A new modulation scheme using asymmetric error-correcting codes embedded in optical orthogonal codes for optical CDMA

An embedded-modulation scheme is proposed for optical code division multiple access (CDMA). In this scheme, codewords in an asymmetric error-correcting (AEC) code is embedded in a signature sequence in an optical orthogonal code (OOC) used for identification. We classify the codewords of the AEC code according to the number of "1"s in each codeword, and then derive the bit error rate (BER) of the embedded-modulation scheme. Numerical results show that although the performance has the error floor, for achieving the floor value, the embedded-modulation scheme requires less optical energy per bit than the traditional modulation scheme with the correlation and chip-level receivers. The error floor is primarily due to multiaccess interference (MAI), we furthermore apply Reed-Solomon (RS) coding to the embedded-modulation scheme. Consequently, RS coding reduces the floor value to be negligibly small.