Impact of wideband CDMA signals on smart antenna systems

Adaptive antenna array systems have been shown to play a central role in removing narrowband multiple-access interference (MAI) in wireless communications. However, due to the actual need for increasing channel capacity, the required bandwidth is becoming wider and can bring significant deterioration to narrowband adaptive systems. These performance degradations are mainly caused by the fact that the inter-element phase shift becomes a function of the frequency while the adaptation weights are kept independent of frequency. This paper specifically deals with the effects of wideband CDMA signals on the narrowband adaptive system. The performance evaluation for different chip rates is carried out in terms of the adaptive array pattern. The basic adaptive algorithm used is the CMA (constant modulus algorithm), which has the major advantage of not requiring an estimate of the desired signal for its implementation.