Optimal power splitting for MIMO SWIPT relaying systems with direct link in IoT networks

Ultra-high reliability communications are greatly vital for massive user connections and network sensors such as Internet of Things (IoT) devices in the beyond 5th generation (B5G) communication networks. Simultaneous Wireless Information and Power Transfer (SWIPT) has evolved as an efficient strategy through prolonging the battery life by harvesting energy from radio-frequency (RF) signals. Moreover, cooperative relay sensors in IoT network can enhance the network coverage. In this paper, we investigate the multiple-input multiple-output (MIMO) SWIPT relaying systems with direct link, where the relay node splits the received RF signals into two power streams, one for information decoding (ID) and the other for energy harvesting (EH). Under per-antenna power constraints, the relay node forwards the ID signal to the destination. We propose a channel diagonalization scheme based on singular value decomposition (SVD) and eigenvalue decomposition (EVD) to design the precoding matrix of source and the amplifying matrix of relay respectively. Moreover, the closed-form expression of the optimal power splitting (PS) factor diagonal matrix is obtained to maximize the sum-rate of MIMO SWIPT relaying system. Finally, the efficiency of proposed precoding and PS factor design is verified by the presenting numerical results.