Channel Tracking Using Particle Filtering in Unresolvable Multipath Environments
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Channel Tracking Using Particle Filtering in Unresolvable Multipath Environments Tanya Bertozzi Diginext, 45 Impasse de la Draille, 13857 Aix-en-Provence Cedex 3, France Email: [email protected] Conservatoire National des Arts et M´etiers (CNAM), 292 rue Saint-Martin, 75141 Paris Cedex 3, France
Didier Le Ruyet Conservatoire National des Arts et M´etiers (CNAM), 292 rue Saint-Martin, 75141 Paris Cedex 3, France Email: [email protected]
Cristiano Panazio Conservatoire National des Arts et M´etiers (CNAM), 292 rue Saint-Martin, 75141 Paris Cedex 3, France Email: [email protected]
Han Vu Thien Conservatoire National des Arts et M´etiers (CNAM), 292 rue Saint-Martin, 75141 Paris Cedex 3, France Email: [email protected] Received 1 May 2003; Revised 9 June 2004 We propose a new timing error detector for timing tracking loops inside the Rake receiver in spread spectrum systems. Based on a particle filter, this timing error detector jointly tracks the delays of each path of the frequency-selective channels. Instead of using a conventional channel estimator, we have introduced a joint time delay and channel estimator with almost no additional computational complexity. The proposed scheme avoids the drawback of the classical early-late gate detector which is not able to separate closely spaced paths. Simulation results show that the proposed detectors outperform the conventional early-late gate detector in indoor scenarios. Keywords and phrases: sequential Monte Carlo, multipath channels, importance sampling, timing estimation.
1.
INTRODUCTION
In wireless communications, direct-sequence spread spectrum (DS-SS) techniques have received an increasing interest, especially for the third generation of mobile systems. In DS-SS systems, the adapted filter typically employed is the Rake receiver. This receiver is efficient to counteract the effects of frequency-selective channels. It is composed of fingers, each assigned to one of the most significant channel paths. The outputs of the fingers are combined proportionally to the power of each path for estimating the transmitted symbols (maximum-ratio combining). Unfortunately, the performance of the Rake receiver strongly depends on the quality of the estimation of the parameters associated with the channel paths. As a consequence, we have to estimate the delay of each path using a timing error detector (TED). This goal is generally achieved in two steps: acquisition and
tracking. During the acquisition phase, the number and the delays of the most significant paths are determined. These delays are estimated within one half chip from the exact delays. Then, the tracking module refines the first estimation and follows the delay variations during the permanent phase. The conventional TED used during the tracking phase is the early-late gate-TED (ELG-TED) associated with each path. It is well known that the ELG-TED works very well in the case of a single fading path. However, in the presence of multipath propagation, the interference between the different paths can degrade its p
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