# An Energy Balance Clustering Routing Protocol for Intra-Body Wireless Nanosensor Networks
## 1 Introduction  
Nanotechnology plays an increasingly important role in many fields such as environment, industry, biomedicine and military with its rapid development. Subsequently, the concepts of nano-communication and Wireless NanoSensor Networks (WNSNs) were proposed [1], nano-devices can communicate cooperatively and share the perceived information. Due to the significant advantages in size, biocompatibility and biostability of nanodevices, WNSNs have great application prospects in intra-body health monitoring and medical treatment. Thus, intra-body Wireless NanoSensor Networks (iWNSNs) have also become a new research hotspot. The development of new materials such as graphene [2] and carbon nanotubes (CNT) [3] that can work at terahertz frequencies (0.1-10 THz) opens new opportunities for applying these nanodevices to the body. This underutilized terahertz spectrum [4; 5; 6; 7] will have a major impact on future medical technologies. First, it can provide a wide bandwidth and the antenna size can be made small. Second, it is less sensitive to propagation effects such as scattering and it is relatively safe for biological tissues [8; 9]. Therefore, terahertz wireless communication is an ideal choice for iWNSN physical layer technology. As one of the key technologies of WNSNs, routing protocols have been studied by scholars in recent years. Currently, researchers mainly study three types of protocols: flooding protocols, proximity routing protocols and energy harvesting-based routing protocols. The flooding protocol is very simple, which is consistent with the characteristics of limited nano-node energy and computational power [10]. However, flooding protocols can cause broadcast storms and excessive retransmissions, thereby increasing energy consumption. Proximity routing protocols attempt to improve the performance of flooding protocols by controlling the number of neighboring nodes. Examples of these protocols include CORONA [11], SFR [12] and EEMR [13]. CORONA is a geographic flooding protocol that assumes that nodes in a nanonetwork consist of two types: anchor nodes and user nodes. Anchor nodes have higher communication and processing capabilities than user nodes. User nodes need to localize their location relative to these anchor nodes. The scheme assumes a square fixed network topology in which four anchor nodes are located at the vertices of the square network. A selective flooding routing (SFR) based on terahertz band communication is proposed in [12]. In order to avoid waste of bandwidth resources caused by repeated forwarding of the same data packet, the protocol optimizes the flooding direction. The trend of forwarding packets to the destination node is guaranteed, thereby reducing the number of messages in the network. [PERSON] et al. proposed a protocol called EEMR [13] to solve the problem that the routing protocols such as CORONA and SFR do not consider the terahertz channel attenuation characteristics. However, the EEMR protocol is a single-path routing protocol, which has poor adaptability to network topology changes. For example, it cannot solve the problems that the nano-nodes' failures due to energy exhaustion or the temporary interruption of the transmission link caused by molecular group disturbance of the channel environment. Energy-based routing protocols [14; 15; 16] are specifically designed for self-powered nanonetworks. The main goal of these protocols is to balance energy harvesting and energy consumption, so that the lifetime of the network tends to infinity. In designing such routing protocols, the tradeoff between the complexity and accuracy of the protocol should be considered. For example, [PERSON] et al. proposed a routing framework based on energy harvesting [14].