Key Technology And Digital Intermediate Frequency Modulation And Demodulation Of Cdma System To Achieve

More and more communication industry experts regard CDMA technology as one of the most important multi-access methods in this century. In recent years, Software Defined Radio (SDR), the new communication architecture, with the rapid development of VLSI technology and remarkable improvement in the performance of universal programmable chips, such as DSP and FPGA, is not the drawing board anymore. IF Digital System is being an economic and efficient compromise which combines the ideal SDR thinking with present hardware level. This dissertation aims to discuss and research the design and implementation of IF digital CDMA system.Synchronization technique is very critical in communication systems. Whether the system works reliably or not sensibly depends on the synchronization performance. Around the synchronization problems in the IF digital DS-CDMA system, this dissertation concentrates on the design of the physical layer modem of CDMA digital IF system and the realization based on the FPGA. The main points are listed as follow:1. Summarized the basic concepts and technical features of DSSS communication system, and then introduced the necessity of synchronization.2. Discussed the design of the IF digital CDMA modem in the forward link, and focused on the carrier synchronization algorithm and digital phase locked loop (DPLL) implementation. A multi-loop switch strategy is also introduced to optimize the synchronization performance in this dissertation.3. Discussed the design of the IF digital CDMA modem in the backward link. An idea which makes use of DPLL in the receiver of substation to synchronize carrier in the backward link is proposed. Moreover, its feasibility is verified by computer simulation.4. Introduced the hardware implementation platform of the CDMA system. The designs for RTL modules written by Verilog HDL language and Modelsim's simulation results are given through parts of the core modules, the testing results of the system are listed as well. The IF digital design proposed by this dissertation can not only be applied to DS-CDMA system, but also equally be used in other non-spread spectrum systems and point-to-point wireless systems. As for the DPLL, the only difference in various kinds of synchronization systems is the phase detector, but the other parts of DPLL are universal. The frequency controllable interpolation mechanism is of great reference value for full-duplex synchronization system.