s used for energy transfer from which the harvested energy is then used for future infor- mation transmission. In the PS mode, upon receiving the radio signal, the energy harvest node splits the signal into two parts. The first part is used for signal decoding, while the second part is used for energy charging. A linear energy harvest model, which assumes the output power of the energy harvest circuit grows linearly with the input power, is applied in most existing works. Cooperative NOMA system with SWIPT is studied in [110], where they proposed different user selection schemes and evaluated the performance with outage probability. This paradigm is proved impractical based on field test results as shown in [21]. As a result, a more practical yet more complicated non-linear model which better matches current circuit design is considered in this chapter. Thus the wireless heterogeneous system in this study consists of higher-power MBSs and low-power relays with SWIPT that is based on the non-linear energy harvesting model. Downlink NOMA is first used to transmit com- posite signals to UE and relay. Relay then harvests the energy by using non-linear model in PS mode. With the harvested energy, relay sends the received signal to the cell edge UE. 4.2.2 System Model The system model is based on a mm Wave downlink wireless heterogeneous system that consists of high-power MBSs, low-power relays, and low-power IoT devices, such as sensors or wearable devices [176]. At mmwave band, MBSs are equipped with a large number of antennas, which have narrow half-power-beamwidth (HPBW) to combat with the severe pathloss and each transmission is conducted with a single antenna. While each low-power 4 NOMA in Relay and loT for 5G Wireless Networks relay or IoT device is equipped with a single antenna due to the size and power constraints. It is assumed that MBSs can coordinate the transmission direction; hence, inter-cell and intra cell interference can be eliminated by carefully aligning the beam directions. Furthermore, relaying 