Category Archives: Communication Networks

Simultaneous localization and clock synchronization (apparently only offsets are estimated) in wireless networks

December 28, 2017 09:53 ,

Y. Liu, Y. Shen, D. Guo and M. Z. Win, Network Localization and Synchronization Using Full-Duplex Radios, IEEE Transactions on Signal Processing, vol. 66, no. 3, pp. 714-728, DOI: 10.1109/TSP.2017.2770090.

Both localization and synchronization of mobile nodes are important for wireless networks. In this paper, we propose new methods for network localization and synchronization (NLS) using full-duplex radios through only two frames of transmission. Specifically, all nodes simultaneously transmit their signature signals in the first frame, while receiving others’ signals via full-duplex radios. In the second frame, nodes transmit either scrambled versions of their received signals in the first frame or a digital packet of the channel parameter estimates of the received signals. We develop distributed algorithms to estimate the arrival times of different components in the received signals. These arrival times are then used to determine the local network geometry and clock offsets. The Cramér-Rao lower bounds for internode distances and clock offsets are derived, and the former can be translated into error bounds of the node positions. Compared with conventional frequency division duplex or time-division duplex, we demonstrate the high efficiency of NLS using full-duplex radios, revealing its potential beyond data communications in future wireless networks.

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A novel method for hard real-time communications using the physical layer of Ethernet and a variation of TDMA

September 20, 2017 08:30 ,

Andrzej Przybył, Hard real-time communication solution for mechatronic systems, Robotics and Computer-Integrated Manufacturing, Volume 49, 2018, Pages 309-316, DOI: 10.1016/j.rcim.2017.08.001.

The paper proposes a method to build a highly efficient real-time communication solution for mechatronic systems. The method is based on the Ethernet physical layer (PHY) and on field programmable gate array (FPGA) technology and offers a better performance when compared to commercially available communication solutions. Although it is not directly compatible with the OSI/ISO model of TCP/IP protocol, vertical integration is done with a gateway. This provides simplicity and safety. Moreover, the use of the FPGA allows for integrating the communication solution with the user algorithm of particular distributed device inside a single chip. Therefore, the proposed solution is efficient and highly integrated.

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Clock synchronization in a wireless network based on consensus method that takes into account the noise (uncertainty) in the system, with a nice related work about consensus-based network clock synchronization

June 30, 2017 11:37 ,

Jianping He, Xiaoming Duan, Peng Cheng, Ling Shi, Lin Cai, Accurate clock synchronization in wireless sensor networks with bounded noise, Automatica, Volume 81, July 2017, Pages 350-358, ISSN 0005-1098, DOI: 10.1016/j.automatica.2017.03.009.

It is important and challenging to achieve accurate clock synchronization in wireless sensor networks. Various noises, e.g., communication delay, clock fluctuation and measurement errors, are inevitable and difficult to be estimated accurately, which is the main challenge for achieving accurate clock synchronization. In this paper, we focus on how to achieve accurate clock synchronization by considering a practical noise model, bounded noise, which may not satisfy any known distributions. The principle that a bounded monotonic sequence must possess a limit and the concept of maximum consensus are exploited to design a novel clock synchronization algorithm for the network to achieve accurate and fast synchronization. The proposed algorithm is fully distributed, with high synchronization accuracy and fast convergence speed, and is able to compensate both clock skew and offset simultaneously. Meanwhile, we prove that the algorithm converges with probability one, which means that an accurate clock synchronization is achieved. We further prove that the probability of the complete synchronization converges exponentially fast. Experiments and simulations are conducted to verify the noise model and demonstrate the effectiveness of the proposed algorithm.

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Simultaneous localization and synchronization (SLAS) for multiple agents, with a nice state of the art including both SLAS for individual and multiple agents

June 30, 2017 10:59 ,

B. Etzlinger, F. Meyer, F. Hlawatsch, A. Springer and H. Wymeersch, “Cooperative Simultaneous Localization and Synchronization in Mobile Agent Networks,” in IEEE Transactions on Signal Processing, vol. 65, no. 14, pp. 3587-3602, July15, 15 2017. DOI: 10.1109/TSP.2017.2691665.

Cooperative localization in agent networks based on interagent time-of-flight measurements is closely related to synchronization. To leverage this relation, we propose a Bayesian factor graph framework for cooperative simultaneous localization and synchronization (CoSLAS). This framework is suited to mobile agents and time-varying local clock parameters. Building on the CoSLAS factor graph, we develop a distributed (decentralized) belief propagation algorithm for CoSLAS in the practically important case of an affine clock model and asymmetric time stamping. Our algorithm is compatible with real-time operation and a time-varying network connectivity. To achieve high accuracy at reduced complexity and communication cost, the algorithm combines particle implementations with parametric message representations and takes advantage of a conditional independence property. Simulation results demonstrate the good performance of the proposed algorithm in a challenging scenario with time-varying network connectivity.

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A novel clock synchronization architecture for networked systems based on forcing the synchronization, with a nice summary of uses of clock synchronization and of existing synchronization architectures

June 8, 2017 10:13 ,

S. Bolognani, R. Carli, E. Lovisari and S. Zampieri, “A Randomized Linear Algorithm for Clock Synchronization in Multi-Agent Systems,” in IEEE Transactions on Automatic Control, vol. 61, no. 7, pp. 1711-1726, July 2016. DOI: 10.1109/TAC.2015.2479136.

A broad family of randomized clock synchronization protocols based on a second order consensus algorithm is proposed. Under mild conditions on the graph connectivity, it is proved that the parameters of the algorithm can always be tuned in such a way that the clock synchronization is achieved in the probabilistic mean-square sense. This family of algorithms contains, as particular cases, several known approaches which range from distributed asynchronous to hierarchical synchronous protocols. This is illustrated by specializing the algorithm for the well-known broadcast and gossip scenarios in wireless communications, and for the standard hierarchical protocol used in the context of wired communications in data networks. In these cases, we show how the feasible range for the algorithm parameters can be explicitly computed. Finally, the performance of this strategy is validated by actual implementation in a real testbed and by numerical simulations.

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Improvement on the classical regression-based estimation algorithm of the relative clock frequency of two remotely connected clocks for better behaviour under outliers, and a good related works section on the estimation of clock relative frequency

December 22, 2015 17:57 ,

Oka Saputra, K.; Wei-Chung Teng; Tsung-Han Chen, Hough Transform-Based Clock Skew Measurement Over Network, in Instrumentation and Measurement, IEEE Transactions on , vol.64, no.12, pp.3209-3216, Dec. 2015, DOI: 10.1109/TIM.2015.2450293.

The accurate clock skew measurement of remote devices over network connections is crucial to device fingerprinting and other related applications. Current approaches use the lower bound of offsets between the target device and the measurer to estimate clock skew; however, the accuracy of estimation is severely affected when even a few offsets appear below the crowd of offsets. This paper adopted the Hough transform to develop a new method, which searches for the densest part of the whole distribution. This method is effective in filtering out the upper and lower outliers such that the skew values derived from the remaining offsets are stable, even when lower outliers occur, or when the measuring time is not long enough for current approaches to achieve stable results. The experimental evaluation of the proposed method has been conducted in order to compare its performance with that of linear programming algorithm (LPA) and two other approaches. During the five consecutive measurements of 1000 offsets each, skews of the proposed method varied within the range of 0.59 ppm, whereas LPA resulted in the range of 0.89 ppm. Both ranges increased to 1.34 and 63.93 ppm, respectively, when the lower bounds encountered interference from lower outliers.

Notes:

  • They assume there is no NTP running in the background; however, their results seem to come from a conventional TCP/IP network, where it is difficult not to find NTP enabled.
Posted in: Communication networks, Real-Time Systems , Tagged: ,

Scheduling of communications between several nodes for better achieving real-time constraints in a distributed control system, and also a very detailed dynamical model of a wheeled vehicle

November 12, 2015 20:08 ,

Naim Bajcinca, Wireless cars: A cyber-physical approach to vehicle dynamics control, Mechatronics, Volume 30, September 2015, Pages 261-274, ISSN 0957-4158, DOI: 10.1016/j.mechatronics.2015.04.016.

A non-conventional drive-by-wireless technology for guidance and control of a redundantly actuated electric car supported by an on-board wireless network of sensors, actuators and control units is proposed in this article. Several optimization-based distributed feedforward control schemes are developed for such powertrain infrastructures. In view of the limitations of the commercial off-the-shelf wireless communication technologies and the harshness of the in-vehicle environments, a pressing design and implementation aspect, in addition to the robustness against information loss, refers to fulfilling the hard real-time computational requirements. In this work, we address such problems by introducing several distributed event-based control schemes in conjunction with adaptive scheduling at the protocol level. Hereby we obtain a simple tuning mechanism to compromise between the outcome accuracy and computation efficiency (i.e., communication traffic intensity). Using simulative evaluations, we demonstrate the viability of the proposed algorithms and illustrate the impact of external interferences in an IEEE 802.15.4 based wireless communication solution.

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Multi-agent Q-learning applied to the defense against DDoS attacks with some provisions for scaling

October 5, 2015 09:16 ,

Kleanthis Malialisa, Sam Devlina & Daniel Kudenkoa, Distributed reinforcement learning for adaptive and robust network intrusion response, Connection Science, Volume 27, Issue 3, 2015, DOI: 10.1080/09540091.2015.1031082.

Distributed denial of service (DDoS) attacks constitute a rapidly evolving threat in the current Internet. Multiagent Router Throttling is a novel approach to defend against DDoS attacks where multiple reinforcement learning agents are installed on a set of routers and learn to rate-limit or throttle traffic towards a victim server. The focus of this paper is on online learning and scalability. We propose an approach that incorporates task decomposition, team rewards and a form of reward shaping called difference rewards. One of the novel characteristics of the proposed system is that it provides a decentralised coordinated response to the DDoS problem, thus being resilient to DDoS attacks themselves. The proposed system learns remarkably fast, thus being suitable for online learning. Furthermore, its scalability is successfully demonstrated in experiments involving 1000 learning agents. We compare our approach against a baseline and a popular state-of-the-art throttling technique from the network security literature and show that the proposed approach is more effective, adaptive to sophisticated attack rate dynamics and robust to agent failures.

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A new algorithm for clock synchronization in wireless sensor networks with bounded delays, that includes interesting references to surveys

July 27, 2015 10:26 ,

Emanuele Garone, Andrea Gasparri, Francesco Lamonaca, Clock synchronization protocol for wireless sensor networks with bounded communication delays, Automatica, Volume 59, September 2015, Pages 60-72, ISSN 0005-1098, DOI: 10.1016/j.automatica.2015.06.014.

In this paper, we address the clock synchronization problem for wireless sensor networks. In particular, we consider a wireless sensor network where nodes are equipped with a local clock and communicate in order to achieve a common sense of time. The proposed approach consists of two asynchronous consensus algorithms, the first of which synchronizes the clocks frequency and the second of which synchronizes the clocks offset. This work advances the state of the art by providing robustness against bounded communication delays. A theoretical characterization of the algorithm properties is provided. Simulations and experimental results are presented to corroborate the theoretical findings and show the effectiveness of the proposed algorithm.

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A quick, formal explanation of the PageRank algorithm and its existing variants

May 29, 2015 16:23 ,

Lei, J.; Chen, H., Distributed Randomized PageRank Algorithm Based on Stochastic Approximation, Automatic Control, IEEE Transactions on , vol.60, no.6, pp.1641,1646, June 2015. DOI: 10.1109/TAC.2014.2359311.

A distributed randomized PageRank algorithm based on stochastic approximation (SA) is proposed to estimate the importance scores of web pages. Compared with the existing methods, the algorithm given here has wider applications in the sense that it can deal with a larger class of randomizations. The strong consistency of the estimates is proved, and the robustness of the PageRank value is analyzed as well. Numerical examples are given to verify the obtained theoretic results.

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