Distributed Compute-and-Forward Based Relaying Strategies in Multi-User Multi-Relay Networks

The compute-and-forward (CMF) relaying technique, proposed by Nazer et al., provides a substantially higher network coding throughput in multiuser cooperative networks, compared to the other conventional relaying techniques. The improvement is due to exploiting the multiuser interference rather than avoiding it. However, a major drawback of this strategy is that the equations decoded by different relays are not necessarily linearly independent, and hence a rank failure may occur at the destination; which results in a substantial reduction of the system rate as well as the diversity order. In this paper, we propose three practical distributed schemes to deal with the problem in a multi-user multi-relay network without central coordinator, in which the relays have not any prior information about each other. In first scheme, a new relaying strategy based on CMF, named incremental compute-and-forward (ICMF), is proposed that requires cooperation among relays. Second, a novel simple strategy, called amplifyforward and compute (AFC), is introduced in which the equations are recovered in the destination rather than in the relays. Finally, the two schemes ICMF and AFC strategies are combined to present hybrid compute-amplify and forward (HCAF) relaying scheme, which improves the performance of the ICMF considerably. We evaluate the performance of our proposed strategies and compare the results with those of the conventional CMF strategy and also the well known Decode and Forward (DF) strategy. The results indicate the substantial superiority of the proposed schemes, specially at the higher number of users and also relays. The authors are with Electrical Engineering Department, Sharif University of Technology, Tehran, Iran. Emails: sm_azimi@ ee.sharif.edu,[email protected],[email protected]. ar X iv :1 40 8. 28 54 v3 [ cs .I T ] 1 N ov 2 01 4