Applications of optical code division multiple access (CDMA) to wireless communication

Abstract

The theoretical foundations for code division multiple access (CDMA) are similar for microwave and optical implementations, and the advantages of this form of multiple access communications are similar, also. The advantages include the ability to support bursty, asynchronous, concurrent communications and to tolerate multipath interference. Optical implementations of CDMA are different in that they tend to require guided lightwaves (e.g., fiber cable), the coding is imposed on the intensity rather that on the amplitude of the lightwave, the various codes are not strictly orthogonal, and the receiver uses direct detection. This gives rise to the term 'optical CDMA'. These pseudo- orthogonal CDMA codes usually require wide bandwidths to represent the encoded data, so that optical CDMA is sometimes considered bandwidth inefficient. Two classes of optical CDMA codes which ar sufficiently bandwidth efficient for wireless communications applications are (1) incoherent spectral CDMA and (2) optical matrix CDMA. In addition, the wireless communications applications may need to support various data rates (for the various services), and these two classes of optical CDMA are both very tolerant of data rate variations. An appropriate topology for applications such as a local area network (LAN) is a star and, for multimedia data distribution, a tree.