13 May 2016 Development and characterisation of FPGA modems using forward error correction for FSOC
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In this paper we report on the performance of a free-space optical communications (FSOC) modem implemented in FPGA, with data rate variable up to 60 Mbps. To combat the effects of atmospheric scintillation, a 7/8 rate low density parity check (LDPC) forward error correction is implemented along with custom bit and frame synchronisation and a variable length interleaver. We report on the systematic performance evaluation of an optical communications link employing the FPGA modems using a laboratory test-bed to simulate the effects of atmospheric turbulence. Log-normal fading is imposed onto the transmitted free-space beam using a custom LabVIEW program and an acoustic-optic modulator. The scintillation index, transmitted optical power and the scintillation bandwidth can all be independently varied allowing testing over a wide range of optical channel conditions. In particular, bit-error-ratio (BER) performance for different interleaver lengths is investigated as a function of the scintillation bandwidth. The laboratory results are compared to field measurements over 1.5km.
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Kerry A. Mudge, Kerry A. Mudge, Kenneth J. Grant, Kenneth J. Grant, Bradley A. Clare, Bradley A. Clare, Colin L. Biggs, Colin L. Biggs, William G. Cowley, William G. Cowley, Sean Manning, Sean Manning, Gottfried Lechner, Gottfried Lechner, "Development and characterisation of FPGA modems using forward error correction for FSOC", Proc. SPIE 9833, Atmospheric Propagation XIII, 98330G (13 May 2016); doi: 10.1117/12.2238759; https://doi.org/10.1117/12.2238759

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