Research Of Spread Spectrum Communication System On FPGA

Spread spectrum communication is an significant communication method in the modern communication system, in which the direct sequence spread spectrum communication system is most widely used. The direct sequence spread spectrum communication system could be applied to numerous fields such as satellite, distance measurement, communication and so on, for the reason that it has many advantages, for instance, high security, well noise immunity and easy network constructing.The theory of spread spectrum communication is studied in this paper firstly, and the characteristics and basic theory of spread spectrum communication system are described, whose working mode includes direct sequence spectrum, time hopping, frequency hopping and so on. Several spreading spectrum sequences are compared. Analysis results indicate that the auto-correlation performance of m-sequences is best, but m-sequences provide only a few address codes; the auto-correlation performance of Walsh sequences is poor and the shift register can't be used to perform simulation intuitionally; the auto-correlation performance of Gold sequences is bad. M-sequences are used as spreading sequences in this paper because we don't need too many address codes. The synchronization technology is one of the most important technologies. The research centers on the synchronization technology of spread spectrum communication system. The synchronization process of pseudo-random codes generally includes acquisition and tracking in the direct sequence spread spectrum communication system. The acquisition includes single-integral sliding correlation method, double-integral sliding correlation method, matched filter method and so on. The synchronous receiving system is designed by using phase-locked loop technology and adopting corresponding schemes, and the reception of signs are realized in the direct sequence spread spectrum communication. Good performance is also obtained. The modulation of one direct sequence spread spectrum communication system is achieved by using Quartus118.1 developed by Altera Company, then the design and simulation are carried out for each module.The principle of spread spectrum communication of global positioning system is described in this paper, that is, propagation delay between transmitters and receivers is used to confirm the distance from transmitters to receivers. Then the modulation and demodulation of satellite signals are described. The demodulation of signals includes square-demodulation technology and replication code technology. At last, the acquisition and tracking module is realized, which is the core of synchronization process in the global positioning system.