Earliest Partial Relay Synchronous Cooperation Scheme for Multi-Relay IoT System with the Tradeoff of AoI, Energy Efficiency and Throughput

Although the use of full duplex (FD) multiple relays is promising in Internet of Things (IoT) systems, this scheme has low energy efficiency. In addition, it is not known whether multi-relay cooperation is always beneficial to freshness of status update. With this, a tradeoff among age of information (Aol), throughput, and energy is designed in a FD multi-relay assisted IoT system. We first propose an earliest partial FD relay selection scheme by jointing automatic repeat request (ARQ). Secondly, the employment of ARQ causes the randomness of the retransmission numbers of the two-hop relay links and the out of order update delivery. To address this complex problem, a synchronous cooperation delivery mechanism is also integrated, where a new round of the packet transmission begins only when both the FD relays and destination successively recover the received status update. Finally, we derive the average Aol by establishing four different cases. The numerical analysis shows that the increase of the number of the selected relays is not always beneficial to the information freshness.