The performance of the generalized RAKE (G-RAKE) receiver in a WCDMA-HSDPA scenario

Abstract

The High-Speed Downlink Packet Access (HSDPA) is a packet-based data service for increased data speed over WCDMA downlink. At high-speed data rate, advanced receivers are needed to realize a reasonable bit error performance. This thesis studies the link-level performance of the G-RAKE receiver for the HSDPA and ways to reduce the receiver's complexity. Unlike the conventional RAKE receiver, the G-RAKE receiver suppresses interference caused by frequency-selective fading channels by accounting for coloured noise found in the fingers' output. Thus, G-RAKE optimizes the placement of fingers and the weighting coefficients in the Maximum Likelihood formulation. In this thesis, performance of the G-RAKE is evaluated via simulations for both static and realistic multipath fading channels described in the literature. According to simulations, G-RAKE receiver compensates for the performance loss experienced by RAKE receivers when the user equipment becomes interference limited. In G-RAKE receiver, calculating the weighting coefficients, which involves inverting the channel impairment matrix, is an expensive operation. It is shown that the complexity and processing time of this operation and, hence, of the overall receiver can be reduced with the Conjugate Gradient or Preconditioned Conjugate Gradient methods.