Coding for coherent optical CDMA networks

The adoption of incoherent optical signal processing in CDMA LANs faces the limitation of the absence of complementary elements which hinder the design of optical code sequences that are fully orthogonal to each other. Coherent optical processing has been shown to be able to overcome the limitation. The paper looks at the coding aspect of CDMA LANs with coherent optical processing. The architectures of encoder/decoder and their basic phase properties are described. Based on the phase properties, methods of generating families of optical phase codes with good correlation properties are presented. The phase code families generated are then compared with optical codes used in incoherent systems, in terms of code length, family size and correlation properties. From the comparison, it is shown that, generally, phase codes exhibit more desired features in these aspects than the conventional optical codes, and, therefore, render higher data rate and more secured transmission