  In this paper, we study Coded relay (Crelay) in multi-hop wireless networks.
Crelay exploits both partial packets and overhearing capabilities of the
wireless nodes, and uses Forward Error Correction code in packet forwarding.
When a node overhears a partial packet from an upstream node, it informs the
upstream node about the number of parity bytes needed to correct the errors,
such that the upstream node need only send a small amount of parity bytes
instead of the complete packet, hence improving the network efficiency. Our
main contributions include the following. First, we propose an efficient
network protocol that can exploit partial packets and overhearing. Second, we
study the routing problem in networks with Crelay and propose a greedy
algorithm for finding the paths. Third, we propose an error ratio estimator,
called AMPS, that can estimate the number of byte errors in a received frame
with good accuracy at a low overhead of only 8 bytes per frame, where the
estimator is needed for a node to find the number of needed parity bytes.
Fourth, we implement the proposed protocol and algorithm within the Click
modular router, and our experiments show that Crelay can significantly improve
the performance of wireless networks.
