Performance Analysis of cooperative SWIPT System: Intelligent Reflecting Surface versus Decode-and-Forward

In this paper, we explore the impacts of utilizing intelligent reflecting surfaces (IRS) in a power-splitting based simultaneous wireless information and power transfer (PS-SWIPT) system and compare its performance with the traditional decode and forward relaying system. To analyze a more practical system, it is also assumed that the receiving nodes are subject to decoding cost, and they are only informed about the imperfect channel state information (CSI). First, we drive the achievable data rate of single IRS-assisted cooperative communications, and to maximize the achievable rate, optimal phase shits for each elements of the IRS node is derived, and finally the optimal power splitting ratio at the destination is obtained. The, the system model is extended to consider two and multiple IRS-assisted system. The respective achievable rates are derived and optimized accordingly. To evaluate the benefits of using the IRS, we have also derived the achievable rate for a two-hop decode and forward relaying scheme, wherein both the relay and the destination not only did they equip with rededicated power but also they can harvest energy from the received signals to provide the required power for the decoding. For this case, optimal power splitting factor at both the relay and the destination are optimized. Finally, the numerical results are presented to examine and compare the performance of the two considered systems. It is shown that by increasing the size of the reflecting surface, IRS-based cooperative transmission outperforms the conventional relaying scheme.