Investigation On Radio Adimission Control In LTE System

As the long term evolution technology of the third generation mobile communication system, LTE will support multimedia services which have different transmission rates and quality of service (QoS), meanwhile provide users with higher data transfer rates. However, wireless network resources are limited, so how to efficiently use and manage the wireless system resources is one problem of the mobile operators'top concerns. Radio admission control (RAC), as an important part of radio resource management, can prevent overloading system by limiting the number of access users in this system, which is an important method for the wireless network to guarantee QoS of access users, and is significant for the system to maintain its normal running.RAC is mostly used to determine whether a new connection request is allowed to access to the work. In the case of insufficient system resources, if no restriction on access users, QoS of access users might be reduced. On one hand, as many users as possible should be allowed to access the system to take full advantage of the wireless network resources. On another hand, some access users could be degraded to release resources for the new connection request. The purpose of introducing RAC is to find a balance between these two respects.In this paper, firstly the characteristics of the LTE system were studied, and then supported service types, QoS mechanisms and resources allocation scheme were analyzed. Finally, based on the universal meaning RAC algorithm of the wireless communication network, two RAC strategies suitable for LTE system were brought forward.In Strategy one, whether new connection requests with different service types are allowed to access the system is determined by a criterion including service priority and service degrade. According the difference priority between the services, the highest priority connection request will be firstly allowed to access the system when there are a few connection requests at same time. When system resources are insufficient, the access lower priority services could be degraded for the higher priority connection request. This strategy could guarantee the access ratio of higher priority services, but no consideration on lower priority services. So it will suit to the case which priority protects the QoS of high-priority service.In Strategy two, besides service priority and serve degrade, a few delay queues were introduced to improve the access equity, according to user daily habits. When system resources are insufficient, a new connection request will be put to the corresponding delay queue, instead of being rejected directly. Once there are sufficient system resources, these requests in queue will be served prior to normal requests. Meanwhile, being benefited from delay queues, system resource utilization ratio could be improved somehow. This strategy could guarantee the access ratio of higher priority services, and give consideration on lower priority services.Finally, the performance of the algorithm was investigated by simulation, it was proved that the two strategies proposed in this paper could do well in improving the performance on blocking rate, dropping rate and the resource utilization.