herefore is capable of transmitting/relaying the message of the far user. This leads to higher reliability [24]. Cooperative relaying only, without NOMA, leads to degradation of spectral efficiency due to transmissions of duplicate messages. With increase in demands by the IoT devices and its underlying challenge of security, NOMA is envisioned as capable of satisfying the secure short-packet communications need in IoT networks [1]. Furthermore, with NOMA, additional security mechanism is also not required by intentionally increasing the co-channel interference at the eavesdropper. Another very interesting application of NOMA is in grant-free transmission. The grant-free transmissions are vulnerable to collisions; however, they achieve low latency which is envisioned for 5G and beyond networks. By exploiting the power domain, and multiplexing the user using different power, NOMA reduces the collisions under grant-free transmission, and this is capable of achieving massive machine-type communication [25, 26]. Another very recent and revolutionizing technique to enable the battery-free IoT is backscatter communication with NOMA. The integration of NOMA and backscatter communication is recognized as spectral and energy-efficient technol- ogy for implementing massive IoT networks [27]. One of the additional advantages of NOMA besides massive connectivity and spectral efficiency is its compatibility. Only minimal changes are required to implement NOMA in the existing networks [4]. The popularity and widespread use of superposition coding and SIC (perfect and imperfect SIC [28]) further ease the implementation of NOMA. Therefore, NOMA is considered as a potential multiple access candidate for the 5G and beyond networks. 5 NOMA for 5G and Beyond Wireless Networks 5.3 Heterogeneous Networks With increasing data demands in cellular networks and with link efficiency approaching its fundamental limits, there emerges a need to improve spectral efficiency. A possible way of doing this is increasing the number of macro base st