Despreading Demodulation Of The Design And Implementation Of Fpga-based Gsm

The spreading spectrum(SS) communication system has stronger ability of resisting narrow band, multipath and jamming interference than that of the conservation communication systems, and it also has the characteristics of low probability of intercept and multiple access secure communication. Nowadays, the SS technology has gotten rapid progress. This thesis primarily focuses on the synchronization of the pseudo-code and the carrier. It researches the structure and performance of DSSS as well as calculates the relevant parameters. In addition, it improves enveloping algorithms. Finally, the de-spread and the demodulator also have been designed and implemented based on ISE9.1 to prove that the projection is correct.The thesis studies characteristics of spread spectrum communication systems, related technology development at home and abroad and related theoretical basis. It designs the de-spread and demodulator of DS-QPSK receiver. The de-spread mainly focuses on the acquisition and tracking, researches the structure and performance as well as calculates the relevant parameters. Then it designs DDC, PN generator, enveloping extractor, mul-channel fast PN arrestor, PN tracking phase discriminator and PN clock accommodator. After programming, the behavior simulation also has been represented based on ISE9.1 to prove the system is correct. Because correlation integral enveloping algorithms is the basis and the core of the entire system, in order to reduce hardware resources occupied real-time, the thesis improves the enveloping algorithms and gives the compared results which doesn't reduces the occupied hardware resources and shorten the delay, but also it plays a decisive role on the optimization of the entire system. It gives the simulation results and occupation of hardware resources which strongly prove that the de-spread has the characteristics of occupying less resources and shorter time-delay.In demodulator section, it analyses frequency deviation and carrier phase errors on the signs, demonstrates the program of carrier synchronization, works out the deep research and behavior simulation of numerical controling oscillator(NCO), arc tangent phase discriminator and loop filter. Then it realizes carrier frequency tracking, gives the simulation results and occupation of hardware resources. The summaries of the thesis and the possible extensions and improvements based on the completed system have been represented at last.