Abstract
For middle/short-range terrestrial high-speed free-space optical (FSO) communication systems employing ON–OFF keying (OOK) and PIN photodiode receivers, the noise distribution is symbol-dependent, and the symmetry of the underlying communication channel cannot be assumed. Therefore, this letter employs the asymmetric density evolution technique and an optimization scheme combining four different search algorithms to optimize low-density parity-check (LDPC) codes for these FSO systems. Compared with the conventional LDPC codes that are designed assuming symbols-independent symmetric channels the optimized codes are much closer to the Shannon limit for OOK modulated binary non-symmetric channels.
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