Research And Implementation Of GSM Femto Handover Mechanism Based On SIP Protocol

The Femtocell is a micro base station which is low power, small covering, works in a licensed band and uses existing xDSL or other cable line as backhaul connectivity. Femtocell technology gives an effective way to solve the ineffective indoor coverage and low capacity of the cellular mobile communication system. Meanwhile, this technology also allows users to enjoy a more low rates and increases user’s viscosity. Therefore, its advent has attracted more and more attention. At present, China’s communications market is still dominated by GSM. New business such as3G and LTE can also be switched back to GSM through the way of vertical handover. So, the research based on the GSM standard Femto base station has important practical significance and application value. Although, Femtocell has many advantages, it is not perfect. There are still many technical problems needed to be solved, such as Radio Frequency, Interference Suppression, handover between Macrocell and Femtocell, and Call Admission Control strategy, etc. More important, the handover of hierarchical network and call admission control have a direct impact on the deployment of Femtocell and user’s QoS. So, it has been a hot topic which needs to be solved in Femto application research.This thesis focuses on these two technical problems and does an in-depth study. Firstly, Femtocell changes the existing network architecture, and also essential differences exists between Femto and traditional base station in framework. So, some modifications of existing network and protocol architecture for the integration of femtocell networks with the existing GSM based macrocell networks are necessary. These modifications change the signal flow for handover procedures due to different2-tier cell (macrocell and femtocell) environment. This thesis selects the SIP protocol instead of the traditional GSM NO.7signaling, analyzes the key steps of the GSM Femto handover process, points out the deficiencies of the traditional GSM handover process in GSM Femto application and designs improved handover signaling process based on SIP under three different scenarios. Frequent and unnecessary handover restriction is another problem for hierarchical network environment that must be optimized to improve the performance of macrocell/femtocell integrated network. Then this thesis proposes an improved call admission control algorithm based on SQ(speed and QoS)for unnecessary handover minimization to enhance the user’s QoS, increase the customer satisfaction and the system capacity. The simulation results show that the algorithm can effectively control the number of frequent Handover. Finally, this thesis designed and implemented the function of GSM Femto handover system based on the previous research, verified the effectiveness of the proposed method.