In recent years, IoT-based wireless systems have seen rapid growth in a variety of industries. IoT heterogeneous machines, which are usually battery-constrained, must operate for longer periods of time in most applications in order to complete their assigned tasks according to end-user requirements. Furthermore, because of the increased contact rate, large-scale deployment results in a higher energy demand, reducing the lifespan of IoT products. As a result, achieving energy efficiency in such devices becomes a major challenge in order to reduce energy usage and prolong the life of the systems. It is, however, important to identify energy-saving strategies in order to maximise their effectiveness. In this paper, we look at a number of energy-efficient techniques that have recently been suggested for green IoT-based wireless systems. IoT-based heterogeneous WSN, to be precise, which is at the core of IoT technology. We conducted a thorough literature review of the strategies used to optimise energy usage and scheduling in smart homes in this paper. IOT energy efficiency is influenced by a variety of elements that have been extensively addressed. Additionally, we examined the application of edge computing and fog in IOT for energy efficiency.