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Fully distributed clock synchronization in wide-range TDMA Ad-Hoc networks
Abstract
In this paper, a fully distributed synchronization scheme for wide-range TDMA Ad-Hoc networks is described. This synchronization scheme provides a simple algorithm with low overhead requirements to achieve high clock synchronization accuracy in a fully distributed approach. Our work is based on the clock sampling mutual network synchronization (CS-MNS) algorithm. It extends it by including the propagation delay between nodes in the problem formulation and by providing a detailed signaling framework to carry out synchronization information. The study based on OPNET simulations finds that 1us clock synchronization accuracy can be achieved in long range TDMA MANETs.
... This is especially important for long-range MANET, where distances between nodes can be large. To evaluate performance of the proposed protocol and to compare it with the protocol, described in [10], we performed simulations. ...
... This protocol does not take propagation delays into account. Algorithm, described in [10], improves protocol [9] and synchronizes wireless nodes with regard for propagation delay. Similar ideas were presented in [11]. ...
... Similar ideas were presented in [11]. Protocols [9], [10], [11] have high accuracy but rather long convergence time. ...
In this paper a new distributed clock synchronization algorithm for wireless multihop ad hoc network is presented. The algorithm is based on TSF (Timing Synchronization Function) used in IEEE 802.11. We extended TSF with determination of propagation delay between neighbors. This is especially important for wide-range networks where propagation delays can be significant. The performance analysis of the protocol is carried out with a simulation model.
... A node adjusts the time and frequency of its clock recursively in the time domain by multiplying the time of its clock by a factor that is updated with any newly received time stamp. The work, proposed in [1], presents a new fully decentralized synchronization algorithm for long range TDMA Ad-Hoc networks. It is based on the clock sampling mutual network synchronization (CSMNS) algorithm that includess the propagation delay in the problem formulation. ...
Synchronizing network nodes becomes a prerequisite to many basic operations in wireless ad hoc networks, such as frequency hopping, power saving, free contention channel access, clustering and security. Clock synchronization requires the availability of a common time reference for all mobile nodes, since these clocks drift naturally. However, a synchronization algorithm cannot converge quickly to a stable point without considering the effects of collision and interference, inherent to wireless environments. In this context, we propose a Fast Synchronization Protocol with Collision Handling, designed for multi hop wireless ad hoc networks. Performance evaluation results have shown the ability of our algorithm to improve convergence time and to assure network wide synchronization accuracy, even in dynamic scenarios.
... In [41], the authors propose a synchronisation mechanism that works for single hop networks. For large networks, other algorithms can be used to keep the clocks in sync [42] [43]. ...
The last twenty years saw the emergence of wireless systems in everyday’s life. They made possible technologies such as mobile phones, WiFi or mobile Internet which are now taken for granted in today’s society. The environmental impact of Information and Communications Technology (ICT) has been raising exponentially to equate the impact of the airline industry. The green computing initiative has been created in response to this observation in order to meet the 15%-30% reduction in green-house gases by 2020 compared to estimations made in 2002 to keep the global temperature increasebelow 2°C. In this thesis, we studied power-saving techniques in wireless networks and how they interact with each others to provide a holistic view of green networking. We also take into account the radio frequency resource which is the most commonly usedcommunication medium for wireless systems and is becoming a scarce resource due to our society’s ever-increasing need for mobile bandwidth. This thesis goes down the network stacks before going up the hardware and software stack. Contributions have been madeat most layers in order to propose an autonomic wireless network where nodes can work collaboratively to improve the network’s performance, globally reduce the radio frequency spectrum usage while also increasing their battery life.
Contention-based distributed synchronization (CDS) protocols, which first standardized in IEEE 802.11 Power Saving Mode (PSM), have been widely used in wireless ad hoc networks. The time required to complete the synchronization progress, i.e., synchronization efficiency, is obviously an important performance metrics for CDS protocols. However, few attempts have been focusing on modeling and analyzing the synchronization efficiency of the CDS protocols. In this letter, we present a two-dimensional Markov chain model for the CDS scheme of IEEE 802.11 PSM. The purpose of our model is to determine the relationship between the time required to complete the synchronization process and the value of the contention parameter, i.e., the contention window size. Through modeling, we derive the optimal values of the contention window size to achieve the minimum synchronization time at different network scales. We also validate the accuracy of our model by comparing the analytical results with that obtained by means of simulations.
We study the problem of distributed time and frequency synchronization for device-to-device communication in LTE [1]. LTE is an OFDMA system that crucially uses tight time and frequency synchronization between UEs and the base station for intracell and intercell interference coordination. For consistency with the cyclic prefix length and tone spacing used in LTE, we target an accuracy of a few microseconds for time synchronization and 150 Hz for frequency synchronization. We examine the problem both from a link and a system-level perspective. Link-level challenges involve designing a synchronization signal for computationally and energy efficient receiver algorithms, and system-level challenges involve achieving consistent timing using a distributed algorithm while leveraging the multiuser aspect of the problem to improve performance.
This document describes a 1-hop and symmetric 2-hop neighborhood
discovery protocol (NHDP) for mobile ad hoc networks (MANETs).
This document specifies a packet format capable of carrying multiple
messages that may be used by mobile ad hoc network routing protocols.
Wireless sensor network applications, similarly to other distributed systems, often require a scalable time synchronization service enabling data consistency and coordination. This paper describes the Flooding Time Synchronization Protocol (FTSP), especially tailored for applications requiring stringent precision on resource limited wireless platforms. The proposed time synchronization protocol uses low communication bandwidth and it is robust against node and link failures. The FTSP achieves its robustness by utilizing periodic flooding of synchronization messages, and implicit dynamic topology update. The unique high precision performance is reached by utilizing MAC-layer time-stamping and comprehensive error compensation including clock skew estimation. The sources of delays and uncertainties in message transmission are analyzed in detail and techniques are presented to mitigate their effects. The FTSP was implemented on the Berkeley Mica2 platform and evaluated in a 60-node, multi-hop setup. The average per-hop synchronization error was in the one microsecond range, which is markedly better than that of the existing RBS and TPSN algorithms.
In this paper, we propose the clock-sampling mutual network synchronization (CSMNS) as a non-hierarchical and mutual network synchronization algorithm for wireless ad hoc networks. CSMNS shows superior performance to the IEEE 802.11 timing synchronization function in terms of accuracy, scalability and robustness. An overall view of the differences between the two approaches is presented. CSMNS is compatible with the beacon messages used in the IEEE 802.11 standard, and it is PHY transparent. CSMNS-RMN (rotating master node) is proposed in order to further reduce beacon collisions and overhead. Stability, is a factor that must be considered in CSMNS. However, values of the proportional gain below 0.3 suggest a good stability performance. The use of larger Cmax values in more dense networks and/or the use of techniques that randomly prioritize the transmission of beacons can further reduce the overhead and risks of instability.
distributed system. For years, protocols such as NTP (the Network Time Protocol) have kept the Internet's clocks ticking in phase. However, a new class of networks is emerging. Advances in miniaturization and low-cost, low-power design have led to active research in large-scale networks of small, wireless, low-power sensors and actuators. These systems are closely coupled to the physical world and have strict energy constraints; this leads to stronger accuracy and precision requirements while limiting the resources that can be used to achieve them. Is NTP the right choice for these new networks? We present Reference-Broadcast Synchronization (RBS), in which nodes send reference beacons to their neighbors using physical-layer broadcasts. A reference broadcast does not contain an explicit timestamp; instead, receivers use its arrival time as a point of reference for comparing their clocks. In this paper, we use measurements from two wireless implementations to show that removing the sender's nondeterminism from the critical path in this way results in a dramatic improvement in synchronization over using NTP. We also present an algorithm that allows time to be propagated across broadcast domains without losing the referencebroadcast property. In this way, nodes in a multi-hop network can form a highly precise relative timescale, or maintain microsecondlevel synchronization to an external timescale such as UTC.
Recent advances in micro-electromechanical (MEMS) technology have led to the development of small, low-cost, and low-power sensors. Wireless sensor networks (WSNs) are large-scale networks of such sensors, dedicated to observing and monitoring various aspects of the physical world. In such networks, data from each sensor is agglomerated using data fusion to form a single meaningful result, which makes time synchronization between sensors highly desirable. This paper surveys and evaluates existing clock synchronization protocols based on a palette of factors like precision, accuracy, cost, and complexity. The design considerations presented here can help developers either in choosing an existing synchronization protocol or in defining a new protocol that is best suited to the specific needs of a sensor-network application. Finally, the survey provides a valuable framework by which designers can compare new and existing synchronization protocols.
Synchronicity is a useful abstraction in many sensor network applications. Communication scheduling, coordinated duty cycling, and time synchronization can make use of a synchronicity primitive that achieves a tight alignment of individual nodes' firing phases. In this paper we present the Reachback Firefly Algorithm (RFA), a decentralized synchronicity algorithm implemented on TinyOS-based motes. Our algorithm is based on a mathematical model that describes how fireflies and neurons spontaneously synchronize. Previous work has assumed idealized nodes and not considered realistic effects of sensor network communication, such as message delays and loss. Our algorithm accounts for these effects by allowing nodes to use delayed information from the past to adjust the future firing phase. We present an evaluation of RFA that proceeds on three fronts. First, we prove the convergence of our algorithm in simple cases and predict the effect of parameter choices. Second, we leverage the TinyOS simulator to investigate the effects of varying parameter choice and network topology. Finally, we present results obtained on an indoor sensor network testbed demonstrating that our algorithm can synchronize sensor network devices to within 100 μsec on a real multi-hop topology with links of varying quality.
Wireless ad-hoc sensor networks have emerged as an interesting and important research area in the last few years. The applications envisioned for such networks require collaborative execution of a distributed task amongst a large set of sensor nodes. This is realized by exchanging messages that are timestamped using the local clocks on the nodes. Therefore, time synchronization becomes an indispensable piece of infrastructure in such systems. For years, protocols such as NTP have kept the clocks of networked systems in perfect synchrony. However, this new class of networks has a large density of nodes and very limited energy resource at every node; this leads to scalability requirements while limiting the resources that can be used to achieve them. A new approach to time synchronization is needed for sensor networks.