Research On Relay Handoff Technology For TD-SCDMA System

With the development of the computer network and the technology of communication, mobil communication develops rapidly. In the second generation (2G) digital mobile communication system, available bandwidth can not satisfy the information content and the growing need for data types. This prompts the rapid development of the third generation (3G) mobile communication system. It is the first time for China to propose the program of TD-SCDMA technology to the ITU.Relay handoff is used in TD-SCDMA system while crossing areas. Each base station has a positioning function of user equipments. It can accurately locate the user equipments to reduce the handoff delay and improve the success rate of handoff.In TD-SCDMA system,the pilot channel and business channel are in the different time slots, and smart antenna technology is used in the business channel, which plays an important role on relay handoff effects and eliminating interference.To solve this problem, this paper distinguishes the users based on the quality of the business channel signal, adjusts the handoff decision threshold of different users with the pilot signal strength so as to optimize relay handoff algorithm and improve the success rate of handoff.The main work of this paper is to research on relay handoff technology in the TD-SCDMA system.The main contents of this paper are as follows:Chapter 1 is an overview. It introduces the development status and future trends of the third generation mobile communication system and the characteristics of TD-SCDMA, and the main contents of the paper.Chapter 2 introduces the basic structure of TD-SCDMA system and states the basic theory of handoff. It analyzes and compares the hard handoff, soft handoff and relay handoff and introduces in detail the basic process of relay handoff-four stages are: measurement, pre-synchronization, adjudication and implementation.Chapter 3 analyzes the influence of interference and the uplink and downlink capacity in TD-SCDMA system. Firstly it analyzes the generation of interference and anti-interference technology and uplink and downlink interference calculation in TD-SCDMA system.Then it analyzes the uplink capacity and the simulation results indicate: the greater multi-user detection factor value becomes, the lower voice rate becomes, the greater the uplink capacity of the system becomes.Finally, it analyzes the downlink capacity and the simulation results indicate: the greater orthogonal factor value becomes, the lower voice rate becomes, the greater the downlink capacity of the system becomes. By the computer simulation of the system capacity using different types of antennas, we can conclude that system capacity increases as Energy to Noise Ratio decreases and in the case of the same Energy to Noise Ratio, the system with smart antenna can accommodate the largest number of users. Then it simulates and compares the relationship between bit error rate and cell capacity on using different types of antennas. We can conclude that in the case of the same number of users accommodated in the district, the use of smart antenna can minimum the BER.System capacity has been essentially improved for relay handoff to use smart antenna.Chapter 4 introduces a variety of handoff strategies.Then study the optimization of previous algorithms.On the base of the study on these algorithms, this paper proposes a reserved channel queuing with priority relay algorithm based on the signal quality of the business channel. According to the signal quality in business channel of user equipments, we can divide user equipments into two types: users with poor business signal quality and users with good business signal quality. Users with poor business signal quality waiting in front of the queue enjoy the priority to handoff. Users with good business signal quality wait behind them in the queue. In this way, users with poor business signal quality have the priority to handoff. It can reduce the blocking probability and call drop rate of the switch call and can efficiently use the channel resources.Chapter 5 studies the relay handoff performance in-depth and the computer simulation.Firstly;establish simulation model of system.Then determine the parameters associated with relay handoff.This paper proposes an improved new algorithm which is a queuing method of distinguish the users based on the business channel signal quality to the previous reserved channels queuing in priority strategies.We do computer simulation on this method and conclusion: comparing with traditional non-priority strategy and reserved channels strategy, the new strategies can significantly lower the call blocking rate.Because classification of the handoff users based on the signal quality of the business channel is added to the reserved channels strategies.It dramatically changes the handoff effect.In the case of the certain of the call intensity and percentage of the handoff users, the handoff users blocking rate of the reserved channels queuing in priority algorithm based on users classification is significantly lower than that of the reserved channels relay handoff algorithm.Finally discuss the effect of the length change of the waiting queue on the handoff. If the queue is too long or too short, it will increase the number of handoff failure. A length of 10 is the best in the handoff.Chapter 6 is a summary of the whole paper and analyzes the limitations of the research. The subject on the research of relay handoff algorithm optimization shows that the proposed optimization method can improve the resource efficiency and service quality in TD-SCDMA system. The research lays a theoretical foundation on the relay handoff algorithm optimization and also has some reference value in the practical application on radio resource planning in TD-SCDMA system.