UBC Theses and Dissertations

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UBC Theses and Dissertations

Performance of an improved MMSE receiver for CDMA systems in Rayleigh fading Martin, David Glenn


In a recent paper an adaptive modified minimum mean squared (MMSE) linear filter is used to mitigate interference caused by other users in a CDMA system. The tap weight vector for this adaptive linear filter is determined by an orthogonal decomposition-based least mean square (LMS) algorithm. This tap weight vector consists of a fixed and an adaptive part whose orthogonality is normally maintained by the LMS algorithm. In this thesis, it is proposed that an explicit orthogonalization procedure be used to reduce problems due to quantization errors. These errors would otherwise accumulate and are shown via fixed-point simulations to cause the components of the tap weight vector to become nonorthogonal, resulting in a decreased signal to interference plus noise ratio (SINR) and an increased BER. It is demonstrated that this explicit orthogonalization procedure results in a higher SINR and a lower BER. A new detector is proposed, which adds two minor improvements to the previously published detector, in addition to the explicit orthogonalization procedure. The advantages of these improvements are illustrated by floating-point simulations. The BER performance of the Proposed Detector is compared to those of previously published detectors for the flat Rayleigh fading channel. Finally, to cope with the frequency-selective fading channel, multiple instances of the Proposed Detector can be used in a precombining RAKE receiver structure. The BER performance for this Proposed RAKE receiver is compared against published results for other detectors.

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