The growing popularity of wireless communications networks has resulted in greater bandwidth contention and therefore spectrally efficient transmission schemes are highly sought after by designers. Space-time block codes (STBCs) in multiple-input, multiple-output (MIMO) systems are able to increase channel capacity as well as reduce error rate. A general linear space-time structure known as linear dispersion codes (LDCs) can be designed to achieve high-data rates and has been researched extensively for flat fading channels. However, very little research has been done on frequency-selective fading channels. The combination of ISI, signal interference from other transmitters and noise at the receiver mean that maximum likelihood sequence estimation (MLSE) requires high computational complexity. Detection schemes that can mitigate the signal interference can significantly reduce the complexity and allow intersymbol interference (ISI) equalization to be performed by a Viterbi decoder. In this thesis, detection of LDCs on frequency-selective channels is investigated. Two predominant detection schemes are investigated, namely linear processing and zero forcing (ZF). Linear processing depends on code orthogonality and is only suited for short channels and small modulation schemes. ZF cancels interfering signals when a sufficient number of receive antennas is deployed. However, this number increases with the channel length. Channel decay profiles are investigated for high-rate LDCs to ameliorate this limitation. Performance improves when the equalizer assumes a shorter channel than the actual length provided the truncated taps carry only a small portion of the total channel power. The LDC is also extended to a multiuser scenario where two independent users cooperate over half-duplex frequency-selective channels to achieve cooperative gain. The cooperative scheme transmits over three successive block intervals. Linear and zero-forcing detection are considered.

This thesis studies the symmetries and phenomenologies of the massive vector fields of indefinite spin with both scalar and spin-one degrees of freedom and Elko. The investigation is conducted by using and extending the quantum field theory formalism developed by Wigner and Weinberg. In particular, we explore the possibility that the W± and Z bosons have an additional scalar degree of freedom and show that Elko is a fermionic dark matter candidate. We show that the massive vector fields of indefinite spin are consistent with Poincaré symmetry and have physically desirable properties that are absent for their pure spin-one counterpart. Using the new vector fields, the decay of the W± and Z bosons to leptons at tree-level are in agreement with the Standard Model (SM) predictions. For higher order scattering amplitudes, the theory has better convergent behaviour than the intermediate vector boson model and the Fermi theory. Elko has the unusual property that it satisfies the Klein-Gordon but not the Dirac equation and has mass dimension one instead of three-half. We show that the Elko fields are local only along a preferred axis and that they violate Lorentz symmetry. Motivated by the results obtained by Ahluwalia and Horvath that the Elko spin-sums are covariant under very special relativity (VSR) transformations, we derive the VSR particle states and quantum fields. We show that the VSR particles can only interact with the SM particles through gravity and massive scalar particles thus making them and hence Elko dark matter candidates.

Space-time block coding (STBC) has added a new dimension to broadband wireless communication systems. Applications such as wireless Internet access and multimedia require the transmission of high data rates over frequency selective fading channels. The reliability of the wireless communication system can be increased by using diversity techniques combined with an equalizer at the receiver to eliminate the inter-symbol interference caused by multipath propagation. Generalizing Alamouti's famous STBC method to frequency selective channels, Time Reversal-Space Time Block Coding (TR-STBC) was first introduced in [1] and has since been shown to be an effective transmit diversity scheme [2, 3, 4]. TR-STBC-based schemes are considered promising candidates for indoor transmission [5] as well as for the enhanced data rates of the global evolution (EDGE) system [2, 3]. The optimal equalizer for a TR-STBC-based transceiver is the Maximum Likelihood Sequence Estimator (MSLE), realized using the Viterbi algorithm. Unfortunately, a Viterbi equalizer is difficult to implement in real-time due its exponential increase in complexity with the number of antennas and the length of the channel impulse response. Thus, we consider an adaptive algorithm-based Decision Feedback Equalizer (DFE). Such a DFE requires only linear processing complexity while maintaining good performance. Theoretically, the two output streams of a 2 x 1 TR-STBC decoder are uncoupled in terms of the input signal statistics and uncorrelated in terms of the channel noise statistics. The standard approach to removing the inter-symbol interference from these streams is to use either two parallel independently-adapted Single-Input Single-Output (SISO) equalizers or to use a single Multiple-Input Multiple-Output (MIMO) equalizer. By exploiting the common second-order statistics of the two output streams, we proposea novel hybrid equalizer structure which shares the statistical information between two SISO equalizers while constraining them to have common tap weights. To accommodate various levels of performance versus computational complexity, we propose novel Least Mean Square (LMS), Normalized Least Mean Square (NLMS), and Recursive Least Squares (RLS)-based adaptive algorithms for this new equalizer architecture. We use both statistical analysis and Monte Carlo simulations to characterize the dynamic convergence of these algorithms and to compare our new structure with the conventional uncoupled SISO equalizers and fully-coupled MIMO equalizer. We show that our new equalizer outperforms the other two equalizers using a reduced computational complexity similar to the uncoupled SISO equalizers. As expected, with increasing complexity, we find that the novel RLS-based algorithms converge the fastest followed by the novel NLMS- and LMS-based algorithms. We also consider alternative packet structures and kick-start methods to increase the convergence speed and reliability of the equalizer at realistic complexity. Finally, adding multiple receiver antennas to our system, we extend our equalizer structures and algorithms to the 2 x NR case. Using analysis and simulations, we demonstrate that the added receiver diversity in this case yields even greater reliability.

In the last decade much interest has been shown in space-time trellis codes (STTCs) since they can offer coding gain along with the ability to exploit the space and time diversity of MIMO channels. STTCs can be flexibly designed by trading off performance versus complexity. The work of Dayal [1] stated that if training symbols are used together with data symbols, then a space-time code can be viewed as a noncoherent code. The authors of [1] described the migration from coherent space-time codes to training assisted noncoherent space-time codes. This work focuses on the development of training assisted noncoherent STTCs, thus extending the concept of noncoherent training codes to STTCs. We investigate the intrinsic link between coherent and noncoherent demod- ulation. By analyzing noncoherent STTCs for up to four transmit antennas, we see that they have similar performance deterioration to noncoherently demodulated M-PSK using a single antenna. Various simulations have been done to confirm the analysis.

Demand for capacity in wireless communication systems has been rapidly growing world- wide. This has been driven by increasing data rate requirements of cellular mobile systems, and demand for wireless Internet and multimedia services. As the available radio spec- trum is limited, higher data rates can only be achieved by designing more efficient signaling techniques. In this thesis, we propose a new transmission scheme, which benefits from the advantages of conventional space-time trellis codes (CSTTCs) but does not have the disadvantages, especially for larger signal constellations. We achieve this by developing a new class of codes, called Multilevel Space-Time Trellis Codes (IMLSTTC). The new scheme provides a scalable and promising alternative to CSTTCs, by providing the system designer with the flexibility to choose any desired balance between code performance, complexity and throughput. The proposed scheme outperforms layered schemes at high SNRs, using a smaller number of antennas.

In recent years, space-time block coding (STBC) has emerged as an effective transmit-diversity technique to combat the detrimental effects of channel fading. In addition to STBC, high-order modulation schemes will be used in future wireless communication systems aiming to provide ubiquitous-broadband wireless access. Hence, advanced receiver schemes are necessary to achieve high performance. In this thesis, advanced and computationally-efficient receiver schemes are investigated and developed for single-carrier space-time (ST) block-coded transmissions over frequency-selective fading (FSF) channels. First, we develop an MMSE-based turbo equalization scheme for Alamouti ST block-coded systems. A semi-analytical method to estimate the bit error rate (BER) is devised. Our results show that the proposed turbo equalization scheme offers significant performance improvements over one-pass equalization. Second, we analyze the convergence behavior of the proposed turbo equalization scheme for Alamouti ST block-coded systems using the extrinsic information transfer (EXIT)-band chart technique. Third, burst-wise (BW)-STBC is applied for uplink transmission over FSF channels in block-spread-CDMA systems with multiuser interference-free reception. The performances of different decision feedback sequence estimation (DFSE) schemes are investigated. A new scheme combining frequency-domain (FD) linear equalization and modified unwhitened-DFSE is proposed. The proposed scheme is very promising as the error-floor behavior observed in the existing unwhitened DFSE schemes is eliminated. Fourth, we develop a FD-MMSE-based turbo equalization scheme for the downlink of ST block-coded CDMA systems. We adopt BW-STBC instead of Alamouti symbol-wise (SW)-STBC considered for WCDMA systems and demonstrate its superior performance in FSF channels. Block spreading is shown to be more desirable than conventional spreading to improve performance using turbo equalization. We also devise approximate implementations (AprxImpls) that offer better trade-offs between performance and complexity. Semi-analytical upper bounds on the BER are derived. Fifth, turbo multicode detection is investigated for ST block-coded downlink transmission in DS-CDMA systems. We propose symbol-by-symbol and chip-by-chip FD-MMSE-based multicode detectors. An iterative channel estimation scheme is also proposed. The proposed turbo multicode detection scheme offers significant performance improvements compared with non-iterative multicode detection. Finally, the impact of channel estimation errors on the performance of MMSE-based turbo equalization in ST block-coded CDMA systems is investigated.

Master of Engineering (Research) / The latest wireless communication techniques such as highspeed wireless internet application demand higher data rates and better quality of service (QoS). However, transmission reliability is still degraded by harsh propagation channels. Multiple-input multiple-output (MIMO) systems can increase the system capacity and improve transmission reliability. By transmitting multiple copies of data, a MIMO system can effectively combat the effects of fading. Due to the high hardware cost of a MIMO system, antenna selection techniques have been applied in MIMO system design to reduce the system complexity and cost. The Nakagami-m distribution has been considered for MIMO channel modeling since a wide range of fading channels, from severe to moderate, can be modeled by using Nakagami-m distribution. The Rayleigh distribution is a special case of the Nakagami-m distribution. In this thesis, we analyze the error performance of two MIMO schemes: maximal-ratio combining with transmit antenna selection (the TAS/MRC scheme) and space-time block codes with transmit antenna selection (the TAS/STBC scheme) over Nakagami-m fading channels. In the TAS/MRC scheme, one of multiple transmit antennas, which maximizes the total received signal-to-noise ratio (SNR), is selected for uncoded data transmission. First we use a moment generating function based (MGF-based) approach to derive the bit error rate (BER) expressions for binary phase shift keying (BPSK), the symbol error rate (SER) expressions for M-ray phase shift keying (MPSK) and M-ray quadrature amplitude modulation (MQAM) of the TAS/MRC scheme over Nakagami-m fading channels with arbitrary and integer fading parameters m. The asymptotic performance is also investigated. It is revealed that the asymptotic diversity order is equal to the product of the Nakagami fading parameter m, the number of transmit antenna Lt and the number of receive antenna Lr as if all transmit antenna were used. Then a Gaussian Q-functions approach is used to investigate the error performance of the TAS/STBC scheme over Nakagami-m fading channels. In the TAS/STBC scheme, two transmit antennas, which maximize the output SNR, are selected for transmission. The exact and asymptotic BER expressions for BPSK are obtained for the TAS/STBC schemes with three and four transmit antennas. It is shown that the TAS/STBC scheme can provide a full diversity order of mLtLr.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.E.)--University of Canterbury, 2008. / Typescript (photocopy). "June 2008." Includes bibliographical references (p. 87-96). Also available via the World Wide Web.

Thesis (Ph.D) -- Australian National University, 2006.