UBC Theses and Dissertations
Performance of wireless communication systems in ultra-wideband interference and non-Gaussian noise Nasri-Nasrabadi, Amir Masoud
The growing demand for high speed wireless applications and the scarcity of the spectral resources has necessitated the development of new concepts that enable more efficient utilization of the frequency spectrum. Ultra-wideband (UWB) is an emerging technology that is capable of utilizing the spectral resources more effectively by sharing the spectrum with other applications. This spectrum sharing however can potentially result in harmful interference from UWB systems to devices co-existing in the same frequency band. Therefore, in order to guarantee peaceful co-existence, the effects of UWB interference on co-existing systems have to be carefully analyzed. Towards this goal, in this thesis, we first study the effects of multi-band (MB) orthogonal frequency-division multiplexing (OFDM) UWB interference on a generic uncoded narrowband (NB) system. For this purpose, we develop analytical expressions for the amplitude probability distribution (APD) and the bit error rate (BER) performance of the NB system in the presence of MB-OFDM interference. We use the obtained results to assess the accuracy of the Gaussian approximation (GA) for MB-OFDM UWB interference. We show that for most channel models and signal bandwidths the GA is unable to accurately predict the NB system performance and the exact BER analysis has to be used to obtain meaningful results. We also analyze the effects of UWB interference in a more general framework that allows us to study the impact of general types of non-Gaussian noise and interference on generic uncoded victim systems. Specifically, we present a unified asymptotic symbol error rate (SER) analysis of linearly modulated systems impaired by fading and generic non- Gaussian noise and interference. Our analysis also encompasses diversity reception with equal gain and selection combining and is extended to binary orthogonal modulation. The obtained asymptotic results show that for high signal-to-noise ratios (SNRs) the SER of the victim system depends on the moments of the non-Gaussian noise and interference. Furthermore, we study the impact of different types of UWB interference on victim systems that employ a combination of bit-interleaved coded modulation (BICM) and OFDM. For the UWB interferer we consider MB-OFDM, direct-sequence UWB (DS-UWB), and impulse radio UWB (IR-UWB) interference formats following recent standards or standard proposals developed by the IEEE or the European Computer Manufacturers Association (ECMA). Besides the exact analysis we calculate the BER of the BICM-OFDM system for the case when the UWB interference is modeled as additional Gaussian noise. Our results show that while the GA is very accurate for DS-UWB interference, it may severely over or underestimate the true BER for MB-OFDM and IR-UWB interference. Finally, we analyze the performance of BICM-based systems in the presence of generic non-Gaussian noise and interference. In particular, we present an asymptotically tight upper bound for the BER and a closed-form expression for the asymptotic performance of receive diversity BICM single-carrier and BICM-OFDM victim systems.. Our analysis shows that, if the popular Euclidean distance metric is used for Viterbi decoding, BICM- based systems optimized for additive white Gaussian noise (AWGN) are also optimum for any other type of noise and interference with finite moments.
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