Single user diversity receivers for frequency selective WCDMA channels

Wideband code division multiple access (WCDMA) forward links are susceptible to performance degradation incurred by multiple access interference (MAI) when the radio channel is frequency selective. This places a tight limit on die channel capacity of die cellular downlink since computationally efficient receiver technologies such as die 2D Rake receiver do not yield significant attenuation of die interference floor for high data rates. The application of optimum spatial processing employing two or more antenna elements is a topic of some interest since an optimum beamformer is one where the desired signal is decoupled into a matched filter while interfering signals are spatially nulled or filtered. However, for realistic radio environments and low number of sensors, array overloading prevents optimum information retrieval (and die required target bit error floor to be met) from a doubly selective spatial radio channel. The work undertaken in the first part of this thesis investigates adaptive two element array receiver structures to enhance die downlink performance. In addition to per-path adaptive beamforming, oversampling can form several technologies utilizing this basic structure. In particular, an oversampled receiver with additional linger assignment (not necessarily matched to the channel delay spectra) forms die basis of a channel equalizer. This thesis extends upon this criterion by developing adaptive dual antenna interference suppressing receivers that jointly optimize die spatial and temporal multipath channel signatures at chip or symbol level. In particular, a chip-level optimization (forming a 2D chip equalizer) can decorrelate die multipath channel spectra allowing interference suppression with a chip-matched filter. This receiver is a generalized broadband antenna beamformer, where die resultant improvement in performance over die 2D Rake receiver is significant with only moderately increased complexity. Optimum spatio-temporal diversity receivers require dial die multipath delay spectra are known and the channel phase/attenuation parameters perfectly reproducible with negligible error. However, matched filtering applying estimation of the channel parameters is unlikely to be error free, nor devoid of die effects of quantization. The second part of this diesis investigates the effect of quantization and logarithmic arithmetic on die 2D Rake receiver and 2D Chip equalizer. Logarithmic arithmetic was found to augment many useful properties such as reducing receiver filter inner products into trivial additions by transforming a linear algorithm into die logarithmic domain using the logarithmic number system. This method was found to offer superior error performance even when utilizing very simple codecs. This makes it a promising technique for integrating an adaptive WCDMA receiver onto low power multiplierless programmable hardware devices