Performance of LMMSE receivers in broadband communication systems

DS-CDMA featuring asynchronous multiple access, robustness to frequency selective fading and multipath combining is chosen as air interface standard in WCDMA. WCDMA works with 5MHz and chip rate of 3.84Mcps. As it supports variable spreading factor to achieve flexible data rate, during high transmission rate uses short spreading code. But users with these smaller spreading codes may experience inter-path interference (IPI) as it exhibits poor correlation. Even today, to exploit receive diversity, RAKE receiver is used as a front end in CDMA systems. The interference becomes a limiting factor for the performance of conventional RAKE receivers. In this paper LMMSE estimator and MSE of error covariance matrix is derived with different optimization criterion is discussed.