Time Synchronization Protocol Research Articles

CESP: A Low-Power High-Accuracy Time Synchronization Protocol

Time synchronization is a fundamental problem in any distributed system. In particular, wireless sensor networks (WSNs) require scalable time synchronization for implementing distributed tasks on multiple sensor nodes. We propose an energy-efficient coefficient exchange synchronization protocol (CESP) based on a receiver–receiver synchronization scheme, which minimizes the impact of access-time delays. Most of the existing synchronization protocols focus on improving the synchronization accuracy by assuming the availability of packet-level timestamping and with little concern for power consumption. The proposed time-synchronization protocol achieves high synchronization accuracy similar to the classic reference broadcast synchronization (RBS) protocol without requiring packet-level timestamping but with a significant reduction on communication overhead to achieve low power consumption. CESP works in a fundamentally different way from RBS: In order to synchronize two receivers, RBS exchanges all beacon packets between two receivers, whereas CESP receivers first process a large number of received beacon packets and only then exchange a small amount of information between the two receivers: synchronization coefficients. The synchronization performance and power consumption are evaluated and compared with that of other well-known synchronization protocols through experimental results.

A Precise and Hardware-Efficient Time Synchronization Method for Wearable Wired Networks

This paper presents and evaluates a high-precision, one-way, and master-to-slave time synchronization protocol to minimize the clock time skew in low-power wearable sensor networks. The protocol is implemented in the media access control layer, and is based on directly eliminating deterministic delays during transmission from source to destination node, at hardware level. The proposed protocol keeps the one-hop average synchronization error close to the signal propagation delay, and the one-hop peak-to-peak jitter equals to the period of each node’s system clock period. Both values grow linearly as the hop count increases. The protocol can achieve synchronization in the range of a few nanoseconds, enough to satisfy the requirements of many applications related to wearable networks, with one-way messages. Both theoretical analysis and experimental results, in wired wearable networks, show that the proposed protocol has a better performance than precision time protocol and a standard timing protocol for both single and multi-hop situations. The proposed approach is simpler, requires no calculations, and exchanges fewer messages. Experimental results obtained with an implementation of the protocol in a 0.35- $\mu \text{m}$ CMOS technology show that this approach keeps the one-hop average clock skew around 4.6 ns and peak-to-peak skew around 50 ns for a system clock frequency of 20 mh.

A Novel Traffic Aware based Routing Integrated Time Synchronization for Slack Time Minimization in NoC System

NoC designs can be accepted to provision general communications between multiple IPs above multi-processor schemes on chip. In this effort we demonstrate the forming and imitation based exploration of some current architectures intended for Network on Chip (NoC). Specifically in this paper focus on the time synchronization based network, it hasthe Routing Integrated Time Synchronization protocol (RITS) that integrates post-facto time sync into a routing service also its achieved high result for QoS improvement in network. RITS, as well as reactive techniques in general, is superior to many proactive time sync protocols with respect to communication overhead. The best effort (BF) analysis of a representative reactive technique, the Routing Integrated Time Synchronization protocol (RITS) shows that in the general case, the presence of slack time cause RITS to Guaranteed throughput with the size of the network. We have using a shortest path based Traffic aware algorithm to time based data transmission quickly and efficiently on their network. It has more secure and easy to transfer data from one mobile node to another mobile node on the network.

Dynamic Logging with Dylog in Networked Embedded Systems

Event logging is an important technique for networked embedded systems like wireless sensor networks. It can greatly help developers to understand complex system behaviors and diagnose program bugs. Existing logging facilities do not well satisfy three practical requirements: flexibility , efficiency , and high synchronization accuracy . To simultaneously satisfy these requirements, we present Dylog, a dynamic logging facility for networked embedded systems. Dylog employs several techniques. First, Dylog uses binary instrumentation for dynamically inserting or removing logging statements, enabling flexible and interactive debugging at runtime. Second, Dylog incorporates an efficient storage system and log collection protocol for recording and transferring the logging messages. Third, Dylog employs a lightweight data-driven approach for reconstructing the synchronized time of the logging messages. Dylog uses MAC-layer timestamping and drift compensation to achieve high synchronization accuracy . We implement Dylog on the TinyOS 2.1.1/TelosB platform. Results show the following: (1) Dylog incurs a small overhead. Indirections in Dylog incur an additional execution overhead of less than 1%. Dylog reduces the logging storage size by approximately 50% compared with the standard TinyOS radio printf library. Dylog reduces the patch size by more than 90%, compared with incremental reprogramming. (2) Dylog reduces the synchronization overhead by 78% in terms of transmission cost, compared with a traditional time synchronization protocol, FTSP, and it can achieve a high time synchronization accuracy of 5.4μs. (3) Dylog can help diagnose system problems effectively at the source-code level for three real-world scenarios.

Clock Skew Estimation of Listening Nodes with Clock Correction upon Every Synchronization in Wireless Sensor Networks

Time synchronization is a significant component in Wireless Sensor Networks (WSNs) for maintaining synchrony among nodes. Most time synchronization protocols in WSNs utilize dedicated synchronization packets for clock accuracy optimization. However, in practical WSNs, the joint design of time synchronization and Media Access Control layer protocols should be considered. One approach is adding timestamps directly into data packets and the corresponding acknowledgements (ACKs). Therefore, communication and energy overhead could be saved greatly and time synchronization could be seamlessly integrated into networks. In this letter, we investigate the time synchronization scheme of listening nodes overhearing the neighboring two-way timing packet exchange based on periodical ACK mechanism and present an efficient clock skew estimation algorithm with clock correction upon every synchronization. The Maximum Likelihood Estimator (MLE) of clock skew for Gaussian random packet delay is derived, and the corresponding Cramer-Rao Lower Bound (CRLB) is obtained. In addition, the MLE shows that the clock skew could be estimated without any prior knowledge of the fixed packet delay and the time of adjustment. Simulation results verify that the MLE is efficient.

On the Optimum Design of L-Estimators for Phase Offset Estimation in IEEE 1588

In packet-based time synchronization protocols such as IEEE 1588, clock phase offsets are determined via two-way message exchanges between a master and a slave. Since the end-to-end delays in packet networks are inherently stochastic in nature, the recovery of phase offsets from message exchanges must be treated as a statistical estimation problem. Recently, minimax estimators for this problem were proposed by the authors, which are optimum in terms of minimizing the mean-squared estimation error over all values of the unknown parameters. In this paper, we consider a restricted class of estimators referred to as L-estimators, which are linear functions of order statistics. The problem of designing optimum L-estimators is studied under several hitherto unconsidered criteria of optimality. Our results address the case where the queuing delay distributions are fully known, as well as the case where network model uncertainty exists. Optimum L-estimators that utilize information from past observation windows to improve performance are also described. The derived L-estimators have a much lower computational complexity than minimax estimators, and also require lesser statistical knowledge of the queuing delays. Simulation results indicate that L-estimators exhibit a mean-squared estimation error very close to minimax estimators under many network scenarios.

Robust and Secure Time-Synchronization Against Sybil Attacks for Sensor Networks

Time synchronization is crucial for cyber-physical systems (CPSs), e.g., wireless sensor and actuator networks. Cyber physical security is an important yet challenging problem. In particular, attacks to the time synchronization service may incur data distortion or even malfunction of the whole system. Sybil attack is one of the most common attack types for sensor networks, where a node illegitimately claims multiple identities. Existing secure time-synchronization protocols; however, cannot well address Sybil attacks in the time synchronization process. We propose a robust and secure time-synchronization protocol (RTSP) to defend against Sybil attacks. Different from previous secure timesync protocols, RTSP employs a novel graph theoretical approach, which is able to perform anomaly detection at the message level instead of the node level. This fine-grained detection ability enables RTSP to become robust against Sybil attacks, as well as node compromise and message manipulation attacks. Extensive experimental results show the effectiveness of our proposed protocol.

A Robust Single Hop Tree Structured Time Synchronization Protocol for Wireless Ad-Hoc Sensor Networks

Wireless ad-hoc sensor networks are deployed in order to observe some real world phenomenon with the intent to improve the daily life of common man, boost industrial processes, facilitate environment protection and enhance law enforcement. Time synchronization is critical for these networks so that the nodes in the network can accurately report event timestamps and fine-tune their coordinated distributed activities. Time synchronization algorithms proposed in the past have considered various critical issues related to nodes such as computing, resources involved in storage and communication, energy efficiency of the algorithm etc. Changing network dynamics still remains a challenge to be addressed by time synchronization algorithms as the nodes are deployed randomly either at the time of network establishment or at a later stage when the network is established and may die or disconnect in the same fashion. In this paper an energy efficient and robust protocol to support network dynamics in time synchronization protocol is presented. The protocol incorporates a mechanism which ensures that synchronization of the nodes in the network remains unaffected even if any of the nodes involved in synchronization process gets disconnected. The number of messages involved in the synchronization process in the suggested protocol is also reduced as compared to earlier protocols that makes the suggested one more energy efficient.

에너지 제한적인 무선 네트워크에서 동작하는 시각 동기화 프로토콜

사물인터넷에서 전력이나 컴퓨팅 등 자원이 한정된 무선 노드 사이에 데이터를 효율적으로 전송하는 무선 네트워크 기술이 중요하며, 의미 있는 데이터 생성과 전송을 위해서 모든 노드 사이에 시각 동기화가 필요하다. 무선 센서 네트워크에서 여러 방식의 시각 동기화 프로토콜이 제안되었는데, 플러딩에 의한 방안도 그중의 하나이다. 이 방식은 다른 방식에 비하여 알고리즘이 간단하고, 토폴로지 변화에 영향을 받지 않는 장점을 가지고 있음에도 불구하고 지나치게 많은 데이터 전송이 요구되어 결과적으로 전력 소모가 많다. 전력이 한정적인 무선 노드에서는 가능한 성능을 저하시키지 않으면서 전력 소모를 줄이는 것이 중요하므로, 이 논문에서는 플러딩에 기반한 에너지 효율적인 시각 동기화 프로토콜을 제안한다. 시뮬레이션을 통하여 가장 대표적인 프로토콜인 FTSP(Flooding Time Synchronization Protocol)와 성능을 비교하고, 에너지 효율 면에서 우수한 프로토콜임을 보인다. In IoT(Internet of Things), it is important for wireless networks to communicate data created among resource-constrained wireless nodes, where time synchronization is needed for meaningful data creation and transmission. Time Synchronization by flooding is one of the mostly used protocols for WSN(Wireless Sensor Networks). Even though this type of scheme has some advantages over other types (i.e. a simple algorithm and independency of topology and so on), too many data transmission is required, leading to large power consumption. So, reducing transmission data is an important issue for energy efficiency in this kind of networks. In this paper, a new Flooding-based time synchronization protocol is proposed to use energy efficiently by reducing a transmitted traffic. The proposed scheme's performance has been evaluated and compared with an representative scheme, FTSP(Flooding Time Synchronization Protocol) by simulation. The results are shown that the proposed scheme is better than FTSP.

Node Synchronization Algorithm in Wireless Sensor Networks

a wireless sensor network there exist a number of nodes; often deployed in remote and inaccessible areas. These nodes take the power from batteries. The nodes are intended for monitoring physical phenomena like temperature changes, Percentage of humidity etc. Over the time, any of the nodes finds itself in a situation that it is difficult to maintain its course of routine. This can happen due to a discharged battery or any physical damage to the node. This situation hampers the synchronization accuracy among nodes. Therefore, in this paper a method is suggested to keep the throughput inside a wireless sensor network, simply by anticipating the situation with an algorithm that is based on consensus approach and using average time synchronization protocol.

A Novel RTS/CTS based Relative Time Synchronization Technique for RFID based Wireless Sensor Network

Wireless Sensor Network (WSN) is a self-configuring and highly flexible distributed network used for real time monitoring and is comprised of a number of wireless, minute, battery-operated independent sensor nodes connected to a common sink. Due to energy considerations, the network is generally divided into clusters and the entire communication is carried out through the cluster heads. The clock mismatch between various nodes and clusters often leads to collisions, delay and data loss. In order to overcome this problem, a novel RTS/CTS based Relative Time Synchronization Protocol is being proposed for Radio-Frequency Identification based WSN. It achieves better performance due to its energy efficiency and lower service messages. Simulation results show a substantial improvement in the net throughput and reliability of the network when compared with the GPS-based Synchronization technique.

A Revised Timing-sync Protocol for Sensor Networks by a Polling Method

TPSN(Timing-sync Protocol for Sensor Networks), the representative of time synchronization protocol for WSN(wireless sensor networks), was developed to provide higher synchronization accuracy and energy efficiency. So, TPSN’s approach has been referenced by so many other WSN synchronization schemes till now. However, TPSN has a collision problem due to simultaneous transmission among competing nodes, which causes more network convergence delay for a network-wide synchronization. A Polling-based scheme for TPSN is proposed in this paper. The proposed scheme not only shortens network-wide synchronization time of TPSN, but also reduce collision traffic which lead to needless power consumption. The proposed scheme’s performance has been evaluated and compared with an original scheme by simulation. The results are shown to be better than the original algorithm used in TPSN.

Proposing a novel method for clock synchronization by Reducing the Number of Synchronization Messages and Eliminating Non-Deterministic Errors in Wireless Sensor Network

Wireless sensor networks (WSNs) of spatially distributed autonomous sensors are used to monitor physical or environmental conditions such as temperature, sound, pressure, etc. They are also used to cooperatively pass the collected data through the network to a main location. Due to the application of wireless sensor networks as a monitoring device in the real world, the physical time of the occurrence of events is important. Since WSNs have particular constraints and limitations, synchronizing the physical times for these networks is considered to be a complex task. Although many algorithms have been proposed for synchronizing time in the network, there are two main error factors in all the proposed algorithms. The first factor is the clock drift which might be caused by the influence of different environmental factors such as temperature, ambient temperature, humidity, it might be generated on crystal oscillator which is inevitable The second error factor is indeterminacy which is attributed to the existence of non-deterministic delays in sending and receiving messages between sensor nodes. These two factors together reduce the precision of synchronization algorithms. In this paper, the researchers proposed a new approach for dealing with the above-mentioned two problems and achieving better synchronization. The proposed approach is a combination of flooding time synchronization protocol (FTSP) and reference broadcast synchronization (RBS).This approach is intended to increase synchronization accuracy and network lifetime by reducing the number of synchronization messages sent between nodes and eliminating the most of non-deterministic errors in sending messages. The results of simulations conducted in the study indicated that the proposed approach is significantly more efficient than the FTSP and RBS methods in terms of parameters such as accurate synchronization, amount of sent packets and power consumption.

Multiplicative composition of clock‐skew components for improving time synchronisation

Time synchronisation is essential to ensure the reliability of distributed computation. Oscillators included in low-cost nodes are highly influenced by temperature variations. Experimental results demonstrate that the clock skew of two nodes (the ratio of the real frequencies of the oscillators) is composed of a multiplicative combination of, at least, two main components: the clock skew due to the variations between the cut of the crystal of each oscillator and the clock skew due to the different temperatures affecting the nodes. By applying a nonlinear filtering, homomorphic filtering, both components are separated in an effective way. Applying a correction factor to the clock skew due to the cut of the crystals, the temperature variations are compensated very accurately. The proposed new approach is called HF2 (homomorphic improved filtering) and can be easily applied to any clock-skew-based time synchronisation protocol. The correction factor has been applied to flooding time synchronisation protocol (FTSP) resulting in HF2-FTSP. An experiment with temperature variation, comparing FTSP, A2T-FTSP and HF2-FTSP is shown. The proposed technique allows the use of cheap and simple oscillators for achieving a quite similar accurate synchronisation level than much more expensive and precise oscillators.

Optimal consensus‐based clock synchronisation algorithm in wireless sensor network by selective averaging

Wireless sensor networks (WSNs) have received much attention in recent years because of its broad area of applications. In the same breadth, it also faces many challenges. Time synchronisation is one of those fundamental and important challenges faced by WSN. Several approaches have been proposed in recent years for time synchronisation. Most of the approaches are based on synchronising to a reference (root) node's time by considering a hierarchical backbone for the network. However, this approach seems to be not purely distributed, higher accumulated synchronisation error for farthest node from the root and subjected to the root node failure problem. In this study, a fully distributed time synchronisation algorithm is proposed which synchronises all nodes’ time to a consensus value, that is, an average of all nodes’ initial clock values. The algorithm exploits a selective pairwise averaging approach with a linear message complexity of O (n), to achieve faster convergence and better synchronisation accuracy than the existing random pairwise average time synchronisation protocol. Simulation results show that almost 50% improvement is achieved in convergence speed, measured in terms of number of iterations, and nearly 30% improvement in total synchronisation error.

Firefly-inspired and robust time synchronization for cognitive radio ad hoc networks

Harnessing the full power of the paradigm-shifting cognitive radio ad hoc networks (CRAHNs) hinges on solving the problem of time synchronization between the radios on the different stages of the cognitive radio cycle. The dynamic network topology, the temporal and spatial variations in spectrum availability, and the distributed multi-hop architecture of CRAHNs mandate novel solutions to achieve time synchronization and efficiently support spectrum sensing, access, decision and mobility. In this article, we advance this research agenda by proposing the novel Bio-inspired time SynChronization protocol for CRAHNs (BSynC). The protocol draws on the spontaneous firefly synchronization observed in parts of Southeast Asia. The significance of BSynC lies in its capability of promoting symmetric time synchronization between pairs of network nodes independent of the network topology or a predefined sequence for synchronization. It enables the nodes in CRAHNs to efficiently synchronize in a decentralized manner, and it is also reliable to changes, faults and attacks. The findings suggest that BSynC improves convergence time, thereby favoring deployment in dynamic network scenarios.

다채널 멀티미디어 전송용 임베디드 Audio Video Bridging 플랫폼 설계 및 구현

In this paper, we designed an embedded audio video bridging (AVB) platform based on IEEE 802.1BA for real-time multimedia transmission in smart-car, smart-home, smart-theater, and then evaluated a performance of the implemented platform by analysis of IEEE 802.1AS (time synchronization protocol) and IEEE 802.1Qat (stream reservation protocol). Especially, the AVB Layer-2 protocol of MRP(Multiple Registration Protocol), MMAP(Multicast Address Acquisition Protocol), IEEE 1722, 1722.1 etc. was and implemented by linux based operating system. It is shown by interoperability tests with commercial products that the implemented platform transmits real-time multichannel AV data over AVB networks for Multichannel Multimedia Transmission. ☞ keyword : AVB, Mutlichannel HD-platform, QoS(Quality of Service), Inter-operability, Realtime Transmission, endpoint

Quantitative and Qualitative Analysis of Time Synchronization Protocols for Wireless Sensor Networks

During the last decade, there has been an efficient use of wireless sensor networks (WSNs) in different fields such as environmental surveillance, military, disaster management, medical, etc. In these applications, large number of sensor nodes are deployed, which work in harsh environment. The main objective of the wireless sensor nodes is to observe the event and inform the same to other node or to sink. There are some applications in the wireless sensor networks which require exact time of the event occurrence. Such applications require that nodes of the WSN should be synchronized with global clock. In this paper, we study the impact of time synchronization and analyze various time synchronization protocols highlighting their features, objectives and perform qualitative and quantitative analysis. Keywords: Delay, offset, skew, time synchronization.

Using physical layer clock recovery to augment application layer time synchronization

Achieving same notion of time remains an important task for most distributed systems. Time synchronization requires a unique combination of high accuracy ($$\upmu $$μs level) and energy efficiency. Several application layer protocols have been developed to meet these requirements. This article proposes that the physical layer clock recovery process can provide application layer clock drift estimate, and the application layer clock can be corrected with the help of this estimate. This eliminates the need of application layer time synchronization protocol i.e. the cross-layer approach reduces the number of message exchanges required by application layer for time synchronization that leads to energy conservation. It argues that such a cross-layer approach can provide a more accurate frequency offset estimation, or can achieve greater energy savings, for a given accuracy, by reducing the message exchanges. Analysis of the proposed method provides concrete bounds on achieved improvement. Experimental evaluation showed that physical layer clock drift can be used to correct application layer clock drift as they are identical.

Software-defined underwater acoustic networking platform and its applications

As underwater communications adopt acoustics as the primary modality, we are confronting several unique challenges such as highly limited bandwidth, severe fading, and long propagation delay. To cope with these, many MAC protocols and PHY layer techniques have been proposed. In this paper, we present a research platform that allows developers to easily implement and compare their protocols in an underwater network and configure them at runtime. We have built our platform using widely supported software that has been successfully used in terrestrial radio and network development. The flexibility of development tools such as software defined radio, TinyOS, and Linux have provided the ability for rapid growth in the community. Our platform adapts some of these tools to work well with the underwater environment while maintaining flexibility, ultimately providing an end-to-end networking approach for underwater acoustic development. To show its applicability, we further implement and evaluate channel allocation and time synchronization protocols on our platform.