In this paper, a number of parallel concatenated convolutionally coded (PCCC) photon communication systems is introduced and investigated. It is assumed that the optical channel is an intensity modulated (IM) channel and that the received optical signal is detected using a direct-detection (DD) scheme. Two modes of operation are considered. In one scenario, it is assumed that the receiver is limited by shot noise (i.e., negligible receiver thermal noise, or Poisson channel). In the other case, we consider a nonnegligible receiver thermal noise where an avalanche photodetector (APD) is employed to detect the received optical signal. It is also considered that the modulation scheme is the binary pulse-position modulation (PPM). With the aid of the best available upper bounds, the performance of the rate 1/n PCCC encoded optical PPM systems is assessed in terms of the upper bound on the system bit error rate (BER) for the shot-noise-limited IM/DD systems with nonnegligible background noise and for the thermal-noise-limited systems with APD detectors when a uniform interleaver is used. Numerical results for the rate 1/3 PCCC encoded PPM channels are presented. The numerical results demonstrate the enormous potential of this novel coding scheme in enhancing the performance of the aforementioned optical channels by a sizeable margin across the board.
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