A study on code construction of optical orthogonal codes with variable chip rates

For flexible multiplexing in optical CDMA networks, optical orthogonal codes (OOCs) have been studied by many researchers. The authors have proposed OOCs with variable chip rates (VC-OOC), in which the orthogonal property of the strict OOC can be kept even when different chip rate codes are used in a common optical CDMA network. In this paper, a code construction scheme is proposed, where the balanced incomplete block design (BIBD) sequences are employed for the slower chip rate codewords, and select them to enlarge free space in distribution of pulse intervals for the faster chip rate codewords. The faster chip rate code can be designed by simple code search.