Cory Dixon

Maintaining optimal communication chains in robotic sensor networks using mobility control

This paper presents a decentralized mobility control algorithm for the formation and maintenance of an optimal cascaded communication chain between a lead sensor-equipped robot and a control station, using a team of robotic vehicles acting as communication relays in an unknown and dynamic RF environment. The gradient-based controller presented uses measurements of the signal-to-noise ratio (SNR) field of neighbor communication links, as opposed to relative position between nodes, as input into a localized performance function. By using the SNR field as input into the control system, the controller is reactive to unexpected and unpredictable changes in the RF environment that is not possible with range-based controllers. Since the operating environment is not known a priori to deployment of a robotic sensor network, an adaptive model-free extremum seeking (ES) algorithm, that uses the motion of the relays to estimate the performance function gradient, is presented to control the motion of 2D nonholonomic vehicles acting as communication relays using the gradient-based controller. Even without specific knowledge of the SNR field, simulations show that the ES decentralized chaining controller using measurements of the SNR field, will drive a team of robotic vehicles to locations that achieve the global objective of maximizing capacity of a cascaded communication chain, even in the presence of an active jamming source.

Lyapunov Guidance Vector Fields for Unmanned Aircraft Applications

This paper presents results implementing Lyapunov vector fields for the guidance of unmanned aircraft. The vector fields yield globally stable tracking of circular loiter patterns. These loiter patterns are used in several unmanned aircraft applications including hierarchical micro air vehicle control for cooperative plume tracking, extremum seeking for electronic chaining, and cooperative tracking of moving targets. Extensions of the basic LGVF approach are made for each application including: warping the circular pattern to form other closed orbit patterns; driving the center of the LGVF orbit using virtual dynamics; and spacing multiple unmanned aircraft around a circular orbit. Hardware-in-the- loop simulation results and flight data are given to validate performance.

Optimizing Cascaded Chains of Unmanned Aircraft Acting as Communication Relays

This work presents a decentralized mobility control algorithm for an optimal end-to-end communication chain using a team of unmanned aircraft acting solely as communication relays. The chaining controller drives the location of a virtual control point, using estimates of the communication objective function gradient calculated using stochastic approximation techniques, to locations of improved relaying for unmanned aircraft. The gradient estimate is derived from observation data of the communication objective function taken along a path generated by the aircraft orbiting about the control point. Flight experiments show that an unmanned aircraft can measure the signal-to-noise-and-interference ratio fields from IEEE 802.11b/g (WiFi) communication links; generate estimates of the field gradients using the least-squares gradient estimation method; and use the gradient estimates to drive a control point to a location that improves communication capacity.

Radio Source Localization by a Cooperating UAV Team

This paper describes the development of a networked UAV communication, command, and control (NetUAVC3) architecture. The NetUAVC 3 project is divided into three stages. Stage 1 focused on developing algorithms for tying network intelligence and mission-level tasking information into automatic flight controls. Stage 2 will conclude with a demonstration of leashing UAVs to mobile nodes, and Stage 3 will conclude with a demonstration of radio source localization by a cooperating UAV team. This presentation will describe the NetUAVC 3 architecture currently under development. The Stage 1 system will be presented, including the onboard flight management architecture and monitoring and command & control software that exploits the existing AUGNet mesh network. The radio localization problem, in which one or more UAVs react cooperatively to localize the location of a radio emitter, will also be introduced. Source localization is cast as a distributed estimation problem. Aircraft mobility is exploited to improve the observability, in terms of the Fisher Information Matrix, of this estimation problem. Aircraft motion is coordinated through iterative consensus by individual receding horizon controllers on each vehicle.

Controlling the Mobility of Network Nodes using Decentralized Extremum Seeking

A decentralized mobility control scheme, using extremum seeking methods, is presented that forms a linked chain of mobile relays, having nonholonomic constraints, that maximizes the total link bandwidth. The factors that determine the final arrangement are numerous and hard to model and predict in real time. Thus controlling the mobile nodes by position alone to form a linked communication chain is not adequate. Instead, an extremum seeking algorithm is used to drive the location of the relay to an optimal place by maximizing a performance function of the received signal-to-noise power ratios of immediate neighbors. A unique application of the ES algorithm is presented where the dither signal that drives the gradient estimation is derived from the motion of mobile relay orbiting about a virtual center point

Networked Communication, Command, and Control of an Unmanned Aircraft System

Fullyautonomous,cooperative,multivehicleoperationrequiresthedevelopmentandintegration of various levels of intra- and intervehicle communication, sensing, control, and autonomy. This paper describes the Networked unmanned aircraft system Communication, Command, and Control (NetUASC3) architecture that combines meshed network intelligence, mission-level tasking information, and automatic flight control into an integrated unmanned aircraft system. The NetUASC3 architecture described includes: the University of Colorado at Boulder Ares unmanned aircraft, the onboard flight management architecture, and monitoring and command and control software that exploits the existing ad hoc Unmanned Aircraft System Ground network mesh network. Results from flight demonstration of the NetUASC3 architecture are provided to highlight the interplay between the various subsystems. Specific results demonstrate sensor-reactive and communicationreactive control, meshed network performance, atmospheric data collection, validation of radio-propagationmodels,anddeliveryofstreamingvideooveramultihopairborne‐ground network.

A reliable sensor data collection network using unmanned aircraft

This paper presents a method for reliably collecting data events from sensors and forwarding the data via a MANET to sensor monitoring stations located on an external network. A the core is a MANET concept that consists of ground and unmanned aircraf nodes. Unmanned aircraf enable a model whereby widely-spaced sensors are intermittently connected to the network and data is sent in stages as connections become available along each stage. The paper describes the sensor data collection model, the reliable multicast data delivery mechanism, and our experiences on a network test bed including the control of an unmanned aircraft through a MANET.

Phase Transitions for Controlled Mobility in Wireless Ad hoc Networks

*† ‡ § In this paper we investigate the phase transitions between different modes of controlled mobility in wireless ad hoc networks. The transmission of data between two nodes can be performed by one of three methods in a mobile ad hoc network: direct transmission between nodes; multi-hop relaying through intermediate nodes; and data ferrying through a node that physically moves between sources and destinations. Assuming the source and destination nodes are stationary, the best choice of transmission mode through the network is a function of several variables including the separation distance between nodes, the required average data throughput, the maximum tolerable delay, and the data ferry speed and buffer capacity. This paper presents the notion of a phase diagram relating separation distance to average data throughput. Contours of maximum packet delay are specified on this phase plot and are used to identify the optimal mode under various configurations. The creation and maintenance of communication channels of specified performance in a mobile ad hoc network can be viewed as a hybrid control problem. Calculation of the boundaries between phases corresponds to determining the transition conditions of the hybrid controller.

Cooperative Electronic Chaining Using Small Unmanned Aircraft

When using a team of small unmanned aircraft, with no satellite communications, the operational range of the team is typically limited by line-of-sight communication constraints between an individual aircraft and a ground station, and not the endurance range of the individual aircraft within the team. By using electronic chaining to form a multi-hop communication link using the team, the overall communication range from an individual vehicle to a ground station can be increased to where the operational range of the team is only limited by the endurance range of an individual aircraft. In addition, using mobile repeaters that are driven by electronic constraints and communication performance objectives support a much greater operational deployment area and environment than would possible using geographic (range) based constraints alone. This paper presents recent developments in electronic chaining using extremum seeking methods and presents application results using the Ares unmanned aircraft system and the AUGNet 802.11 communications network test bed developed in the Research & Engineering Center for Unmanned Vehicles (RECUV) at the University of Colorado, Boulder. While it was hoped that actual ∞ight data results would have been available for publication, no recent ∞ights have been be conducted due to FAA restrictions on unmanned aircraft operations.

Establishment and Maintenance of a Delay Tolerant Network through Decentralized Mobility Control

In this paper we investigate the establishment and maintenance of a delay tolerant network through decentralized mobility control. A set of geographically dispersed wireless radio nodes wish to communicate with one another. These nodes are free to move about the environment and are not constrained to remain in direct communication range of one another. A second set of helper nodes exist in the environment that can form connected chains between nodes and that can ferry data back and forth between sensor nodes and/or other helper nodes. The mobility of the helper nodes is controlled based on local information about neighboring nodes and the communication flow through the network. A hierarchical approach is described in which helper nodes are assigned specific sensor nodes or regions of activity through resource allocation algorithms while communication flow through established links is maintained by decentralized control based on local measures only such as received signal strength or signal to noise ratio