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Thesis (Ph.D.)--City University of Hong Kong, 2009. / "Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [142]-152)

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Thesis (M.S.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 84-85)

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Due to constraints on spectrum availability and transmitter power, both bandwidth and power efficient communication techniques are desirable for mobile radio. Continuous phase modulated (CPM) signals have gained attention because of their attractive power spectra (Steele, 1992). It has been shown that the trellis coded modulation (TCM) schemes could provide better bit error rate performances compared to the uncoded schemes (Ungerboeck, 1982). Therefore, the combination of TCM which improves error probability and CPM signals which yield low spectral occupancy is expected to provide good coding and modulation over bandwidth and power limited channels such as the one encountered in mobile radio communications.In this research, a Trellis Coded Modulation (TCM) scheme, which combines convolutional coding and partial response Continuous Phase Modulation (CPM) such as Gaussian Minimum Shift Keying (GMSK), is investigated. Also, this study concentrates on the use of rate-half convolutional codes, and GMSK (B(subscript)0T=0.3). The latter has been adopted in the Global System for Mobile Communications (GSM) system.Appropriate codes are selected assuming Maximum Likelihood Sequence Detection (MLSD) based on the Viterbi algorithm using an extensive computer search. The bit-error-rate (BER) performances of the selected trellis coded GMSK schemes are theoretically evaluated in the presence of additive white Gaussian noise (AWGN) and frequency-flat fading. In the case of fading, the analysis is simplified to assume only amplitude-fading, and without considering the effect of fading on the phase of the received signal.Computer simulations are used to evaluate the BER performances of the proposed trellis coded GMSK schemes in the presence of AWGN and practical impairments, such as sample timing offset and carrier phase errors. Coding gains of up to 2.2dB at a BER of 10(subscript)-3 ++ / are obtained under ideal sample timing and carrier recovery conditions. This has been achieved without increasing the receiver complexity based on the number of states in the Viterbi decoder, compared to the uncoded GMSK scheme. Furthermore, these coded schemes are more tolerant to sample timing and carrier phase impairments.Also, the BER performances of the proposed trellis coded GMSK schemes have been extensively investigated by computer simulations for frequency-flat and frequency-selective fading channels. In the case of frequency-selective fading, the Viterbi decoding is made adaptive to cater for the channel impulse response variations with time. With this adaptive receiver, the irreducible BERs of the coded scheme is found to be lower than that of the uncoded. Performance improvements are obtained with a trellis coded GMSK scheme using a constraint length 2 code with a Viterbi decoder of 16 states compared to the 128 states required for the uncoded scheme. Further, the coded scheme has shown less sensitivity to carrier phase errors, compared to the uncoded.

This dissertation deals with wireless communications using cooperating relay nodes. Specifically, this dissertation relaxes two restrictive conditions ubiquitous in the current literature. First, the assumption that relay nodes can perform complex calculations is lifted. Demodulate-encode-forward (DEF) is a low-complexity relaying scheme where the relay is asked only to demodulate, not decode, a source transmission. The implementation of DEF and various methods that can be used with DEF to improve the performance while satisfying the hardware complexity limitations are detailed here. Second, we remove the assumption that the relays either transmit the complete source codeword or not transmit at all. When relays have limited resources, each relay may only be able to transmit part of the source codeword. Fractional cooperation, which allows nodes to transmit a fraction of the source codeword, is proposed and analyzed. Fractional cooperation is also very flexible because coordination between relaying nodes is not required. A third contribution of this dissertation is the use of the union-Bhattacharyya bound (UBB) to analyze relay networks. The bound has the significant advantage of accounting for the specifics of the system parameters and coding scheme used. The UBB is shown here to provide an effective and efficient scheme for relay selection, performance prediction, and system design. It can also be used to distribute relay resources in order to optimize the total energy consumed and error rate performance. A sub-optimal distributed algorithm that can be used to solve the optimization problems is introduced.