## 1 Introduction
In addition, there are some related works integrating the SWIPT in WSNs [30; 31; 32; 33; 34; 35; 36; 37]. [PERSON] et al. [30] applied the SWIPT technique to cooperative clustered WSN, a distributed iteration algorithm was proposed by exploiting fractional programming and dual decomposition. Considering different PS abilities of relays in a mobile wireless sensor networks with SWIPT, a resource allocation design (RAD) problem was formulated as a non-convex energy efficiency maximization problem, [PERSON] et al. [31] proposed a cross-layer algorithm for rate control, PS, and power allocation. A unified framework was developed to study the impact of SWIPT on the performance with both time splitting (TS) and power splitting (PS) schemes [32] in a WSN over Nakagami-m fading channels. In the MIMO wireless powered underground sensor network, the optimal RAD problem was considered for throughput the system throughput maximization with quality of service (QoS) assurance in regard to communication reliability and diverse data traffic demands [33]. Focusing on two relaying strategies, a downlink (DL) multiple-input single-output (MISO) WSN with the nonorthogonal multiple access technique (NOMA) and SWIPT was investigated over Nakagami-m fading [34], where three antenna-relay-destination selection algorithms were proposed through analysis on downlink (DL) and UL transmissions. Assuming the sensor nodes always work in harvesting-transmitting mode, [PERSON] et al. [35] studied the PLS of uplink (UL) transmission in SWIPT deployed in WSNs, in which the energy/secrecy outage probabilities were derived through comprehensive analysis on DL and UL transmissions, respectively. As for IoT sensor networks with a PS-enabled SWIPT technology, [PERSON] et al. [36] proposed a novel SWIPT strategy where the access point have a choice over either sending a private/common message, and a hybrid beamforming design algorithm was proposed by considering the total transmit power minimization problem. By exploiting a fountain codes in the SWIPT WSNs, [PERSON] et al. [37] proposed a new PS mechanism to adaptively divide data packets into the information data packets and the energy data packets. To the best of our knowledge, secure beamforming design to achieve secrecy capacity, particularly assuming practical power splitting (PS)-based heterogeneous wireless sensor networks (HWSN) with SWIPT transmission, has not been considered previously. Motivated by the above analysis, in this paper, we consider a SWIPT-enabled two-tier HWSN with MIMO system, where a macrocell sink node and a femtocell sink node transmit co-channel information to the corresponding macrocell sensor nodes (M-SNs), high-priority sensor nodes (HP-SNs) and low-priority sensor nodes (LP-SNs), respectively. In order to harvest more energy from the ambient environment, the HP-SNs can use a power splitter. According to the ambient interference signals, the LP-SNs not only eavesdrop the confidential messages from the M-SNs, but also harvest wireless energy. By applying the interference, an AN-aided secrecy transmission is utilized at the femtocell sink node. In addition, we study the jointly optimization design of the transmit beamforming vectors at the macrocell sink node and femtocell sink node, the AN and PS ratio to maximize the minimal secrecy capacity (MSC) of the wiretapped M-SNs under the secrecy capacity constraint at the HP-SNs, the harvested energy constraint at the HP-SNs and LP-SNs, the transmit power constraint at the macrocell sink node and femtocell sink node. More explicitly, the main contributions of this paper can be summarized as follows:  
* Firstly, we establish the system model of a two-tier MIMO HWSN, where SWIPT technique is performed at the femtocell sink node to recharge the HP-SNs and LP-SNs. To be specific, each HP-SN is equipped with power splitter. We consider a general system case where both the M-SNs and HP-SNs are faced under threat of secrecy leakage from the LP-SNs, where each LP-SN act as a malicious user.