Research On Handover Mechanism In Relay Enhanced Cellular Networks

As a novel network architecture, the relay enhanced cellular network introduces the relay technology into the conventional cellular systems. The direct link between Base Stations and User Equipment develops into two-hop or multi-hop relaying links. Then, the communication distance is reduced, the data rate can be improved, the coverage can be extended and the system capacity can be increased. So the relay enhanced cellular networks support more subscribers in the need of high data-rate services. However, the introduction of relay has brought the new challenges. This paper focuses on the handover mechanism in the relay enhanced cellular networks.Firstly, this paper investigates the problem of handover measurement in the relay networks. We analyze the difference between the traditional cellular networks and the cellular relaying networks, and point out that these differences make a great impact on the handover measurement. Based on this analysis, we propose a handover measurement scheme based on state information assisted. According to the state information of neighbor access stations (BS and RS) and user equipmen(tUE), the scheme limits the UE measurement objects. Thus it can reduce the number of neighbor access stations which UE need to measure, shorten the handover measurement time and reduce the handover latency. At last, the efficiency of UE handover measurement is improved and the fast handover is effectively implemented.Secondly, we analyze the problem which the group users in the high speed will face in the handover process, based on which we intend to introduce the mobile relay station (MRS) to simplify the problem, so the problem of the multi-user simultaneously and frequently handover converts into the problem of MRS handover, it can simplify the handover process and signaling overhead. We consider that the high-speed group users have some characteristics, for example, the movement line is clear, the movement speed is relatively stable. A group handover scheme based on prediction is proposed to solve the problem of MRS handover. This scheme stores some information about the road and combines with information on the location of MRS to predict the movement direction, pre-handover cell and pre-handover trigger time, so it makes MRS pre-handover at the right time, greatly reducing the handover latency and increasing user service satisfaction.Finally, we study the relay networks handover decision algorithm and point out the traditional cellular networks handover decision algorithm is no longer suitable for cellular relay networks. We design a novel handover decision algorithm based on movement state, which combines with movement direction and velocity to choose a more accurate access station as the handover target, i.e. encouraging the low-speed users to handover to the stations that the UE is approaching and that are relatively close to the UE, however encouraging the high-speed users to handover to the stations that the UE is approaching and that are relatively far from the UE. So this can lessen the"ping-pong"effect, reduce handover cost and enhance the transmission efficiency. In the end, the handover performance of proposed algorithm is demonstrated by simulation.