Cooperative Multicast Transmission Strategy For Energy-Efficient Dynamic Network Coding

Network coding has been proved an efficient technology to increase the system throughput. Instead of simply forwarding data, nodes may recombine several input packets into a combined version for forwarding, so throughput of the network can be improved efficiently. Network coding was originally considered mainly in the context of wired communications, but there have been great interests in applying network coding into wireless communication scenarios.Although wireless multicast is a bandwidth efficient method to deliver popular services to many users, the same data must go through different wireless channels from the base station (BS) to different mobile users, and the multicast transmission rate is determined by the worst channel condition experienced by the users. Obviously, the conventional scheme results in inefficient use of rare radio resources, which is especially undesirable when most users are in good channel conditions and capable for high rate transmission while only a small fraction of the users are far away from BS or suffer deep fading.Two-stage cooperative multicast schemes has been widely applied to a wireless multicast system, where the users who have successfully received the data at the1st stage can serve as relays to help forwarding the data to the other users at the2nd stage. In this way, the BS can transmit the packets at a high rate at the1st stage, and at the same time, those whose channel condition are too bad to successfully receive the packets from the BS can be aided by the users who have successfully received the packets from the BS. Therefore, both efficiency and fairness can be guaranteed. However, if all the users can successfully receive the data from the BS at the1st stage, and all of them are chosen as relays at the2nd stage, the total energy consumption will increase significantly.With much attention directed towards energy efficient communication, on the other hand, the energy efficiency is of crucial importance consideration in multicast transmission scheme design. Previously, the main work pays attention to how to select relays at the2nd stage. With less relays helping multiple users cooperation, and those who are selected as relays having better transmission quality due to their closer distances to the unsuccessful users, less energy may be consumed.In this paper, network coding will be applied to the multicast design. Energy efficiency of different network coding schemes at the selected relays will be addressed. By applying XOR at the selected relays, retransmission time can be saved and energy consumption will decrease. For dynamic network coding (DNC) in Galois Field (q), more information will be received by the users at the2nd stage at one time. Thus, more energy will be saved. The theoretical analysis and simulations will demonstrate the advantages of the proposed schemes.