Research On And Improvement Of Soft Handoff In CDMA System

Handoff will become an increasingly important issue in mobile phone communications, especially in microcellular systems with the increase of handoff traffic between cells. The soft handoff is one of the key technologies in the CDMA system which plays an important role in controlling and optimizing radio resources of the system. Soft handoff can make channel of mobile station be switched to the target BS with the new link before breaking the old link. This feature makes the system get a great many advantages such as seamless communication, higher performance, lower blocking probability, better user experience.The paper makes a study of soft handoff in CDMA system. Firstly, the principle of CDMA and its key techniques are briefly introduced. Secondly, the hard handoff and soft handoff call flows are further studied. Also, Markov chain is applied to analyze and simulate the four typical different handoff schemes. Based on BSC-crossing model, BSC interconnection can cause call-drop in actual network. Solutions are derived from the hard handoff and soft handoff. As an extension of previous studies, this solution refines the sercice quality by transfering BSC control right to another without changing the current handoff protocol. After realizing this, the next BSC can initial another soft handoff. Compared to the original approach, the proposed approach can achieve that BSC-crossing terminals can be handovered smoothly so as to reduce the outage probability. Hexagon soft handoff model is used to make the analysis and research of the mutual relationship among speed, arrival rate, handoff region and blocking probability of the system. Finally, by the means of Matlab tool, the analysis and simulation results show that the proposed approach can make the terminals's signal strength continuous high and the outage probability lower.