Research And Digital Design On Rake Receiver In Spread Spectrum Communication Systems

With the further development of wireless communication, the 3G has been gradually used in daily life. At the same time, due to its unique capacity of anti-interference, anti-multipath, soft capacities and so on, the top three 3G communication standards ,which are commonly used around the world, are all on the basis of Code-Division Multiple Access (CDMA) . Rake receiver is the core part in the CDMA systems when implementing multi-path diversity reception, and also one of the keys to the CDKA spreading spectrum communication systems. It can separate multi-path signals, and implement time diversity. By using multi-path vectors effectively, It overcomes the influence of multi-path effects, and finally receives an improvement on the system's performance.In this thesis, the structure of the Rake receiver based on DMF is introduced firstly, and then the acquisition and Bit Error Performance (BER) is deeply analyzed and simulated. The spread spectrum communication system with Rake receiver based on DMF is digitally designed under QUARTUS finally. The main work and conclusions are as follows:Firstly, interrelated theories on spread spectrum communication are introduced detailedly. This part studys multi-path fading and channel models in wireless channel, and then analyzes and simulates the BER of traditional receiver in the multi-path channel.Secondly, after simulating combination gains of several often-used diversity combination patterns, this thesis deeply studys the working procedure and determination of parameters for Rake receiver.Then a spread spectrum communication system with Rake-receiver based on DMF is built under Simulink. On this basis, the BER curves of Rake receiver in multi-path channel are obtained. The simulated results indicate that, compared to traditional receiver, Rake receiver has a better capacity of anti-multi-path.After an analysis of its structure, the acquisition of Rake-receiver based on DMF is mainly researched in. By using the state transition diagram, this thesis derives analytic expressions of the mean acquisition time of single-dwell and double-dwell Rake-receiver, and then derives and simulates the acquisition probability and false alarm probability.Finally, a spread spectrum communication system with Rake-receiver based on DMF is digitally designed under QUARTUS. And a FPGA hardware circuit is designed, made, and debugged subsequently.