Network coding is known to benefit the downlink retransmissions by the AP in a wireless LAN from exploiriting overhearing at the client nodes. However, designing an efficient and practical retransmission scheme remains a challange. We present an (asymptotically) optimal scheme, ECR, for reduing the downlink retransmissions by the AP in a wireless LAN from exploiting overhearing at the client nodes. The design of ECR, consisting of three components: batch-based operations, a systematic phase-based network coding decision policy, and smooth integration of inter-flow and intra-flow coding, is accompanied by a theoretical underpinning, yet enables practical implementation on off-the-shelf 802.11 hardware. We analytically show ECR can achieve much higher reduction in packet retransmissions than previous schemes, and validate its performance gain via simulations and testbed implementation. To our knowledge, ECR is the first protocol that leverages both intra-flow and inter-flow network coding to solve a real-world problem in the single-hop wireless networks.
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