Generalized OOC assisted PPM and overlapping PPM, considering thermal noise and APD effect

The effect of thermal noise and avalanche photodiode (APD) noise in a code division multiple access (CDMA) system using generalized optical orthogonal codes (GOOC) are investigated for the first time. The modulations used are pulse position modulation (PPM) and overlapping PPM (OPPM). Double optical hardlimiter receiver structure is selected because of its efficient performance. We show that, in a system with all mentioned noise sources, known parameter values, and a bit error rate of 10^-7, GOOC codes with cross correlation (λ) equal to 2 support 20 more users compared to strict OOC. We have also analyzed the spectral efficiency of the GOOC OPPM system and compared it with GOOC PPM. The results demonstrate that GOOC OPPM has a better spectral efficiency. Using the obtained results, we have provided a parameter selection procedure that can be used to choose a good set of signaling parameters for GOOC OPPM modulation systems.