Cross-layer design of network-coded transmission with a delay constraint

We investigate the cross-layer design of wireless networks where end-to-end data transmission is subject to delay constraint and there is no end-to-end feedback. The transmission is coded by random linear network coding (RLNC) on packet level to recover from packet erasures and by forward error-correction coding (FEC) on bit level to combat channel distortions. Based on the two-layer model developed by Adams et al. where the end-to-end coded transmission is characterized by a throughput-reliability function, we formulate the cross-layer design as a goodput optimization problem relax the integrality constraint. We show that for single-hop transmissions there exists a globally optimal operating point for the relaxed problem. For multiple-hop transmissions, the goodput function is component-wise concave with respect to the physical layer data rate over each individual link.