We present a new sub-optimal near-maximum-likelihood (ML) detection method for the family of variable-rate space-time block codes (VRSTBC). The proposed detection method is based on the concept of symbol reliability and provides a wide range of performance-complexity trade-offs. The reliability measures are defined with the help of a recent generic ML metric expression. The error performance and complexity analysis of the method via simulations show an achievable near-ML error performance with significant reduction in complexity. The performance of the proposed method is also compared with the group interference cancellation (GIC) method which was the detection method originally applied to VRSTBCs and the results show a significant improvement. The new method offers various levels of error protection via a simple parameter and hence can provide the users of a wireless network with different performance levels according to their cost allowance. Unequal error protection by VRSTBCs under the new detection method was explored. Several applications integrating data with different levels of sensitivity to error can benefit from the wide range of possibilities that the combination of the proposed detection method and VRSTBCs provides. To further explore these flexibilities, four practically interesting power allocation schemes were applied to the transmission and the behaviors were observed through case studies. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-09-26 23:45:07.81

The thesis presents an implementation of a multiple input single output orthogonal frequency division multiplex (MISO OFDM) communication system testbed. The project was developed in order to evaluate whether the channel estimation algorithms developed by Dr Oyerinde [1] could be implemented in a real time communication system that uses today’s technology. This implementation based validation would help determine the practicality of algorithms and methods that promise better performance for communication systems from a simulation point of view. The benefits of using multiple orthogonal carriers are discussed as well as how an OFDM system works. The benefits of using multiple antennas at the transmitter, as opposed to using just one, are also discussed. The Alamouti scheme which allows space diversity to be achieved without the cost of having a lower data rate is presented. Modules common to all communication systems, such as those dedicated to synchronization, channel estimation, symbol detection and channel coding, are discussed. The different methods of synchronization for OFDM communication systems are presented and compared. The channel estimation algorithm developed by Dr Oyerinde is presented and is adopted for an indoor channel. Most of the system blocks and parameters used in the testbed are the same as those used in [1] in order to easily compare the results obtained by simulation and those obtained by implementation. The system bandwidth required for the project was too high for the processor chosen for the testbed. A qualitative evaluation of the practicality of Dr Oyerinde’s channel estimation algorithms was performed instead. From this evaluation it was derived that Dr Oyerinde’s non-iterative decision directed channel estimation algorithm was more suitable for real time non-iterative decision directed channel estimation communication systems than for iterative versions. Apart from processing demands that couldn’t be met, the other aspects of the project were implemented successfully. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Several efficient low complexity interference management techniques were developed for improving the performance of multiple-input multiple-output (MIMO) networks. Sub-optimal techniques involving optimal antenna selection-aided stream control were proposed for joint optimization of co-channel MIMO links in a space division multiple access (SDMA) network. Results indicated that the use of the SDMA scheme along with partial channel state information at the transmitters significantly reduces the signaling overhead with minimal loss in throughput performance. Next, a mean squared error (MSE) based antenna selection framework was presented for developing low complexity algorithms for finite complexity receivers. These selection algorithms were shown to provide reasonable bit-error rate performance while keeping the overall system complexity low. Furthermore, some new algebraic properties of linear orthogonal space-time block codes (OSTBCs) were utilized to develop a single-stage and minimum MSE optimal detector for two co-channel users employing unity rate real and derived rate-1/2 complex OSTBCs. A sub-optimal space-time interference cancellation (IC) technique was also developed for a spatial-multiplexing link subjected to Alamouti interference. The performance of proposed interference management techniques and their implications for future research are discussed.

In the field of wireless multiple-input multiple-output (MIMO) communications, remarkable capacity enhancements may be achieved in certain environments relative to single-antenna systems. In a non-line of sight (NLOS) environment with rich multipath, the capacity potential is typically very good, but in a line of sight (LOS) environment with a high Rician K-factor, the capacity improvement may be severely limited or almost disappear. The objective of the research described in this dissertation has been to develop a more thorough understanding of the capacity limitations of MIMO in a LOS environment and explore methods to improve that capacity. It is known that for a LOS link with a given range, an optimal antenna configuration, which usually involves large antenna spacings, can be computed to maximize the capacity. A method is here proposed for achieving near-maximum MIMO capacity in LOS environments with suboptimal array configurations. Suboptimal arrays may include small antenna spacings and/or arrays rotated off normal. The method employs single-antenna full-duplex, amplify-and-forward relays, otherwise known as "wireless repeaters." We have designated this concept repeater-assisted capacity enhancement (RACE) for MIMO. Potential applications include tower-mounted or building-top cellular backhaul and high-speed wireless bridge links (explored in Chapter 5) and ground-to-air sensor network backhaul links and base-to-mobile links in a cellular configuration (explored in Chapter 7). We have analyzed this concept in simulation for point-to-point and point-to-multipoint links and have found the following critical parameters for system design and deployment: orientation, antenna spacing, and antenna patterns of the transmit (TX)/receive (RX) MIMO arrays; and position, noise figure, TX/RX isolation, and antenna patterns associated with the repeater(s). Simulation results for an n[subscript R] xn[subscript T] MIMO link demonstrate nearly a factor of n=min{n[subscript R], n[subscript T] } improvement in capacity relative to a single-input single-output (SISO) link using n-1 optimally placed wireless repeaters supporting the link. Other portions of analysis presented include the development of a determinant-based metric for capacity (D) and an exploration of upper and lower bounds of capacity as a function of D. The position of repeaters is analyzed theoretically and a metric introduced based on D intended to quickly and intuitively determine optimal positions for repeaters assisting a given MIMO link based on TX/RX node steering vectors.

Multiple-input multiple-output (MIMO) technology, originated in the 1990s, is an emerging and fast growing area of communication research due to the ability to provide diversity as well as transmission degrees-of-freedom. Recent research focus on MIMO systems has shifted from the point-to-point link to the one-to-many multiuser links due to the ever increasing demand for multimedia-intensive services from users. The downlink of a multiuser transmission is called the broadcast channel (BC) and the reverse many-to-one uplink is termed the multiple access channel (MAC). Early studies in the MIMO BC and the MIMO MAC were mostly information-theoretic in nature. In particular, the characterizations of the capacity regions of the two systems were of primary concerns. The information-theoretic results suggest the optimal uplink detection scheme involves successive interference cancellation while successive application of dirty paper coding at the transmitter is optimal in the downlink channels. Over the past few years, after the full characterizations of the capacity regions, several practical precoders had been suggested to realize the benefits of MIMO multiuser transmission. However, linear precoders such as the zero-forcing (ZF) and the MMSE precoders fall short on the achievable capacity despite their simple structure. Nonlinear precoders such as the ZF dirty paper (ZF-DP) and the the MMSE generalized decision feedback equalizer-type (MMSE-GDFE) precoders demonstrated promising performance but suffered from either restriction on the number of antennas at users, i.e. ZF-DP, or high computational load for the transmit filter, i.e. MMSE-GDFE. An novice MMSE feedback precoder (MMSE-FBP) with low computational requirement was proposed and its performance was shown to come very close to the bound suggested by information theory. In this thesis, we undertake investigation of the causes of the capacity inferiority and come to the conclusion that power control is necessary in a multiuser environment. New schemes that address the power control issue are proposed and their performances are evaluated and compared. Adaptive modulation is an effective and powerful technique that can increase the spectral efficiency in a fading environment remarkably. It works by observing the channel variations and adapts the transmission power and/or rate to counteract the instabilities of the channel. This thesis extends the pioneering study of adaptive modulation on single-input single-output (8180) Gaussian channel to the MIMO BC. We explore various combinations of power and rate adaptions and observe their impact on the system performance. In particular, we present analytical and simulation results on the successiveness of adaptive modulation in maximizing multiuser spectral efficiency. Furthermore, empirical research is conducted to validate its effectiveness in optimizing the overall system reliability.

Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: leaf 216-228.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 117-124).

Thesis (Ph.D.)--Victoria University (Melbourne, Vic.), 2007.

Thesis (M.E.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (leaves 90-108). Also available via the World Wide Web.

Thesis (M.Eng.Stud.)--University of Wollongong, 2008. / Typescript. Includes bibliographical references: leaf 84-95.