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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 C 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 1 American Institute of Aeronautics and Astronautics 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 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 21cm 16cm 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 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 2 American Institute of Aeronautics and Astronautics 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 only seeks a route to a destination when it has data to send Thus nodes do not waste bandwidth trying to establish routes they will never use When a node needs to send a packet it initiates a route request process among nodes in the network to establish a route DSR also uses source routing whereby a packet source precisely specifies which route the packet will follow We implemented DSR ourselves using the Click modular router

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