Performance Bounds for Free-Space Optical MIMO Systems with APD Receivers in Atmospheric Turbulence

  • Authors:
  • N. Cvijetic;S. G. Wilson;M. Brandt-Pearce

  • Affiliations:
  • Univ. of Virginia, Charlottesville;-;-

  • Venue:
  • IEEE Journal on Selected Areas in Communications - Part 2
  • Year:
  • 2008

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Abstract

Performance bounds of free space optical (FSO) systems with multiple laser transmitters and multiple avalanche photodetectors (APDs) are evaluated for terrestrial, line-of- sight communication. Specifically, analytical upper bounds on average uncoded error rate in turbulent multiple-input multiple- output (MIMO) channels with Q-ary pulse position modulation (PPM) are derived for arbitrary observable densities, and are used to quantify APD-based performance improvements over pin detector arrays in non-fading, lognormal, and negative exponential channels. Moreover, it is shown that despite the high complexity of APD array statistics, these performance gains can be accurately predicted using a jointly-Gaussian model for APD array outputs. Both maximum likelihood (ML) and sub-optimal combining rules are derived, and a simple equal gain combiner (EGC) that performs close to optimum is demonstrated. Finally, APD gain selection is discussed.