Communication Architecture in Mixed-Reality Simulations of Unmanned Systems

2018 Sensors  
Verification of the correct functionality of multi-vehicle systems in high-fidelity scenarios is required before any deployment of such a complex system, e.g., in missions of remote sensing or in mobile sensor networks. Mixed-reality simulations where both virtual and physical entities can coexist and interact have been shown to be beneficial for development, testing, and verification of such systems. This paper deals with the problems of designing a certain communication subsystem for such
more » ... ly desirable realistic simulations. Requirements of this communication subsystem, including proper addressing, transparent routing, visibility modeling, or message management, are specified prior to designing an appropriate solution. Then, a suitable architecture of this communication subsystem is proposed together with solutions to the challenges that arise when simultaneous virtual and physical message transmissions occur. The proposed architecture can be utilized as a high-fidelity network simulator for vehicular systems with implicit mobility models that are given by real trajectories of the vehicles. The architecture has been utilized within multiple projects dealing with the development and practical deployment of multi-UAV systems, which support the architecture's viability and advantages. The provided experimental results show the achieved similarity of the communication characteristics of the fully deployed hardware setup to the setup utilizing the proposed mixed-reality architecture. Introduction In recent years, there is a growing utilization of autonomous vehicles in areas of remote sensing and mobile sensor networks, especially if these vehicles can be operated beyond-line-of-sight (BLOS) as autonomous teams. However, development and validation of such multi-vehicle systems are complicated tasks since there are many complex issues that need to be taken into account. Some of them, such as complex interactions among individual entities (such as collision and obstacle avoidance, team cooperation, and coordinated movement), can be modeled with the help of software simulations [1, 2] . However, since the goal of the development process is to deploy algorithms in the real world, software simulations and computational models by themselves are not satisfactory. The effects of real-world phenomena such as those of the weather, communication issues, sensor and actuator errors, or limited computational resources, which are difficult to model on high fidelity levels, need to be verified on real hardware assets. The proper design of a communication subsystem (as any of the vehicle-to-vehicle or vehicle-to-base options) is one of the most important challenges of multi-vehicle system development. It is crucial for the control, cooperation, and collaboration of the vehicles themselves, for the purposes of routing and topology management [3, 4] , message relay [5], communication constrained exploration [6], network-aware mission planning [7], or improvement in communication throughput and delay [8, 9] . Experiments performed in a virtual world and a real world both have their limits and justifications, whereas simulations are much easier to set up and repeat; they can be used to model the basic functionality of the developed system and allow quick observations of results of interactions among entities and the environment. They can also save costs in cases of malfunctions and accidents. However, it is challenging for software simulations to incorporate all sources of inputs from the real world for realistic modeling of the behavior of the developed system. That is why real-world experiments should be an obligatory step in obtaining realistic results in later stages of the development of robotic systems and in the validation of the robustness of software before it is deployed. Mixed-reality (MR) [10,11] simulations gain benefits of both these worlds. They present a world where both virtual (SW) and physical (HW) objects and entities (further referred as the SWEs and HWEs for the virtual entities and entities embodied in the physical world, respectively) can co-exist and interact in real time. A combination of entities allows the system developers to obtain more insight into the behavior of the entities (e.g., by visualization of their inner states) and to perform much cheaper and safer experiments, with a part of the system being real and another part virtualized [12, 13] . MR simulations also relieve simulators from recreating entire worlds since simulation occurs in a partially real world where certain phenomena, such as noise and complex physics, do not have to be modeled [14, 15] . Figure 1. Visualization of the problem of maintaining high fidelity in communication system models in mixed-reality (MR) simulations. One of the biggest challenges of integrating SWEs and HWEs in an MR simulation is to handle differences in the message transfer among the entities while preserving a high fidelity of the simulations (see Figure 1 ). The focus of this work is on designing communication architecture that would serve as a communication middleware for MR simulations and allow broadcast and directed message exchange between SWEs and HWEs while providing simultaneous wireless network simulation and movement of the entities in real time. The communication architecture must provide common addressing and message routing processes between SWEs and HWEs, as well as suitable models of media utilization and communication reachability for the MR world. In this paper, all of these problems are addressed within the context of an unmanned aerial system (UAS) as a reference system and practical deployment; however, the presented approach can be applied to other vehicular systems with direct communication among vehicles (vehicle-to-vehicle, V2V). The communication architecture presented in this work has been utilized and verified during the development of different aviation applications within the projects funded by the Czech Ministry of Defence, the U.S. Air Force Research Lab., and the U.S. Army CERDEC [15] [16] [17] . The architecture has been used as a part of an MR simulation framework for the incremental development of complex systems and their verification in high fidelity testing. The rest of this paper is organized as follows. After a discussion of related work, mechanisms of message exchange in MR systems are described in Section 3. Based on them, requirements for MR communication architecture are stated in Section 4. Then, in Section 5, a communication architecture for the MR simulations is proposed. Aspects of the fidelity of this architecture together with the precise communication modeling are addressed in Section 6. In Section 7, a set of experiments are presented to show a similarity in characteristics of the fully deployed hardware communication and Sensors 2018, 18, 853 3 of 20
doi:10.3390/s18030853 pmid:29538290 pmcid:PMC5877314 fatcat:tuglxciyzjhmnnnq22t6q6pvua