Time Synchronization Protocol with Minimum Message Communication for High Latency Networks
TL;DR: A new method is described for time synchronization that takes into account clock skew, clock offset, and also propagation delay and minimum message communication is used as a performance measure of the quality of this new time synchronization protocol.
Abstract: Time synchronization is a critical component of the infrastructure of wireless sensor networks (WSN). In a high latency environment such as underwater, traditional approaches to time synchronization have limited accuracy. A new method is describe for time synchronization that takes into account clock skew, clock offset, and also propagation delay. Minimum message communication is used as a performance measure of the quality of this new time synchronization protocol.
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01 Jun 2013
TL;DR: The proposed modified RSS-Aloha for underwater is modified by accommodating the error in delay estimate while deciding the receiver-end slot size, and the throughput of the proposed modified protocol is consistently higher compared to the transmitter synchronized S- aloha when operating under the same propagation delay uncertainty.
Abstract: In a wireless network, where propagation delay is high but known, slotted Aloha (S-Aloha) is synchronized with respect to the receiver's time slots. Since the transmitter knows the propagation delay to its receiver, after a frame is generated, the transmitter introduces a suitable delay before its transmission, such that the frame arrives exactly in a slot at the receiver. However, in an underwater wireless network, due to significantly less signal propagation speed, the channel dynamics has a significant effect on the time dispersion of propagation speed. Due to this uncertainty in propagation speed, even if the transmitter-receiver distance is exactly known, it is likely that a perfect synchronization at the receiver is not possible. In this paper, we first show that, even a little-less-than-perfect synchronization at the receiver reduces the throughput of receiver synchronized S-Aloha (RSS-Aloha) to that of pure Aloha. We modify the RSS-Aloha for underwater by accommodating the error in delay estimate while deciding the receiver-end slot size. Via probabilistic analysis, supported by simulations, we show that our proposed modified protocol offers a gradual increase in throughput as the propagation delay uncertainty decreases. We also show that the throughput of our proposed modified protocol is consistently higher compared to the transmitter synchronized S-Aloha when operating under the same propagation delay uncertainty. However, when the uncertainty is high, delay performance of the modified RSS-Aloha remains poorer than that of the transmitter synchronized S-Aloha in a system with smaller nodal communication range.
26 citations
Cites methods from "Time Synchronization Protocol with ..."
...In [23], synchronization was proposed using a two phase protocol....
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TL;DR: This paper proposes two system state aware dynamic approaches to suitably adjust the number of access slots, and investigates the optimum slotting strategy to maximize the system utilization, which shows that the proposed optimized dynamic slotting offers a much better system utilization performance compared to a similar underwater reservation multiaccess protocol.
Abstract: In a wireless network, where propagation delay is high and communications are sporadic, some kind of reservation protocol is generally used. Reservation access protocols were proposed earlier in earth stations-to-satellite communication with known propagation delay. However, optimality of the number of access slots with respect to the system performance parameters, such as system utilization, blocking probability, and delay, were not thoroughly studied. Besides, the effect of propagation delay uncertainty, which predominantly happens in underwater communications, are yet to be addressed. In this paper, we first analyze the system performance in many-to-one multiaccess data transfer scenario in underwater wireless ad hoc sensor networks with a fixed number of access slots and with the assumption of perfect propagation delay information. We propose two system state aware dynamic approaches to suitably adjust the number of access slots, and investigate the optimum slotting strategy to maximize the system utilization. Next, by accounting the propagation delay uncertainty, we relook into the optimality criteria on the number of access slots, where we apply a modified receiver-synchronized slotted Aloha principle to maximize the access performance. Via mathematical analysis, supported by discrete event simulations, we show that the system utilization and blocking probability performances with our proposed dynamic reservation protocols are consistently better compared to the competitive reservation protocols with fixed as well as variable access slots. Further, we conduct NS3 simulations to study the protocol performances under more realistic channel and traffic conditions, which also demonstrate that the proposed optimized dynamic slotting offers a much better system utilization performance compared to a similar underwater reservation multiaccess protocol.
16 citations
TL;DR: This paper studies RS-TDMA and TS-TD MA in the presence of distance dependent propagation delay deviation, which is one of the most important parameters for underwater wireless ad hoc networks and finds the optimum parameters to get the maximum frame utilization.
9 citations
11 Nov 2013
TL;DR: A clock synchronization independent localization scheme (CSILS) for underwater wireless sensor networks (UWSNs), which improves localization accuracy with a proper level of localization coverage and communication overhead in terms of mobility model of water currents.
Abstract: Almost all the existing range-based localization schemes for underwater wireless sensor networks (UWSNs) assume that clocks of different nodes are well synchronized. However, clock synchronization is very challenging in UWSNs. In this paper, we design a clock synchronization independent localization scheme (CSILS). Instead of trying to estimate distances between unknown nodes and anchor nodes, we design a scheme for obtaining the distance differences based on the local clocks. In order to convert the distance differences into node's location, we propose distance-difference-based maximum likelihood estimation (D-D-BMLE). Finally, we give some suggestions on how to deploy anchor nodes Simulation results show that CSILS works well without clock synchronization when anchor nodes are deployed reasonably. Compared to a clock-synchronization-based localization scheme, CSILS improves localization accuracy with a proper level of localization coverage and communication overhead in terms of mobility model of water currents.
3 citations
TL;DR: In this adaptive algorithm, ensemble empirical mode decomposition (EEMD) is employed to decompose original data to different intrinsic mode functions (IMFs) and principal components analysis (PCA) is proposed for accurately abandoning IMFs which contain plentiful noises.
Abstract: Clock bias is a vital element in clock calibration system. Aiming at effectively eliminating noises contained in clock bias and improving accuracy of time synchronization, we propose an adaptive algorithm. In this adaptive algorithm, ensemble empirical mode decomposition (EEMD) is employed to decompose original data to different intrinsic mode functions (IMFs). For accurately abandoning IMFs which contain plentiful noises, principal components analysis (PCA) is proposed. Eigenvalues of all IMFs are ascertained on the bias of PCA. Then, bias between adjacent eigenvalues is used to evaluate level of noises contained in each IMF. Finally, residual IMFs are used to reconstruct the signal. Clean signal with adding noises is used to evaluate this improved algorithm. Consequence indicates that this improved algorithm is effective. We design a clock calibration experiment, where the time signal is transferred through a wireless channel. The adaptive algorithm is used to dispose bias, which is acquired in clock calibration experiment. Consequence also demonstrates that this algorithm can effectively and adaptively eliminate noises contained in actual data.
References
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Book•
01 Jan 1975
3,596 citations
"Time Synchronization Protocol with ..." refers background in this paper
...However, implementation in high latency environments such as underwater networks [1] require new approaches due to the communication channel differences and the use of acoustic transmission [2,3]....
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01 May 2005
TL;DR: In this paper, several fundamental key aspects of underwater acoustic communications are investigated and a cross-layer approach to the integration of all communication functionalities is suggested.
Abstract: Underwater sensor nodes will find applications in oceanographic data collection, pollution monitoring, offshore exploration, disaster prevention, assisted navigation and tactical surveillance applications. Moreover, unmanned or autonomous underwater vehicles (UUVs, AUVs), equipped with sensors, will enable the exploration of natural undersea resources and gathering of scientific data in collaborative monitoring missions. Underwater acoustic networking is the enabling technology for these applications. Underwater networks consist of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area. In this paper, several fundamental key aspects of underwater acoustic communications are investigated. Different architectures for two-dimensional and three-dimensional underwater sensor networks are discussed, and the characteristics of the underwater channel are detailed. The main challenges for the development of efficient networking solutions posed by the underwater environment are detailed and a cross-layer approach to the integration of all communication functionalities is suggested. Furthermore, open research issues are discussed and possible solution approaches are outlined. � 2005 Published by Elsevier B.V.
2,864 citations
"Time Synchronization Protocol with ..." refers background in this paper
...However, implementation in high latency environments such as underwater networks [1] require new approaches due to the communication channel differences and the use of acoustic transmission [2,3]....
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09 Dec 2002
TL;DR: Reference Broadcast Synchronization (RBS) as discussed by the authors is a scheme in which nodes send reference beacons to their neighbors using physical-layer broadcasts, and receivers use their arrival time as a point of reference for comparing their clocks.
Abstract: Recent 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. Time synchronization is critical in sensor networks for diverse purposes including sensor data fusion, coordinated actuation, and power-efficient duty cycling. Though the clock accuracy and precision requirements are often stricter than in traditional distributed systems, strict energy constraints limit the resources available to meet these goals.We present Reference-Broadcast Synchronization, a scheme 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 produces high-precision clock agreement (1.85 ± 1.28μsec, using off-the-shelf 802.11 wireless Ethernet), while using minimal energy. We also describe a novel algorithm that uses this same broadcast property to federate clocks across broadcast domains with a slow decay in precision (3.68 ± 2.57μsec after 4 hops). RBS can be used without external references, forming a precise relative timescale, or can maintain microsecond-level synchronization to an external timescale such as UTC. We show a significant improvement over the Network Time Protocol (NTP) under similar conditions.
2,537 citations
03 Nov 2004
TL;DR: The FTSP achieves its robustness by utilizing periodic flooding of synchronization messages, and implicit dynamic topology update and comprehensive error compensation including clock skew estimation, which is markedly better than that of the existing RBS and TPSN algorithms.
Abstract: 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.
2,267 citations
"Time Synchronization Protocol with ..." refers background or methods in this paper
...TPSN [4], FTSP [5] and RBS [6] are quite popular protocols for RF communication and have been implemented in a number of sensor network applications....
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...TPSN [4] and FTSP [5] also use this model....
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05 Nov 2003
TL;DR: It is argued that TPSN roughly gives a 2x better performance as compared to Reference Broadcast Synchronization (RBS) and verify this by implementing RBS on motes and use simulations to verify its accuracy over large-scale networks.
Abstract: 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 time-stamped 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.In this paper, we present Timing-sync Protocol for Sensor Networks (TPSN) that aims at providing network-wide time synchronization in a sensor network. The algorithm works in two steps. In the first step, a hierarchical structure is established in the network and then a pair wise synchronization is performed along the edges of this structure to establish a global timescale throughout the network. Eventually all nodes in the network synchronize their clocks to a reference node. We implement our algorithm on Berkeley motes and show that it can synchronize a pair of neighboring motes to an average accuracy of less than 20ms. We argue that TPSN roughly gives a 2x better performance as compared to Reference Broadcast Synchronization (RBS) and verify this by implementing RBS on motes. We also show the performance of TPSN over small multihop networks of motes and use simulations to verify its accuracy over large-scale networks. We show that the synchronization accuracy does not degrade significantly with the increase in number of nodes being deployed, making TPSN completely scalable.
2,215 citations
"Time Synchronization Protocol with ..." refers background or methods in this paper
...TPSN [4], FTSP [5] and RBS [6] are quite popular protocols for RF communication and have been implemented in a number of sensor network applications....
[...]
...TPSN [4] and FTSP [5] also use this model....
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