QoS-aware retransmission with network coding based on adaptive cooperation with IEEE 802.11e EDCA

Recently, network coding (NC) has been popularly applied to wireless networks in order to improve scarce wireless capacity. In wireless LANs, NC can be applied to packet retransmission in which multiple packets can be equivalently transmitted by a single retransmission trial at base station (BS). In this paper, retransmission based on NC cooperates with IEEE 802.11e EDCA. In EDCA, when network load is high, QoS is significantly degraded even in high priority class. To solve this, existing methods improve backoff control, and decrease packet loss caused by collision. However, backoff control cannot prevent packet loss caused by multipath channel fading. In the proposed cooperation between NC and EDCA, QoS of high priority class is improved from the aspect of efficient loss recovery. Unlike NC method with no QoS control, we encounter transmission scheduling problem among NC packet, single lost packet, and new packet. Moreover, in the constitution of packets encoded into NC packet, priority and traffic load of each priority class should be considered. Therefore, we propose how to determine the packet to be transmitted at next transmission opportunity in BS and how to constitute NC packets encoded by adequate set of lost packets. Finally, we show the effectiveness of the proposed method by extensive computer simulation.