Abstract
Atmospheric turbulence and pointing errors cause intensity fluctuation of free space optical
communication signals and impair link performance. Several receiver structures which could mitigate the signal
fluctuations were proposed in the past, but these existing receivers depend highly on the channel model and the model
parameters. The performance deteriorates if the channel model or the model parameters are inaccurate. In this paper,
we develop a Viterbi-type trellis-search sequence receiver based on the generalized likelihood ratio test principle
that jointly detects the data sequence and estimates the unknown channel gain. This receiver requires very few pilot
symbols, and therefore, does not significantly reduce the bandwidth efficiency. It is robust in that it continuously
performs maximum likelihood (ML) estimation of the unknown channel gain without the knowledge of the channel model,
and adapts the decision metric accordingly. It works well in a slowly time-varying environment and its error
performance approaches that of ML detection with perfect knowledge of the channel gain, as the memory length used for
forming the sequence detection metric increases. A new, decision-feedback, symbol-by-symbol receiver with lower
implementation complexity and higher memory efficiency is obtained as an approximation to the sequence receiver. The
performance improvement and implementation simplicity of our receivers compared to existing receivers are pointed out.
© 2013 IEEE
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