# UVCS: Unit Virtual Coordinate System for UAV Intra-Swarm Routing in GPS-Denied Environment
###### Abstract  
Wireless ad hoc networks are the solution for providing network connectivity in challenging environments with a lack or absence of infrastructure. Data transmission in such networks typically adopts geographic routing protocols, which use geographic coordinates as addresses of network devices. However, geographic coordinates are not always obtainable, as traditional localization systems (GNSS, Wi-Fi, terrestrial infrastructure) might not be available due to signal loss. In this paper, we propose a method that assigns virtual coordinates to network nodes, which can be used as input for geographic routing protocols. The numerical results demonstrate the high topological similarity between the physical and the virtual network. Our method exhibits convergence advantages over conventional approaches and outperforms them in terms of the total number of discovered paths. U  
A 1220  
There are many aspects to consider when designing an intelligent autonomous drone swarm system: control and management of the swarm, its efficiency, and performance of the distributed computations. Nevertheless, one of the main challenges is to maintain the connectivity of an autonomous drone swarm [8]. Connectivity is needed (i) to maintain swarm integrity (if any drone is lost, the swarm loses its structure, resulting in reduced functionality) (ii) to traverse various complex objects (e.g., tree crowns), and (iii) to perform distributed or a centralized computation within the swarm and exchange information between drones. Thus, it is necessary to ensure the efficient routing of information within the swarm. As it was mentioned before, the support of UAVs (or drones) connectivity is challenging. One of the solutions is wireless ad hoc networks--decentralized wireless networks with no permanent structure [9]. Due to the simplicity and low cost of deployment, wireless ad hoc networks perfectly fit many applications in medical, intelligent transport, and other fields. Among all the possible use cases, UAV ad hoc networks remain the most promising one--for instance, the specifics of ad hoc networks perfectly suit the purposes of search and rescue operations [10]. Traditional routing protocols based on the awareness of each network node about the location of all other nodes require regular exchange of signaling information between all network nodes and are inefficient in these conditions due to excessive overheads. Alternatively, one might use data about the local position of devices obtained from external sources for routing in ad hoc networks. Geographical routing is an example of a protocol that uses the geographical coordinates of the device to deliver data. However, as mentioned above, external information may not always be available. In this paper, we propose an iterative algorithm for positioning nodes in the developed Unit Virtual Coordinate System (UVCS), which allows, using the information available in the node only about the presence of neighbors in a given radius and the distance to each of them, to determine its coordinates in the UVCS. Based on the UVCS, it becomes possible to apply one of the geographic routing algorithms to build a route to any network node, without even knowing the direction to the destination node. The developed approach, which combines the UVCS system and a geographic routing algorithm, allows maintainance self-organization and topology to ensure the connectivity of a drones swarm. The iterative algorithm for positioning nodes in the UVCS system works on the principle of fast gradient descent and minimizes the difference between the known estimate of the distance to a neighboring node and the distance in the UVCS system, averaged over all neighboring nodes.