The Research Of Multi-user Experiment And Multi-rate Simulation In Two-dimensional OCDMA System

Optical code division multiple access (OCDMA) is a communication mode which introduces the code division multiple access (CDMA) technology into optical fiber communication system. Besides providing asynchronous communications access, OCDMA system has many advantages, such as high capacity, security against interception, suppression of narrow band disturbances, capability in forming variable bit rate networks and multi-rate networks. It implies a great challenge for the development of future communication networks, especially all optical networks.The main research of this paper is focused on two dimension optical code division multiplexing access system. In 2-D OCDMA system, the code sequence for each user is spread in time chip and wavelength, or in time chip and space.2-D OCDMA system has good performance compared with 1-D OCDMA system because of the increasing of one dimension.Firstly, the basic principle, system characteristic, system classification and the key technologies are introduced in section one. The development, research status and trends of OCDMA technologies are also summarized.T/S-OCDMA, WDM+OCDMA, MW-OCDMA two-dimensional OCDMA system encoding and decoding are researched, and the performance of three kinds of two-dimensional OCDMA system are compared by simulation in the second section. The simulation results show that the performance of two dimensions OCDMA system is better than one dimensions OCDMA system in many factors, such as the simultaneous users, the capacity of the system and the bite error rate. Meanwhile, some significant suggestion and conclusion on improving two-dimensional OCDMA system are given.The 2-D OCDMA system based on fiber Bragg grating Arrays is studied experimentally in the third section. The structure principle of fiber Bragg grating encoder/decoder and 2-D OOC code is discussed, the two-dimension optical orthogonal code designed in our laboratory is applied, and then the 2-D FBGs encoder/decoder based on the OOC is designed and fabricated. Two-user parallel transmission incoherent OCDMA system is achieved, the rate is up to 2.5Gb/s.The encoding and decoding of the system is studied when the transmission rate is beyond the critical value determined by the distance between Fiber Bragg gratings. It is proved that the 2-D FBGs encoder/decoder designed can be encoded and decoded correctly for OCDMA system transmission. The theoretical maximum data rate of the system can be exceeded.In the forth section, the possibility of supporting the data with multi-rate and various QoS(quality of service)demands in the future OCDMA access network is discussed. Scheme of encoding and decoding in traditional multi-rate OCDMA system is compared and analyzed. The scheme of encoding and decoding with fixed spread spectrum address code cycle is proposed. The performance characteristic of this scheme is analyzed in theory. The relevant simulation is done to verify the theory.The summarization of all the paper is got in the last section.