A Network of Kalman Filters for MAI and ISI Compensation in a Non-Gaussian Environment
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A Network of Kalman Filters for MAI and ISI Compensation in a Non-Gaussian Environment Bessem Sayadi Laboratoire des Signaux et Syst`emes (LSS), Sup´elec CNRS, Plateau de Moulon, 3 rue Joliot Curie, 91192 Gif-sur-Yvette Cedex, France Email: [email protected]
Sylvie Marcos Laboratoire des Signaux et Syst`emes (LSS), Sup´elec CNRS, Plateau de Moulon, 3 rue Joliot Curie, 91192 Gif-sur-Yvette Cedex, France Email: [email protected] Received 4 September 2003; Revised 30 November 2004 This paper develops a new multiuser detector based on a network of kalman filters (NKF) dealing with multiple-access interference (MAI), intersymbol interference (ISI), and an impulsive observation noise. The two proposed schemes are based on the modeling of the DS-CDMA system by a discrete-time linear system that has non-Gaussian state and measurement noises. By approximating the non-Gaussian densities of the noises by a weighted sum of Gaussian terms and under the common MMSE estimation criterion, we first derive an NKF detector. This version is further optimized by introducing a feedback exploiting the ISI interference structure. The resulting scheme is an NKF detector based on a likelihood ratio test (LRT). Monte-Carlo simulations have shown that the NKF and the NKF based on LRT detectors significantly improve the efficiency and the performance of the classical Kalman algorithm. Keywords and phrases: multiuser detection, Kalman filtering, Gaussian sum approximation, impulsive noise, likelihood ratio test.
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INTRODUCTION
Direct-sequence code-division multiple access (DS-CDMA) is emerging as a popular multiple-access technology for personal, cellular, and satellite communication services [1, 2, 3] for its large capacity that results from several advantages [4], such as soft handoffs, a high-frequency reuse factor, and the efficient use of the voice activity. However, in the case of a multipath transmission channel, the signals received from different users cannot be kept orthogonal and multiple-access interference (MAI) arises. The need for an increased capacity in terms of the number of users per cell and a higher-bandwidth multimedia data communication constraints us to overcome the MAI limitation. One solution to this problem is multi-user detection, which is covered in [5] and the references within. In addition, high-speed data transmission over communication channels is subject to intersymbol interference (ISI). The ISI is usually the result of the restricted bandwidth allocated to the channel and/or the presence of multipath distortions in the medium through which the information is transmitted. This leads to a need for multiuser detection techniques that jointly suppress ISI as well as MAI, in order to obtain reliable estimates of the symbols transmitted by a particular user (or all the users).
A class of DS-CDMA receivers known as linear minimum mean-squared error (MMSE) detectors has been discussed in recent years. The Kalman filter is known to be the linear minimum variance state estimator. It is well known that the Kalman
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