Récepteurs SIMO MLSE Widely Linear
Structures et performances en présence d’interférences non circulaires
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This paper derives the maximum likelihood sequence estimation (MLSE) single input multiple output (SIMO) receiver for the demodulation of a quadrature amplitude modulated (QAM) signal of interest (SOI) corrupted by inter-symbol interference (ISI) and total noise composed of co-channel (CCI) interference and background noise. The receiver is derived under the assumption of a zero-mean, potentially noncircular, stationary, temporally and spatially colored Gaussian total noise. It is proved that this receiver is composed of a widely linear filter followed by a sampling operation at the symbol rate and a ML decision box implementing a modified version of the Viterbi algorithm. This WL filter is interpreted as a spatio-temporal matched filter (STMF) which maximizes the signal to interference plus noise ratio (SINR) on the current symbol. The case of quasi rectilinear modulation is also considered, where the MLSE receiver is proved to have a similar structure provided post rotation processing. Despite the fact that in practice, CCI are cyclostationary and non Gaussian, it is shown that the proposed receiver outperforms the conventional ones for cyclostationary and noncircular CCI.
RÉSUMÉ
Cet article présente le récepteur mono entrée multiples sorties (SIMO) optimal au sens du maximum de vraisemblance de séquence pour la détection de modulation d’amplitude en quadrature en présence à la fois d’interférences inter symboles (ISI) et d’un bruit total composé d’interférences co-canal (CCI) et d’un bruit de fond. Ce récepteur est développé sous l’hypothèse d’un bruit total centré gaussien, potentiellement non circulaire, stationnaire et coloré. Il est démontré que ce récepteur est composé d’un filtre widely linear (WL) suivi d’un échantillonnage au rythme symbole et d’une version modifiée de l’algorithme de Viterbi. Ce filtre WL est interprété comme un filtre spatio-temporel adapté (WL STMF) qui maximise le rapport signal à interférence plus bruit (SINR) sur le symbole courant. Le cas des modulations linéaires quasi rectilignes est aussi considéré dans ce cadre, où nous démontrons que le ré-cepteur SIMO MLSE a la même structure moyennant un post-traitement de rotation. En dépit du fait qu’en pratique l’interférence co-canal soit cyclostationnaire et non gaussienne, il est démontré et illustré que le récepteur proposé a de meilleures performances que le récepteur conventionnel en présence d’interférence co-canal circulaire aussi bien stationnaire que cyclostationnaire.
Single Input Multiple Output (SIMO), Maximum Likelihood Sequence Estimation (MLSE), rectilinear modulation, quasi rectilinear modulation, Gaussian Minimum Shift Keying (GMSK), noncircular interference
MOTS-CLÉS
SIMO, MLSE, modulation rectiligne, modulation quasi rectiligne, GMSK, interfé-rences non circulaires
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