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Frequency domain equalization and multiuser detection techniques for DS-UWB systems Kaligineedi, Praveen


Ultra wideband (UWB) is an emerging technique for high data rate transmissions over short distances. Direct sequence (DS)-UWB approach is one of the two competing high data rate UWB standards, along with multiband orthogonal frequency division multiplexing (OFDM). One of the major challenges in a DS-UWB receiver design is the intersymbol interference (ISI). Several time domain equalization schemes to eliminate IS1 have been proposed in the literature for DS-UWB systems. However, for long dispersive channels, these time domain equalization schemes require very high computational complexity in order to achieve desired bit error performance. Frequency domain equalization schemes which give better performance than time domain equalization schemes for single carrier systems, over highly dispersive channels, are well known in the literature. In this thesis, performances of frequency domain minimum mean square error (MMSE) linear, decision feedback and iterative decision feedback equalizers are studied for uncoded single user BPSK and 4BOK DS-UWB systems. We compare bit error rate (BER) performance of various time domain and frequency domain equalization techniques and evaluate their computational complexity. We show that the frequency domain equalization techniques can offer better trade off between complexity and performance compared to the time domain equalization techniques for DS-UWB systems. We then consider frequency domain multiuser detection techniques for DS-UWB systems. We employ frequency domain successive interference cancellation and parallel interference cancellation schemes combined with frequency domain equalization schemes and study their average BER performance. We derive low complexity frequency domain MMSE turbo equalization schemes for coded BPSK and 4BOK DS-UWB systems. Soft interference cancellation is used in the multiuser systems to remove multiple access interference (MAI). The average BER performance is obtained using simulations. The performance gain due to turbo equalization is shown to be significant, particularly, for DS-UWB systems with lower spreading gain. The improvement in the performance due to turbo detection is found to be very high for multiuser systems.

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