A Hybrid-Combine-and-Forward Relaying Scheme for Network Coded Cooperative Systems

Network Coded Cooperation (NCC) proved itself worthy to meet the ever increasing demands of the next generation wireless users. In the prevalent relaying schemes, the relay either uses Amplify-and-Forward (AF) or Decode-and-Forward (DF) rigidly over all the signals received. However, some networks use Adaptive Decode-Forward (ADF) where relay only forwards the decoded data which causes resource wastage as the sources need to re-transmit the data which were not sent by the relay. This paper proposes a Hybrid-Combine-and-Forward (HCF) relaying scheme for a multi-user scenario to improve the Quality-of-Support (QoS) in a cost effective manner. With the HCF scheme, the relay dynamically performs AF on some of the received signals while DF on the rest, and stores them within a communication cycle. This decision is taken by the relay based on the Instantaneous Signal-to-Noise Ratio (SNRi) of the signal received from the respective sources. Finally, it combines all the stored signals received and transmits a hybrid superposed data to the destinations which is required to extract the second copy of the desired data. Extensive simulations provide results showing the superiority of the proposed HCF scheme over the widely used AF and DF schemes. Such a scheme can be used in a Device-to-Device (D2D) communication/ Vehicle-to-Everything (V2X) networks or in scenarios like disaster management where sources aided by a drone/relay require reliable data at a low operational cost of the relay.