Frederico Santos

Self-configuration of an adaptive TDMA wireless communication protocol for teams of mobile robots

Interest on using mobile autonomous agents has been growing, recently, due to their capacity to cooperate for diverse purposes, from rescue to demining and security. However, such cooperation requires the exchange of state data that is time sensitive while achieving timeliness with RF communication is intrinsically difficult due to the openess of the medium. This paper describes a communication layer that improves the timeliness of periodic data exchanges among the team reducing the chances of lost packets caused by collisions between team members. In particular, the paper extends a previous proposal for an adaptive TDMA protocol with new self-configuration capabilities according to the current number of active team members. This feature further reduces the likelyhood of collisions within the team. Several experimental results with an actual system implementation show the effectiveness of the proposed solution.

Coordinating distributed autonomous agents with a real-time database: the CAMBADA project

Interest on using mobile autonomous agents has been growing, recently, due to their capacity to cooperate for diverse purposes, from rescue to demining and security. However, such cooperation requires the exchange of state data that is time sensitive and thus, applications should be aware of data temporal coherency. In this paper we describe the architecture of the agents that constitute the CAMBADA (Cooperative Autonomous Mobile roBots with Advanced Distributed Architecture) robotic soccer team developed at the University of Aveiro, Portugal. This architecture is built around a real-time database that is partially replicated in all team members and contains both local and remote state variables. The temporal coherency of the data is enforced by an adequate management system that refreshes each database item transparently at a rate specified by the application. The application software accesses the state variables of all agents with local operations, only, delivering both value and temporal coherency.

A loose synchronisation protocol for managing RF ranging in mobile ad-hoc networks

Robot motion coordination and cooperative sensing are nowadays two important and inter-related components of multi-robot cooperation. Particularly, when concerning motion coordination, distance information plays a very important role in mobile robotics. In this work, we investigate a new solution based on ad-hoc communication without global knowledge, particularly clock synchronisation, to measure distance between mobile units and to share that information. In order to improve ranging, medium throughput, and application predictability, we propose using a synchronisation protocol that keeps transmissions in the team as separated as possible in time, independently of the topology. Results show around 3.3 times reduction in the number of failed ranges without external interference and an order of magnitude reduction in the asymmetries among the nodes concerning the number of failed ranges when using the proposed synchronisation protocol.

CAMBADA Soccer Team: from Robot Architecture to Multiagent Coordination

Robotic soccer is nowadays a popular research domain in the area of multi-robot systems. RoboCup is an international joint project to promote research in artificial intelligence, robotics and related fields. RoboCup chose soccer as the main problem aiming at innovations to be applied for socially relevant problems. It includes several competition leagues, each one with a specific emphasis, some only at software level, others at both hardware and software, with single or multiple agents, cooperative and competitive. In the context of RoboCup, the Middle Size League (MSL) is one of the most challenging. In this league, each team is composed of up to 5 robots with a maximum size of 50cm× 50cm, 80cm height and a maximumweight of 40Kg, playing in a field of 18m× 12m. The rules of the game are similar to the official FIFA rules, with minor changes required to adapt them for the playing robots CAMBADA, Cooperative Autonomous Mobile roBots with Advanced Distributed Architecture, is the MSL Soccer team from the University of Aveiro. The project started in 2003, coordinated by the Transverse Activity on Intelligent Robotics group of the Institute of Electronic and Telematic Engineering of Aveiro (IEETA). This project involves people working on several areas for building the mechanical structure of the robot, its hardware architecture and controllers (Almeida et al., 2002; Azevedo et al., 2007) and the software development in areas such as image analysis and processing (Caleiro et al., 2007; Cunha et al., 2007; Martins et al., 2008; Neves et al., 2007; 2008), sensor and information fusion (Silva et al., 2008; 2009), reasoning and control (Lau et al., 2008), cooperative sensing approach based on a Real-Time Database (Almeida et al., 2004), communications among robots (Santos et al., 2009; 2007) and the development of an efficient basestation. The main contribution of this chapter is to present the new advances in the areas described above involving the development of an MSL team of soccer robots, taking the example of the CAMBADA team that won the RoboCup 2008 and attained the third place in the last edition of the MSL tournament at RoboCup 2009. CAMBADA also won the last three editions

Communicating among robots in the robocup middle-size league

The RoboCup Middle-Size League robotic soccer competitions pose a real cooperation problem for teams of mobile autonomous robots. In the current state-of-practice cooperation is essential to overcome the opponent team and thus a wireless communication protocol and associated middleware are now fundamental components in the multi-robots system architecture. Nevertheless, the wireless communication has relatively low reliability and limited bandwidth. Since it is shared by both teams, it is a fundamental resource that must be used parsimoniously. Curiously, to the best of our knowledge, no previous study on the effective use of the wireless medium in actual game situations was done. In this paper we show how current teams use the wireless medium and we propose a set of best practices towards a more efficient utilization. Then, we present a communication protocol and middleware that follow such best practices and have been successfully used by one particular MSL team in the past four years.

Enhancing the reactivity of the vision subsystem in autonomous mobile robots using real-time techniques

Interest on using mobile autonomous agents has been growing, recently, due to their capacity to cooperate for diverse purposes, from rescue to demining and security. In many of these applications the environments are inherently unstructured and dynamic, requiring substantial computation resources for gathering enough sensory input data to allow a safe navigation and interaction with the environment. As with humans, who depend heavily on vision for these purposes, mobile robots employ vision frequently as the primary source of input data when operating in such environments. However, vision-based algorithms are seldom developed with reactive and real-time concerns, exhibiting large variations in the execution time and leading to occasional periods of black-out or vacant input data. This paper addresses this problem in the scope of the CAMBADA robotic soccer team developed at the University of Aveiro, Portugal. It presents an evolution from a monolithic to a modular architecture for the vision system that improves its reactivity. With the proposed architecture it is possible to track different objects with different rates without losing any frames.

A web-based monitoring approach for power systems in industrial plants

This article presents an Ethernet remote monitoring system for electric industrial power distributions. This system permits monitoring through the spread of low cost remote platforms, with synchronous acquisition, Ethernet communication, computational analysis programs, statistical treatment and creation of automatic reports. The dissemination of this system allows a fast and systematic approach to the harmonics disturbances problematic. It has the capability to remotely study the propagation of these disturbances in the industrial installations, to determine waveform distortion caused by harmonics sources, to quantify the impact of these disturbances and to elaborate daily quality indexes reports (IEEE Standard 519-1992) based on recent harmonics analysis techniques. This paper describes the hardware prototype of the data acquisition system architecture for power quality monitoring and analysis. The prototype was validated by statistical procedure and are presented experimental results made in real industrial plant, proving the system viability and value added in this problematic area.

A Modular Control Architecture for a Small Electric Vehicle

This paper presents a fault-tolerant modular control architecture for an electrical vehicle (VEIL) equipped with x-by-wire sub-systems. The proposed architecture is based on COTS components and includes steer-by-wire, brake-by-wire and accelerate-by-wire safety critical functions. The communication infrastructure is based on the FTT-CAN protocol, which provides the joint scheduling of message and tasks, according to a holistic approach.

Comparing Adaptive TDMA against a Clock Synchronization Approach

Teams of cooperating robots are getting more popular fostered by hardware platforms as well as technologies and techniques for coordination that are becoming widely available. The wireless communication is one such technology that impacts directly on the quality provided by the cooperative applications running atop. In cases where the team robots transmit periodically, it has been shown that synchronizing their transmissions so that they occur out of phase is beneficial, e.g. in a TDMA manner. However, persisting periodic interfering traffic may increase collisions with the team traffic and thus downgrade the channel quality. The Adaptive TDMA self-synchronized protocol was then proposed to improve the resilience to this type of interference. In this paper we assess the effectiveness of Adaptive TDMA in comparison with a traditional TDMA implementation based on clock synchronization. The results of practical experiments show a reduction in packet losses when the interfering traffic is short, typically single packet.

Structuring Communications for Mobile Cyber-Physical Systems

Mobile autonomous agents, particularly robots, are becoming commonplace in many application domains, e.g., search and rescue, demining, agriculture and surveillance. These so-called Mobile Cyber-Physical Systems (M-CPS) allow relocating sensors and actuators dynamically in the environment to improve some global performance metric. However, the necessary agents cooperation is hindered by their heterogeneity, dynamic communication links and network topology, and by an error-prone communication channel. This chapter focuses on the networking and middleware support for a class of M-CPS and proposes the Reconfigurable and Adaptive TDMA protocol to handle data transmission under communication-related uncertainties, and the RTDB shared memory middleware to provide seamless data access across the cooperating agents. This combination of network protocol and middleware layer is particularly suited to support state sharing among agents in dynamic teams. Several experimental results confirm the advantage over other potential options. Moreover, this protocol and middleware combination have been thoroughly validated in demanding operational scenarios namely in robotic soccer teams from RoboCup Middle-Size League, which exhibit the typical requirements and constraints of M-CPS.