Research On The Handover Algorithms Of Hierarchical Cell Structures In TD-SCDMA System

TD-SCDMA which was proposed by China is one of the three mainstream 3rd mobile communication standards. Currently, TD-SCDMA in china has entered a phase of large-scale commercial and it has a promising future.In real life, especially in large cities, as the existing of transportation such as underground, UE often change its speed to high speed or low speed. Such continually handover often leads to serious decline in quality of communication when user use their mobile telephone, sometimes may the drop-call happens in bad condition. Only by addressing this issue in order to improve the quality of TD-SCDMA network, it can be in the highly competitive communications market dominance.In brief, the concept of hierarchical cell structures is macro-cell override several micro-cells and form hierarchical structure. The handover algorithms of hierarchical cell structures use hierarchical cell structures in network topology, and it gives the verdict by the movement velocity of UE.When UE moves at high speed, it makes a handover to macro-cell and when UE moves at low speed, it makes a handover to micro-cell.Using this method, it can give consideration to both network capacity and quality, and it can improve network performance.This discourse recommends the principle and implementation process of the handover algorithms of hierarchical cell structures in detail.In the algorithm, how to determine the movement velocity and handover UE to the opposite cell is a key of the algorithms. At present, there are several decision methods:judged by the residence time of UE in the cell;or judged by times of UE handover between cells with the same level in unit time; or judged by change times of the micro-cell with best signal quality in unit time. These methods have some limitations which may cause inaccuracy of the speed judge. The innovation of this paper is that we lead in the concept of slide window into the handover algorithms of hierarchical cell structures. We calculate the valid handover event number within a certain period of time, and we compare it with a located threshold of high speed or low speed and then verdict the movement speed of UE.Based on its movement velocity, we choose the opposite processing procedures, handover the UE to the macro-cell or micro-cell.To validate the algorithm,we used the method of field test and amply tested the function and capability of the algorithm in the Expo Site.The test results prove that the handover algorithms of hierarchical cell structures used slide window can improve the performance of network.