Characterization and Development of Algorithms for Array Processing Architectures of Adaptive Antennas in Wireless Communication

Abstract

To set up an efficient wireless and mobile communication system, requires characterization of its environments and its components, in particular, its array processing architecture. This research work has been prompted by the current thrust in wireless and mobile communication technology to look for new approaches and technologies to improve performance of array processing architectures, thereby improving spectrum efficiency and to be able to support the projected capacity demands with the introduction of new personal communication services. The results presented in this thesis constituted four targets. First, new side lobe control beamforming algorithms for array processing architectures of CDMA based wireless communication systems are developed for interference reduction. It is shown that conventional arrays based on nulling procedure are unlikely to be applicable in practical CDMA based wireless communication systems for large number of interferers. The role of FrFT in providing taper of varying side-lobe level and beamwidth is investigated. A procedure for tapering in FrFT domain is proposed, which can be used with optimal array processing also. The weights obtained by FrFT taper are found to be practically realizable weights. The one to one relationship between capacity and beampattern is established. A relationship between the side-lobe level and number of interferers is derived. A new algorithm capable of synthesizing Chebyshev-like low side-lobe beam patterns with adjustable beamwidth and steering invariance is developed. The proposed algorithm is shown to handle large angular spreads of interference effectively. The increase in information capacity and the performance improvement in various performance metrics viz; Signal-to-interference-plus-noise ratio (SINR), Normalized SINR (NSNIR), Array gain (AG) and Mean square error (MSE), of array processing architectures, by implementation of new beamforming algorithm, are investigated. It is shown through Monte Carlo simulations that for large number of interferers the proposed algorithm outperforms the adaptive algorithm. The second target of this thesis has been the development and application of advanced array signal processing techniques to wireless and mobile communication systems that have a practical implementation complexity and achieve high performance levels. The second target is achieved by development of FrFT based beamforming algorithms, in non stationary environments, towards improving the performance of array processing architectures of adaptive antenna from the point of view of reducing mean squared error. It is shown that the FrFT based optimal beamformer reduces the Mean Square Error to a greater extent for multipath fading signal over the additive white Gaussian channel. The proposed optimum FrFT beamformer is shown yielding small errors in case of accelerating source problems also which are common in wireless communication. The proposed FrFT based beamforming algorithm is investigated in different fading channels to demonstrate the merits of the algorithm. The superiority of the proposed beamforming technique over time and frequency domain beamforming is established in fading channels. The proposed FrFT based optimum beamformer outperforms the time domain and frequency domain optimum beamformer in terms of bit error rate in Rayleigh and Nakagami fading channels. The use of FrFT based arrays for MIMO systems is proposed for decreasing channel estimation errors caused by Gaussian noise. A new optimum FrFT based MIMO receive beamformer is proposed. The performance of proposed beamformer is evaluated for spatial multiplexed systems in terms of bit error rate and block error rate. The use of proposed beamformer with rate one systems is also demonstrated. It is shown that BER of spatial multiplexed as well as rate one system can be decreased with use of proposed beamformer. The use of adaptive antennas on handheld radios is a new area of research. All the research in the field of smart antennas at handset is in the area of diversity, capacity improvement, reduction of multi- path fading, suppression of interference signals, improvements of call reliability, mitigation against dead zones, increased data rates, spectral efficiency etc. The effectiveness of smart antenna in controlling radiation hazards at handset is explored in the light of establishing the advantages of smart antenna over a single antenna system at the handset. The adaptive antenna at the handset constantly forms a broad null towards the user head. The power absorbed and rise in temperature of various tissues of head is compared for omni directional as well as adaptive antenna. It is established that future mobile handset employing adaptive antenna, could also reduce the RF hazards.