Transmission scheme of embedding the transmitted symbols in the desired user´s weighted positions in PPM-OCDMA systems

We propose the transmission scheme to increase the maximum number of simultaneous users for embedded PPM-OCDMA systems without degrading the bit error rate (BER). In the conventional scheme, each PPM slot position and its transmitted symbol are embedded in the desired user´s weighted positions to M-ary PPM-OCDMA, so the number of weights is equal to the number of PPM slots, and the number of codes is limited to be small. In the proposed scheme, only the transmitted symbols are embedded in the desired user´s weighted positions to M-ary PPM-OCDMA. So, the number of weights doesn´t depend on the number of PPM slots. As the number of weights is decreased, the number of codes is increased compared to the conventional scheme under the condition that the bit rates are constant. We analyze the BER of the proposed scheme under the Poisson photon counting process. We show that the proposed scheme can increase the maximum number of simultaneous users compared to the conventional scheme under the conditions of achieving BER ≤ 10^-9 and keeping the information rate constant.