Channel-aware transmission of feedback messages for WiMAX ARQ

In the 4G communications standards, including Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE), Automatic Repeat reQuest (ARQ) is one of the important tools to coop with error-prone transmission environments. The primary function of ARQ is to provide reliable communication between a transmitter and its receivers through the retransmission of lost ARQ blocks. The retransmission at the sender can be triggered by either of the two events. The first one is for the sender to retransmit an ARQ block whose retry timer expires. The second one is when the transmitter receives the feedback message reports, which indicate block reception situation from the receiver, the flagged lost ARQ blocks will then be sent again. There are four types of feedback messages defined in the WiMAX standard. How and when the receiver reports feedback messages will have impact on the transmission efficiency. If the receiver reports feedback messages more frequently, the lost ARQ blocks can be retransmitted more promptly at the cost of higher bandwidth consumption of the feedback channel. By contrast, if the receiver waits for a longer time before sending a feedback message, feedback messages can be formed more efficiently in terms of bandwidth usage with longer transmission time incurred. In this paper, a performance evaluation metric is defined to consider the influence of both transmission latency and the required bandwidth to transmit feedback messages. A feedback message transmission scheme is further proposed to determine the interval and the types of feedback messages dynamically, based on the condition of channel conditions. The proposed method is aimed to find a balance between the transmission delay and the bandwidth usage efficiently, and the improvement of the proposed method is confirmed by the experiment results.