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Multipath Channels (multipath + channel)

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Engineering100%

Selected Abstracts

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]

A novel approach to enable decorrelating multiuser detection without matrix inversion operations

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2004
Hsiao-Hwa Chen
Abstract This paper proposes a non-matrix inversion based algorithm to implement decorrelating detection (DD), namely quasi-decorrelating detector (QDD), which uses truncated matrix series expansion to overcome the problems associated with the matrix inversion in DD, such as noise enhancement, computational complexity and matrix singularity, etc. Two alternative QDD implementation schemes are presented in this paper; one is to use multi-stage feedforward filters and the other is to use an nth order single matrix filter (neither of which involves matrix inversion). In addition to significantly reduced computational complexity if compared with DD, the QDD algorithm offers a unique flexibility to trade among MAI suppression, near-far resistance and noise enhancement depending on varying system set-ups. The obtained results show that the QDD outperforms DD in either AWGN or multipath channel if a proper number of feed-forward stages can be used. We will also study the impact of correlation statistics of spreading codes on the QDD's performance with the help of a performance-determining factor derived in the paper, which offers a code-selection guideline for the optimal performance of QDD algorithm. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Study of the passive microwave RFID tag range using distance-dependent reflection coefficient over multipath channel

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2009
Fu Wei
Abstract The distance-dependent reflection coefficients are investigated based on a multi-ray model at microwave frequency bands. Tag range of passive microwave radio-frequency identification (RFID) systems is then calculated taking into account the tagged object material characteristic. Obtained values are verified through the precise simulations based on a 3-D physical finite element model. The results shown that the proposed method provides a good agreement than that obtained by existing methods. The analytical method can be used for the empirical tag range value to avoid reader collision while ensuring system reliability. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2266,2268, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24602 [source]

Load-Adaptive MUI/ISI-Resilient Generalized Multi-Carrier CDMA with Linear and DF Receivers

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2000
Georgios B. Giannakis
A plethora of single-carrier and multi-carrier (MC) CDMA systems have been proposed recently to mitigate intersymbol interference (ISI) and eliminate multiuser interference (MUI). We present a unifying all-digital Generalized Multicanier CDMA framework which enables us to describe existing CDMA schemes and to highlight thorny problems associated with them. To improve the bit error rate (BER) performance of existing schemes, we design block FIR transmitters and decision feedback (DF) receivers based on an inner-code/outer-code principle, which guarantees MUI/ISI-elimination regardless of the frequency-selective physical channel. The flexibility of our framework allows further BER enhancements by taking into account the load in the system (number of active users), while blind channel estimation results in bandwidth savings. Simulations illustrate the superiority of our framework over competing MC CDMA alternatives especially in the presence of uplink multipath channels. [source]

Performance of robust symbol-timing and carrier-frequency estimation for OFDM systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2009
Nan-Yang YenArticle first published online: 7 NOV 200
Abstract In recent years, many maximum likelihood (ML) blind estimators have been proposed to estimate timing and frequency offsets for orthogonal frequency division multiplexing (OFDM) systems. However, the previously proposed ML blind estimators utilizing cyclic prefix do not fully characterize the random observation vector over the entire range of the timing offset and will significantly degrade the estimation performance. In this paper, we present a global ML blind estimator to compensate the estimation error. Moreover, we extend the global ML blind estimator by accumulating the ML function of the estimation parameters to achieve a better accuracy without increasing the hardware or computational complexity. The simulation results show that the proposed algorithm can significantly improve the estimation performance in both additional white Gaussian noise and ITU-R M.1225 multipath channels. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Performance of multilevel-turbo codes with blind/non-blind equalization over WSSUS multipath channels

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2006
Osman N. Ucan
Abstract In this paper, in order to improve error performance, we introduce a new type of turbo codes, called ,multilevel-turbo codes (ML-TC)' and we evaluate their performance over wide-sense stationary uncorrelated scattering (WSSUS) multipath channels. The basic idea of ML-TC scheme is to partition a signal set into several levels and to encode each level separately by a proper component of the turbo encoder. In the considered structure, the parallel input data sequences are encoded by our multilevel scheme and mapped to any modulation type such as MPSK, MQAM, etc. Since WSSUS channels are very severe fading environments, it is needed to pass the received noisy signals through non-blind or blind equalizers before turbo decoders. In ML-TC schemes, noisy WSSUS corrupted signal sequence is first processed in equalizer block, then fed into the first level of turbo decoder and the first sequence is estimated from this first Turbo decoder. Subsequently, the other following input sequences of the frame are computed by using the estimated input bit streams of previous levels. Here, as a ML-TC example, 4PSK 2 level-turbo codes (2L-TC) is chosen and its error performance is evaluated in WSSUS channel modelled by COST 207 (Cooperation in the field of Science & Technology, Project #207). It is shown that 2L-TC signals with equalizer blocks exhibit considerable performance gains even at lower SNR values compared to 8PSK-turbo trellis coded modulation (TTCM). The simulation results of the proposed scheme have up to 5.5 dB coding gain compared to 8PSK-TTCM for all cases. It is interesting that after a constant SNR value, 2L-TC with blind equalizer has better error performance than non-blind filtered schemes. We conclude that our proposed scheme has promising results compared to classical schemes for all SNR values in WSSUS channels. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Dual diversity combining and decision feedback equalizer in indoor millimetre-wave channel

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2002
Chien-Ching Chiu
Abstract Wideband communication characteristics of wireless indoor millimetre-wave channel for arched and rectangular buildings are investigated. The impulse responses of arched and rectangular buildings for any transmitter,receiver location are computed by shooting and bouncing ray/image (SBR/Image) techniques. By using the impulse responses of these multipath channels, the impact of shapes of building is presented and the bit error rate performance of binary phase shift keying (BPSK) system with phase and timing recovery circuits are also calculated. Moreover, dual space antenna diversity technique and decision feedback equalizer (DFE) with four forward and three feedback taps are used to combat the multipath fading. Numerical results show that the mean root mean square (rms) delay spread for the arched building is smaller than that for the rectangular building. In addition, it is also found that the transmission rate can be up to 20 Mbps for indoor millimetre-wave channel of these two buildings by using dual space diversity and DFE. Copyright © 2002 John Wiley & Sons, Ltd. [source]