An embedded transmission method using asymmetric error correcting codes with optical orthogonal codes for optical CDMA

摘要

We propose an embedded transmission method using asymmetric error correcting codes with optical orthogonal codes for optical code division multiple access (CDMA). In the method, multiple bits are embedded in a signature sequence used for identification, and the embedded bits are transmitted in the weighted positions of the signature sequence. Therefore, the transmission rate is increased, however, at the same time, the embedded bits are vulnerable to MAI because the correlation detection can not be used. To compensate this vulnerability, the increased transmission rate of the embedded method allows us to use an asymmetric error correcting (AEC) code, without reducing the information rate and expanding the system bandwidth. Consequently, the effect of MAI is reduced in the decoding procedure of the AEC code. We classify the codewords of the AEC code according to the number of l's in each codeword, and then derive the bit error rate (BER). Numerical results show that for achieving a particular BER, the embedded modulation scheme requires less optical energy per bit than the traditional modulation scheme with the correlation and chip-level receivers, although the performance of the proposed scheme has the error floor, which is primarily due to multiaccess interference (MAI) beyond the error correction capability. Furthermore, we apply Reed-Solomon (RS) coding to the embedded modulation scheme. Consequently, RS coding reduces the floor value to be negligibly small.