Patel, Milan; (2004) Investigations in bandpass sampling for wireless communications and software defined radio. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis presents modelling, limitations and simulation based performance assessment of bandpass sampling receivers. An overview of software radio and fourth generation wireless systems is presented, as well as theoretical and practical aspects of bandpass sampling for such systems. An investigation to determine the effects of various front-end bandpass filters on the BER performance of a bandpass sampling receiver in noise and adjacent channel interference is undertaken, since this filtering process is essential to bandpass sampling. Both narrowband and wideband front-end implementations are considered. The research concludes that great care has to be taken when choosing the receive filters in accordance with specific system parameters. Consideration of aperture jitter becomes increasingly important when sampling at IF and RF and its effect is regarded as an amplitude error on the sampled signal. The hypothesis that oversampling improves system performance is tested by developing analytical expressions verified by computer simulation. Results indicate that oversampling causes performance degradation due to jitter effects. The effect of aperture jitter on the performance of multicarrier bandpass sampling receivers is investigated, using OFDM. The effect of aperture jitter is assessed via BER measurements and by varying a number of key system parameters. Results indicate that aperture jitter causes a random frequency deviation in the centre frequency of the sampled signal, thus resulting in ICI and loss of orthogonality between subcarriers. The performance of a multimode bandpass sampling receiver for the simultaneous reception of an OFDM and a single carrier signal is investigated by varying system parameters. For optimum BER performance it is necessary to examine carefully the interactions between the signals and their spectral copies that occur due to the sampling process. Finally, design trade-offs are identified for receiver architecture simplicity and BER performance. Overall, the thesis addresses different design and optimisation issues of bandpass sampling for the use in future software radio receivers.

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