# Joint Balanced Routing and Energy Harvesting Strategy for Maximizing Network Lifetime in WSNs
## 1 Introduction
To mitigate the irregular energy harvesting problem, wireless power transfer (WPT) transmits power distantly to the sensors, which provides an attractive opportunity for harvesting ambient energy [22]. Given the wireless charger, the energy transfer to the sensors can be controlled and make the network optimization in lifecycle extension. In [23], the authors optimize the network lifecycle performance under the condition that the energy consumption by each sensor is less than its harvested energy. Hence, the network operation lifecycle depends on not only how the wireless charger transfers the power to the sensors, but also how the sensors spend the reception power. To jointly consider the energy balanced routing and energy harvesting benefits, a Shortest Path Tree with Energy Balance Routing strategy (SPT-EBR) is proposed in this article. In SPT-EBR, two methods are presented including the power consumption and the energy harvesting schemes to select the forwarding node according to the awareness factors of link weight. The SPT-EBR is a positive and early-intervention method, and includes the following contributions:  
1. To avoid excessive load concentration among SCA, a power consumption scheme is presented to generate the multiple shortest path trees in the early stage for data dissemination and distributes traffic load to the path trees according to the packet forwarding rate factor. The contribution is to improve the construction of routing solution and avoid the frequent routing update messages causing the excessive load concentration, thus prolonging the network lifecycle. 2. In addition, the power consumption scheme is utilized to transfer some traffic load in the congested SCA to several sub-trees with the lowest load. This makes a part of paths with good load-balance level and high energy efficiency during the iteration process of the algorithm. As a result, each intra-layer from the sink can be expected to have the similar traffic load in terms of the balanced power consumption. The intra-layer is defined as the nodes with the same hop length to the sink. 3. Using the late-remedy routing solutions [15; 16], hotspot nodes are usually spatially distributed. With the assistance of the power consumption scheme, hotspot nodes can be transferred from the irregular location to the same intra-layer and this benefit makes the implementation of efficient wireless power charging over a large area is possible. 4. To achieve the design aim of immortal WSNs, an energy harvesting scheme is proposed to jointly combine both the packet forwarding rate and the power charging rate factors together to make the energy charging efficient for the hotspots in the SCA. With the assistance of load balancing on SCA and energy harvesting, the contribution helps to accelerate the generation of the whole network balance routing solution, improving both the routing survivability and energy harvesting efficiency, as well as prolonging the network longevity. The remainder of this paper is arranged as follows. The literature review is introduced in Section 2. Section 3 presents the problem statement and motivation. In Section 4, a network model is introduced and the SPT-EBR is presented including the power consumption and the energy harvesting schemes. In Section 5, the power consumption performances between the SPT-EBR and the Dijkstra algorithms are compared and the benefits of energy harvesting scheme are also demonstrated with computer simulations. Finally, conclusions are described in Section 6.