American Institute of Aeronautics and Astronautics 1 Ad Hoc UAV Ground Network (AUGNet) Timothy X Brown*, Brian Argrow†, Cory Dixon‡, Sheetalkumar Doshi§, Roshan-George Thekkekunnel**, Daniel Henkel††. University of Colorado, Boulder, CO 80303 This paper describes an implementation of a wireless mobile ad hoc network with radio nodes mounted at fixed sites, on ground vehicles, and in small (10kg) UAVs. The ad hoc networking allows any two nodes to communicate either directly or through an arbitrary number of other nodes which act as relays. We envision two scenarios for this type of network. In the first, the UAV acts as a prominent radio node that connects disconnected ground radios. In the second, the networking enables groups of UAVs to communicate with each other to extend small UAVs' operational scope and range. The network consists of mesh network radios assembled from low-cost commercial off the shelf components. The radio is an IEEE 802.11b (WiFi) wireless interface and is controlled by an embedded computer. The network protocol is an implementation of the Dynamic Source Routing ad hoc networking protocol. The radio is mounted either in an environmental enclosure for outdoor fixed and vehicle mounting or directly in our custom built UAVs. A monitoring architecture has been embedded into the radios for detailed performance characterization and analysis. This paper describes these components and performance results measured at an outdoor test range. I. Introduction ommunication networks between and through aerial vehicles are a mainstay of current battlefield communications. Present systems use specialized high-cost radios in designated military radio bands. Current aerial vehicles are also high-cost manned or unmanned vehicles. Small low-cost Commercial Off-The-Shelf (COTS) radio equipment combined with powerful computer processing can be mounted on small (10kg) Unmanned Aerial Vehicles (UAV) and has the potential to revolutionize battlefield communication and open up many scientific and commercial applications. One example COTS technology is IEEE 802.11b wireless LANs (so called WiFi) which can connect mobile nodes to a fixed infrastructure. This is being widely deployed, including in UAV applications.7 More interesting applications are possible when the different mobile nodes connect to each other in peer-to-peer ad hoc (aka mesh) wireless networks.3,8 In this paper we consider ad hoc networks consisting of ad hoc nodes on the ground and ad hoc nodes mounted in small UAVs, which we denote Ad hoc UAV-Ground Networks (AUGNets). We envision two broad AUGNet scenarios as shown in Figure 1. In the first scenario, an ad hoc network of ground nodes is disconnected because of distance and/or terrain. The UAV, with a better view of the nodes, maintains connectivity as an ad hoc relay. In the second scenario, a small UAV because of power and payload constraints has limited communication range which in turn may limit operational range. Ad hoc relaying between multiple UAVs extends communication range. In this paper we describe our efforts to construct such an ad hoc network. It builds on our earlier work in 802.11b ad hoc network protocols and small UAV construction. We present performance results that focus on the role of the UAV in the first scenario obtained on a full scale UAV communication test bed. * Professor, Electrical and Computer Engineering and Interdisciplinary Telecommunications, CB 530 † Professor, Aerospace Engineering Sciences, CB 429 ‡ Student, Aerospace Engineering Sciences, CB 429 § Student, Electrical and Computer Engineering, CB 425 ** Student, Electrical and Computer Engineering, CB 425 †† Researcher, Interdisciplinary Telecommunications, CB 530 CAmerican Institute of Aeronautics and Astronautics 2 II. Approach An AUGNet poses several challenges. Ad hoc nodes can be in a variety of configurations. Some potential configurations include a fixed site mounted on a high pole, a mobile node mounted on a vehicle, a personnel-carried node, or an aerial node mounted in a small UAV. The design should be modular enough so that it can be applied to all of these configurations. The UAV nodes present special considerations. The UAV can usually communicate with most of the ground nodes.‡‡ Ad hoc routing algorithms will tend to route the traffic through the UAV thus limiting communication to the UAV bottleneck bandwidth. The UAV may also have additional pilot control radios that can interfere with the ad hoc communication. Note that our use of the UAV differs with the use for ad hoc networking in Ref. 4 where the UAV is large, flies at high-altitude (60kft), and has a separate radio for UAV-ground communication. Our approach consists of four efforts: (1) ad hoc network software, (2) communication hardware, (3) UAV platform, and (4) test bed monitoring architecture. The ad hoc network software combined with the communication hardware we denote the mesh network radio (MNR). The MNR is shown in . The MNR hardware consists of a Soekris single board computer, Orinoco 802.11b card, a Fidelity-Comtech bidirectional amplifier with up to 1W output, and a GPS. A key to our approach is that all nodes whether mounted in a UAV, at a fixed ground site, or mounted on a vehicle node, use the same core MNR. The radios only differ in their packaging. This greatly simplifies our software and hardware development. ‡‡ The small UAV is capable of high altitude flight. But, AMA RC rules limit the UAV to visual contact close to the ground for our testing. Even so, a UAV communicating with a ground node will be more likely to have line-of-site transmission and less interference with the ground than other ground nodes. 16cm 21cm Figure 2. Mesh Network Radio (MNR) (left). MNR mounted in environmental enclosure for vehicle or fixed ground mounting (center). MNR mounted in UAV (foreground right) Figure 1. Scenario 1 (left): ad hoc networking with the UAV increases ground node connectivity. Scenario 2 (right): ad hoc networking between UAVs to increase operational range.American Institute of Aeronautics and Astronautics 3 The MNR runs the dynamic source routing protocol (DSR)5 communicating with other nodes via 802.11b. We chose DSR because its routing is on-demand. In on-demand routing, a traffic source