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Tracking of timevarying mobile radio channels. Part II: A case study
 IEEE Trans. Commun.(to be published) [Online]. Available: www.signal.uu.se/Publications/abstracts/r004.html
, 2001
"... Abstract—Adaptation algorithms with constant gains are designed for tracking smoothly timevarying parameters of linear regression models, in particular channel models occurring in mobile radio communications. In a companion paper, an application to channel tracking in the IS136 TDMA system is disc ..."
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Cited by 35 (8 self)
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Abstract—Adaptation algorithms with constant gains are designed for tracking smoothly timevarying parameters of linear regression models, in particular channel models occurring in mobile radio communications. In a companion paper, an application to channel tracking in the IS136 TDMA system is discussed. The proposed algorithms are based on two key concepts. First, the design is transformed into a Wiener filtering problem. Second, the parameters are modeled as correlated ARIMA processes with known dynamics. This leads to a new framework for systematic and optimal design of simple adaptation laws based on prior information. The algorithms can be realized as Wiener filters, called Learning Filters, or as “LMS/Newton ” updates complemented by filters that provide predictions or smoothing estimates. The simplest algorithm, named the Wiener LMS, is presented here. All parameters are here assumed governed by the same dynamics and the covariance matrix of the regressors is assumed known. The computational complexity is of the same order of magnitude as that of LMS for regressors which are either white or have autoregressive statistics. The tracking performance is, however, substantially improved. Index Terms—Adaptive estimation, channel modeling, least mean squares method. I.
Adaptive ChipRate Equalization of Downlink Multirate Wideband CDMA
 Proc. Asilomar Conf. on Signals, Systems and Computers
, 2002
"... Abstract—We consider a downlink direct sequencecode division multiple access (DSCDMA) system in which multirate user signals are transmitted via synchronous orthogonal short codes overlaid with a common scrambling sequence. The transmitted signal is subjected to significant time and frequencysel ..."
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Cited by 13 (3 self)
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Abstract—We consider a downlink direct sequencecode division multiple access (DSCDMA) system in which multirate user signals are transmitted via synchronous orthogonal short codes overlaid with a common scrambling sequence. The transmitted signal is subjected to significant time and frequencyselective multipath fading. In response to this scenario, a novel twomode receiver is proposed that accomplishes chiprate adaptive equalization aided by filtering and/or cancellation of multiaccess interference (MAI). In the acquisition mode, a codemultiplexed pilot is used to adapt the equalizer from cold start or lossoflock. The use of MAI filtering results in a thirdorder least mean squares (LMS) algorithm, which has significant advantages over standard (i.e., firstorder) LMS in nonstationary environments. In the tracking mode, decisiondirection facilitates MAIcancellation in the equalizer update, which enhances performance. The receiver monitors pilot decision quality as a means of switching between the two modes. The performance of the adaptive receiver is studied through analysis and simulation. Index Terms—Adaptive equalization, averagederror averagedregressor LMS (AEARLMS), code division multiple access
SpaceTime Coding Ambiguities in Joint Adaptive Channel Estimation and Detection
 IEEE Trans. Signal Processing
, 2004
"... This paper studies the error propagation effect that is caused by certain ambiguities in joint data detectionchannel tracking algorithms for transmission diversity schemes. Here, we use a SpaceTime (ST) receiver based on the Maximum A Posteriori (MAP) method that takes into account the channel ..."
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Cited by 2 (0 self)
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This paper studies the error propagation effect that is caused by certain ambiguities in joint data detectionchannel tracking algorithms for transmission diversity schemes. Here, we use a SpaceTime (ST) receiver based on the Maximum A Posteriori (MAP) method that takes into account the channel estimation error assuming the unknown channel to have a given complex multivariate Gaussian probability density function (pdf) (i.e., a Ricean channel). The decision criterion that is expressed in quadratic form represents either a linear detector or a noncoherentnonlinear detector in extreme cases. Then, the channel pdf for the next iteration is updated by estimates of the second order statistics of the channel coefficients, and a very simple decisiondirected adaptive algorithm is derived for adaptive channel estimation. The adaptive algorithm can efficiently track a fast Rayleigh fading channel and as a result achieves robust performance. However, the occurrence of two types of ambiguities initiated in deep fades result in error propagation.
Wideband CDMA By
, 2002
"... We consider a downlink DSCDMA system in which multirate user signals are transmitted via synchronous orthogonal short codes overlaid with a common scrambling sequence. The transmitted signal is subjected to significant time and frequencyselective multipath fading, e.g., a channel with delay spre ..."
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We consider a downlink DSCDMA system in which multirate user signals are transmitted via synchronous orthogonal short codes overlaid with a common scrambling sequence. The transmitted signal is subjected to significant time and frequencyselective multipath fading, e.g., a channel with delay spread potentially longer than the bit interval of highrate users. In response to this scenario, a novel twostep receiver is proposed that combines chiprate adaptive equalization with error filtering. In the first step, a codemultiplexed pilot is used to adapt the equalizer. Singlepole averaging of the chiprate error signal used in adaptation reduces MAI and implies thirdorder LMS, which has advantages over standard LMS in tracking the timevarying channel. In the second step, decisiondirection is used to improve the error signal, resulting in improved tracking performance. The performance of the adaptive receiver is studied through analysis and simulation. ii
Adaptive ChipRate Equalization of Downlink Multirate Wideband CDMA
"... We consider a downlink DSCDMA system in which multirate user signals are transmitted via synchronous orthogonal short codes overlaid with a common scrambling sequence. The transmitted signal is subjected to significant time and frequencyselective multipath fading. In response to this scenario, a ..."
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We consider a downlink DSCDMA system in which multirate user signals are transmitted via synchronous orthogonal short codes overlaid with a common scrambling sequence. The transmitted signal is subjected to significant time and frequencyselective multipath fading. In response to this scenario, a novel twostep receiver is proposed that combines chiprate adaptive equalization with error filtering. In the first step, a codemultiplexed pilot is used to adapt the equalizer. The use of error filtering implies a thirdorder LMS algorithm which has significant advantages over standard LMS in tracking the timevarying channel. In the second step, decisiondirection is used to improve the error signal used in adaptation, resulting in improved tracking performance. The performance of the adaptive receiver is studied through analysis and simulation. 1
ChipRate Adaptive TwoStage Receiver for Scrambled Multirate CDMA Downlink i
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"... Abstract—The least mean square (LMS) algorithm is one of the most wellknown algorithms for mobile communication systems due to its implementation simplicity. However, the main limitation is its relatively slow convergence rate. In this paper, a booster using the concept of Markov chains is proposed ..."
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Abstract—The least mean square (LMS) algorithm is one of the most wellknown algorithms for mobile communication systems due to its implementation simplicity. However, the main limitation is its relatively slow convergence rate. In this paper, a booster using the concept of Markov chains is proposed to speed up the convergence rate of LMS algorithms. The nature of Markov chains makes it possible to exploit the past information in the updating process. Moreover, since the transition matrix has a smaller variance than that of the weight itself by the central limit theorem, the weight transition matrix converges faster than the weight itself. Accordingly, the proposed Markovchain based booster thus has the ability to track variations in signal characteristics, and meanwhile, it can accelerate the rate of convergence for LMS algorithms. Simulation results show that the LMS algorithm can effectively increase the convergence rate and meantime further approach the Wiener solution, if the Markovchain based booster is applied. The mean square error is also remarkably reduced, while the convergence rate is improved. Keywords—LMS, Markov chain, convergence rate, accelerator. I.