An embedded transmission method of PPM signaling constructed of parallel error correcting codes for optical CDMA

We propose an embedded transmission method using pulse position modulation (PPM) signaling with symmetric error correcting codes for optical code division multiple access (CDMA). In the method, 2^J slots of 2^J -ary PPM signaling are embedded in a user's signature sequence with 2^J weighted positions. Therefore, the proposed method increases the number of bits per signature sequence. This increase in the number of transmission bits allows us to adopt J error correcting codes without decreasing the information rate and expanding the system bandwidth. Consequently, the effect of multiaccess interference (MAI) is removed within the error correction capability. Considering the effect of MAI, we analyze the BER under Poisson photon counting process. Numerical results show that the proposed method has an advantage of good energy efficiency over the conventional PPM method in applying error correcting codes.