Iterative near maximum-likelihood sequence detection for MIMO optical wireless systems

Nestor D. Chatzidiamantis, Murat Uysal, T. A. Tsiftsis, G. K. Karagiannidis

Research output: Contribution to journalArticlepeer-review


A major performance-limiting factor in terrestrial optical wireless (OW) systems is turbulence-induced fading. Exploiting the additional degrees of freedom in the spatial dimension, multiple laser transmitters combined with multiple receive apertures provide an effective solution for fading mitigation. Although multiple-input multiple-output (MIMO) OWsystems have been extensively studied in recent years, most of these works are mainly limited to symbol-by-symbol decoding. MLSD exploits the temporal correlation of turbulence-induced fading and promises further performance gains. In this paper, we investigate MLSD for intensity-modulation/direct-detection MIMO OW systems over log-normal atmospheric turbulence channels. Even with a low-order modulation scheme such as OOK, which is typically used inOWsystems, the complexity ofMLSD might be prohibitive. e therefore present an iterative sequence detector based on the expectation-maximization (EM) algorithm. The complexity of the proposed algorithm is considerably less than a direct evaluation of the log-likelihood function, and it is independent of the channel'a fading statistics. The Monte Carlo simulation results demonstrate that the EM-based algorithm outperforms the symbol-by-symbol decoder and achieves a performance, which lies within 0.3 dB of that of the optimal MLSD.

Original languageEnglish (US)
Pages (from-to)1064-1070
Number of pages7
JournalJournal of Lightwave Technology
Issue number7
StatePublished - 2010


  • Atmospheric turbulence
  • Expectation maximization (EM) algorithm
  • Free-space optical communication
  • MLSD
  • Maximum-likelihood (ML) symbol-by-symbol detection
  • Spatial diversity

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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