# Energy and Distance-Aware Hopping Sensor
## 2 The Proposed Protocol to Relocate Hopping Sensors
### Characteristics and Assumptions of Hopping Sensors  
The feature of the hopping sensor is that it can move in a rough surface region such as rock or sand by jumping rather than using a wheel. In addition, the data transmission radius of the hopping sensor node can be expanded by jumping. The authors of References [18; 19] explained that the sensor node can jump to the appropriate height and adjust the communication radius. Reference [18] introduced the \"Airborne communication scheme\" in which the communication radius was expanded by jumping when two hopping sensors were out of the communication radius on the ground. In Reference [19], when the sensor node jumped 1 m from the ground, they showed a six-fold increase of the radius compared with that on the ground. The connectivity of the sensor nodes to the entire network could be improved in this way, and a method for covering the whole area of the network was proposed. The authors of Reference [20] actually implemented the hopping sensor, using a launcher for the jump, and measured the transmission radius. In Reference [20], the variation of the transmission radius according to the height was compared with the result of Reference [19] and confirmed that the two results were similar.  
In the research area of wireless sensor network, there are various algorithms for clustering the network area and selecting the headers [21]. It is assumed that the clustering and the selection of the headers have already been set up, since the objective of this paper is to research a method to efficiently relocate mobile hopping sensor nodes.  
In detail, the sensor nodes are randomly distributed in the area where the initial data is desired to be collected. The network area is then divided into clusters by various algorithms, and a cluster header suitable for each cluster is selected. The cluster header communicates periodically with the sensor node members in its cluster. The cluster headers can jump to extend the transmission radius to establish a connection with the relay node in Figure 2. Furthermore, sensor nodes include a GPS unit that can identify their current position [22].  
Figure 2 briefly describes each term used in this paper. The sensors in this figure are different in shape and color, but in fact, they are all the same sensors, and all sensor nodes are hopping sensor nodes. Since the sensor nodes can move while jumping, the sensors are called as \"hopping sensors\". The hopping sensor may be a \"cluster header\" or a \"cluster member node\". Since the maximum transmission radius when the cluster headers take the highest jump is defined as a \"cluster zone\", communication between the cluster headers cannot be directly established. Some member sensor nodes in the overlapping region of the neighbor cluster zone can  
more cluster headers. Their role is similar to those of helper nodes in the middle of a routing path between two nodes to increase the reliability of communication [23]. In this paper, we will refer to this sensor node as a \"relay node\", and the role of the relay node will play a role in intermediating the communication between the cluster headers. Again, a hopping sensor jumps only when moving and when communication between a cluster header and a relay node is made.