A Research On Critical Technology Of Physical Layer Of TDD CDMA System And Interference Analyse

With the increasing of mobile phone users and high-speed asymmetrical data service, the second generation mobile communication system (2G) which can only provide symmetrical speech service and low-speed data service can't meet demand. So the third generation mobile communication system (3G) appeared with high-speed, big capacity and integrated service, and the standards for 3G have been established.TD-SCDMA and TD-LAS proposed by China both adopt TDD-CDMA technology which very adapts to the asymmetrical data service of 3G mobile communication. TDD-CDMA has so much technology advantage such as high spectrum effectiveness, big capacity, supporting asymmetrical uplink and downlink and so on, that it can especially solve the problem of some areas in our country which have overpopulation and scarcity of spectrum resource.But in TDD-CDMA system, there are many problems to solve including multipath fading, perspective effect, multiple access interference which influence its capacity and quality of service. So this paper deeply research the critical technology of physical layer of TDD-CDMA system , especially its smart antenna, and analyze its system interference in detail, which is significative to promote the development of mobile communication in our country.This paper firstly introduce the background and signification of this research, TDD-CDMA communication principle including its technology advantage, then research the critical technology of its physical layer such as power-control technology, soft handover, multiuser detection, diversity technology and Rake receiver, software radio and smart antenna and so on.The author's main research work is focused on interference analyse and smart antenna of TDD-CDMA system.The interference problem directly influence the capacity and service quality, so how to eliminate interference is the main factor to improve the performance of mobile communication system. This paper analyse all kinds of interference of TDD-CDMA system in detail, establish interference model; based on this, establish multiple accessinterference module of uplink.In some sense, TDD-CDMA is based on smart antenna. This paper deeply research smart antenna technology of TDD-CDMA system. At first, the author generally introduce the basal conception and theory, then discuss the existed optimal criterion and adaptive beamforming algorithm.The research of smart antenna at present is usually about theory discussion, and the theory analyzing object is usually linear array antenna, but TD-SCDMA adopt circinal array antenna. This paper analyze circinal array antenna and establish its input and output signal module.Adaptive algorithm is the heart of smart antenna. But because of complex processing, larger computation, lower convergence speed and even error convergence in some instance, the existed adaptive criterion and algorithm is difficultly tracking the user real-timely. Adaptive algorithm is the bottle-neck of smart antenna, resulting in adaptive antenna can't be achieved fully adaptive aims in practice and only studied in theory.In order to put smart antenna into practice easily, the author propose a new criterion and algorithm, Maximal Signal Criterion and Step-Change Searching Prestore-Weight algorithm which adapt to circinal array antenna and can be implemented into practice easily. This paper farther simulate the new algorithm using Matlab software by computer, which show the algorithm can meet the demand of mobile communication in convergence speed and performance.At last, the author summarize the shortage of this paper and point out the farther research direction.