Channel tracking for RAKE receivers in closely spaced multipath environments

Abstract

This paper deals with the problem of channel tracking for RAKE receivers in propagation environments characterized by closely spaced multipath components. After outlining why conventional single-path channel tracking algorithms fail in such scenarios, several new estimation algorithms are developed that are tailored to channels with closely spaced multipaths. This is achieved by removing or minimizing self-interference caused by multipath components. Other interfering users are treated as noise. Both timing tracking and phasor tracking and their interaction are covered in this paper. The derived algorithms are benchmarked against perfect channel knowledge on one hand and conventional tracking algorithms on the other hand, both in a UMTS test scenario. In moderate scenarios, the use of these new algorithms leads to performance improvements of up to 2 dB, in terms of signal-to-noise ratio (SNR) at moderate bit error rates, and even manages to track the channel in conditions where conventional tracking algorithms fail completely.

Performance Evaluation of a Non-Coherent Digital Delay-Locked Loop in Rayleigh Fading Channels

“…We remark that, for a given false alarm probability, the threshold η can be obtained from (10). However, the value obtained is actually normalized by the variance of the noise at the output of the correlator.…”

“…However, this is generally not an easy task to achieve especially for fast varying mobile radio channels. Recognizing that a noncoherent DLL is what practically works over such hostile channel conditions, various noncoherent DLL with diversity and/or multipath interference cancellation techniques [8][9] [10] and tracking algorithms based on maximum likelihood delay estimation [11], were investigated. To avoid channel estimation, a differentially coherent delay-lock loop was proposed in [12] but only the case of AWGN channel was considered.…”

Multipath Mitigation Techniques for Satellite-Based Positioning Applications

“…The most known feedback delay estimator is the Early-Minus-Late (EML) DLL, where two correlators spaced at one chip from each other, are used in the receiver in order to form a discriminator function, whose zero crossings determine the path delays of the received signal Baltersee et al (2001); Bischoff et al (2002);Chen & Davisson (1994); Fine & Wilson (1999);Fock et al (2001);Laxton (1996);Lohan (2003). The classical EML usually fails to cope with multipath propagation Dierendonck et al (1992).…”

“…Baltersee, J., Fock, G. & Schulz-Rittich, P. (2001). Adaptive code-tracking receiver for direct-sequence Code Division Multiple Access (CDMA) communications over…”

Advanced Multipath Mitigation Techniques for Satellite-Based Positioning Applications

“…The classical correlation-based code tracking structure used in GNSS is based on a feedback delay estimator and is implemented via a feedback loop. The most known feedback-delay estimator is the Delay Lock Loop (DLL) or Early-Minus-Late (EML) loop, where two correlators spaced at one chip from each other are used in the receiver in order to form a discriminator function, whose zero crossings determine the path delays of the received signal [2][3][4][5][6][7]. The classical EML fails to cope with multipath propagation [1].…”