# Stability-Aware Geographic Routing in Energy Harvesting Wireless Sensor Networks
## 1 Introduction  
Wireless sensor networks (WSNs) are widely used, although battery capacity is a major limitation of their applicability. A new class of sensors, equipped with an energy harvesting module, is a likely solution to this problem because these energy-harvesting wireless sensor networks (EH-WSNs) can provide longer network lifetimes using harvest-aware energy management [1; 2]. In [3], the authors utilized solar-powered WSNs to establish a topology in which some nodes received and transmitted packets without consuming limited battery resources. While a wide variety of harvesting modalities are now feasible, solar energy harvesting through photo-voltaic conversion provides the highest power density, which makes it the best option for powering embedded systems that consume several mW through small harvesting modules [4]. Solar cells can generate a power density of 15 mW/cm\({}^{2}\), compared to the 330 uW/cm\({}^{3}\), 116 uW/cm\({}^{3}\), 40 uW/cm\({}^{3}\), and 960 nW/cm\({}^{3}\) generated by piezoelectric shoe inserts, small vibration microwave ovens, thermoelectricity, and acoustic noise, respectively. Therefore, solar energy harvesting-based WSNs were adopted for the proposed protocol and performance evaluations. Many routing protocols for EH-WSNs have been proposed. In [5; 6], the authors maximized workloads that were autonomously sustained by a network, although these studies only used some of the power map patterns that represent the influence of shadowing areas on the amount of energy harvested at each node. Because the shapes of the power map patterns are very simple, this model is somewhat ideal but unrealistic. Therefore, the authors in [7] used the solar irradiation statisticsdatabase from the National Solar Radiation Database (NSRDB) to create simulations and proposed a route selection method that chooses a route based on the amount of energy consumed by transmitting packets and the harvested energy's wastage due to overcharge. This paper only considered how to optimize the average residual energy and minimize residual energy at each node, and traffic was characterized by sequential and non-overlapping connection streams from one source to one sink. Additionally, the authors in [8] designed an adaptive opportunistic routing (AOR) protocol for EH-WSNs, which divides possible sets of intermediate nodes into different priority transmission regions, such that an intermediate node in the \(k_{th}\) region will be transmitted in the \(k_{th}\) time slot as long as the node has enough energy and the packet has not been relayed by higher-priority nodes. For high data rate applications using EH-WSNs, lots of duplicated data packets may be generated, although this can be overcome by using a stability-aware cooperative routing scheme for reliable high-speed data transmission in multi-rate mobile _ad-hoc_ wireless networks [9]. In WSNs, connectivity requires global topology information, which can be significant in large-scaled networks and can cause increased overhead in these networks. The geographic routing method in [10; 11; 12; 13; 14] is considered an appropriate approach for large-scale WSNs because it does not require global topology information from WSNs. Therefore, this paper proposes a geographically-based routing selection method that selects routes based on residual energy, energy harvesting, link quality, and location information to improve the performance of EH-WSNs. Actually, the performance of conventional _ad-hoc_ wireless networks under the effect of imperfect link quality has been widely studied. However, to the best of our knowledge, the impact of link quality on network performance of energy harvesting wireless sensor networks still remains an open issue. The proposed Stability-Aware Geographic Routing in Energy-Harvesting wireless sensor networks (SAGREH) can be classified as geographic routing protocol like ORPL [15]. However, the method of obtaining link quality information to take it into consideration is different compared with that of ORPL.