Performance analysis of adaptive PPM-GMSK-SIM modulation over F-turbulence channel model in FSO communication

In this paper, we have proposed an adaptive pulse position modulation-Gaussian minimum shift keying-subcarrier intensity modulation (PPM-GMSK-SIM) system over F distribution channel model with pointing error. Here, in our proposed system, an adaptive method is used to mitigate the performance degradation due to atmosphere turbulence (AT). In this method, the modulation order adapts according to instantaneous AT under a target an average bit error rate (ABER) and automatically adjust the modulation order at the receiver accordingly and inform it to the transmitter to adapt the modulation order via a feedback path. We derived ABER for PPM-GMSK-SIM system over F distribution channel model. Moreover, we derived an achievable spectral efficiency and ABER expressions for the adaptive PPM-GMSK-SIM system. Here, we compared the performance of proposed PPM-GMSK-SIM modulation system with the PPM-MSK-SIM modulation system over F distribution channel model and observed that the proposed PPM-GMSK-SIM gives better performance than the PPM-MSK-SIM system and the improvement in the ABER performance is approximately 6 dB at ABER value is 10(-3) in weak, moderate and strong atmospheric turbulence conditions. Also, the ABER versus received average irradiance performance is approximately 2 dB better in the weak AT and it is approximately 3 dB for moderate AT and strong AT conditions at ABER value is 10(-3). We compared the spectral efficiency of the adaptive PPM-GMSK-SIM for target ABER values 10(-2) and 10(-3) and observed that the spectral efficiency improves as target ABER decreases and compared the ABER performance of the PPM-GMSK-SIM with the adaptive PPM-MSK-SIM system over F distribution channel model and observed that the system performance improves about 11 dB at SNR value is 10(-3).