Linear space—time diversity receivers for the downlink of UMTS with WCDMA

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Abstract
Simple linear demodulation schemes exploiting the space and time diversity of the mobile radio channel are derived for the downlink of the Univeral Mobile Telecommunication System (UMTS) employing wideband codedivision multiple access (WCDMA). Using different stochastic models of the signals at the M × 1 receiver antennas and different objective functions including minimum—mean square error (MMSE) and maximum—likelihood approaches, we obtain time—invariant and time—variant detection schemes which make use of channel and receiver parameter estimates being calculated upon observation of a single slot. It turns out that the bit—error rate (BER) of the conventional receiver carrying out a maximum—ratio combining w. r. t. time and space can be improved considerably, where the achievable gain depends critically on the accuracy of the aforementioned estimates. Efficient ways for implementation are proposed and quantified in terms of the computational complexity. Analytical approximations and simulations of the BER for different system parameters reveal that the schemes represent means to get robust against both channel fading and multiple access interference caused by multipath propagation.

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