A PAPER ON DECISION FEEDBACK EQUALIZATION (DFE) WITH SPACE-TIME SPREADING (STS) IN WCDMA DOWNLINK CHANNEL

Abstract

In third generation commercial wideband code division multiple access (WCDMA) systems, orthogonal codes are used to spread transmitted signal in the downlink channel to accommodate different users. But, the frequency selective fading destroys the orthogonility and produces multiple access interference (MAI). One can use Rake receiver in the WCDMA downlink channel. Although a Rake receiver provides reasonable performance due to path diversity, it doe not restore the orthogonality. A linear equalizer followed by a spreader may be an attractive alternative receiver to restore the orthogonality and to suppress the MAI. However, the performance of a linear equalizer depends on the spectral characteristics of the channel and thus may not be satisfactory for some channels. To overcome this difficulty, a decision feedback equalizer (DFE) can be used. In this paper, we have investigated a decision feedback equalizer (DFE) for WCDMA downlink channel with multiple antennas. The work includes the design of the DFE when the space-time spreading scheme is employed at the transmitter. Simulation results show significant performance gains compared to the Rake receiver and the linear equalizer. Keywords : Decision feedback equalizer (DFE), Wideband Code Division Multiple Access (WCDMA), Rake receiver, multiple access interference (MAI).

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