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

Conventionally, optical CDMA systems with on-off keying (OOK) require a time duration equalling a signature sequence length to transmit only one bit. Since the crosscorrelation between the signature sequences results in multi-access interference (MAI), the signature sequences are designed so that their weight distribution is sparse for their long length, and then MAI rarely occurs. With this view, optical orthogonal codes (OOC) are investigated, which are characterized by a quadruple (L,W,/spl lambda//sub a/,/spl lambda//sub c/), where L and W are length and weight of sequences, respectively, and /spl lambda//sub a/, and /spl lambda//sub c/, are maximum off-peak autocorrelation and maximum crosscorrelation, respectively. Thus, the use of OOC makes the effect of MAI small, but has to spend a long duration for one bit. In this paper, we propose an embedded modulation scheme, where an asymmetric error correcting (AEC) code is embedded in an OOC used for identification in optical CDMA. We show that the proposed scheme achieves the same bit error rate (BER) as conventional systems, with less average number of photons.