Alexei Makarenko

Information based adaptive robotic exploration

Exploration involving mapping and concurrent localization in an unknown environment is a pervasive task in mobile robotics. In general, the accuracy of the mapping process depends directly on the accuracy of the localization process. This paper address the problem of maximizing the accuracy of the map building process during exploration by adaptively selecting control actions that maximize localisation accuracy. The map building and exploration task is modeled using an Occupancy Grid (OG) with concurrent localisation performed using a feature-based Simultaneous Localisation And Mapping (SLAM) algorithm. Adaptive sensing aims at maximizing the map information by simultaneously maximizing the expected Shannon information gain (Mutual Information) on the OG map and minimizing the uncertainty of the vehicle pose and map feature uncertainty in the SLAM process. The resulting map building system is demonstrated in an indoor environment using data from a laser scanner mounted on a mobile platform.

Towards component-based robotics

This paper gives an overview of component-based software engineering (CBSE), motivates its application to the field of mobile robotics, and proposes a particular component model. CBSE is an approach to system-building that aims to shift the emphasis from programming to composing systems from a mixture of off-the-shelf and custom-built software components. This paper argues that robotics is particularly well-suited for and in need of component-based ideas. Furthermore, now is the right time for their introduction. The paper introduces Orca - an open-source component-based software engineering framework proposed for mobile robotics with an associated repository of free, reusable components for building mobile robotic systems.

Information-theoretic coordinated control of multiple sensor platforms

This paper describes an information-theoretic approach to distributed and coordinated control of a multi-robot sensor system. The approach is based on techniques long established for the related problem of decentralised data fusion (DDF). The DDF architecture uses information measures to communicate state estimates in a network of sensors. For coordinated control of robot sensors, the control objective becomes maximisation of these information measures. This yields platform trajectories, which maximise the total information, gained by the system. This approach inherits the many benefits of the DDF method including scalability, robustness to sub-system failure and addition, and interoperability among heterogeneous systems. The approach is applied to a practical bearings-only multi-feature localisation problem.

Orca: A Component Model and Repository

This Chapter describes Orca: an open-source project which applies Component-Based Software Engineering principles to robotics. It provides the means for defining and implementing interfaces such that components developed independently are likely to be inter-operable. In addition it provides a repository of free re-useable components. Orca attempts to be widely applicable by imposing minimal design constraints. This Chapter describes lessons learned while using Orca and steps taken to improve the framework based on those lessons. Improvements revolve around middleware issues and the problems encountered while scaling to larger distributed systems. Results are presented from systems that were implemented.

Parametric POMDPs for planning in continuous state spaces

Abstract This work addresses the problem of decision-making under uncertainty for robot navigation. Since robot navigation is most naturally represented in a continuous domain, the problem is cast as a continuous-state POMDP. Probability distributions over state space, or beliefs, are represented in parametric form using low-dimensional vectors of sufficient statistics. The belief space, over which the value function must be estimated, has dimensionality equal to the number of sufficient statistics. Compared to methods based on discretising the state space, this work trades the loss of the belief space’s convexity for a reduction in its dimensionality and an efficient closed-form solution for belief updates. Fitted value iteration is used to solve the POMDP. The approach is empirically compared to a discrete POMDP solution method on a simulated continuous navigation problem. We show that, for a suitable environment and parametric form, the proposed method is capable of scaling to large state-spaces.

Decentralized Bayesian algorithms for active sensor networks

The paper presents two algorithms for Decentralized Bayesian information fusion and information-theoretic decision making. The algorithms are stated in terms of operations on a general probability density function representing a single feature of the environment. Several specific density representations are then considered-Gaussian, discrete, Certainty Grid, and hybrid. Well known algorithms for these representations are shown to fit the general pattern. Stating the algorithms in Bayesian terms has a practical advantage of allowing a generic software implementation. The algorithms are described in the context of the active sensor network architecture-a modular framework for decentralized cooperative information fusion and decision making. An example of decentralized target tracking is provided. The algorithms and the framework implementation is illustrated with the results of two indoor deployment scenarios.

Scalable control of decentralised sensor platforms

This paper describes an information-theoretic approach to decentralised and coordinated control of multi-robot sensor systems. It builds on techniques long established for the related problem of Decentralised Data Fusion (DDF). The DDF architecture uses information measures to communicate state estimates in a network of sensors. For coordinated control of robot sensors, the control objective becomes maximisation of these information measures. A decentralised coordinated control architecture is presented. The approach taken seeks to achieve scalable solutions that maintain consistent probabalistic sensor fusion and payoff formulations. It inherits the many benefits of the DDF method including scalability, seamless handling of sub-system activation and deactivation, and interoperability among heterogeneous units. These features are demonstrated through application to practical multi-feature localisation problems on a team of indoor robots equipped with laser range finders.

A decentralized architecture for Active Sensor Networks

The paper presents a decentralized approach to the solution of the distributed information gathering problem. The main design objectives are scalability with the number of network components, maximum flexibility in implementation and deployment, and robustness to component and communication failure. The design approach emphasizes interactions between components rather than the definition of the components themselves. The architecture specifies a small set of interfaces sufficient to implement a wide range of information gathering systems. The results of two deployment scenarios on an indoor sensor network are presented.

Implementation of an Indoor Active Sensor Network

This paper describes an indoor Active Sensor Network, focussing on the implementation aspects of the system, including communication and the application framework. To make the system description more tangible we describe the latest in a series of indoor experiments implemented using ASN. The task is to detect and map motion of people (and robots) in an office space using a network of 12 stationary sensors. The network was operational for several days, with individual platform coming on and off line. On several occasions the network consisted of 39 components. The paper includes a section on the lessons learned during the project’s design and development which may be applicable to other heterogeneous distributed systems with data-intensive algorithms.

Gaussian Process Models for Indoor and Outdoor Sensor-Centric Robot Localization

This paper presents an approach to building a map from a sparse set of noisy observations, taken from known locations by a sensor with no obvious geometric model. The basic approach is to fit an interpolant to the training data, representing the expected observation, and to assume additive sensor noise. This paper takes a Bayesian view of the problem, maintaining a posterior over interpolants rather than simply the maximum-likelihood interpolant, giving a measure of uncertainty in the map at any point. This is done using a Gaussian process (GP) framework. The approach is validated experimentally both in an indoor office environment and an outdoor urban environment, using observations from an omnidirectional camera mounted on a mobile robot. A set of training data is collected from each environment and processed offline to produce a GP model. The robot then uses that model to localize while traversing each environment.