Flow Control Strategies Of LTE-Advanced Relay Networks

3GPP LTE-Advanced, based on LTE (Long Term Evolution), is a radio interface technology for the next generation mobile communication system (IMT-Advanced). In order to fulfill the requirement of high data rate wireless services in the future wireless communication system, LTE-Advanced systems need to provide better performance in terms of both cell average and cell edge throughput. Wireless relay, as a lower-power and lower-cost network node compared to eNB, has been introduced in LTE-Advanced, offering more flexible deployment options and provideing an attractive means of augmenting network for coverage extension and throughput enhancement.In LTE, no special flow control mechanism is defined in radio protocols. In LTE-Advanced, a Relay Node is placed between two radio interfaces, i.e. Uu and Un. Since the two interfaces are independent, i.e. eNB does not know the Uu situation, and UE does not know the Un situation; at the RN, the queues reserved for its serving UEs may have buffer overflow problem due to the mismatch of the data rates between the access link and the backhaul link. So a flow control mechanism might be needed for Relay Node.First, we analyze the buffer overflow of RN in this paper. Existing mechanisms of cross-layer analysis focus on wireless link between base stations and users in cellular networks. With the adoption of relay node in the LTE-A system, there are two types of wireless link, the link between base station and relay(backhaul link) and that between relay and user (access link). In this thesis, we expand the mechanisms of cross-layer analysis to wireless relay network. We assume that adaptive modulation and coding (AMC) schemes are used at physical layer and that both the eNB and RN have a finite-length queue at data link layer. We analyze the joint effects of finite-length queuing and AMC for transmissions over wireless links; and then derive the system performance parameters including packet loss rate, average throughput, and average spectrum utilization. In the performance analysis, special focus is put on the analysis of the buffer overload of relay.Based on the analysis of buffer overflow, three flow control schemes, based on the queue length information, are then proposed to deal with the buffer overflow problems. The principle of the three schemes are that based on the feedback about buffer queue status information of RN, eNB adjust the packets sending rate to control congestion. And we compare the advantages and disadvantages of the three flow control schemes. Numerical results are then conducted to verify the effectiveness of the proposed algorithms.