Management Mechanism Of Cell Outage Compensation In LTE Radio Access Network

The concept of Self-Organizing Network (SON) is introduced in Long Term Evolution (LTE) system. Main purpose of SON is to improve the self organizing ability of the network by the self-configuration, self-optimization and self-healing functions, to replace the high cost man-powered network operations, so as to reduce the manpower and operating costs, while enhance the efficiency and quality of the network. Cell Outage Compensation (COC) is one of the important functions of the self-healing. Cell outage is the total loss of radio services in the coverage area of a cell. There are diverse reasons for the cell outage in mobile communication network,including system hardware or software failures, power supply outage or configuration error etc. The aim of COC is to mitigate the performance degradation induced by the outage to the utmost extent by automatically analyzing the corresponding measurement data and adjusting the related radio parameters of the neighboring cells. The research of COC management mechanism plays an important role in the self-healing of the system, and becomes the hot spot in the wireless communication filed and network management field.The research of paper includes two aspects: autonomous COC management architecture and multiple objectives oriented COC algorithm. The main content of the paper are depicted as follows:(1) To satisfy the requirements of autonomous COC management, an evaluation step is added to the general autonomous management control loop. In the evaluation step,the effect of autonomous management is evaluated and management policies can be adjusted. Thus a closed control loop without human intervention is designed, which becames the theoretical base to realize the COC mechanisms and algorithms.(2) For the early development scenario of LTE/LTE-A network, where network elements and SON functions are few,the paper studies the centralized autonomous management architecture and corresponding centralized COC management mechanism, and proposes the Reference Signal (RS) adjustment based COC scheme generation algorithm. Simulation results show that the algorithm is effective in compensating the coverage problem induced by cell outage while the performance degradation of the compensating cells can be kept on the accepted levels.(3) With the development of LTE/LTE-A network, the number of network elements and SON functions is increased, in this case, the problems of centralized management architecture are emerged, such as low efficiency and bad expandability.To resolve the problems, the paper studies the distributed autonomous management architecture and corresponding distributed COC management mechanism, and proposes the Reference Signal (RS) adjustment based COC scheme generation algorithm. Simulation results show that the algorithm is effective to achieve outage compensation, ensuring regional coverage at a higher level, and reducing the emergence of coverage overlap. Meanwhile the performance is kept on the accepted levels guaranteeing the quality of services.(4) The adjustment of reference signal transmission power is limited. When the transmission power of base stations reaches the adjustment limitation, the coverage gap could not be compensated effectively, especially in the suburb area where transmission power has already been at its maximum because of the less stations and long distances. Thus the paper proposes the automated cell outage compensation mechanism and algorithm based on downtilt adjustments. The simulation results prove that the proposed optimization scheme can effectively solve the weak coverage problems caused by cell outage while the service quality can be maintained, and the performance of downtile based scheme is better than that of RS based scheme, especially in the suburb area.(5) COC can be realized by adjusting the single parameter or multiple parameters. In the scenario of large scale and complicated networks, the hybric autonomous network management architecture can be adopted. The paper studies the hybric autonomous network management architecture and proposes the COC mechanism based on joint optimization of power and tilt. The simulation results show that the joint adjustment scheme can reach the requirements of gap compensation, while the optimization objectives are realized well.