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We consider a retrial queueing model for random access protocols arising in local area networks such as carrier sense multiple access networks. In our model, one channel is shared among multiple nodes. Each node accesses the channel according to a Poison process and the holding time of the channel is exponentially distributed. Blocked users join the orbit and retry to access again after an exponentially distributed time depending on the number of retrials so far. As the model under study is not amenable for exact analysis, we focus on its performance in the light traffic regime. In particular, we describe a fast algorithm for calculating the terms in the Maclaurin series expansion of various performance measures, the arrival rate being the independent parameter of the expansion. We illustrate our approach by various numerical examples and verify the accuracy of the light traffic approximation by means of simulation. [ABSTRACT FROM AUTHOR]

This paper proposes a large-scale wireless powered communication network (WPCN), which consists of a hybrid access point (H-AP) and numerous nodes. The H-AP broadcasts energy to all nodes, and the nodes harvest the energy and then use the harvested energy to transmit information. For the large-scale WPCN, we also propose a novel hybrid multiple access protocol, termed hybrid multiple access-based dual harvest-then-transmit. The proposed protocol utilizes both time division multiple access (TDMA) and carrier-sense multiple access (CSMA), in order to deal with various traffic patterns and transmission reliability of different applications in large-scale networks. We consider a dual wireless energy transfer (WET) at the H-AP. The main WET is performed in TDMA and the other WET is performed at space holes in CSMA, to increase the channel utilization and harvested energy. For the considerations, we study the sum-throughput maximization in the large-scale WPCN based on hybrid multiple access-based dual harvest-then-transmit. Simulation results show that the proposed protocol outperforms the conventional protocol in large-scale WPCN. [ABSTRACT FROM AUTHOR]

Multi-robot patrolling is a key feature for various applications related to surveillance and security, and it has been studied from several different perspectives, ranging from techniques that devise optimal off-line strategies to implemented systems. However, still few approaches consider on-line decision techniques that can cope with uncertainty and non-determinism in robot behaviors. In this article we address on-line coordination, by casting the multi-robot patrolling problem as a task assignment problem and proposing two solution techniques: DTA-Greedy, which is a baseline greedy approach, and DTAP, which is based on sequential single-item auctions. We evaluate the performance of our system in a realistic simulation environment (built with ROS and stage) as well as on real robotic platforms. In particular, in the simulated environment we compare our task assignment approaches with previous off-line and on-line methods. Our results confirm that on-line coordination approaches improve the performance of the multi-robot patrolling system in real environments, and that coordination approaches that employ more informed coordination protocols (e.g., DTAP) achieve better performances with respect to state-of-the-art online approaches (e.g., SEBS) in scenarios where interferences among robots are likely to occur. Moreover, the deployment on real platforms (three Turtlebots in an office environment) shows that our on-line approaches can successfully coordinate the robots achieving good patrolling behaviors when facing typical uncertainty and noise (e.g., localization and navigation errors) associated to real platforms. [ABSTRACT FROM AUTHOR]

Simulation is often used in order to evaluate the behavior and the performance of computing systems. Specifically, in the field of high-performance interconnection networks for HPC clusters the simulation has been extensively considered to verify and validate network operation models and to evaluate their performance. Nevertheless, experiments conducted to evaluate network performance using simulation tools should be fed with realistic network traffic from real benchmarks and/or applications. This approach has grown in popularity because it allows to evaluate the simulation model under realistic traffic situations. In this paper, we propose a family of tools for modeling realistic workloads which capture the behavior of MPI applications into self-related traces called VEF traces. The main novelty of this approach is that it replays the MPI collective operations with their corresponding messages, offering an MPI message-based task simulation framework. The proposed framework neither provides a network simulator nor depends on any specific simulation platform. Besides, this framework allows us to use the generated traces by any third-party network simulator working at message level. [ABSTRACT FROM AUTHOR]

This paper proposes a method to reduce overhead packets and end-to-end delay and improve reachability over an ad hoc network that uses a location-aided routing protocol. Location-aided routing is useful in emergency situations where both the infrastructure network and consistent address assignment mechanisms do not work. The existing location-aided routing protocols, however, have several defects such as needing many overhead packets to capture the location information, and difficulty in handling void zones. The proposed technique consists of location-aided route discovery based on a two-hop neighbor information and forwarding mechanism. By knowing more about the location of other nodes, the proposal can solve the existing problems. This paper compares our approaches with existing approaches through computer simulation and analysis, showing that our proposed method achieves better performance than those of the existing approaches. [ABSTRACT FROM AUTHOR]

In this paper, we design a novel hybrid remote display for mobile thin-client system. The remote frame buffer (RFB) protocol and motion JPEG (M-JPEG) protocol are assigned to handle remote display tasks in the slow-motion region and high-motion region, respectively. Graphic processing units (GPU) are utilized to do a part of a real-time JPEG compression task. A novel quality of experience (QoE)-based high-motion detection algorithm is also proposed to reduce the network bandwidth consumption and the server-side computing resource consumption. The continuity of screen delivery remains whenever the JPEG compression is applied to different screen regions. The proposed hybrid remote display approach has many good features which have been justified by comprehensive simulation studies. [ABSTRACT FROM AUTHOR]

The operational patterns of multifarious backup strategies on AODV-based (Ad-hoc On-Demand Vector) routing protocols are elaborated in this article. To have a broader picture on relevant routing protocols together, variants of AODV-based backup routing protocols are formulated by corresponding algorithms, and also each of them are simulated to obtain the necessary performance metrics for comparisons in terms of packet delivery ratio, average latency delay, and the normalized routing load. Then to make the process of data salvation more efficiently in case of link failure, we explore the possibility of combining the AODV backup routing strategy and on-demand node-disjoint multipath routing protocols. This article proposes an improved approach named DPNR (Dual Paths Node-disjoint Routing) for data salvation, a routing protocol that maintains the only two shortest backup paths in the source and destination nodes. The DPNR scheme can alleviate the redundancy-frames overhead during the process of data salvation by the neighboring intermediate nodes. Our simulation results have demonstrated that DPNR scheme delivers good data delivery performance while restricting the impacts of transmission collision and channel contention. The mathematical rationale for our proposed approach is stated as well. [ABSTRACT FROM AUTHOR]

This paper addresses mobility control routing in wireless networks. Given a data flow request between a source-destination pair, the problem is to move nodes towards the best placement, such that the performance of the network is improved. Our purpose is to find the best nodes selection depending on the minimization of the maximum distance that nodes have to travel to reach their final position. We propose a routing protocol, the Routing Protocol based on Controlled Mobility (RPCM), where the chosen nodes' path minimizes the total travelled distance to reach desirable position. Specifically, controlled mobility is intended as a new design dimension network allowing to drive nodes to specific best position in order to achieve some common objectives. The main aim of this paper is to show by simulation the effectiveness of controlled mobility when it is used as a new design dimension in wireless networks. Extensive simulations are conducted to evaluate the proposed routing algorithm. Results show how our protocol outperforms a well-known routing protocol, the Ad hoc On Demand Distance Vector routing (AODV), in terms of throughput, average end-to-end data packet delay and energy spent to send a packet unit. [ABSTRACT FROM AUTHOR]

To bring VANET into reality, it is crucial to devise routing protocols that can exploit the inherited characteristics of VANET environment to enhance the performance of the running applications. Previous studies have shown that a certain routing protocol behaves differently under different presumed mobility patterns. Bypass-AODV is a new optimization of the AODV routing protocol for mobile ad-hoc networks. It is proposed as a local recovery mechanism to enhance the performance of the AODV routing protocol. It shows outstanding performance under the Random Waypoint mobility model compared with AODV. However, Random Waypoint is a simple model that may be applicable to some scenarios but it is not sufficient to capture some important mobility characteristics of scenarios where VANETs are deployed. In this paper, we will investigate the performance of Bypass-AODV under a wide range of mobility models including other random mobility models, group mobility models, and vehicular mobility models. Simulation results show an interesting feature that is the insensitivity of Bypass-AODV to the selected random mobility model, and it has a clear performance improvement compared to AODV. For group mobility model, both protocols show a comparable performance, but for vehicular mobility models, Bypass-AODV suffers from performance degradation in high-speed conditions. [ABSTRACT FROM AUTHOR]

A new method of analytical modeling of the broadband wireless networks with hidden terminals operating under the IEEE 802.11 protocol was proposed. It was assumed that the network stations operate in saturation and access the wireless channel using both the basic and alternative RTS/CTS methods. Results of analytical modeling and simulation were presented. [ABSTRACT FROM AUTHOR]

Abstract  Task assignment in multi-agent systems is a complex coordination problem, in particular in systems that are subject to dynamic and changing operating conditions. To enable agents to deal with dynamism and change, adaptive task assignment approaches are needed. In this paper, we study two approaches for adaptive task assignment that are characteristic for two classical families of task assignment approaches. FiTA is a field-based approach in which tasks emit fields in the environment that guide idle agents to tasks. DynCNET is a protocol-based approach that extends Standard Contract Net (CNET). In DynCNET, agents use explicit negotiation to assign tasks. We compare both approaches in a simulation of an industrial automated transportation system. Our experiences show that: (1) the performance of DynCNET and FiTA are similar, while both outperform CNET; (2) the complexity to engineer DynCNET is similar to FiTA but much more complex than CNET; (3) whereas task assignment with FiTA is an emergent solution, DynCNET specifies the interaction among agents explicitly allowing engineers to reason on the assignment of tasks, (4) FiTA is inherently robust to message loss while DynCNET requires substantial additional support. The tradeoff between (3) and (4) is an important criteria for the selection of an adaptive task assignment approach in practice. [ABSTRACT FROM AUTHOR]

A new medium access control (MAC) protocol is proposed for quality-of-service (QoS) support in wireless local area networks (WLAN). The protocol is an alternative to the recent enhancement 802.11e. A new priority policy provides the system with better performance by simulating time division multiple access (TDMA) functionality. Collisions are reduced and starvation of low-priority classes is prevented by a distributed admission control algorithm. The model performance is found analytically extending previous work on this matter. The results show that a better organization of resources is achieved through this scheme. Throughput analysis is verified with OPNET simulations. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the performance of an enhanced cooperative MAC with busy tone (eBT-COMAC) protocol in mobile ad hoc networks via a combination of theoretical analysis and numerical simulation. Our previously proposed BT-COMAC protocol was enhanced by (1) redesigning the minislots used in the helper node selection procedure; (2) specifying complete frame formats for newly defined and modified control frames; and (3) using a new metric (the received SNR rather than the received power) in the helper node competition. In this eBT-COMAC protocol, cooperation probability is calculated based on a geometric analysis, and a Markov chain-based model is used to derive steady-state probabilities for backoff-related parameters. These results are used to analytically characterize two performance measures: system throughput and channel access delay. Numerical simulation of a mobile wireless network where all communication nodes are assumed to be uniformly distributed in space and move independently based on a random waypoint model is used to validate the analytical results and demonstrate the performance gains achieved by the proposed eBT-COMAC protocol. [ABSTRACT FROM AUTHOR]