Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 71-78). Also available in electronic version.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 99-111).

Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2004. / Includes bibliographical references (p. 53-54).

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 2004. / Thesis advisor(s): Frank Kragh. Includes bibliographical references (p. 93-94). Also available online.

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The shortage of radio spectrum has become the bottleneck of achieving broadband wire-less access. Overcoming this bottleneck in next-generation wireless networks hinges on successful implementation of multiple-input-multiple-output (MIMO) technologies, which use antenna arrays rather than additional bandwidth for multiplying data rates. The most efficient MIMO techniques require channel state information (CSI). In practice, such information is usually inaccurate due to overhead constraints on CSI acquisition as well as mobility and delay. CSI inaccuracy can potentially reduce the performance gains provided by MIMO. This dissertation investigates the impact of CSI inaccuracy on the performance of increasing complex MIMO networks, starting with a point-to-point link, continuing to a multiuser MIMO system, and ending at a mobile ad hoc network. Furthermore, this dissertation contributes algorithms for efficient CSI acquisition, and its integration with beamforming and scheduling in multiuser MIMO, and with interference cancelation in ad hoc networks. First, this dissertation presents a design of a finite-rate CSI feedback link for point-to-point beamforming over a temporally correlated channel. We address various important design issues omitted in prior work, including the feedback delay, protocol, bit rate, and compression in time. System parameters such as the feedback bit rate are derived as functions of channel coherence time based on Markov chain theory. In particular, the capacity gain due to beamforming is proved to decrease with feedback delay at least at an exponential rate, which depends on channel coherence time. This work provides an efficient way of implementing beamforming in practice for increasing transmission range and throughput. Second, several algorithms for multiuser MIMO systems are proposed, including CSI quantization, joint beamforming and scheduling, and distributed feedback scheduling. These algorithms enable spatial multiple access and multiuser diversity in a cellular system under the practical constraint of finite-rate multiuser CSI feedback. Moreover, this dissertation shows analytically that the throughput of the MIMO uplink and downlink using the proposed algorithms scales optimally as the number of users increases. Finally, the transmission capacity of a MIMO ad hoc network is analyzed for the case where spatial interference cancelation is applied at receivers. Most important, this dissertation shows that this MIMO technique contributes significant network capacity gains even if the required CSI is inaccurate. In addition, opportunistic CSI estimation is shown to provide a tradeoff between channel training overhead and CSI accuracy. / text

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The demand for high data rate wireless communication systems is evident today as indicated by the rapid growth in wireless subscribers and services. High data rate systems are bandwidth intensive but bandwidth is an expensive and scarce commodity. The ability of future wireless systems to efficiently utilise the available bandwidth is therefore integral to their progress and development. The wireless communications channel is a harsh environment where time varying multipath fading, noise and interference from other users and systems all contribute to the corruption of the received signal. It is difficult to overcome these problems and achieve the high data rates required using single antenna technology. Multiple-input-multipleoutput (MIMO) systems have recently emerged as a promising technique for achieving very large bandwidth efficiencies in wireless channels. Such a system employs multiple antennas at both the transmitter and the receiver. These systems exploit the spatial dimension of the wireless channel to achieve significant gains in terms of capacity and reliability over single antenna systems and consequently achieve high data rates. MIMO systems are currently being considered for 3rd generations cellular systems. The performance of MIMO systems is heavily dependent on the environment in which the system is utilised. For this reason a realistic channel model is essential for understanding the performance of these systems. Recent studies on the capacity of MIMO channels have focused on the effect of spatial correlation but the joint effect of spatial and temporal correlation has not been well studied. The first part of this thesis proposes a new spatially and temporally correlated MIMO channel model which considers motion of the receiver and nonisotropic scattering at both ends of the radio link. The outage capacity of this channel is examined where the effects of antenna spacing, array angle, degree of scattering and receiver motion are investigated. It is shown that the channel capacity still increases linearly with the number of transmit and receive antennas, despite the presence of both spatial and temporal correlation. The capacity of MIMO channels is generally investigated by simulation. Where analytical expressions have been considered for spatially correlated channels, only bounds or approximations have been used. In this thesis closed form analytical expressions are derived for the ergodic capacity of MIMO channels for the cases of spatial correlation at one end and both ends of the radio link. The latter does not lend itself to numerical integration but the former is shown to be accurate by comparison with simulation results. The proposed analysis is also very general as it is based on the transmit and receive antenna correlation matrices. Low-density parity-check (LDPC) codes have recently been rediscovered and have been shown to approach the Shannon limit and even outperform turbo codes for long block lengths. Non-binary LDPC codes have demonstrated improved performance over binary LDPC codes in the AWGN channel. Methods to optimise non-binary LDPC codes have not been well developed where only simulation based approaches have been employed, which are not very efficient. For this reason, a new approach is proposed which is based on extrinsic information transfer (EXIT) charts. It is demonstrated that by performing curve matching on the EXIT chart, good non-binary LDPC codes can be designed for the AWGN channel. In order to approach the theoretical capacity of MIMO channels, many space-time coded, multiple antenna (MA) systems have been considered in the literature. These systems merge channel coding and antenna diversity and exploit the benefits of both. Binary LDPC codes have demonstrated good performance in MA systems but nonbinary LDPC codes have not been considered. Therefore, the application of non-binary LDPC codes to MA systems is investigated where the codes are optimised for the system of interest, using a simulation and EXIT chart based design approach. It is shown that non-binary LDPC codes achieve a small gain in performance over binary LDPC codes in MA systems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2005.

In recent years, space-time block co'des (STBC) for multi-antenna wireless systems have emerged as attractive encoding schemes for wireless communications. These codes provide full diversity gain and achieve good performance with simple receiver structures without the additional increase in bandwidth or power requirements. When implemented over broadband channels, STBCs can be combined with orthogonal frequency division multiplexing (OFDM) or single carrier frequency domain (SC-FD) transmission schemes to achieve multi-path diversity and to decouple the broadband frequency selective channel into independent flat fading channels. This dissertation focuses on the SC-FD transmission schemes that exploit the STBC structure to provide computationally cost efficient receivers in terms of equalization and channel estimation. The main contributions in this dissertation are as follows: • The original SC-FD STBC receiver that bench marks STBC in a frequency selective channel is limited to coherent detection where the knowledge of the channel state information (CSI) is assumed at the receiver. We extend this receiver to a multiple access system. Through analysis and simulations we prove that the extended system does not incur any performance penalty. This key result implies that the SC-FD STBC scheme is suitable for multiple-user systems where higher data rates are possible. • The problem of channel estimation is considered in a time and frequency selective environment. The existing receiver is based on a recursive least squares (RLS) adaptive algorithm and provides joint equalization and interference suppression. We utilize a system with perfect channel state information (CSI) to show from simulations how various design parameters for the RLS algorithm can be selected in order to get near perfect CSI performance. • The RLS receiver has two modes of operation viz. training mode and direct decision mode. In training mode, a block of known symbols is used to make the initial estimate. To ensure convergence of the algorithm a re-training interval must be predefined. This results in an increase in the system overhead. A linear predictor that utilizes the knowled~e of the autocorrelation function for a Rayleigh fading channel is developed. The predictor is combined with. the adaptive receiver to provide a bandwidth efficient receiver by decreasing the training block size.· The simulation results show that the performance penalty for the new system is negligible. • Finally, a new Q-R based receiver is developed to provide a more robust solution to the RLS adaptive receiver. The simulation results clearly show that the new receiver outperforms the RLS based receiver at higher Doppler frequencies, where rapid channel variations result in numerical instability of the RLS algorithm. The linear predictor is also added to the new receiver which results in a more robust and bandwidth efficient receiver. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

Multi-input multi-output (MIMO) control system design is much more difficult than single-input single output (SISO) design due to the combination of cross-coupling and uncertainty. An investigation is undertaken into both the classical Quantitative Feedback Theory (QFT) and modern H-infinity frequency domain design methods. These design tools are applied to a bank-to-turn (BTT) missile plant at multiple operating points for a gain scheduled implementation. A new method is presented that exploits both QFT and H-infinity design methods. It is shown that this method gives insight into the H-infinity design and provides a classical approach to tuning the final H-infinity controller. The use of “true” inversionfree design equations, unlike the theory that appears in current literature, is shown to provide less conservative bounds at frequencies near and beyond the gain cross-over frequency. All of the techniques investigated and presented are applied to the BTT missile to show their application to a practical problem. It was found that the H-infinity design method was able to produce satisfactory controllers at high angles of attack where there were no QFT solutions found. Although an H-infinity controller was produced for all operating points except the last, the controllers were found to be of very high-order, contain very poorly damped second order terms and generally more conservative, as opposed to the QFT designs. An investigation into simultaneous stabilization of multiple plants using Hinfinity is also presented. Although a solution to this was not found, a strongly justified case to entice further investigation is presented. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.