Wireless Spread Spectrum Communication System And Its Multi-user Interference Suppression And Realization

As one of the most important multiple access of the third generation mobile system, the CDMA technology has gotten more and more attention. CDMA system is a sophisticated and typical wireless spread spectrum communication system with some merits: anti-interference, high bandwidth efficiency, confidentiality and can be multiplexed accessed and so on. However, the users'random signal access shares a channel and frequency spectrum at the same time, the incomplete orthogonal address-code has caused Multiple Access Interference. The existence of MAI has affected the performance and capacity of CDMA system seriously. So, inhibiting MAI, increasing system capacity, and improving system performance are the extremely urgent request. Therefore, focusing on the problem of MAI, this paper discussed and studied the related solutions of MAI, carried on the simulation confirmation and the realization to the related methods.Firstly, this paper introduced the background and system architecture of the DS-CDMA wireless network system from the development history of the wireless spread spectrum communication in detail, and analyzed the causes of multiple access interference as well as the effects to this system. In addition, this paper suggest one kind of variable speed interpolation mechanism used in this system, and confirmed that this plan is favorable of the carrier frequency synchronization of the reverse link through simulation.Secondly, this paper mainly studied two solutions to inhibit MAI, including multi-user detection technology and designing one kind of address-code which had good correlation properties. This paper introduced multi-user detection technology in detail firstly.This paper analyzed the theory, the characteristics and performance of the best multi-user detection, linear multi-user detection and non-linear multi-user detection, and then combining the characteristics of the system, carrying on contrastive simulation of the system performance influence which traditional detector and decorrelating detector has worked on this system, and finally came to the conclusion that decorrelating detector outperformed the conventional method in suppressing the MAI.Then, this paper introduced the second method of suppressing the MAI: designing one kind of address code which has good correlation performance. First, this paper proposed one kind compound spreading sequence of the m sequence and the Walsh sequence as this system's address code through unifying advantages and disadvantages of several kinds of spreading sequences that were commonly used. Then, this paper proved that this address code has a huge advantage to reduce the MAI through simulating the influences of various sequences to the system performance.Finally, this paper introduced the system's hardware platform and testing programs and gived the results of the system debugging.