Multiple input multiple output chip level decision feedback equalizer for CDMA downlink channel

Abstract

When downlink of a code division multiple access (CDMA) system uses orthogonal spreading codes, frequency selective fading destroys the orthogonality and introduces multiple access interference (MAI). A chip level linear equalizer followed by a correlator is an attractive method to restore the orthogonality and then to suppress MAI. However, the performance of chip level linear equalizer still depends on the spectral characteristic of the channel and it may not be satisfactory for some channels. To overcome this difficulty, the chip level decision feedback equalizer (DFE) can be used. To improve the performance further, multiple input multiple output (MIMO) channels (by using multiple antennas) can also be employed. Therefore, in this paper we investigate the MIMO chip level DFE for CDMA downlink channel. Simulation results show significant performance gains on CDMA downlink channel when the MIMO chip level DFE is used.