## 1 Introduction
Furthermore, if EH is employed in such IoT relay systems, it has the potential to provide unlimited energy to sensor nodes and thus enabling self-sustainable green communications [26]. Also, in order for small IoT device to communicate and transmit data, M2M relaying has been proposed as a suitable heterogeneous architecture for 802.16p IoT, Third Generation Partnership Project (3 GPP) machine type communications (MTC) and European Telecommunications Standards Institute (ETSI) M2M communication [27]. Hence, we believe that our considered scenario for IoT relay EH system fits to the standardization activities of ETSI and 3 GPP projects for self-sustainable green communications. In SWIPT, time splitting (TS) relaying and power splitting (PS) relaying schemes are very popular for energy harvesting and decoding the information separately. In TS relaying scheme, the receiver switches between energy harvesting and information decoding over time. However, in PS relaying scheme, the receiver uses a portion of received power for energy harvesting purpose and then uses the remaining power for information decoding. [PERSON] et al. studied amplify-and-forward (AF) relaying network based on TS and PS relaying schemes [28]. They derived the analytical expressions for outage probability and the ergodic capacity for delay-limited and delay tolerant transmission modes. [PERSON] et al. investigated outage analysis of multi-user cooperative transmission network with TS and PS relay receiver architectures [29]. They theoretically analyze the system outage probability based on TS and PS relaying protocols. A cooperative SWIPT NOMA protocol has been studied in [30]. Here, near NOMA users that are close to source node acts as EH-based relay to help far NOMA users. Considering user selection schemes, they derived the closed-form expressions for the outage probability and system throughput. [PERSON] et al. [31] studied the outage performance of EH-based decode-and-forward (DF) relaying NOMA networks by deriving the closed form equation of the outage probability. Two copies of same information from the source node direct link and EH-based relay link were received at the destination nodes. [PERSON] et al. [32] studied TS and PS with EH and NOMA in a spectrum sharing environment. The secondary transmitter acts as an EH-based relay and then transmits the primary transmitter data along with its data using NOMA protocol. [PERSON] et al. [33] also proposed an EH-based spectrum sharing protocol for wireless sensor networks. However, although a myriad of such EH works have been carried out in the literature, EH considering the energy-efficient data transmission of source and IoT relay node together based on TS, PS and NOMA suitable for IoT relay systems has not been considered in the previous works. This motivated us to propose an RF EH and information transmission based on TS, PS and NOMA for IoT relay systems and analyze their performance by deriving the analytical expressions for outage probability, throughput and sum-throughput. In summary, the main contribution of this paper is as follows:  
* Realizing the energy constrained nature of IoT nodes, we have considered and investigated an RF EH-based on TS, PS and NOMA for IoT relay systems. * Although a myriad of works have been carried out in the literature for EH, the absolute vast majority of those works only consider RF EH at relay node and transmission of source node data successfully to its destination node. Those approaches do not consider the data transmission of the relay node that may be an IoT node which needs to transmit its data along with the source node data to their respective destinations. In this paper, we rather focus on RF EH and information transmission based on TS, PS relaying and NOMA for IoT relay systems. * We have mathematically derived the outage probability, throughput and sum-throughput for our proposed system.