Reducing delays by network coding for wireless broadcasting in networks using relay stations

We consider the problem of reducing delays in block transmissions of packets over multicast erasure channels in heterogeneous networks using relay stations. The macro base station performs random linear network coding over a block of packets which are relayed to the relay station which broadcasts the packets to the users. We propose a fluid approximation to our problem, and obtain the optimal solution for the fluid model when the users' channels are homogeneous. For the general case we propose an approximate algorithm which is simple to implement. We observe that it is crucial to explore the trade-off between the opportunity in the users' channels and moving packets out of the system. Simulation results show that our scheme achieves a decoding delay which is close to a theoretical lower bound.