Adaptive and reliably acknowledged FSO communications

Michael P. Fitz; Thomas R. Halford; Cenk Kose; Jonathan Cromwell; Steven Gordon

doi:10.1117/12.2182617

19 May 2015 Adaptive and reliably acknowledged FSO communications

Michael P. Fitz, Thomas R. Halford, Cenk Kose, Jonathan Cromwell, Steven Gordon

Proceedings Volume 9465, Laser Radar Technology and Applications XX; and Atmospheric Propagation XII; 94650Z (2015) https://doi.org/10.1117/12.2182617
Event: SPIE Defense + Security, 2015, Baltimore, MD, United States

Abstract

Atmospheric turbulence causes the receive signal intensity on free space optical (FSO) communication links to vary over time. Scintillation fades can stymie connectivity for milliseconds at a time. To approach the information-theoretic limits of communication in such time-varying channels, it necessary to either code across extremely long blocks of data – thereby inducing unacceptable delays – or to vary the code rate according to the instantaneous channel conditions. We describe the design, laboratory testing, and over-the-air testing of an FSO modem that employs a protocol with adaptive coded modulation (ACM) and hybrid automatic repeat request. For links with fixed throughput, this protocol provides a 10dB reduction in the required received signal-to-noise ratio (SNR); for links with fixed range, this protocol provides the greater than a 3x increase in throughput. Independent U.S. Government tests demonstrate that our protocol effectively adapts the code rate to match the instantaneous channel conditions. The modem is able to provide throughputs in excess of 850 Mbps on links with ranges greater than 15 kilometers.

Citation Download Citation

Michael P. Fitz, Thomas R. Halford, Cenk Kose, Jonathan Cromwell, and Steven Gordon "Adaptive and reliably acknowledged FSO communications", Proc. SPIE 9465, Laser Radar Technology and Applications XX; and Atmospheric Propagation XII, 94650Z (19 May 2015); https://doi.org/10.1117/12.2182617

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