Modified LMMSE receiver for DS-CDMA-Part II. Performance in FMA2 downlink

Abstract

For pt.1 see ibid., p.652-7. The wideband code-division multiple access (CDMA) concept FMA2; developed in the European FRAMES project supports variable data rate transmission. The data rate can be altered by changing either the spreading factor or by using multiple spreading codes in parallel. In order to facilitate flexible changing of the data rate, variable length orthogonal Walsh codes are used for channel separation, followed by a scrambling code. Optional short scrambling codes can be used if interference suppression is used. In this paper the downlink performance of the FMA2 system using both the conventional RAKE and the LMMSE-RAKE receivers is studied. According to the results, the performance of the conventional RAKE receivers is insufficient at lowest spreading factors, whereas the LMMSE-RAKE receiver performs well regardless of the spreading factor.