Systematic network coding for transmission over two-hop lossy links

Packet transmission over two-hop lossy link is increasingly important in communication networks. In this paper, we present a systematic network coding scheme for packet-level transmissions over two-hop lossy links. In the scheme, a source node sends out uncoded packets in their original order first, followed by a potentially unlimited number of coded packets using random linear network coding. The intermediate node forwards a packet if it receives an uncoded packet, and sends a coded packet from previously buffered packets using random linear network coding if it does not receive a packet or the received packet is coded. We show that, compared to the scheme in which random linear network coding is used all the time at the source and intermediate nodes, the proposed method requires much less computation in encoding and decoding and also achieves a higher end-to-end rate. The benefit is appreciable when the number of source packets is not large and the finite field in which network coding is performed is small. To analytically assess the performance, we employ a Markov chain based technique to calculate the expected completion time of the proposed scheme given the number of source packets, link erasure rates and finite field size.