Distributed Coordination

The development of industrial robotics applications is a complex and often a very expensive task. One of the core problems is that a lot of implementation and adaptation effort can only be done after the robotic hardware has been installed. This paper shows how Microsoft Robotics Studio (MSRS) can facilitate the fast prototyping of novel industrial applications and thus lower the overall development costs. Microsoft Robotics Studio is a development tool for creating software for robotic applications. It includes an asynchronous, serviceoriented runtime and a realistic physics-based simulation environment. This allows for testing and improving software prototypes before any hardware is installed. As an example control software for a vision of tomorrow's production automation systems has been implemented and evaluated in the simulation environment of MSRS.

In this paper we discuss the use of cooperative game theory for analyzing interference channels. We extend our previous work, to games with N players as well as frequency selective channels and joint TDM/FDM strategies. We show that the Nash bargaining solution can be computed using convex optimization techniques. We also show that the same results are applicable to interference channels where only statistical knowledge of the channel is available. Moreover, for the special case of two players 2 × K frequency selective channel (with K frequency bins) we provide an O(K log 2 K) complexity algorithm for computing the Nash bargaining solution under mask constraint and using joint FDM/TDM strategies. Simulation results are also provided.

In this paper we analyze the interference channel as a conflict situation. This viewpoint implies that certain points in the rate region are unreasonable to one of the players. Therefore these points cannot be considered achievable based on game theoretic considerations. We then propose to use Nash bargaining solution as a tool that provides preferred points on the boundary of the game theoretic rate region. We provide analysis for the 2x2 intereference channel using the FDM achievable rate region. We also outline how to generalize our results to other achievable rate regions for the interference channel as well as the multiple access channel.

In this paper we study the computation of the Nash bargaining solution for the two players, K frequency bands case, under joint FDMlTDM spectrum allocations and total power constraint. The results improve previous analysis by Han et ale We provide a computationally efficient algorithm as well as detailed analysis of the Karush-Kuhn-Thcker (KKT) equations necessary for proving the correctness of the algorithm. Simulation results demonstrating the gain of the NBS over competitive approaches are also provided.

In this paper we extend our previous work on the Nash bargaining solution for the interference channel. We consider two alternative technqiues using generalized Nash bargaining and the Kalai Smorodinsky solution. These solutions are relevant for allocating spectrum to users with non-symmetric requirements.

In this paper we analyze the interference channel as a conflict situation. This viewpoint implies that certain points in the rate region are unreasonable to one of the players. Therefore these points cannot be considered achievable based on game theoretic considerations. We then propose to use Nash bargaining solution as a tool that provides preferred points on the boundary of the game theoretic rate region. We provide analysis for the 2x2 intereference channel using the FDM achievable rate region. We also outline how to generalize our results to other achievable rate regions for the interference channel as well as the multiple access channel.

The delight of this collaboration has been each author's firm belief that the others made the essential contributions. Accordingly, the order currently shown does not represent an equilibrium. We are grateful for the contributions of many colleagues to the ideas presented here, and especially to Markus Becker, Phanish Puranam, and Jason Owen-Smith for comments on an earlier draft. 1 We do not wish to enter here the controversy on similarity measures originating with Tversky (1977). For a critical appraisal and a defense of geometric measures of similarity, see Gärdenfors (2000).

This paper presents an experimental study on the spectrum coexistence 1 problems between multi-radio platforms in dense-radio physical world environments. Computing and communication devices such as laptops and cellular phones with multiple radios including WiFi, Bluetooth, UWB, WiMax and Zigbee in a small conference room face significant interference problems. A realistic small office/home office (SOHO) scenario with ~10-25 multi-radio platforms is mapped onto the ORBIT radio grid testbed, and system throughput results are obtained experimentally, demonstrating significant degradation due to inter-platform interference. The CSCC (Common Spectrum Coordination Channel) protocol proposed in earlier work is used as the basis for implementing a set of distributed spectrum coexistence algorithms intended to improve system performance. Detailed results from ORBIT testbed experiments are given for the proposed CSCC-based distributed spectrum coordination algorithms. The results show significant performance gains due to CSCC coordination, typically achieving ~2x improvement in system throughput for WiFi/Bluetooth dual radio scenarios.

In this study, we explore the coordination performance of the geographically distributed software development teams by exploring OSS (Open Source Software) development dataset available through SourceForge.com. OSS team structures have traditionally been geographically dispersed and therefore, the coordination of post release activities such as testing efforts have been carried out by means of communication via electronic forms, such as email or message boards and forums. In our current communication-enriched environment, best practices for coordination are adopted by all software projects yet some still fail to achieve their target performance. Does team structure have any bearing on the performance outcome of the project? How does the communication between teams and their external parties affect ultimate success or failure of projects? We seek to answer above questions by applying existing theories and analytical methods from social networks for exploring the coordination performance of defect management activities found in OSS projects. We propose social networks based theoretical model for exploring distributed coordination structure and apply that for the case of OSS defect management process for exploring the structural properties, which induce the greatest coordination performance. The outcome of our suggest that there is correlation between certain network measures such as density, centrality and betweenness and coordination performance measures of defect management systems such as quality and timeliness.

Multi-gigabit outdoor mesh networks operating in the unlicensed 60 GHz "millimeter (mm) wave" band, offer the possibility of a quickly deployable broadband extension of the Internet. We consider mesh nodes with electronically steerable antenna arrays, with both the transmitter and receiver synthesizing narrow beams that compensate for the higher path loss at mm-wave frequencies, achieving ranges on the order of 100 meters using the relatively low transmit powers attainable with low-cost silicon implementations. Such highly directional networking differs from WiFi networks at lower carrier frequencies in two ways that have a crucial impact on protocol design: (1) directionality drastically reduces spatial interference, so that pseudowired link abstractions form an excellent basis for protocol design; (2) directionality induces deafness, which makes medium access control (MAC) based on carrier sensing infeasible. Interference analysis in our prior work shows that, in such a setting, coordination between transmitters and receivers, rather than interference management, becomes the key MAC performance bottleneck. However, the question of whether such coordination can be achieved in a distributed fashion while achieving high medium utilization, was left open. In this paper, we answer this question in the affirmative, presenting a distributed MAC protocol that employs memory to achieve approximate time division multiplexed (TDM) schedules without explicit coordination or resource allocation. The efficacy of the protocol is demonstrated via packet level simulations, while a Markov chain fixed-point analysis provides insight into the effect of parameter choices.

standard is the most popular Medium Access Control (MAC) protocol for wireless local area networks. However, in an ad-hoc environment, the Point Coordination Function (PCF), defined in the standard, cannot be readily used. This is due to the fact that there is no central authority to act as a Point Coordinator (PC). Peer-to-peer ad-hoc mode in the IEEE 802.11 standard only implements the Distributed Coordination Function (DCF). In this paper, an efficient and on-the-fly infrastructure is created using our proposed Mobile Point Coordinator (MPC) protocol. Based on this protocol, we also develop an efficient MAC protocol, namely MPC-MAC. Our MAC protocol extends the IEEE 802.11 standard for use in multihop wireless ad-hoc networks implementing both the DCF and PCF modes of operation. The goal, and also the challenge, is to achieve QoS delivery and priority access for real-time traffic in adhoc wireless environments while maintaining backward compatibility with the IEEE 802.11 standard. The performance of MPC-MAC is compared to the IEEE 802.11 DCF-based MAC without MPC. Simulation experiments show that in all cases the use of PCF benefits real-time packets by decreasing the average delay and the discard ratio. However, this may come at the expense of increasing the average delay for non-real-time data. On the other hand, the discard ratio for both real-time and non-real-time packets improves with the use of PCF. Therefore, our MPC-MAC outperforms the standard

It is increasingly recognized that human, social, and political factors have a signi"cant impact on software systems design. To address this, ethnographic studies of work have been used to inform the systems design process, especially in cooperative work settings where systems support several users working together. Based on our experience of these studies, we have investigated the integration of social analysis into the systems design process by developing an integrated approach to social and object-oriented analysis. New methods are unlikely to be adopted in industry unless they can be integrated with existing practice. Our approach, called Coherence, addresses this issue by helping identify use cases, generating initial use case models, and by using the Uni"ed Modelling Language (UML) to represent social aspects of work that may have an impact on the design of computer-based systems. Coherence is the fusion of two well-established strands of research on ethnographically informed design and viewpoint-oriented requirements engineering. This paper introduces Coherence, and focuses on the support provided for social analysis. We have identi"ed three social viewpoints, namely a distributed coordination viewpoint, a plans and procedures viewpoint and an awareness of work viewpoint. Coherence is illustrated using a case study based on an air tra$c control system.

In this paper we extend transactive memory systems (TMS) theory to develop an understanding of the distributed coordination of expertise in high-reliability organizations. We illustrate our conceptual developments in a study of emergency management and response in Greece. We focus on the interaction between operators/dispatchers, ambulance crew, and specialist doctors, including the information and communication technologies (ICT) they use to respond to emergency incidents. Our case contributes to an in-depth understanding of the ways in which high-reliability organizations can sustain a distributed coordination of expertise over the duration of emergency incidents. This is achieved through the cultivation of TMS during a socialization and training period, the dynamic development of trust in emergent actions, and a commitment to shared protocols, which allow for improvisation and bricolage during unexpected incidents. Our findings also explore the role of ICTs in inscribing TMS in computerized protocols, while mediating the development of trust across the team, as well as mediating the construction of running narratives, which enable leaders to coordinate expertise in unexpected incidents.

In the IEEE 802.11 Wireless Local Area Networks (WLANs), network nodes experiencing collisions on the shared channel need to backoff for a random period of time, which is uniformly selected from the Contention Window (CW ). This contention window is dynamically controlled by the Binary Exponential Backoff (BEB) algorithm. The BEB scheme, as shown in some studies in the literature, suffers from a fairness problem and low throughput under high traffic load. In this paper, we propose a new backoff algorithm, termed the Linear/Multiplicative Increase and Linear Decrease (LMILD) backoff algorithm, for use with the IEEE 802.11 Distributed Coordination Function. In the LMILD scheme, colliding nodes increase their contention windows multiplicatively, while other nodes overhearing the collisions increase their contention windows linearly. After successful transmissions, all nodes decrease their contention windows linearly. Our preliminary study shows that the LMILD scheme out-performs the BEB scheme employed in the IEEE 802.11 MAC standard and the Multiplicative Increase Linear Decrease (MILD) scheme over a wide range of network sizes.

Causal consistency has been introduced to increase wait-free concurrent accesses to a shared memory. Contrarily to sequential consistency, causal consistency allows independent write operations, with respect to the causality relation, to be executed in different orders at each distinct process. This paper introduces a protocol for fully replicated settings which exploits the writing semantic and piggybacks on each update message related to a write operation an amount of control information which is O (n) where n is the ...

This paper investigates and describes a new provisioning technique for IEEE 802.11 based networks, focusing on the ad-hoc Distributed Coordination Function (DCF) to redefine stability of the network throughput to support QoS. This paper propose better techniques to achieve stable throughput in Wireless LAN networks by assigning new values to the Contention Window to high priority traffics which will guarantee better throughput to the selected network traffic. A simulation is done using Network Simulator 2 (NS-2) and findings are then presented. Results showed that stable throughput can be achieved to provide better traffic flows especially for real-time traffic and multimedia applications.

A significant body of work exists on effectively allowing multiple agents to coordinate to achieve a shared goal. In particular, a growing body of work in the Distributed Constraint Optimization (DCOP) framework enables such coordination with different amounts of teamwork. Such algorithms can implicitly or explicitly trade-off improved solution quality with increased communication and computation requirements. However, the DCOP framework is limited to planning problems; DCOP agents must have complete and accurate knowledge about the reward function at plan time. We extend the DCOP framework, defining the Distributed Coordination of Exploration and Exploitation (DCEE) problem class to address real-world problems, such as ad-hoc wireless network optimization, via multiple novel algorithms. DCEE algorithms differ from DCOP algorithms in that they (1) are limited to a finite number of actions in a single trial, (2) attempt to maximize the on-line, rather than final, reward, (3) are unab...

Wireless Sensor and Actuator Networks (WSANs) are emerging as a new generation of Wireless Sensor Networks (WSNs). Due to the coupling between the sensing areas of the sensors and the action areas of the actuators, the efficient coordination among the nodes is a great challenge. In this paper, we address the problem of distributed node coordination in WSANs aiming at meeting the user's requirements on the states of the Points of Interest (POIs) in a real-time and energyefficient manner. The node coordination problem is formulated as a non-linear program. To solve it efficiently, the problem is divided into two correlated subproblems: the Sensor-Actuator (S-A) coordination and the Actuator-Actuator (A-A) coordination. In the S-A coordination, a distributed federated Kalman filter-based estimation approach is applied for the actuators to collaborate with their ambient sensors to estimate the states of the POIs. In the A-A coordination, a distributed Lagrange-based control method is designed for the actuators to optimally adjust their outputs, based on the estimated results from the S-A coordination. The convergence of the proposed method is proved rigorously. As the proposed node coordination scheme is distributed, we find the optimal solution while avoiding high computational complexity. The simulation results also show that the proposed distributed approach is an efficient and practically applicable method with reasonable complexity.

Recent advance in IEEE 802.11 based standard has pushed the wireless bandwidth up to 600Mbps while keeping the same wireless medium access control (MAC) schemes for full backward compatibility. However, it has been shown that the inefficient protocol overhead casts a theoretical throughput upper limit and delay lower limit for the IEEE 802.11 based protocols, even the wireless data rate goes to infinitely high. Such limits are important to understand the bottleneck of the current technology and develop insight for protocol performance improvements. This paper uses a queuing system approach to extend the discussions of IEEE 802.11 protocol throughput and delay limits to the situation that arbitrary non-saturated background traffic is present in the network. We derive analytical models to quantify the limits for Distributed Coordination Function (DCF) of legacy 802.11a/b/g and Enhanced Distributed Coordination Access (EDCA) of IEEE 802.11e. We find such limits are functions of the underlying MAC layer backoff parameters and algorithms, and are highly dependent on the load that background traffic injects into the network. Surprisingly, depending on the rate of arrival traffic, the packet delay limit may become unbounded such that no delay sensitive services can be operated under such condition. Moreover, we also discuss the effects of different frame aggregation schemes on the performance limits when data rate is infinite. The developed model and analysis provide a comprehensive understanding of the performance limitations for IEEE 802.11 MAC, and are useful in gauging the expected QoS for the purposes such as admission control.

Orléans Skeleton Library (OSL) is a library of parallel algorithmic skeletons in C++ on top of MPI. It provides a structured approach towards parallel program-ming. Skeletons in OSL are based over the bulk synchronous parallelism model. Applications can be developed using different combinations and compositions of the skeletons. This paper illustrates the expressivity of OSL with two applications: a two dimensional heat diffusion simulation, and an exact n-body simulation. Ex-periments using these applications are performed on parallel machines. 1

Today, Cognitive Radio (CR) have a promising solution to both spectrum inefficiency and spectrum scarcity issues by enabling secondary users (SUs) to exploit the idle frequency bands temporarily in opportunistic manner as long as the primary users (PUs) do not occupy their spectrum. The SUs must vacate these frequency bands when the PUs come back and reuse them. This is one of challenge in CR technology. In this case, the communication links of the SUs must be finding another idle frequency bands to resume their communication links. This is called spectrum handoff which is affecting to the performance of system by main factors such as: link maintenance probability, the number of spectrum handoff, switching delay. Spectrum handoff may be happen more than once for a wide range of the spectrum available in CR. This switching change the characteristics of propagation transmission loss which is affects the overall system performance. Thus, in this thesis, the path loss and coverage area ...

Once a critical mass of nodes is infected by a worm it becomes very difficult to stop the worm from infecting a large fraction of vulnerable nodes. Therefore, the focus of strategies for worm defense has been to detect the worm before it reaches that critical mass. In this paper we present a novel distributed coordination technique for worm propagation and synchronization that can persist under the radar of detection mechanisms long enough to achieve critical mass for a full fledged attack. We discuss the stealthy worm propagation and synchronization approach exploiting a P2P file-sharing network.

When we design multi-agent systems for realistic, worth-oriented environments, solving the coordination problems they present involves understanding the intricate and sophisticated interplay between the domain and the various system components. In this paper, we examine this interplay ...

In this paper, we provide a throughput analysis of the IEEE 802.11 protocol at the data link layer in nonsaturated traffic conditions taking into account the impact of both transmission channel and capture effects in Rayleigh fading environment. The impact of both non-ideal channel and capture become important in terms of the actual observed throughput in typical network conditions whereby traffic is mainly unsaturated, especially in an environment of high interference. We extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel, along with a state characterizing the system when there are no packets to be transmitted in the buffer of a station. Finally, we derive a linear model of the throughput along with its interval of validity. Simulation results closely match the theoretical derivations confirming the effectiveness of the proposed model.

Recent advances in communication and computing have made the control and coordination of dynamic network agents to become an area of multidisciplinary research at the intersection of the theory of control systems, communication and linear algebra. The advances of the research in multi-agent systems are strongly supported by their critical applications in different areas as for example in consensus problem of communication networks, or formation control of mobile robots. Mainly, the consensus problem has been studied from the point of view of stability. Nevertheless, recently some researchers have started to analyze the controllability problems. The study of controllability is motivated by the fact that the architecture of communication network in engineering multi-agent systems is usually adjustable. Therefore, it is meaningful to analyze how to improve the controllability of a multi-agent system. In this work we analyze the stability and controllability of multiagent systems consis...

DENEGOT is a distributed planning framework that bases conflict resolution on decentralized peer negotiation. Negotiation is viewed as a distributed search through potential compromises. The framework assumes that a satisflcing solution is acceptable (a reasonable assumption in many complex domains). To estimate the quality of potential solutions, the negotiation search space is structured into a lattice of sets of potential compromise solutions based on hard constraints. A solution in a higher set in the lattice, if it is achievable, will be preferable over a solution in a lower set. Agents first search under the hard constraint level representing the highest quality solution standard achievable in the current situation. By relaxing hard constraints, the set of compromises that qualify as a solution are enlarged. Agents search for a resolution under the relaxed hard constraint set when a solution cannot be found under the current set of constraints. The framework consists of three iterative problem-solving phases: coordinated search, negotiation state analysis, and constraint relaxation. The application of the DENEGOT framework to distributed planning problems in two domains is demonstrated.

The advanced electric power grid promises a self-healing infrastructure using distributed, coordinated, power electronics control. One promising power electronics device, the Flexible AC Transmission System (FACTS) device, can modify the power flow locally within a power grid. Embedded computers within the FACTS devices, along with the links connecting them, form a communication and control network that can dynamically change the advanced electric power grid to achieve higher dependability. The goal is to reroute power distribution in the event of transmission line failure. Such a system over a widespread area, is a cyber-physical system. The overall reliability of the advanced electric power grid is function of the respective reliabilities of its two major subsystems, namely, the FACTS network and the physical components that comprise the power grid. This paper presents a mathematical model based on the Markov chain imbeddable structure that utilizes a priori knowledge of reliability estimates for the FACTS devices and the communications links among them to predict the overall reliability of the power grid.

In this paper we extend transactive memory systems (TMS) theory to develop an understanding of the distributed coordination of expertise in high-reliability organizations. We illustrate our conceptual developments in a study of emergency management and response in Greece. We focus on the interaction between operators/dispatchers, ambulance crew, and specialist doctors, including the information and communication technologies (ICT) they use to respond to emergency incidents. Our case contributes to an in-depth understanding of the ways in which high-reliability organizations can sustain a distributed coordination of expertise over the duration of emergency incidents. This is achieved through the cultivation of TMS during a socialization and training period, the dynamic development of trust in emergent actions, and a commitment to shared protocols, which allow for improvisation and bricolage during unexpected incidents. Our findings also explore the role of ICTs in inscribing TMS in computerized protocols, while mediating the development of trust across the team, as well as mediating the construction of running narratives, which enable leaders to coordinate expertise in unexpected incidents.

Linda is a coordination model which, amongst other things, provides means for abstracting away from the location of information in distributed environments. Although the concept of location abstraction is important, and eases the programming task, it is incomplete in the Linda case. Whenever I/O operations are necessary, users have to be aware of the locations of devices. The use of computational language specic details for distributed I/O restricts the portability of Linda programs. Hitherto Linda has shown us how to write portable distributed algorithms for a variety of applications but for applications involving I/O the portability is compromised. In order to achieve maximum portability, a Linda application has to access I/O using proper Linda facilities. This paper describes a generalisation of Linda that includes coordination of distributed I/O. The advantages of such a generalisation and the problems involved in the implementation are also discussed.

This paper proposes a new QoS control method for the ad hoc Wireless LAN (W-LAN), which adjusts the Contention Window (CW) size dynamically based on the required and achieved bit rate. By the proposed method, a node with higher bit rates can have better chance to send the data in order to satisfy the Quality of Service (QoS) requirement. This paper also shows the effectiveness of the proposed method based on the results of computer simulations.

A novel cooperative spectrum sensing algorithm is implemented and analyzed using Raspberry Pi. In the proposed setup, Nokia cell phone is used as a spectrum sensing device while Raspberry Pi functions as a FC device to collect sensing results from local sensing devices. The investigation results of the proposed setup show significant improvement in detection performance as compared to local spectrum sensing techniques. Furthermore, results show a successful communication between sensing nodes and FC.

We propose several self-stabilizing protocols for unidirectional, anonymous, and uniform synchronous rings of arbitrary size, where processors communicate by exchanging messages. When the size of the ring $n$ is unknown, we better the service time by a factor of $n$ (performing the best possible complexity for the stabilization time and the memory consumption). When the memory size is known, we present a protocol that is optimal in memory (constant and independant of $n$), stabilization time, and service time (both are in $\Theta(n)$).

In emergency scenarios, network coverage constitutes a fundamental requirement for both crisis management and rescue operations. However, coverage might not be sufficient to avoid chaotic crowd behaviours that could possibly occur when there is lack of accurate sensing data, and of distributed coordination among the main actors. In this paper, we investigate the role that Commercial Off-The-Shelf (COTS) smartphones can play in emergency scenarios. Modern smartphones hide a great potential for emergency monitoring and management: (i) they are truly pervasive, (ii) they can establish peer-to-peer wireless links using short-range communication technologies, thus guaranteeing coverage even when fixed infrastructures are unavailable, and finally (iii) they can sense the environment through several embedded sensors. In order to maximally exploit such capabilities, we propose the SENSE-ME framework, which enables the creation of a spontaneous phone-sensing platform, by providing integrated functionalities of opportunistic networking, mobile sensing, and distributed information processing. Moreover, we introduce a realistic usage scenario (building evacuation), characterized by the presence of Android devices deployed over a two-dimensional space. Through SENSE-ME, each smartphone is able to quantify its level of danger by analysing its sensor data, to share such metrics with the surrounding devices via Wi-Fi Direct links, and finally to detect an emergency event, and com

We will consider the three phases of the procedure and approach the methodological issues of interest in order to compute the structure of interest in the image. 1) Detection. The first available image frame is analyzed searching for an underlying network structure, which is then extracted leveraging the use of a random walk model to navigate the network edges combined with a network agent to organize the retrieved information into a complex structure. The first frame is taken as a reference frame, also for the warping function w and the outcome of this procedure is a network graph (vertices, edges) with spatial information. 2) Tracking. The networked structure is then deformed in time starting from the information given by the reference frame and according to the visual data

In this position paper, we investigate the use of wireless sensor network (WSN) technology for ground surveillance. The goal of our project is to develop a prototype of WSN for outdoor deployment. We aim to design a system, which can detect and classify multiple targets (e.g., vehicles and troop movements), using inexpensive off-the-shelf wireless sensor devices, capable of sensing acoustic and magnetic signals generated by different target objects. In order to archive our goals, we intend to design a system, which is capable of automatic selforganization and calibration. Such a system would need to be capable of performing detection and tracking of targets as well as sending the real time enemy mobility information to a command centre. Real-time tacking with WSN is extremely challenging since it requires high system robustness, real time decision making, high frequency sampling, multi-modality of sensing, complex signal processing and data fusion, distributed coordination and wide area coverage. We propose a Hybrid Sensor Network architecture (HSN), tailored specifically to meet these challenges. We investigate data fusion technologies such as particle filters, to handle both environmental and sensing noises of inexpensive sensors.

IEEE 802.11 Distributed Coordination Function (DCF) uses a binary exponential backoff algorithm to arbitrate simultaneous channel access by multiple stations. When a station senses that either the shared wireless channel is busy or a collision has occurred, that station must delay the transmission by backoff time. This backoff time, in legacy DCF, is uniformly selected from a common contention window range that, in turn, ensures equal chance of grabbing the wireless medium by each station. Therefore, legacy DCF does not support service differentiation or priority access to the channel. To support service differentiation and increased Quality of Service (QoS), we propose two enhancements to the procedures used for managing contention window in original protocol. These two enhancements can be easily incorporated within the legacy DCF mechanism. First, instead of a common window for all classes, each traffic class is assigned a contention window with minimum and maximum values which are specific to that class. Second, the backoff algorithm is adjusted to follow a Multiple Increase Multiple Decrease (MIMD) procedure. First enhancement provides service differentiation and the second improves performance for all traffic classes. Unlike previous schemes, our proposed scheme does not require protocol changes in the legacy DCF. We evaluate our scheme using extensive simulations and demonstrate that, in comparison with legacy DCF, our newly proposed scheme provides a throughput increase of about 30% for high priority flows and of about 20% for medium priority flows.

This dissertation is dedicated to my children, Alejandro and Victor, they fulfill my life and make this a life worth lived. Additionally, I dedicate this work to my family, they always believed in me and never gave up on me, their expectations and desired for me to succeed kept me trying. To my close and dear friends Jaime and Manuel, they were always there for me when the frustrations arrived, and all those difficult moments I went thorough during this journey. Furthermore, this work is dedicated to Tere Ortega, her love for science and knowledge always inspired me, and I will always admire in her. xiii

In this article we have tried to establish how the nature of professional routines affects the ICT supported standardization and scripting of work performed by operators in Dutch colocated emergency response control rooms. In this type of multidisciplinary emergency control room three professions-police, fire rescue services and ambulance services-share the same technical facilities and are housed under the same roof. In the control rooms under study, efforts to create a more integrated control room are accompanied by a pursuit to further script and standardize operator intake and dispatch routines with the help of ICTs. Findings suggest that important impediments to the ICT supported scripting and standardization of operator intake and dispatch routines are not of a Human-Machine Interface (HMI) nature, but can mainly be attributed to differences in the nature of each of the three disciplines' professional routines themselves. These impediments are primarily related to ostensive as well as performative aspects of distinct sets of routines in the colocated control room.

In this paper we extend transactive memory systems (TMS) theory to develop an understanding of the distributed coordination of expertise in high-reliability organizations. We illustrate our conceptual developments in a study of emergency management and response in Greece. We focus on the interaction between operators/dispatchers, ambulance crew, and specialist doctors, including the information and communication technologies (ICT) they use to respond to emergency incidents. Our case contributes to an in-depth understanding of the ways in which high-reliability organizations can sustain a distributed coordination of expertise over the duration of emergency incidents. This is achieved through the cultivation of TMS during a socialization and training period, the dynamic development of trust in emergent actions, and a commitment to shared protocols, which allow for improvisation and bricolage during unexpected incidents. Our findings also explore the role of ICTs in inscribing TMS in computerized protocols, while mediating the development of trust across the team, as well as mediating the construction of running narratives, which enable leaders to coordinate expertise in unexpected incidents.

This paper presents an evolving method for a self-organizing multirobot exploration of an unknown environment. In such problem, a big consideration is given to the coordination behavior of robots in order to achieve the common tasks in an optimal way. Ant algorithms are proved to be very useful in solving such distributed control problems. We present here a modified version of the known ant algorithm, called Counter-Ant Algorithm (CAA). Indeed, the robots'collective behavior is based on repulsion instead of attraction to pheromone, which is a chemical matter open to evaporation and representing the core of ants' cooperation. A series of experimentations with MINDSTORMS LEGO robots, and simulations under Madkit platform, in laboratory conditions similar to real ones, show the usefulness of our algorithm for self-organizing and cooperative exploration.

We derive the access delay generating function of the IEEE 802.11 DCF protocol. Our analysis corrects a model recently presented in [6]. We demonstrate that numerical transform inversion can be used to efficiently obtain values of the distribution. Simulations show that our analytical results are highly accurate.

We consider single-hop broadcast packet erasure channels (BPEC) with degraded message sets and instantaneous feedback regularly available from all receivers, and demonstrate that the main principles of the virtual-queue-based algorithms in [1], which were proposed for multiple unicast sessions, can still be applied to this setting and lead to capacity-achieving algorithms. Specifically, we propose a generic class of algorithms and intuitively describe its rationale and properties that result in its efficiency. We then apply this class of algorithms to three examples of BPEC channels (with different numbers of users and 2 or 3 degraded message sets) and show that the achievable throughput region matches a known capacity outer bound, assuming feedback availability through a separate public channel. If the feedback channel is not public, all users can still decode their messages, albeit at some overhead which results in an achievable throughput that differs from the outer bound by O(N/L), where L is the packet length. These algorithms do not require any prior knowledge of channel statistics for their operation.

We consider single-hop broadcast packet erasure channels (BPEC) with degraded message sets and instantaneous feedback regularly available from all receivers, and demonstrate that the main principles of the virtual-queue-based algorithms in [1], which were proposed for multiple unicast sessions, can still be applied to this setting and lead to capacity-achieving algorithms. Specifically, we propose a generic class of algorithms and intuitively describe its rationale and properties that result in its efficiency. We then apply this class of algorithms to three examples of BPEC channels (with different numbers of users and 2 or 3 degraded message sets) and show that the achievable throughput region matches a known capacity outer bound, assuming feedback availability through a separate public channel. If the feedback channel is not public, all users can still decode their messages, albeit at some overhead which results in an achievable throughput that differs from the outer bound by O(N/L), where L is the packet length. These algorithms do not require any prior knowledge of channel statistics for their operation.

In some contexts, like for example complex games and puzzles, the search of solutions for problems leads to discover different procedures, none of which can be considered "the best" one. In these contexts, in fact, the different solutions can be compared only in some specific well known domain of application, while in other domains the comparison is incomplete or vague, or the domain may have imperfectly known boundaries: it is therefore impossible to put the different procedures in a precise preference order over the entire domain of applicability. Moreover these procedures may be "locally stable" because small local changes in the instructions that define them do not lead to any improvement, and therefore individuals that discover one solution may remain locked in it without trying to search alternative solutions. The search of solutions in puzzles shows striking analogies with the search of new theoretical approaches that take place when a consolidated theory fails to explain new phenomena. The properties of search in puzzles-multiplicity, local stability and incompleteness of solutions-also affect the new theoretical approaches, i.e. the new solutions to a scientific puzzle, that emerge challenging a dominant theory. The state of the art of new theoretical proposals in the field of decision-making interestingly illustrates this situation. After the numerous violations of traditional expected utility theory discovered since the experiments by Maurice Allais (1952), new theoretic proposals, such as prospect theory, regret theory, and others, have contended with it for the status of the "right" theory. To date, comparisons among the competing theoretical proposals has singled out none of them as unequivocally preferable. (Hey 1991) This situation, which has persisted for many years, prompts explanations which work in two directions: on the one hand, it suggests that epistemological elements relating to the existence and permanence of competing theories should be rethought; on the other, it suggests that cognitive aspects of human thinking should be examined in order to explain why alternative solutions to a problem may persist and stabilize and thereby provide a cognitive foundation for decision theory. The paper explores mainly the last question. The stability of "cognitive traps" is analyzed within the formal framework of the theory of problem solving. The core of the discussion will be based on analysis of the process by which players in complex games construct solutions, by editing the problem, decomposing it into basic building blocks, and defining the categories that allow to represent the problem. This process leads different players to construct different representations of the problem and therefore to adopt different solutions. Experiments show that players may discover different solutions according to the training that they have received, and that they may remain locked in these solutions

Quorum-based distributed coordination protocols provide decentralized control of a shared resource in a distributed system. To guarantee mutually exclusive or mutually consistent access to a resource, each processor in a distributed system obtains permission from a quorum of processors before accessing the resource. To ensure that resource requests made by different processors are arbitrated, the quorums of any two processors must intersect. To prevent failed quorum members from blocking access to the resource, or to optimize quorums for improved performance, it is desirable to adapt quorums as the state of the system changes. Adapting quorums on-line, while the quorum-based coordination protocol continues to operate normally, allows the resource to be accessed with minimum delay. Unless changes to the quorums of different processors are globally coordinated, on-line quorum adaptation can lead to violation of the quorum intersection property essential for correct coordination. In this research, a fault-tolerant, decentralized, and efficient solution to on-line quorum adaptation is given. The solution allows a changing quorum assignment that can consist of any preferred set of intersecting quorums, allowing any desired quorum adaptations that remove failed processors or optimize performance. A decentralized system model is assumed that allows processors to communicate only via unordered point-to-point messages. The synchronization that is necessary and sufficient to solve on-line quorum adaptation in the given system model is derived. Lower bounds are derived on the communication cost of a solution to on-line quorum adaptation. A fully distributed, fault-tolerant algorithm called QADAPT is given that solves the on-line quorum adaptation problem. The algorithm is shown to be correct and to require minimal message passing overhead. Experimental on-line quorum adaptation results using an implementation of QADAPT are reported. iv v Acknowledgments Doing research challenges one to grow in many capacities, whatever the particular focus of one's research. This thesis is dedicated to those who encouraged me to grow as a scientist, an engineer, a professional, and a person of character in the past five years. Because growth of the latter type sustains growth of the former type, I must thank many people who contributed in rather indirect ways to the completion of this thesis work.

The Intelligent Power Router (IPR), a concept based on scalable coordination, is proposed to control the next generation power network. Our goal is to show that by distributing network intelligence and control functions using the IPR, we will be capable of achieving improved survivability, security, reliability, and reconfigurability. Each IPR has embedded intelligence into it allowing it to switch power lines, shed load, and receive/broadcast local state-variable information to and from other IPRs. The information exchange capability of the routers will provide coordination among themselves to reconfigure the network when subject to a natural or man-made disaster. In this paper, we report our progress on six different activities around the creation of the IPR: IPR architecture; Communication Protocols among IPR; distributed controls; risk assessment of a system operated with and without IPR; power system reconfiguration based on a controlled islanding scheme using IPR; and the definition of the power routing as an ancillary service, since the IPR may provide improved efficiency and security in the context of a realistic market structure, such as Standard Market Design with LMP pricing algorithm. Finally, we present our effort to link this new concept to an education plan that addresses the socio-technical nature of power systems and the education needs of the new workforce.

Recently, the 802.11e Working Group (WG) has proposed the Hybrid Coordination Function (HCF), which has a HCF Controlled Channel Access (HCCA) and an Enhanced Distributed Coordination Access (EDCA), in order to provide QoS in WLANs. In this paper an innovative HCCA-based algorithm, which will be referred to as Power Save Feedback Based Dynamic Scheduler (PS FBDS) providing bounded delays while ensuring energy saving, has been developed. The performance of PS FBDS has been extensively investigated using ns-2 simulations; results show that the proposed algorithm is able to provide a good trade-off between QoS and power saving at both low and high network loads.