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  • 1
    Language: English
    In: Journal of Intelligent & Robotic Systems, 2016, Vol.82(2), pp.325-337
    Description: Work on coordinated multi-robot exploration often assumes that all areas to be explored are freely accessible. This common assumption does not always hold, especially not in search and rescue missions after a disaster. Doors may be closed or paths blocked detaining robots from continuing their exploration beyond these points and possibly requiring multiple robots to clear them. This paper addresses the issue how to coordinate a multi-robot system to clear blocked paths. We define local collaborations that require robots to collaboratively perform a physical action at a common position. A collaborating robot needs to interrupt its current exploration and move to a different location to collaboratively clear a blocked path. We raise the question when to collaborate and whom to collaborate with. We propose four strategies as to when to collaborate. Two obvious strategies are to collaborate immediately or to postpone any collaborations until only blocked paths are left. The other two strategies make use of heuristics based on building patterns. While no single strategy behaves optimal in all scenarios, we show that the heuristics decrease the time required to explore unknown environments considering blocked paths.
    Keywords: Collaboration ; Robot exploration ; Mobile robot teams ; Indoor exploration ; Multi-robot systems ; Autonomous systems
    ISSN: 0921-0296
    E-ISSN: 1573-0409
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  • 2
    Language: English
    In: ACM Transactions on Autonomous and Adaptive Systems (TAAS), 01 September 2012, Vol.7(3), pp.1-23
    Description: Solutions for time synchronization based on coupled oscillators operate in a self-organizing and adaptive manner and can be applied to various types of dynamic networks. The basic idea was inspired by swarms of fireflies, whose flashing dynamics shows an emergent behavior. This article introduces such a synchronization technique whose main components are "inhibitory coupling" and "self-adjustment." Based on this new technique, a number of contributions are made. First, we prove that inhibitory coupling can lead to perfect synchrony independent of initial conditions for delay-free environments and homogeneous oscillators. Second, relaxing the assumptions to systems with delays and different phase rates, we prove that such systems synchronize up to a certain precision bound. We derive this bound assuming inhomogeneous delays and show by simulations that it gives a good estimate in strongly-coupled systems. Third, we show that inhibitory coupling with self-adjustment quickly leads to synchrony with a precision comparable to that of excitatory coupling. Fourth, we analyze the robustness against faulty members performing incorrect coupling. While the specific precision-loss encountered by such disturbances depends on system parameters, the system always regains synchrony for the investigated scenarios.
    Keywords: Synchronization ; Delayed System ; Engineering Emergent Behavior ; Heterogeneous System ; Inhibitory Coupling ; Networked Systems ; Pulse Coupled Oscillators ; Self-Organization ; Computer Science
    ISSN: 15564665
    E-ISSN: 1556-4703
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  • 3
    Language: English
    In: IEEE Transactions on Vehicular Technology, January 2014, Vol.63(1), pp.178-190
    Description: An important building block in cooperative diversity is relay selection, which has to ensure that a well-suited node is employed as a relay. The required coordination among nodes causes signaling overhead, which in turn can significantly devalue the performance benefits gained by cooperative diversity. A relay update policy defines when a new relay is selected; it can balance the tradeoff between performance and overhead. This tradeoff is studied using mathematical methods. We consider three relay selection schemes, i.e., permanent, reactive, and adaptive, which have different relay update rules. We develop an analytical framework using semi-Markov processes to evaluate the throughput and energy efficiency of cooperative automatic repeat request (ARQ) protocols in time-correlated multipath fading channels. Results reveal potential performance gains of different selection schemes under various conditions. The reactive and adaptive schemes make use of better suited relays due to frequent selections. If their selection overhead, however, is significant, a permanent relay can achieve higher throughput due to negligible overhead. The impact of temporal correlation of fading channels on throughput and energy efficiency is also shown. These insights can be applied for development of cooperative communication protocols.
    Keywords: Automatic Repeat Request (Arq) ; Cooperative Communication ; Fading ; Relay Selection ; Semi-Markov Process ; Engineering
    ISSN: 0018-9545
    E-ISSN: 1939-9359
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  • 4
    Language: English
    In: IEEE Communications Magazine, July, 2005, Vol.43(7), p.78(8)
    Description: The principles and the four design paradigms for developing self-organized network function in communication networks are presented. The benefits of such functions include potential to reduce costs, complexity and improve the robustness of network.
    Keywords: Wireless Networking Equipment -- Design And Construction ; Self-organizing Systems -- Analysis
    ISSN: 0163-6804
    E-ISSN: 15581896
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  • 5
    Language: English
    In: Computer Networks, 2012, Vol.56(1), pp.142-156
    Description: This article investigates probabilistic information dissemination in stochastic networks. The following problem is studied: A source node intends to deliver a message to all other network nodes using probabilistic flooding, i.e., each node forwards a received message to all its neighbors with a common network-wide forwarding probability . Question is: what is the minimum -value each node should use, such that the flooded message is obtained by all nodes with high probability? We first present a generic approach to derive the global outreach probability in arbitrary networks and then focus on Erdős Rényi graphs (ERGs) and random geometric graphs (RGGs). For ERGs we derive an exact expression. For RGGs we derive an asymptotic expression that represents an approximation for networks with high node density. Both reliable and unreliable links are studied.
    Keywords: Probabilistic Flooding ; Stochastic Networks ; Graph Theory ; Stochastic Geometry ; Processes on Networks ; Engineering
    ISSN: 1389-1286
    E-ISSN: 1872-7069
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  • 6
    Language: English
    In: Wireless Networks, 2005, Vol.11(5), pp.571-579
    Description: This article analyzes the connectivity of multihop radio networks in a log-normal shadow fading environment. Assuming the nodes have equal transmission capabilities and are randomly distributed according to a homogeneous Poisson process, we give a tight lower bound for the minimum node density that is necessary to obtain an almost surely connected subnetwork on a bounded area of given size. We derive an explicit expression for this bound, compute it in a variety of scenarios, and verify its tightness by simulation. The numerical results can be used for the practical design and simulation of wireless sensor and ad hoc networks. In addition, they give insight into how fading affects the topology of multihop networks. It is explained why a high fading variance helps the network to become connected.
    Keywords: wireless multihop networks ; wireless sensor networks ; ad hoc networking ; connectivity ; node isolation
    ISSN: 1022-0038
    E-ISSN: 1572-8196
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  • 7
    Conference Proceeding
    Conference Proceeding
    Springer Berlin Heidelberg, Berlin, Heidelberg
    Language: English
    Keywords: Computer Science -- Computer Communication Networks; Computer Science -- Software Engineering; Computer Science -- Information Systems Applications (incl.Internet); Computer Science -- Information Storage and Retrieval; Computer Science -- Data Mining and Knowledge Discovery; Computer Science -- Communications Engineering, Networks
    ISBN: 978-3-642-19166-4
    Source: Springer Science & Business Media B.V.
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  • 8
    In: IEEE Transactions on Mobile Computing, 12/2012, Vol.11(12), pp.2109-2120
    Description: In conventional Wireless Mesh Networks (WMNs), multihop relays are performed in the backbone comprising of interconnected Mesh Routers (MRs) and this causes capacity degradation. This paper proposes a hybrid WMN architecture that the backbone is able to utilize random connections to Access Points (APs) of Wireless Local Area Network (WLAN). In such a proposed hierarchal architecture, capacity enhancement can be achieved by letting the traffic take advantage of the wired connections through APs. Theoretical analysis has been conducted for the asymptotic capacity of three-tier hybrid WMN, where per-MR capacity in the backbone is first derived and per-MC capacity is then obtained. Besides related to the number of MR cells as a conventional WMN, the analytical results reveal that the asymptotic capacity of a hybrid WMN is also strongly affected by the number of cells having AP connections, the ratio of access link bandwidth to backbone link bandwidth, etc. Appropriate configuration of the network can drastically improve the network capacity in our proposed network architecture. It also shows that the traffic balance among the MRs with AP access is very important to have a tighter asymptotic capacity bound. The results and conclusions justify the perspective of having such a hybrid WMN utilizing widely deployed WLANs.
    Keywords: Computing and Processing;
    ISSN: 1536-1233
    E-ISSN: 15580660
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  • 9
    Language: English
    In: IEEE Transactions on Mobile Computing, 13 April 2019, pp.1-1
    Description: A thorough understanding of the temporal dynamics of interference in wireless networks is crucial for the design of communication protocols, scheduling, and interference management. This article applies stochastic geometry to investigate the interference dynamics in a network of nodes that use carrier sense multiple access (CSMA). This type of network is approximated by a Matérn hard-core point process of type II with Nakagami fading. We derive and analyze expressions for the variance, covariance, and correlation of the interference power at an arbitrary location. Results show that even though the commonly used Poisson approximation to CSMA may have the same average interference as the Matérn model, the interference dynamics behaves significantly different. In this way, this study reveals a pitfall in the modeling of wireless systems and contributes to the theory of interference calculus.
    Keywords: Wireless Networks ; Stochastic Geometry ; Interference Dynamics ; Correlation ; Matérn Point Process ; Hard-Core Process ; Modeling Pitfalls ; Nakagami Fading ; Csma ; Computer Science
    ISSN: 1536-1233
    E-ISSN: 1558-0660
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  • 10
    In: IEEE Transactions on Wireless Communications, 2019
    Description: In this paper, an interference-aware path planning scheme for a network of cellular-connected unmanned aerial vehicles (UAVs) is proposed. In particular, each UAV aims at achieving a tradeoff between maximizing energy efficiency and minimizing both wireless latency and the interference level caused on the ground network along its path. The problem is cast as a dynamic game among UAVs. To solve this game, a deep reinforcement learning algorithm, based on echo state network (ESN) cells, is proposed. The introduced deep ESN architecture is trained to allow each UAV to map each observation of the network state to an action, with the goal of minimizing a sequence of time-dependent utility functions. Each UAV uses ESN to learn its optimal path, transmission power level, and cell association vector at different locations along its path. The proposed algorithm is shown to reach a subgame perfect Nash equilibrium (SPNE) upon convergence. Moreover, an upper and lower bound for the altitude of the UAVs is derived thus reducing the computational complexity of the proposed algorithm. Simulation results show that the proposed scheme achieves better wireless latency per UAV and rate per ground user (UE) while requiring a number of steps that is comparable to a heuristic baseline that considers moving via the shortest distance towards the corresponding destinations. The results also show that the optimal altitude of the UAVs varies based on the ground network density and the UE data rate requirements and plays a vital role in minimizing the interference level on the ground UEs as well as the wireless transmission delay of the UAV.
    Keywords: Computer Science - Information Theory ; Computer Science - Artificial Intelligence ; Computer Science - Computer Science And Game Theory
    Source: Cornell University
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