ECTX: A high-throughput path metric for multi-hop wireless routing exploiting MAC-layer cooperative retransmission

We present a cross-layer approach for enabling high-throughput routing in multi-hop wireless networks. This approach builds on a MAC-layer cooperative retransmission mechanism, which is explicitly designed to exploit the benefits of MAC-layer retransmission-based reliability, cooperative communications, and link-quality awareness. Based on this mechanism, we devise a routing metric, called the expected cooperative transmission count (ECTX), to capture the combined effects of MAC-layer cooperative retransmission and per-link estimates of packet delivery ratios. We show that, compared to conventional approaches using the well-known expected transmission count (ETX) metric, our approach has two advantages in principle: 1) with the cooperative retransmission mechanism, one can effectively reduce the expected total number of packet transmissions (including retransmissions) on the same path found by ETX; 2) with the ECTX metric, one may indeed identify a more effective path and further reduce the transmission count. We discuss modifications to IEEE 802.11 MAC to incorporate the cooperative retransmission mechanism, and implement ECTX-based routing using the DSR protocol. Extensive simulations on QualNet demonstrate that ECTX-based routing is significantly more efficient than ETX-based routing, in many instances reducing the transmission count by more than 30% and yet improving the network throughput by up to 80%.