Institute for Systems Research Technical Reports

Permanent URI for this collectionhttp://hdl.handle.net/1903/4376

This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.

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Author: search.filters.author.Al-Semari, Saud A.Subject: search.filters.subject.robust information processing

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    I-Q TCM: Reliable Communication Over the Rayleigh Fading Channel Close to the Cutoff Rate
    (1996) Al-Semari, Saud A.; Fuja, Tom E.; ISR
    This paper presents some trellis codes that provide high coding gain over the frequency non-selective slowly Raleigh distributed fading channel. It is shown that the use of two encoders in parallel - used to specify the in-phase and quadrature components of the transmitted signal - results in greater minimum time diversity than the conventional design in which a single encoder is used. Using this approach - which we label ﲉ-Q TCM - codes with bandwidth efficiencies of 1,2, and 3 bits/sec/Hz are described for various constraint lengths. The performance of these codes is bounded analytically and approximated via simulation; the results show a large improvement in the BER when compared with conventional TCM schemes when perfect channel state information (CSI) is available to the receiver. Indeed, when this approach is applied to channels with independent Rayleigh fading, the resulting coding gain is close to that implied by the cutoff rate limit, even for only moderately complex systems.

    The proposed codes are also simulated under less ideal assumptions. For instance, results for a 1 bit/sec/Hz IQ-TCM code without CSI show a significant gain over conventional coding. Finally, simulations over channels with correlated fading were undertaken; it is concluded that an interleaver span of 4v yields performance close to what is achieved with ideal interleaving.

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    Performance Analysis of Coherent TCM Systems with Diversity Reception in Slow Rayleigh Fading
    (1996) Al-Semari, Saud A.; Fuja, Tom E.; ISR
    Coherent trellis coded modulation (TCM) systems employing diversity combining are analyzed. Three different kinds of combining are considered: maximal ratio, equal gain, and selection combining. For each combining scheme, the cutoff rate parameter is derived assuming transmission over a fully- interleaved channel with flat, slow, Rayleigh fading; in addition, tight upper bounds on the pairwise error probabilities are derived. These upper bounds are expressed in product form to permit bounding of the BER via the transfer function approach. In each case it is assumed that the diversity branches are independent and that the channel state information (CSI) can be recovered perfectly.

    Also included is an analysis of maximal ratio combining when the diversity branches are correlated; the cutoff rate and a tight upper bound on the pairwise error probability are derived. It is shown that, with double diversity, a branch correlation coefficient as high as 0.5 results in only slight performance degradation.