Some issues in enabling technologies for high data rate reliable wireless communications: OFDM and adaptive ARQ

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dc.contributor.author Minn, Hlaing
dc.date.accessioned 2018-10-31T00:12:23Z
dc.date.available 2018-10-31T00:12:23Z
dc.date.copyright 2001 en_US
dc.date.issued 2018-10-30
dc.identifier.uri https://dspace.library.uvic.ca//handle/1828/10210
dc.description.abstract Generation by generation, wireless communication has advanced in various ways and provided reliable communication services at higher and higher data rates to the needs of more and more advanced wireless applications. Two main issues towards future wireless communications are high-speed transmission technique to provide high data rate services and reliable communication to ensure the required performance. This dissertation focuses on these two issues. Since orthogonal frequency division multiplexing (OFDM) has emerged as an enabling technique for high-speed transmission in dispersive environments, major and fundamental issues in OFDM, namely, synchronization, channel estimation, and peak-to-average power ratio (PAPR) reduction are addressed. For the required reliability, automatic repeat request (ARQ) schemes must be applied. Due to large potential performance improvement, adaptive ARQ schemes have recently attracted much attention and are also addressed here. We propose two improved OFDM timing synchronization methods which overcome the drawbacks of existing methods. We present a time-domain-based OFDM channel estimation which outperforms the existing time-domain-based approach and has a similar performance to the linear minimum mean square error estimator but with less complexity. For OFDM systems with transmit diversity, we present a reduced complexity channel estimation which has a comparable performance to the existing method for channels with relatively small delay spreads, but achieves much complexity saving. An approach to find the number of most significant channel taps is described for diverse channel environments. We analyze the effect of non-sample-spaced channel path on the channel estimation and propose a modification for further improvement. Timing synchronization, frequency synchronization and channel estimation are usually addressed separately. Since they can affect each other, the idea of jointly addressing all of them together is much desirable and pursued here. This joint approach reflects the actual performance and gives an opportunity to exploit some information obtained from one task in another, hence promising more improvement. The proposed training preamble-based joint timing and frequency synchronization utilizes some information from the channel estimation. The sync detection is also considered. We design the training symbol to achieve a better coarse timing synchronization. Methods to suppress or circumvent the interference in the frequency estimation caused by timing errors are presented. A new performance measure for OFDM timing synchronization is proposed which leads to obtaining optimal timing estimation setting. Next, we present a joint timing synchronization, frequency synchronization and channel estimation based on training preamble based maximum likelihood realization. Further complexity reduction by an adaptive scheme is also proposed. We address some fundamental questions on peak factors, sampling theorem and sampling series. We present several bounds of bandlimited functions and peak factor ratio bound of a continuous signal and its sampled signal. Some discussion on the requirements of sampling theorems and related aspects on sampling series are presented. We study PAPR behavior of some Reed-Muller codes in OFDM systems in an attempt to find a code with good error correction, low PAPR, efficient encoding/decoding and reasonable code rate. Some regularities of the second and third-order cosets of first order Reed-Muller codes with low PAPR are presented which indicates possibility of finding such code for OFDM. The main issues in adaptive ARQ schemes are how to design the adaptive system parameters and how to effectively sense the channel conditions. We present an approach for designing the adaptive ARQ system parameters based on the through put calculation and optimization. An alternative approach which avoids the tedious throughput calculation is also presented. An effective channel sensing algorithm which utilizes the error correcting capability is proposed. Incorporation of the adaptive frequency hopping concept into the ARQ scheme with adaptive error control is introduced which has a significant throughput improvement in slow fading channels. en_US
dc.language English eng
dc.language.iso en en_US
dc.rights Available to the World Wide Web en_US
dc.subject Wireless communication systems en_US
dc.subject High data-rate en_US
dc.subject Automatic repeat request en_US
dc.title Some issues in enabling technologies for high data rate reliable wireless communications: OFDM and adaptive ARQ en_US
dc.type Thesis en_US
dc.contributor.supervisor Bhargava, Vijay K.
dc.degree.department Department of Electrical and Computer Engineering en_US
dc.degree.level Doctor of Philosophy Ph.D. en_US
dc.description.scholarlevel Graduate en_US

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