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User Signals (user + signal)

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Selected Abstracts

Sequential detection CDMA multi-user receiver

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2005
Mitsuhiro Tomita
Abstract This paper proposes a sequential detection technique for a multi-user receiver that is constructed over a CDMA system. In this system, the transmitter transmits a symbol made by spreading the spectrum with an enveloped sequence protected by guard sequences, and a receiver de-modulates the core-sequence part of the received symbol with either a de-correlating detector or an MMSE detector. The advantage is that performance is improved without reducing the number of the active users. This sequential detection system estimates the best user signal from all of the soft outputs, which are obtained by solving a de-correlating system of equations. Once detected, the best user component is removed from the received symbol. The resultant symbol composed of the remaining user signals is then sequentially detected by repeating the method stated above. A computer simulation of this system reveals a remarkable improvement in the bit-error rate performance compared to conventional systems. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Adaptive group detection for DS/CDMA systems over frequency-selective fading channels,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2003
Stefano Buzzi
In this paper we consider the problem of group detection for asynchronous Direct-Sequence Code Division Multiple Access (DS/CDMA) systems operating over frequency-selective fading channels. A two-stage near-far resistant detection structure is proposed. The first stage is a linear filter, aimed at suppressing the effect of the unwanted user signals, while the second stage is a non-linear block, implementing a maximum likelihood detection rule on the set of desired user signals. As to the linear stage, we consider both the Zero-Forcing (ZF) and the Minimum Mean Square Error (MMSE) approaches; in particular, based on the amount of prior knowledge on the interference parameters which is available to the receiver and on the affordable computational complexity, we come up with several receiving structures, which trade system performance for complexity and needed channel state information. We also present adaptive implementations of these receivers, wherein only the parameters from the users to be decoded are assumed to be known. The case that the channel fading coefficients of the users to be decoded are not known a priori is also considered. In particular, based on the transmission of pilot signals, we adopt a least-squares criterion in order to obtain estimates of these coefficients. The result is thus a fully adaptive structure, which can be implemented with no prior information on the interfering signals and on the channel state. As to the performance assessment, the new receivers are shown to be near-far resistant, and simulation results confirm their superiority with respect to previously derived detection structures. Copyright © 2003 AEI. [source]

Sequential detection CDMA multi-user receiver

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2005
Mitsuhiro Tomita
Abstract This paper proposes a sequential detection technique for a multi-user receiver that is constructed over a CDMA system. In this system, the transmitter transmits a symbol made by spreading the spectrum with an enveloped sequence protected by guard sequences, and a receiver de-modulates the core-sequence part of the received symbol with either a de-correlating detector or an MMSE detector. The advantage is that performance is improved without reducing the number of the active users. This sequential detection system estimates the best user signal from all of the soft outputs, which are obtained by solving a de-correlating system of equations. Once detected, the best user component is removed from the received symbol. The resultant symbol composed of the remaining user signals is then sequentially detected by repeating the method stated above. A computer simulation of this system reveals a remarkable improvement in the bit-error rate performance compared to conventional systems. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Blind MIMO equalization with optimum delay using independent component analysis

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 3 2004
Vicente Zarzoso
Abstract Blind space,time equalization of multiuser time-dispersive digital communication channels consists of recovering the users' simultaneously transmitted data free from the interference caused by each other and the propagation effects, without using training sequences. In scenarios composed of mutually independent non-Gaussian i.i.d. users' signals, independent component analysis (ICA) techniques based on higher-order statistics can be employed to refine the performance of conventional linear detectors, as recently shown in a code division multiple access environment (Signal Process 2002; 82:417,431). This paper extends these results to the more general multi-input multi-output (MIMO) channel model, with the minimum mean square error (MMSE) as conventional equalization criterion. The time diversity introduced by the wideband multipath channel enables a reduction of the computational complexity of the ICA post-processing stage while further improving performance. In addition, the ICA-based detector can be tuned to extract each user's signal at the delay which provides the best MMSE. Experiments in a variety of simulation conditions demonstrate the benefits of ICA-assisted MIMO equalization. Copyright © 2004 John Wiley & Sons, Ltd. [source]