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Online ISSN 1751-9683 Print ISSN 1751-9675

IET Signal Processing

Volume 3, Issue 6, November 2009

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Volume 3, Issue 6

November 2009

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  • Advanced signal processing for wireless and mobile communications

    • Editorial: Advanced signal processing for wireless and mobile communications
      Accelerated sphere decoding for multiple-input multiple-output systems using an adaptive statistical threshold
      • Author(s): X. Wu  and  J.S. Thompson
      • Source: IET Signal Processing, Volume 3, Issue 6, p. 433 –444
      • DOI:  10.1049/iet-spr.2009.0028
      • Type: Article
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      • p. 433 –444 (12)
        The authors present a complexity reduced near-maximum-likelihood (ML) scheme for the decoding of multiple-input multiple-output (MIMO) systems, which is targeted at a recently proposed fixed-complexity sphere decoder (FSD). The proposed decoder that the authors call the statistical threshold-based FSD (ST-FSD) combines a threshold constraint strategy with the FSD search region, thus speeding up the FSD algorithm by avoiding unnecessary search paths. As a consequence, higher efficiency and lower complexity can be obtained. The optimum threshold is derived through analysis of the statistical distributions of the correct and erroneous estimates. Furthermore, a tight lower bound on the threshold has been obtained by using the singular value decomposition (SVD) method and applied to the FSD. From simulation results, the proposed scheme is shown to be able to achieve a significant reduction in computational complexity with almost no performance degradation compared to the original FSD algorithm. Moreover, a novel grouped architecture for efficient hardware implementation of the proposed ST-FSD algorithm is motivated through simulation results and shown to compare favourably with the alternative options. This confirms that the ST-FSD is advantageous with respect to the original FSD in terms of the overall complexity.
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      Space–time blind equalisation in impulsive noise
      • Author(s): S. Li ; T.Sh. Qiu ; Sh.F. Zhang
      • Source: IET Signal Processing, Volume 3, Issue 6, p. 445 –458
      • DOI:  10.1049/iet-spr.2009.0005
      • Type: Article
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      • p. 445 –458 (14)
        The presence of non-Gaussian impulsive noise in wireless system can degrade the performance of existing equalisers and signal detectors. The problem of blind source separation and equalisation for multiple-input/multiple-output (MIMO) channels under heavy-tailed impulsive noise environment is studied. A generalised multi-user constant modulus (CM) cost function is proposed by employing the fractional lower order CM property of the equaliser input signals as well as the fractional lower order cross-correlations between them. The associated adaptive blind equalisation algorithm based on a stochastic gradient descent method is defined as fractional lower order multi-user constant modulus algorithm (FMU_CMA), which is able to mitigate impulsive channel noise while recovering all input signals simultaneously. The steady-state mean-square error (MSE) performance of the FMU_CMA is studied in a noise-free environment; the approximate expression is derived based on the energy-preserving relation and the Taylor series expansion. Simulation studies are undertaken to support the analysis with CM and non-CM signal.
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      Channel prediction for precoded spatial multiplexing multiple-input multiple-output systems in time-varying fading channels
      • Author(s): A.S. Khrwat ; B.S. Sharif ; C.C. Tsimenidis ; S. Boussakta
      • Source: IET Signal Processing, Volume 3, Issue 6, p. 459 –466
      • DOI:  10.1049/iet-spr.2009.0019
      • Type: Article
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      • p. 459 –466 (8)
        Conventional precoded spatial multiplexing multiple-input multiple-output (MIMO) systems using limited feedback are mainly based on the notion of time invariant channels throughout transmission. Consequently, the precoding matrix can be found during the training symbols and used over the subsequent data symbols. In this study, the authors consider a more practical system where the channel varies from one block of symbols to another. In such a scenario, the precoding matrix designed at the receiver based on the previous training symbols becomes outdated, which results in significant system performance degradation. In order to avoid this problem and reduce performance degradation, the authors propose the use of a Kalman filter linear predictor at the receiver to provide the transmitter with the precoding matrix for the next block of symbols. The performance of this method is assessed using computer simulation, and the obtained results for the proposed channel prediction demonstrate improved bit error rate performance for time-varying Rayleigh fading channels.
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      Frequency-selective multiple-input multiple-output channel estimation with transmitter non-linearities
      • Author(s): M.-W. Liu  and  J.F. Doherty
      • Source: IET Signal Processing, Volume 3, Issue 6, p. 467 –475
      • DOI:  10.1049/iet-spr.2009.0021
      • Type: Article
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      • p. 467 –475 (9)
        The authors propose an algorithm based on the knowledge of training sequences to obtain an asymptotically unbiased estimator of non-linear multiple-input multiple-output (MIMO) channels, which involves the radio frequency front-end non-linearity and linear frequency selective MIMO channels. Although the impact of non-linearity in the transmitter side has been widely studied, most work on the channel estimation assumes linear channel models and ignores the non-linear effects. In this study, we develop a non-linear channel estimator that can simultaneously estimate the linear MIMO channel model and non-linearity of the transmitter is developed. With these two sets of parameters, the non-linear channel model can be fully described. This channel estimation algorithm is implemented over an empirical MIMO channel model using an orthogonal frequency division multiplexing system.
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    • Extended balanced space-time block coding for wireless communications
      • Author(s): A. Ekşim  and  M.E. Çelebi
      • Source: IET Signal Processing, Volume 3, Issue 6, p. 476 –484
      • DOI:  10.1049/iet-spr.2009.0020
      • Type: Article
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      • p. 476 –484 (9)
        Diversity techniques are very effective tools to increase signal reception quality in Rayleigh fading channels. A well-known method to increase diversity in multi-input multi-output (MIMO) communication is transmit antenna selection (TAS). However, TAS is very sensitive to feedback errors. One of the alternative techniques to TAS is balanced space-time block coding (BSTBC) which guarantees full diversity for any number of transmit antennas, provided that few bits of feedback from the destination to the source are available. The main drawback of the BSTBC is limited coding gain since few numbers of code matrices can be generated in the originally proposed scheme. In this work, the authors extend the balanced space-time block code family to improve its coding performance. In our proposed scheme, larger number of codes can be generated for improved coding gain. The performance of the proposed scheme is investigated for both multi-input single-output (MISO) and cooperative communication cases. Relay selection (RS) algorithm – the TAS equivalent in the cooperative communications – is also considered. Simulation results show that near optimal (infinite feedback) performance can be achieved with four bit extension of the BSTBC and better signal-to-noise ratio can be obtained compared to TAS or RS schemes. The difference in performance becomes more prevalent in the presence of feedback errors.
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