Design And Implementation Of Core Functions In The TDM-CDMA-PON System

Passive optical network (PON) has the advantages of high-bandwidth and high reliability, and it gradually becomes the mainstream of cable access technology. Code Division Multiple Access (CDMA) technology is superior in strong anti-interference and flexible access. CDMA-PON technology based on electronic coding and decoding is novel for optical access network. The main advantage of CDMA-PON technology is that it offers coding gain, thus it can improve the receiver sensitivity and provide a higher power budget. CDMA-PON could support longer distance transmission and greater branching ratio and it has become an important development tendency of optical access area.With the support of national 863 project of "The research of key technologies in CPON system and development of system equipment", this thesis is mainly deployed on the design and implementation of core functions in OLT board. The main contents of this thesis are as follow:1. Receiver sensitivity improvement due to coding gain has been analyzed. The feasibility of quasi-synchronous CDMA-PON system has been proved by simulation, and proper spreading codes have been determined.2. Core functions of the OLT board have been implemented by FPGA. This thesis has completed the analysis on function demands of the OLT board and division of the modules. Decoding scheme based on high-speed digital correlator and phase capture synchronization scheme based on PN code have been proposed. The core functions implemented by FPGA include high-speed decoding, high-speed phase capture synchronization, the uplink and downlink transceiver and so on. System test results show that the accuracy of the synchronization scheme meets our expectation and the decoding scheme could work under 2.5Gchips/s and the expected system throughput requirement. The experimental results show that the receiver sensitivity of uplink TDM-CDMA-PON system reaches -36 dBm. The system supports a transmission distance of 50km and a maximum branching ratio of 256.3. The basic anti-interference principle of CDMA-PON system has been studied, and the ability to resist DC interference, narrow-band interference and wideband interference has been analyzed. System test results reveal that CDMA-PON system has better anti-interference performance comparing the TDM-PON system. And the anti-interference ability is proportional to the coding gain.