Performance of RAKE-LMMSE Receivers in Wideband Communication Systems

High speed multimedia services with flexible data rate are main cause of popularity of 3 G WCDMA. WCDMA air interface of UMTS has the bandwidth of 5 MHz and chip rate of 3.84 Mcps. The flexibility in data rate is achieved by varying the length of its spreading code. WCDMA supports seamless connections of dynamic data rate ranging from 15 Kbps to 1 Mbps and respective spreading factors are 256 and 4 respectively for indoor and outdoor applications. The conventional RAKE receiver is near far and interference limited. Its performance at high data is limited due to short spreading factor of a code. A simple MIMO receiver structure of LMMSE in downlink asynchronous direct-sequence code division multiple access is proposed in this paper. This paper investigates RAKE receiver characteristics and does the analysis of zero forcing and LMMSE equalizer for MIMO channels.

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