## 1 Introduction  
The Internet of Things (IoT) is a promising technology that aims to provide connectivity solutions. With the expeditious expansion of IoT technology across the globe, it is expected that billions of small sensors or devices will be connected with each other over the next few years [1; 2; 3]. The technological development in IoT integrates various sensors, devices, smart objects to be fully operated as autonomous device-to-device (D2D), machine-to machine (M2M) without any human intervention [4; 5; 6]. IoT is considered as one of the most important part of the fifth generation (5G) wireless systems as it can support massive object communications [7; 8]. These massive object communications in the context of IoT is expected to consume a huge power. Therefore, energy efficient green communication within the context of 5G and IoT is a challenging problem to be solved [9]. Sensor nodes are the principal components which brings the idea of IoT into reality [10]. These massive IoT sensor nodes and devices are usually battery operated and hence replacement of battery in such small objects is not a feasible option. Moreover, cooperative communication has been widely studied to mitigate wireless impairments such as fading and other environmental factors [11; 12; 13; 14]. However, conventional cooperative relaying techniques requires the participating relaying nodes to spend extra energy for data transmission which may prevent the battery operated IoT nodes to take an active part in relaying. Therefore, wireless energy harvesting (EH) from ambient Radio Frequency (RF) signals is considered as a buoyant energy efficient solution to combat the issue of powering massive IoT sensor and devices [15; 16; 17]. RF EH is thus considered as an appealing solution in extending the lifetime of these IoT sensors and devices from months to years and even decades, that ultimately enable their self-sustaining operations [18]. In wireless communication systems, simultaneous information and power transfer (SWIPT) is another emerging paradigm that allows the wireless nodes to recharge themselves through RF signals directed to them from the source node and then relaying or transmitting the information [19]. Meanwhile, accommodating multiple users that can be multiplexed in power domain, non-orthogonal multiple access (NOMA) has been proposed as another important candidate for future 5G technology for providing spectral efficiency and power gains [20; 21]. The main idea of NOMA is to serve multiple users in the same frequency band, but with different power levels, which is fundamentally different from conventional orthogonal multiple access schemes [22]. In particular, power-domain NOMA allocates more transmit power to users with worse channel conditions and less transmitting power to users with better channel conditions in order to achieve a balanced trade-off between system throughput and user fairness. Therefore, users can be separated by successive interference cancellation (SIC) at the receiver side [23]. An illustration of generic RF EH relay communication system is shown in Figure 1, where a source node selects one of the RF EH relaying node to transmits its information to its intended destination. The harvested energy from RF source signals allows the relay node to power up themselves for simultaneous information processing and transmission (SWIPT) [24]. It is also understood that using more than one relay increases the complexity of the systems greatly [25]. Such cooperative RF EH relay communication systems as depicted by Figure 1, only considers the transmission of source node data successfully. In this paper, we envisioned an ubiquitous IoT relay system where an IoT node that can acts as a relay for transmitting source node information data to its intended destination and at the same time, it also transmits its own data to its destination node based on NOMA protocol.