A generalized RAKE receiver for interference suppression

摘要

Currently, a global third-generation cellular system based onncode-division multiple-access (CDMA) is being developed with a widernbandwidth than existing second-generation systems. The wider bandwidthnprovides increased multipath resolution in a time-dispersive channel,nleading to higher frequency-selectivity. A generalized RAKE receiver forninterference suppression and multipath mitigation is proposed. Thenreceiver exploits the fact that time dispersion significantly distortsnthe interference spectrum from each base station in the downlink of anwideband CDMA system. Compared to the conventional RAKE receiver, thisngeneralized RAKE receiver may have more fingers and different combiningnweights. The weights are derived from a maximum likelihood formulation,nmodeling the intracell interference as colored Gaussian noise. Thisnlow-complexity detector is especially useful for systems with orthogonalndownlink spreading codes, as orthogonality between own cell signalsncannot be maintained in a frequency-selective channel. The performancenof the proposed receiver is quantified via analysis and simulation forndifferent dispersive channels, including Rayleigh fading channels. Gainsnon the order of 1-3.5 dB are achieved, depending on the dispersivenessnof the channel, with only a modest increase in the number of fingers.nFor a wideband CDMA (WCDMA) system and a realistic mobile radio channel,nthis translates to capacity gains of the order of 100%