code division multiple access (WCDMA). Third generation wideband code division multiple access (WCDMA) has employed transmit diversity. In the paper, we have considered a WCDMA downlink channel in which transmitted signal is spread by orthogonal codes. Orthogonality in WCDMA is destroyed because of frequency selective fading. This causes multiple access interference (MAI). A RAKE receiver does not restore the orthogonality. As a powerful receiver algorithms, we investigate a MMSE DFE with Alamouti transmit diversity scheme to suppress the MAI and restore the orthogonality condition. Simulation results show significant performance improvement over an adaptive linear equalizer (LE) and a RAKE receiver.