Hybrid Precoding for an Adaptive Interference Decoding SWIPT System With Full-Duplex IoT Devices

In this article, a simultaneous wireless information and power transfer (SWIPT) system with full-duplex (FD) Internet of Things (IoT) nodes is considered and investigated. We induce the adaptive interference decoding (AID) strategy as well as the switch and inverter structure with antenna selection (SIAS)-based hybrid precoding scheme to the SWIPT system. A joint optimization of hybrid precoder, decoding rule, and power splitting (PS) ratio problem is formulated to minimize the total transmission power, while satisfying the data rate and harvested energy constraints. As it is a nonconvex problem, we propose a suboptimal solution with three stages. In the first stage, a search algorithm which can reduce the complexity of exhaustive search is proposed to decide the sending mode of each node. In the second stage, we utilize the semidefinite relaxation (SDR) approach to find the optimal digital precoder and PS ratios. In the last stage, we propose an alternate minimization algorithm to obtain the hybrid precoding vectors. The simulation results show that our proposed suboptimal solutions can achieve a better performance in terms of power consumption and outage probability compared with those for treating interference as noise (IAN) systems and the digital precoding schemes. Both AID strategy and SIAS-based hybrid precoding are beneficial to the FD SWIPT system. Moreover, the self-interference causes little effect on the system performance as long as it can be eliminated up to 30 dB, which can be easily achieved by the antenna separation technique.

I. Introduction

Internet of Things (IoT) has become one of the main-stream emerging communication paradigms that links the Internet with everyday physical objects [1]. It creates a worldwide network of interconnected things that can exchange information and work together with each other to support new applications, such as unmanned aerial vehicles (UAVs)and mobile crowd sensing (MCS), which play a key role in a wide range fields, including smart city, smart grid, and industrial automation [2]–[4], etc. Meanwhile, the explosion of the number of IoT devices raises new requirements for communication technologies. One extremely important issue is to improve the utilization of spectrum resources. Among the emerging technologies for next generation communication systems, full-duplex (FD) is considered as a way to potentially double the spectrum efficiency and increase the capacity of wireless networks. FD methods must transmit and receive signals in the same frequency band simultaneously and thus result in serious self-interference (SI) [5]. Nevertheless, thanks to recent research progress on SI suppression technologies [6], [7], FD becomes a key enabling technique for next generation communication systems.