On the design of uplink and downlink group-orthogonal multicarrier wireless systems

Dept. of Math. & Inf., Univ. of the Balearic Islands (UIB), Palma de Mallorca
IEEE Transactions on Communications (Impact Factor: 1.98). 11/2008; DOI: 10.1109/TCOMM.2008.060497
Source: IEEE Xplore

ABSTRACT Group-orthogonal multicarrier code-division multiple access (GO-MC-CDMA) has been proposed as an attractive multiplexing technique for the uplink segment of wireless systems. More recently, a variant of this scheme has also been proposed for the downlink. This paper presents a unified bit error rate (BER) performance analysis of group-orthogonal wireless systems when using maximum likelihood (ML) multiuser/multisymbol detection covering both link directions. Valuable design rules regarding the number of subcarriers per group and the selection of spreading codes are derived. Simulations results using realistic system parameters and ETSI BRAN channel models are also presented which serve to validate the analytical results.

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    EURASIP Journal on Wireless Communications and Networking 2012(1). · 0.81 Impact Factor
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    ABSTRACT: Optimum detection based on maximum likelihood (ML) has been recently explored within the context of linearly precoded subcarrier cooperative MIMO-OFDM systems, showing that large performance gains can be obtained in comparison to an all-linear setup (i.e., linear transmitter/receiver) at the cost of increased computational complexity. Nonetheless, low complexity alternatives, yet retaining optimality, have been also proposed. Most of these previous works have assumed the availability of perfect channel state information at the transmitter (CSIT) despite this is rarely the case since feedback delay and/or quantisation effects will usually render imperfect CSIT. This paper studies how these imperfections affect the performance of the ML-based receiver. Particularly, it focuses on fully loaded setups, that is, those configurations where the number of independent streams transmitted equals the number of available spatial modes. Remarkably, for these configurations, an interesting interplay arises between the presence of CSIT imperfections, the spreading of the information symbols in the frequency and spatial domains and the diversity order achieved.
    Information Sciences and Systems (CISS), 2012 46th Annual Conference on; 01/2012
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    ABSTRACT: This paper proposes a novel receiver structure based on soft information for linearly precoded MIMO-OFDM systems. The architecture combines an MMSE-based front end with an iterative technique based on maximum likelihood detection (MLD) in a structure that exhibits two very attractive features. Firstly, it can fully exploit the diversity benefits of spreading the information sym-bols in the space and frequency domains by optimally estimating them. Secondly, and under the realistic as-sumption of the presence of a cyclic redundancy check (CRC) mechanism, the far more computationally de-manding MLD component needs only be used when the MMSE front end has failed. Simulation results reveal that the MLD iterative mechanism adds only a negligi-ble amount of computations to the simple MMSE detec-tor while significantly improving its performance.

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