Throughput Maximization for Multi-hop T2T Backscatter Communications in Cooperative IoT.

This paper proposes a novel cooperative transmission protocol for a three-user backscatter communication (BackCom) in the Internet of Things. Specifically, the optimal time-division multiple access based transmission protocols for the 2-hop and 3-hop cooperative schemes in the BackCom system have been developed to maximize the underlying system throughput. In the investigated monostatic BackCom system, a reader simultaneously transmits the radio frequency signal to the backscatter tags in the downlink and receives the backscattered signals in the uplink. In the 2-hop cooperative scheme, either one of the near-apart tags serves as a cooperative decode-and-forward agent that relays the far-apart tag's information to the reader. On the other hand, the farthest tag collaborates with the two near-apart tags to relay its information to the reader in the 3-hop cooperative scheme. Since we aim to maximize the system throughput of the cooperative BackCom system, we formulate the maximization problem of minimum throughput among the tags in both 2hop and 3-hop cooperative schemes. Then, we investigate the optimal time allocation for maximizing the minimum system throughput for both 2-hop and 3-hop cooperative schemes. Subsequently, we introduce auxiliary variables to the original problems and convert them into equivalent linear programming problems. The numerical results verify the utility of the cooperative schemes in different transmission channels and tags' placement. In our investigation, the proposed 3-hop cooperative scheme obtained an average gain above 30% over the non-cooperative scheme.