Multi-Layer Network Coding for Multiuser Relay Networks with Non-Uniform-Rate Users

Existing finite field network coding (FFNC) can be applied in networks where all users have the same data rate and can thus use the same modulation type. In most practical scenarios, different users typically have different data rates. With simple changes such as zero-padding and repetition to the data sequences of different users received at relays, it is still possible to employ the existing FFNC scheme, but the network throughput and error performance will be compromised. In this paper, we design a network coding scheme for multiuser multiple-relay networks where users' data rates are different. Specifically, we develop a layered network coding approach that allows the use of the existing FFNC for each layer in a hierarchical structure and derive the corresponding decoding process. The bit error (BER) and computational complexity of the proposed scheme are derived. Because the proposed scheme could fully exploit the additional diversity gain from decoding the codewords in each layer separately, it achieves a better BER performance than the existing FFNC scheme, which is validated in simulation.