Performance analysis of differential coding for hybrid PIM-CDMA optical wireless communication systems

The use of differential coding is proposed in hybrid pulse interval modulation-optical code division multiple access (hPIM-OCDMA) for optical wireless communication systems. In hPIM-OCDMA, although the 2^m-ary symbol modulates the interval between pulses, the interval is vulnerable to multiple access interference (MAI), which can cause false-alarm pulses, resulting in consecutive errors in symbol detection. The differential coding improves the tolerance to MAI and enhances the channel coding against MAI. We analyze the bit error rate (BER) of hPIM-OCDMA with differential coding, considering that the dominant interference is due to the self-interference and MAI, which are caused by autocorrelation and cross-correlation constraints of strict optical orthogonal code (SOOC), respectively. Numerical results show that the use of the differential coding together with Reed-Solomon (RS) code offers better BER and high information rate, compared to the case without differential coding.