Performance comparison of linear MMSE and coherent RAKE receivers in multipath asynchronous random-CDMA

This paper investigates the design of a linear minimum mean square error (MMSE) receiver for interference suppression in asynchronous random code-division multiple-access (random-CDMA) systems, such as IS-95 and wideband-CDMA (WCDMA), operating in multipath environments. Its performance is compared with that of the coherent RAKE receiver. The figure of merit is average output signal-to-noise-ratio (SNR). The proposed receiver maximizes SNR and considers all the desired user's paths unlike the standard RAKE receiver which selects a subset of them. The performance improvement is supported and quantified by numerical examples. The achieved gain is shown to be substantial in nonuniform power conditions (typical of next-generation CDMA systems) and dense multipath environments where the signals are received via many paths. The chip pulse shape is the square-root raised cosine (Sqrt-RC) pulse with 22% excess bandwidth.