A Dynamic Flow Control Algorithm for LTE-Advanced Relay Networks

Relay technology is a candidate for extending the coverage or enhancing the throughput of next-generation cellular systems. In the downlink of a Long Term Evolution Advanced (LTE-A) relay network, a relay node (RN) normally reserves a small buffer for each user equipment (UE) such that the RN can minimize the number of forwarding packets during UE handover. The small buffer and a mismatch of the data rates between the access link and the relay link may result in buffer overflow for some UE and in buffer underflow for the other UE served by the same RN. This paper presents a simple analytical model to illustrate the buffer-overflow and buffer-underflow problems in the downlink of an LTE-A relay network. A dynamic flow control algorithm (DFCA) is then proposed to minimize the buffer-overflow and buffer-underflow probabilities. The proposed DFCA is designed to minimize the feedback signaling overhead by dynamically adjusting the window size and the feedback frequency based on the relevant measures obtained from individual UE. Simulation results showed that most of the flow control schemes can effectively prevent the buffer-overflow problem. However, only DFCA can provide lower buffer-underflow probabilities and higher throughput for most UEs versus what the other flow control schemes can do.