Date of Award

2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

Committee Chair

Laurie Joiner

Committee Member

Adam Panagos

Committee Member

Jia Li

Committee Member

W. David Pan

Committee Member

Reza Adhami

Subject(s)

Signal processing--Digital techniques., Nyquist (Computer file), Wireless communication systems.

Abstract

Fast and reliable data transmission together with high bandwidth efficiency are among the main design aspects in a modern digital communication system. There are many options available to meet these requirements, but the approach adopted in this dissertation is the nonorthogonal transmission scheme, faster-than-Nyquist (FTN). In FTN, the data bits are transmitted at a rate higher that that allowed by Nyquist criterion. This transmission occurs while keeping a fixed power spectral density (PSD) of the system. This technique was proposed by Mazo in 1975, and since then has been extended in many directions. Considering the bandwidth-efficiency as a key factor, more data bits can be sent over a given time duration if the time it takes for a signal to be transmitted is reduced. This way, more data is conveyed through the channel in a given time duration. The signal pulses are no longer orthogonal, and this admits intersymbol interference (ISI) in the transmitted signal. FTN comes at the tradeoff between high data rates and degraded error performance. Efficient receiver designs have to exist in order to compensate between the two factors. One main problem in the context of FTN is to tackle the unavoidable intentional intersymbol interference (ISI) introduced in the transmitted signal. Since FTN is an inherently bandwidth efficient scheme and typical FTN signals can carry 4-8 bits/Hz-s in a fixed spectrum, most research in this field has focused on binary modulation schemes. The contribution of this dissertation is in employing a non-binary modulation scheme along with a non-binary convolutional code and processing the signals with reduced-complexity receivers for FTN and general linear channels that achieve optimal or near-optimal performance. In this work, FTN is applied in two ways: by itself as an uncoded narrowband scheme, or as the inner ISI mechanism in a coded serial concatenated system. Turbo equalization, where soft information in the form of log likelihood ratios (LLRs) is to be exchanged between the equalizer and the decoder, is the commonly used detection technique for coded FTN signals. This work compares several decoding algorithms to overcome the effects of the ISI.

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