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Title: Low complexity receiver architectures for high-speed wireless multiple-input multiple-output (MIMO) systems
Author: Claussen, Holger
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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In modern wireless networks the demand for high-speed transmissions is ever increasing to provide access to data and enable new services anywhere and anytime. Mobile internet, video telephony, music and video on demand are examples for the possible applications which demand high data rates. However, the available frequency spectrum is limited and expensive. To satisfy the demand for high data-rates, turbo-encoded multiple-input multiple-output (MIMO) radio links have been recently proposed for the support of high-speed downlink packet access (HSDPA) in UMTS, where the re-use of spreading codes across the transmitter antennas results in high levels of interference. In this thesis, low complexity MIMO receiver architectures and their components are investigated to enable high-speed receivers capable of dealing with high-order modulations. For detection, multi-stage partial parallel interference cancellation (MS-PPIC) and matched-filter based ordered serial interference cancellation (MF-SIC) are proposed as low complexity alternatives to the a posteriori probability (APP) detector and its Max-Log-APP variant. Non-linear cancellation metrics are derived for the MS-PPIC and the performance of the proposed detectors is investigated for different channel conditions. It is shown that the MS-PPIC can provide similar performance compared to the APP and, for low coding rates, superior performance compared to the Max-Log-APP, at a substantially lower computational complexity. While the MF-SIC cannot compete with the APP and MS-PPIC detectors in non-iterative receivers, it provides impressive performance when used in an iterative receiver architecture where a priori information from a decoder is available for ordering and interference cancellation. For decoding, a novel modification of the turbo decoder using the Max-Log-MAP algorithm is proposed, which results in a performance approaching that of a turbo decoder using the optimum Log-MAP or MAP algorithms. The approach aims to maximise the mutual information at the input of each component decoder by correcting the bias in the a priori information caused by the Max-Log approximation in the previous component decoder. This is performed by scaling the a priori information by optimised iteration-specific weight factors at each turbo iteration. Another contribution is a method for the off-line computation of the optimal weights according to the maximum mutual information criterion. Subsequently, different versions of non-iterative and iterative MIMO receiver architectures are proposed and compared in terms of performance and computational complexity for a wide range of detection algorithms using 4-QAM modulation. For iterative receivers which rely on hard cancellation, a soft-output combining scheme which maximises the mutual information at each iteration is proposed and a corresponding method for the offline computation of the optimal combining weights is presented. Finally a novel layered encoding scheme is proposed which overcomes the problem of exponential growth in complexity of the APP detector when higher order modulations such as 16- and 64-QAM are employed. This could be achieved without any loss in performance. Layered encoding also solves the performance and convergence problems of low complexity detectors such as the proposed MS-PPIC and the MF-SIC which occur at higher order modulations. In addition, the applicability of high order modulations in MIMO systems is investigated using system-level simulations for a 2-cell indoor and a 7-cell urban scenario. The results indicate that high-order modulations could be used in a substantial area of the cell.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available