Performance analysis of atmospheric optical subcarrier multiplexing systems and atmospheric optical code division multiplexing systems

In this paper the performance of the atmospheric optical subcarrier multiplexing (AO-SCM) systems and the atmospheric optical code division multiplexing (AO-CDM) systems is analyzed and the average received carrier-to-interference-plus-noise ratio (CINR) of the AO-SCM systems and the AO-CDM systems on a turbulence channel with the scintillation and the nonlinearity of an Ld is derived. We show that the received CINR of the AO-CDM systems is larger than that of the AO-SCM systems when the number of channels is small for the same optical modulation index (OMI), and vice versa when the number of channels is large for the same OMI. For instance, when the logarithm variance of scintillation σ_X² is 0.3, a constant of the nonlinearity of an LD a₃ is 0.17, and the number of channels K is 4, the maximum CINR of the AO-CDM systems is about 4 dB better than that of the AO-SCM systems. Also, when K is 16, the maximum CINR of the AO-SCM systems is about 3 dB better than that of the AO-CDM systems. The difference of CINR results in the difference of the maximum achievable number of channels for the systems. When the required BER is 10^-9, AO-SCM and AO-CDM systems can accomodate 16 and 8 BPSK channels, respectively.