Abstract
Multiple-input multiple-output (MIMO) and multiple-input single-output (MISO) schemes have yielded promising results in free space optical (FSO) communications by providing diversity against fading of the received signal intensity. In this article, we have analyzed the probability of error performance of a muliple-input single-output (MISO) free-space optical channel that employs array(s) of detectors at the receiver. In this regard, we have considered the maximal ratio combiner (MRC) and equal gain combiner (EGC) fusion algorithms for the array of detectors, and we have examined the performance of these algorithms subject to phase and pointing errors for strong atmospheric turbulence conditions. It is concluded that when the variance of the phase and pointing errors are below certain thresholds, signal combining with a single array of detectors yields significantly better performance than a multiple arrays receiver. In the final part of the paper, we examine the probability of error of the single detector array receiver as a function of the beam radius, and the probability of error is minimized by (numerically) optimizing the beam radius of the received signal beams.
Highlights
The availability of large chunks of unlicensed spectrum in the optical domain makes free-space optical (FSO) communications an attractive solution for transmitting high data-rates for the generation of wireless communication systems
An avalanche photodiode (APD) array is commonly used in satellites that acts as a photon counter when operated in the Geiger mode [1]–[5]
There is a need to study the free-space optical multiple-input singleoutput (MISO) channel in terms of the phase and pointing errors corresponding to different beams when such beams are combined on a single aperture
Summary
In most research studies conducted on noncoherent multipleinput multiple-output (MIMO) and multiple-input singleoutput (MISO) FSO systems, the sufficient statistic is formed by first weighting the data with the channel coefficients, and adding the resulting weighted data. The authors in [17] have derived the outage probability expressions for the MIMO FSO system when the FSO links suffer from strong turbulence and pointing errors. The authors in [18] investigated the dual-hop relaying channel over mixed RF/FSO links which is modeled as η-μ/ΓΓ and κ-μ/ΓΓ channels In this work, they derived the cumulative distribution function and the probability density function of the end-to-end SNR in terms of Meijer’s G-function. The authors in [11] have proposed a modified Alamouti coding scheme for intensity modulated direct detection FSO channels They have concluded that their proposed scheme produces a diversity of order two for a channel corresponding to two transmitters and one receiver, and the two transmitted symbols can be detected independently of each other. For a discussion on pointing error with a single detector receiver in free-space optical communications, the interested readers may refer to [21]–[24]
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