Cooperative Multirelay Network Design With Hybrid Backscatter and Wireless-Powered Relaying

Abstract

In this article, a wireless multirelay network in which the relays are energy constrained is studied. Especially, in order to consume the harvested energy efficiently at the relays so as to improve the network throughput, a new hybrid relaying protocol is first proposed. In the proposed protocol, each relay can flexibly switch its operation among energy harvesting (EH), information receiving (IR), active information transmission (IT), and two passive backscatter communication (BC) modes according to the channel states as well as its data buffer states and energy states in each transmission block, by which the harvested energy can be efficiently utilized and superior throughput performance can be achieved. However, under the hybrid relaying protocol, it is challenging to achieve a strategy to optimally determine the operation mode for each relay, and the energy and information scheduling at the relays that operate in the IR, IT, and BC modes. To address this issue, the involved optimization problem is formulated as a stochastic optimization problem, which cannot be tackled directly. To make it tractable, the stochastic optimization problem is transformed into a Markov decision process (MDP) with finite state and action spaces. By solving the MDP via a dynamic programming (DP) algorithm, the optimal strategy for the multirelay network is achieved. Furthermore, to reduce the computational complexity in the DP algorithm, an efficient algorithm with low complexity is developed by using a Lyapunov optimization framework. Numerical simulations show that our proposed hybrid relaying strategy can achieve superior throughput performance in wireless multirelay networks.