The increasing demand for mobile communication services without a corresponding increase in RF spectrum allocation motivates the need for new techniques to improve spectrum utilization. The CDMA and adaptive antenna array are two approaches that shows real promise for increasing spectrum efficiency. In this research, we investigate the performance of different blind adaptive array algorithms in the CDMA systems. Two novel algorithms, least-squares despread respread multitarget array (LS-DRMTA) and least-squares despread respread multitarget constant modulus algorithm (LS-DRMTCMA), are developed, and a MATLAB simulation testbed is created to compare the performance of these two novel algorithms with those of the multitarget least-squares constant modulus algorithm (MT-LSCMA) and multitarget steepest-descent decision-directed (MT-SDDD) algorithm. It is shown from the simulation results that these two novel algorithms can outperform the other algorithms in all the test situations (e.g., AWGN channel, timing offset case, frequency offset case, and multipath environment). It is also shown that these two algorithms have less complexity and can converge faster than the other algorithms. / Master of Science

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Recent studies have shown that considerable system capacity gains in mobile communication systems can be obtained by exploiting the use of antenna arrays at the base station. Unfortunately, these studies make little mention of practical issues concerning implementation. It is thus one of the objectives of the Centre of Excellence (CoE) in Radio Access Technologies at the University of Natal to investigate the development of a widehand CDMA adaptive array transceiver using Alcatel software radios as the transceiver platforms. Such a transceiver system can be subdivided into three major sections: RF front-end, signal digitization and baseband processing stages. Due to the enormity of such an undertaking, the research outlined in this thesis is focused on (but not isolated to) some aspects of the RF front-end implementation for the proposed system. The work in this thesis can be catergorized into two sections. The first section focuses on the theoretical and practical (or implementation) aspects of antenna arrays and beamforming. In particular, it is evident that digital (rather than analogue) beamforming in a multi user environment, is a more viable option from both a cost and implementation standpoint. The second section evaluates the impact of RF component noise and local oscillator generated phase noise in a DS-CDMA system. The implementation of a RP front-end for a BPSK transceiver also forms part of the work in this section. LO phase noise and Error Vector Magnitude (EVM) measurements are performed on this system to support relevant theory. By use of the HP89410A phase noise measurement utility and the phase noise theory developed in this thesis, a quantitative phase noise comparison between two frequency sources used in the system were made. EVM measurement results conclusively verified the importance of an LNA in the system. It has also been shown that the DS-CDMA simulated system exhibits superior performance to the implemented BPSK system. Furthermore, an EVM troubleshooting methodology is introduced to identify possible impairments within the BPSK receiver RF front-end. However, this thesis was written with the intention of bridging the gap between the theoretical and practical implementation aspects of RP wireless communication systems. It is the author's opinion that this has been achieved to a certain extent. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

Wireless communication systems continue to face the challenge of time varying quality of the underlying communication channel. When a slow fading channel goes into a deep fade, the corresponding communication system might face successive decoding failures at the destination, and for delay-sensitive communication systems, this amounts to delays that are not desired. In such situations, it becomes a priority to get out of the deep fades. Many techniques and approaches are already available in the literature to counteract fading effects. This work is motivated by recent advances in fast reconfigurable antennas, which provide new means to change the statistical profile of fading channels, and hence reduce the probability of prolonged fades. Fast reconfigurable antennas are poised to improve overall performance, especially for delay-sensitive traffic in slow-fading environments. This potential enhanced performance motivates this study of the queueing behavior of point-to-point communication systems with reconfigurable antennas. We focus on finite-state channels with memory, and we analyze the queueing behavior of the wireless communication system over erasure channels, for a traditional system versus a reconfigurable antenna implementation. We provide numerical results for situations where using reconfigurable antennas yield substantial performance gains in terms of throughput, delay and buffer overflow.

Thesis (Ph.D.) - Carleton University, 2005. / Includes bibliographical references (p. 200-213). Also available in electronic format on the Internet.

Thesis (Ph.D.) - Carleton University, 2006. / Includes bibliographical references (p. 157-167). Also available in electronic format on the Internet.

Thesis (M.S.)--California Polytechnic State University, 2010. / Mode of access: Internet. Title from PDF title page; viewed on April 20, 2010. Major professor: John Saghri. "Presented to the Electrical Engineering Department faculty of California Polytechnic State University, San Luis Obispo, California." "In partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering." "March 2010." Includes bibliographical references (p. 119-125).

Thesis (Ph.D.) - Carleton University, 2007. / Includes bibliographical references (p. 211-219). Also available in electronic format on the Internet.

M.Ing. / This study considers improving the azimuth beam steering resolution of the circular Switched Parasitic Array (SPA) antennas (made up of dipoles) by a factor of two or more. In circular SPA antennas, beam steering is conventionally achieved by open-circuiting and shortcircuiting different parasitic elements and usually only one parasitic element is open-circuited at a time. However, such an approach results in low beam steering resolutions especially for the SPA antennas with few parasitic elements. In order to increase the azimuth beam steering resolution for the circular SPA antennas, two beam steering methods are proposed in this research work. In the first method, parasitic elements are open-circuited and short-circuited based on different combinations of the parasitic elements and the possible switch states. The proposed method was first validated by simulation tests using the MATLAB tool and WIPL-D. A prototype of the circular SPA antenna consisting of five elements was then implemented. It is noted that the simulation and measurement results match very well at 2.4 GHz. In order to have at least two combinations (from the first method) with almost similar gain and return loss, another simpler beam steering method was developed. The latter method is based on simultaneously open-circuiting either two or three neighbouring parasitic elements. The performance of the second method was studied through simulations using the circular SPA antenna geometries consisting of five, seven and nine elements. These geometries were first optimized (for gain and input impedance) and then modelled using WIPL-D. It was observed that the two methods double the azimuth beam steering resolution of the circular SPA antennas when compared to the conventional beam steering approaches of open-circuiting one parasitic element at a time. Variations in the structural parameters of the five elements circular SPA antenna at 2.4GHz were also investigated. In this procedure, the effects of variations (also considered as random errors) in the structural parameters (or antenna dimensions) on the performance of the SPA antennas were examined. Firstly, variations in each structural parameter were modelled with other structural parameters fixed as per specifications. Thereafter, effects of combined errors were also investigated. The simulation results demonstrated that variations in the structural parameter can either increase or decrease the gain and input impedance of the SPA antenna depending on the given specifications. The gain and input impedance sensitivities per variations in each structural parameter were computed to determine the degree at which the gain and input impedance can vary for a predefined change (error) in the structural parameter.

The spatially distributed adaptive array is defined and analyzed. It is applied to both time division multiple access (TDMA) and code division multiple access (CDMA) cellular networks to improve the outage probability at either the base station or mobiles. In a TDMA network, the distributed array consists of three sub-arrays at alternate corners of a hexagonal cell. It is shown analytically that the SINR of combined beamforming of the distributed sub-arrays is greater than or equal to the SIR or independent beamforming of the sub-arrays. Closed form solutions are derived for estimating the BER performance of Rayleigh fading mobile signals received at a distributed adaptive array with combined beamforming of the sub-arrays. The simulated TDMA uplink outage probability of multiple same-cell co-channel users in a fading environment is compared between conventional, spatially distributed arrays with independent beamforming of the sub-arrays and combined beamforming of the sub-arrays. The effect of the antenna element spacing, number of elements and angular spread is also investigated. Spatially distributed arrays are formed in a CDMA network on the downlink with arrays in multi-way soft handoff with the mobiles. The outage probability performance of combined beamforming of the arrays in handoff is compared to independent beamforming of the arrays as well as to conventional sectorized antennas. The range between mobiles and distributed sub-arrays in the case of a spatially distribu-ted array can be larger than between conventional center cell arrays and mobiles. Therefore, the effect of interference on the range increase relative to an omni antenna of adaptive and phased arrays in a multipath environment for both narrowband and wideband spread spectrum systems is investigated. An analytical model for predicting the asymptotic range limitation of phased arrays when the angular spread exceeds the array beamwidth is derived. / Thesis (PhD (Electronic Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted