## 2 Literature Review
For obtaining the ideal SP, PA, and PS factors, a joint improvement technique was proposed in which the active subcarriers are combined at the relay node as per two hops channel gains. To assess the performance of the system, massive simulation experiments were conducted where the results exhibited that by utilizing their proposed RA approach, maximum feasible data rate of the system can be obtained. However, with similar total accessible power utilization, the SWIPT-empowered OFDM Decode-and-Forward (DF) relay systems have shown some performance impairments compared to the ordinary non-SWIPT OFDM DF relay systems.The authors in [19] introduced an exploratory examination of simultaneous energy and information transmissions in RF-controlled WSNs. In particular, they examined the impact of information transmissions and energy transfer in the same frequency band. In addition, they measured not only the effect of long-extend interference of energy transmitters, but also the energy charging range required to viably revive or recharge nodes. They further demonstrated the interference between RF energy transmitters and wireless nodes when both operate simultaneously in the same spectrum. They likewise distinguished safe frequency detachment for simultaneous information and energy transmission. The destructive interference effect of having various energy transmissions utilizing the same frequency has been also reported. Moreover, the effect of power cancellation on the power harvested has been effectively measured. The practicality and productivity of multi-frequency band RF energy harvesting considering RF energy circuits with a wide response range of frequency have been demonstrated too. In addition, to this end, the authors have exhibited that multi-band RF harvesting and frequency separation are promising for enhancing in general the performance of the system in terms of the throughput. The authors in [20] summarized many research works, which are based on RF energy harvesting in which the energy limitation of WSNs was addressed using Powercast harvesters. Not only to this extent, but rather they detailed the approach in utilizing ant colony optimization meta-heuristic mechanism. In addition, the authors primarily proposed down-to-earth RF energy harvesting using Powercast harvesters. Furthermore, the harvested and accessible energy of the sensor network's was managed with an improved energy efficient ant-based routing protocol, which basically helped much in optimizing the available power. Their major goal was to get the sensor networks powered efficiently with/without batteries to keep the network lifetime at the greatest level and avoid any degradation in the network's performance. In [21], the authors have taken up the problem of individual energy requirement in a sensor network for each of the sensor nodes, and proposed a scheme for optimum charger placements that would lead to a minimum number of chargers, while satisfying the energy requirement of each sensor node. Furthermore, the authors have shown that the problem is NP-hard, and presented two approximation algorithms based on the greedy and relax rounding schemes to achieve better and guaranteed performance in the context of charger placements. Extensive numerical simulations have been conducted to substantiate their claim in terms of the efficacy of the proposed algorithms. A wireless system on chip energy harvesting sources that are capable of harvesting ambient energy has been addressed in [22] along with a power management model that processes and distributes the harvested power using low power radio communication. The basic idea of this work is to present end deployment solutions for energy harvesting. The research work in [23] proposes a new clustering scheme called the Distance Energy Evaluated (DEE) for WSN to increase its lifetime. It has been demonstrated by the authors that DEE has the advantage of utilizing minimum energy for routing and load balancing.