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Atmosphere Laser Communication (ALC) has the great capability, the better quality of anti-jamming and security, so
ALC is adapt to the military application in particular. But because ALC's channel is atmosphere, ALC will be influenced
by Atmospheric fading and turbulence, which reduce communication reliability. As a result, studying the suitable
modulation and coding becomes the important problems for ALC.
From these, people has put forward plenty of modulation and coding technologies, including On-off keying (OOK),
pulse position modulation (PPM), digital pulse interval modulation (DPIM), dual-header pulse interval modulation(DHPIM)
and so on. Among these, the mean transmit power and error symbol rate of PPM are all less than the others, so
PPM has some applied advantage. People has also studied channel coding technology for PPM in ALC, George Stephen
Mecherle applied RS code to PPM and analyzed error bit performance in 1986, Jon Hamkins and Meera Srinivasan
analyzed the error bit rate of applying Turbo code to PPM through APD detecting in 1998, J. Hamkins analyzed the error
bit performance of 256-ray PPM for Turbo code in 1999, and HU Hongfei analyzed the combined mode and applying
approach of binary LDPC and multi-system PPM. But all of these have not involved the influence of atmosphere weak
turbulence.
The paper introduces LDPC as the channel code to ALC, and combines with PPM, discusses the error performance of
LDPC in weak turbulence, then compares the performance in weak turbulence, Gauss channel and uncoded system. The
emulation results indicate that the LDPC-coded performance of Gauss channel is better than that in weak turbulence
channel, and introducing LDPC can efficiently improve the error performance in Gauss channel and weak turbulence
channel, which has some applied value.
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