Design And Implementation Of CDMA Communication System Based On The Rake Receiving

Due to the multi-path propagation of radio waves, signal fading and signal phase shifting can be caused in the wireless communication. The Rake Receiving technology, one of key technologies in the CDMA system, realizes diversity reception for multi-path signals by the use of the correlation of pseudo random code. Such method not only solves the multi-path propagation for signal, but also enhances the signal-to-noise ratio and reduces the signal fading caused by multi-path propagation with transforming signal interference into its gain.A CDMA communication system based on the Rake technology is proposed in this paper, after studying the knowledge of the composition of the CDMA system, such as the technology of Direct Sequence Spread Spectrum signal and the Rake receiving technology. It consists of spread spectrum signal sending, multi-path channel simulation and Rake receiving modules. All modules are designed with Verilog hardware description language. The spreading spectrum modulation of source signal and the carrier modulation of spread spectrum signal are achieved in sending module. The delay of sending signals and their propagation of multi-path are accomplished in the multi-path channel simulation module. In the receiving module, receiving signals are demodulated with the method of homodyne reception. On the premise of completing pseudo random code synchronization, diversity receiving are completed for multi-path signals can be received with the Rake technology. In the Rake Receiver, the three strongest multi-path signals that have the highest related value with local PN code are selected and the delay is used to align the phase among these signals. They are weighted merged and the multi-path interference can be eliminated, so that strength of signal gets improved. After system designing, simulations with Modelsim6.5are carried out for unit and system verification which verify the effective of our design. The programs of system baseband are downloaded to FPGA device, and used to analyze the results through software and hardware testing.The simulation results show that this system can realize the sending, capture and tracking of spread spectrum signal, and the Rake receiving of multi-path signals. Hardware tests verify the spreading spectrum of baseband signal, pseudo random code synchronizing, and combining of the despreaded multi-path signals.