Multiple-symbol detection for photon-counting MIMO free-space optical communications

TitleMultiple-symbol detection for photon-counting MIMO free-space optical communications
Publication TypeJournal Article
Year of Publication2008
AuthorsRiediger, M. L. B., R. Schober, and L. Lampe
JournalWireless Communications, IEEE Transactions on
Pagination5369 -5379
Date Publisheddec.
Keywordsamplitude shift keying, atmospheric turbulence, automatic repeat request, bit-decision basis, closed-form decision metric, decision-feedback receiver, diversity gains, equal gain combined statistics, error-free feedback, fast search algorithm, free-space optical communications, MIMO communication, MIMO communications, modulation coding, modulation format, multiple-symbol detection, on-off keying, optical modulation, optical receivers, optical transmitters, photon counting, photon-counting signal model, reduced-complexity implementation, repetition coding, signal detection, suboptimal metrics, symbol-by-symbol detection, transmitters

We employ a photon-counting signal model of a multiple-input multiple-output (MIMO) free-space optical (FSO) system and investigate detection assuming the absence of channel state information (CSI) at the receiver, in moderate to strong atmospheric turbulence. The considered modulation format is on-off keying with repetition coding across the transmitters. To partially recover the performance loss associated with symbol-by-symbol detection without CSI, we consider the application of multiple-symbol detection (MSD) to equal gain combined (EGC) statistics. We develop a fast search algorithm for EGC-MSD and propose a suboptimal closed-form decision metric suitable for reduced-complexity implementation; performance results confirm that the true and suboptimal metrics perform comparably well. Significantly, the complexity of our receiver, on a per bit-decision basis, is only logarithmically dependent on the observation window length N, and is effectively independent of the size of the MIMO array. We also present the framework for a decision-feedback receiver and obtain performance expressions for the ideal case of error-free feedback; these expressions serve as an upper bound to the performance of EGC-MSD. Analytical and simulation results indicate that the system effectively realizes the diversity gains expected from a MIMO configuration and that the performance of the EGC-MSD receiver approaches the EGC with CSI lower bound with increasing N.


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