# A Green Routing Protocol with Wireless Power Transfer for Internet of Things
## 3 Related Works
Indeed, the SWIPT has been introduced as a promising solution to prolong lifetime of the energy-constrained IoT devices. Usually, SWIPT receiver captures RF radiation mainly in cellular networks or WiFi environment and converts it into a direct current voltage through rectenna circuits [16]. In ref. [27], the tradeoff between information rate and harvested energy in a simultaneous wireless information and power transfer system under PS and TS schemes is evaluated providing the outer boundary of robust outage capacity-harvested power region. Several papers consider SWIPT technology integrated into IoT cognitive networks. For example, in ref. [28] the IoT devices harvest energy from the radio-frequency signals received from the primary users (PU) and act as decode-and-forward relays for a cooperative relaying communications to PUs. The same issue of sharing spectrum between PUs and IoT devices acting as relays to assist the transmission between the primary users is investigated in ref. [29], where two data-driven relay selection methods based on the neural network are proposed while in ref. [30] cooperative spectrum sharing and SWIPT are considered to improve the spectrum and energy efficiency for 6G Cognitive IoT Network. Current research on SWIPT generally address one hop and two-hops wireless networks and the interest is now extended to multi-hop wireless networks for balancing the remaining energy among nodes [31]. A main issue in SWIPT receiver design is that RF-EH is usually small and may not be sufficient for RF communications in multi-hop networks. Therefore, new SWIPT receiver has to be designed as proposed in refs. [32, 33, 34] to extend SWIPT in a multi-hop wireless network. The authors in ref. [35] consider a hierarchical architecture using SWIPT to provide the so called energy neutral operation (ENO), where the nodes can perpetually work if the energy consumption is less than the harvested energy. In the proposed SWIPT structure, a Hybrid Access Point powers the wireless sensor nodes by the RF waves sent and the sensor nodes, organized in clusters, transmit the sensing data to the Cluster Head (CH). The CH is the node which requires more energy in the network due to more processing need to aggregate data and to transmit it to HAP. The nodes into the cluster transfer their remaining energy to the CH and, as a consequence, it allows to guarantee the ENO. In ref. [31] is the SWIPT method for energy-aware routing in a multi-hop energy-constrained wireless network. The energy-aware SWIPT routing algorithm allocates the information and energy of link with allocation algorithm during path finding process. An interference-aware SWIPT routing algorithm (ISWIPTR) is proposed in ref. [36] for multi-hop multi-flow wireless sensor networks. In a WSN network of \(N\) nodes, each node has PS energy harvester and information decoder and receives the desired signal plus interferences from other flows. ISWIPTR selects a node's next-hop before allocating information and energy for the node as receiver and with the complete use of the SWIPT technique and interference can improve the capacity information and energy allocation of a new flow. The cited works [31, 35, 36] consider SWIPT method to manage the end-to-end routes selection in multi-hop energy constrained wireless network while our paper mainly addresses the use of SWIPT technique to create a new OF for the RPL protocol. This new OF based on SWIPT provides an optimized route selection to forward data towards the root node balancing the remaining energy among the nodes thanks to the recharge effect.