Research On Techniques Of Optical Code Division Multiple Access (OCDMA) Systems

Optical code division multiple access (OCDMA) communication technique becomes a hotspot in optical communication fields because of its superior advantages, such as capacity, high security, asynchronous access and etc. This dissertation focuses on the OCDMA system and some key technology, based on some of the precedents'research works.The main works are as follows:First, The basic theories about the code word of OCDMA system are studied, including set theory, group theory, ring theory, field theory and Galois theory. And the graph theory is also introduced, which provides a theoretical basis for the later direct construction method of the optical orthogonal codes.Second, some one-dimensional time-spreading codes which commonly used are analyzed, including optical orthogonal code(OOC), prime code(PC)and various of correlative improved codes. The study content include auto-correlation, cross-correlation, code capability and system bit errorrate (BER) performance caused by multi-user interference(MUI). And an inproved direct construction of OOC was proposed, with the significantly reduced of computation, effective saves system resources.Last, two kinds of two-dimensional frequeney-hop time-spreading(FH-TS)codes—2D-OOC and 2D-PC are analyzed, including auto-correlation, cross-correlation, code capability and system BER performance caused by MUI. The analysis shows that FH-TS codes'performances at code sizes and system BER performance caused by MUI are all better than one-dimensional time-spreading codes. This thesis making use of the characteristics of extended quadratic congruencies (EQC) and OOC, to design a new construction for two-dimensional FH-TS codes. The basic idea of this construction is analyzed. Through some instances, the process of detail design for FH-TS code is given. The code sizes and correlation properties are analyzed and calculated.