CorTiS: Correlation-Based Time Synchronization in Internet of Things

The successful commissioning of the proposed methodology to synchronize the NIC-NKN in Delhi and Hyderabad with Indian Standard Time (IST) maintained by NPLI over NTP protocol over IoT framework is a significant accomplishment in the field of time synchronization. The proposed methodology utilizes an IoT framework along with a unique Stratum 1 NTP architecture that is supported by a pre-calibrated Rubidium frequency source. This architecture enables the establishment of stratum 1 synchronization at the two locations, thereby ensuring that the time is accurately synchronized with the NPLI maintained Indian Standard Time (IST). The successful implementation of this methodology has several benefits. Firstly, it ensures that the time at the NIC-NKN in Delhi and Hyderabad is accurate and synchronized with the Indian Standard Time (IST) maintained by NPLI. This is crucial for various applications where precise timing is critical, such as in telecommunications, financial transactions, and scientific research. Secondly, this methodology can be extended to other locations and organizations that require accurate time synchronization. With the increasing use of IoT devices, the need for accurate time synchronization is only going to increase. This methodology provides a reliable and scalable solution that can be easily implemented in various organizations and locations. Thirdly, the use of pre-calibrated Rubidium frequency sources ensures that the time synchronization is accurate and stable over a long period. This is important as small inaccuracies in time synchronization can accumulate over time and result in significant errors. The use of pre-calibrated Rubidium frequency sources ensures that the time synchronization is accurate and stable over a long period, thereby avoiding such errors. In conclusion, the successful commissioning of the proposed methodology to synchronize the NIC-NKN in Delhi and Hyderabad with Indian Standard Time (IST) maintained by NPLI over NTP protocol over IoT framework is a significant accomplishment. This methodology provides a reliable and scalable solution that can be easily implemented in various organizations and locations to ensure accurate time synchronization.

Precision time synchronization provides essential services for wireless ad hoc networks, which are required for applications such as communication, positioning and power management. Precision frequency synchronization not only plays an important role in improving the accuracy and energy efficiency of time synchronization, but also greatly improves the data reliability and communication quality. This paper proposes a precision time and frequency joint synchronization protocol, combining time synchronization with frequency synchronization. The two-stage protocol, consisting of coarse and fine synchronization, obtains improvements in accuracy, energy efficiency and time continuity. Experiments validate the correctness and feasibility of the proposed protocol, obtaining timing accuracy of 17.4 ns with standard deviation 6.61 ns and frequency accuracy within 0.3Hz for 128MHz clock.

Internet of Things (IoT) devices that are wirelessly connected in mesh networks often need mutual clock time synchronization, to enable chronological ordering of sensor events, coordination of asynchronous processes across devices, or network-wide coordination of actuators. Accurate time synchronization is also critical for IoT device event logging and debugging. The widely-adopted Network Time Protocol (NTP) is less suitable for constrained mesh networks due to its high network load and sensitivity to asymmetric network delays. In this paper, Mesh Time-synchronization Protocol (MTP) is proposed for IP-based IoT wireless mesh networks and shown to outperform NTP. MTP exploits one resource-rich node on the mesh, the gateway or border router, to be the time reference or to synchronize with a (global/UTC) time reference. This reference time is efficiently disseminated throughout the mesh, using radio broadcasts. Our MTP implementation achieves a median accuracy of 0.48 ms, 1.01 ms, 1.50 ms, 2.06 ms on an event-driven embedded OS platform and 0.74 ms, 1.60 ms, 2.43 ms, 3.28 ms on a multi-threaded embedded platform respectively for mesh nodes 1, 2, 3 and 4 hops away from the gateway. Compared to NTP, the accuracy error variability over repeated measurements is an order of magnitude lower for MTP.

Time synchronization is critical to sensor networks at many layers of its design and enables better duty-cycling of the radio, accurate localization, beamforming and other collaborative signal processing. While there has been significant work in sensor network synchronization, measurement based studies have been restricted to very short-term (few minutes) datasets and have focused on obtaining accurate instantaneous synchronization. Long-term synchronization has typically been handled by periodic re-synchronization schemes with beacon intervals of a few minutes based on the assumption that long-term drift is too hard to model and predict. Thus, none of this work exploits the temporally correlated behavior of the clock drift. Yet, there are incredible energy gains to be achieved from better modeling and prediction of long-term drift that can provide bounds on long-term synchronization error across a sensor network. Better synchronization can lead to significantly lower duty-cycles of the radio, simplify signal processing and can enable an order of magnitude greater lifetime than current techniques.We measure, evaluate and analyze in-depth the long-term behavior of synchronization skew and drift on typical Mica sensor nodes and develop an efficient long-term time synchronization protocol. We use four real time data sets gathered over periods of 12-30 hours in different environmental conditions to study the interplay between three key parameters that influence long-term synchronization - synchronization rate, history of past synchronization beacons and the estimation scheme. We use this measurement-based study to design an online adaptive time-synchronization algorithm that can adapt to changing clock drift and environmental conditions while achieving application-specified precision with very high probability. We find that our algorithm achieves between one and two orders of magnitude improvement in energy efficiency over currently available time-synchronization approaches.

Existing time synchronization schemes in sensor networks were all developed to be energy-efficient, precise, and robust, but none of them were developed with security in mind. We have developed a secure, accurate and energy-efficient time synchronization protocol (SAEP). SAEP achieves accurate time synchronization service with significantly reducing the number of message exchanges. Also, it safeguards against Byzantine failure, in which nodes drop, modify, or delay time information in an attempt to disrupt the time synchronization service in multi-hop networks. SAEP takes a distributed approach where each sensor independently makes decisions based only on the information collected from multiple adjacent nodes, thus achieving a high level of resistance to various attacks while minimizing the energy cost. We investigate the misbehavior of a maliciously compromised node and analyze how SAEP can combat these attacks. In our experiment SAEP outperforms the existing time synchronization protocol in accuracy, energy consumption and it is even resilient to multiple capture attacks.

With the advancement of mobile communication and industrial internet technologies, the demand for time syn-chronization in various scenarios has significantly increased. This paper investigates a multi-UE cooperative time synchronization scheme based on Proximity Services (ProSe). Leveraging ProSe's off-network operation and direct communication capabilities, the proposed method utilizes the Pairwise Broadcast Synchronization (PBS) protocol for time information transmission. This approach aims to achieve reliable time synchronization in emergency rescue scenarios, particularly where infrastructure may be compro-mised. The simulation results demonstrate that the proposed scheme improves synchronization accuracy and convergence speed compared to existing methods. Additionally, the incorpo-ration of Kalman filtering enhances the estimation precision. The findings indicate that this approach holds significant potential for applications in public safety, emergency rescue, and industrial automation, paving the way for more reliable and efficient time synchronization in critical scenarios.

Wide-area monitoring (WAM) applications for power distribution rely on accurate global time synchronization. Furthermore, there is interest in replacing current time synchronization methods such as Inter Range Instrumentation Group (IRIG), with distributed time synchronization protocols that utilize the data communication lines eliminating the need for dedicated timing signals within the substation. By understanding the factors impacting synchronization performance, the testbed facilitates the characterization of metrics needed to meet industry requirements. The testbed provides an experimental venue to explore IEEE 1588 Precision Time Protocol (PTP) technologies and determine how new features and requirements for time synchronization can impact the performance of next-generation power distribution applications. Initial results indicate PTP has the capabilities to support an accurate and scalable time synchronization solution given the components are interoperable.

Study of consensus-based time synchronization in wireless sensor networks

Achieving precise time synchronization among wireless sensor devices within Internet-of-Things (IoT) networks poses a significant challenge. Various approaches have been proposed to efficiently synchronize time in wireless sensor networks (WSNs) used in the IoT. However, these solutions typically involve extensive message exchanges to achieve synchronization, leading to notable communication and energy overheads. In this context, we introduce a clustering approach aimed at enhancing the Reference Broadcast Synchronization (RBS) protocol to suit large multihop IoT networks. This paper discusses existing cluster- based time synchronization methods and compares their effectiveness. Moreover, our proposed clustering approach seamlessly integrates existing time synchronization protocols, thereby enhancing both power efficiency and synchronization accuracy, which are specifically tailored for multihop IoT networks. To validate the effectiveness of our approach, we conducted emulations, which demonstrated a significant improvement in minimizing synchronization error by 78% compared to existing RBS methods, along with a 40% reduction in the power consumption of reference nodes. Overall, our proposed method yields satisfactory results with less overhead in scalable IoT networks.

Generalized frequency division multiplexing (GFDM) is a waveform for the next-generation communication but requires a step dedicated to time and frequency synchronization. The current time and frequency synchronization methods of GFDM do not fully address the requirements on accuracy, robustness to a large frequency offset, and low complexity. This paper develops an accurate synchronization method tailored to large time and frequency offsets. The proposed method jointly synchronizes time and frequency and derives a decision variable from the real part of an inner product. The accuracy of time and frequency synchronization increases because an error in the frequency offset is corrected simultaneously during the process of time synchronization and because the decision variable does not depend on the imaginary part, which we show to be noise. The proposed method can correct a full range of frequency offsets. We compare synchronization accuracy of the proposed method to the state of the art analytically, numerically, and experimentally, in terms of the discriminant probability, the range of correctable frequency offsets, the probability of perfect time synchronization, the root mean square error (RMSE) between estimates and actual offsets, and the bit error ratio. The proposed method outperforms existing methods on all of these metrics. Moreover, it has practical utility and increases the transmission reliability for GFDM-based communication systems.

Communication redundancy and time synchronization are two important requirements commonly found in industrial systems. However, achieving high redundancy performance in combination with highly accurate time synchronization at all times is a challenging task. EtherCAT is a high performance, functionality rich communication technology offering both advanced redundancy features and accurate time synchronization. This paper will describe a robust solution where an EtherCAT system offers high redundancy performance in combination with accurate time synchronization. The solutions is based on using Ether-CAT slaves integrated into the EtherCAT master nodes. In the redundant case there is a need for two of these integrated slaves and they need to be configured appropriately to offer a robust solution.

Global navigation satellite systems (GNSS) are often integrated with inertial measurement units (IMU) for navigation in urban environments. The ability of these integrated systems to achieve precise positioning and navigation is highly dependent on accurate time synchronization. While the current time synchronization algorithms are capable of achieving millisecond-level synchronization in open environments, their performance deteriorates significantly in complex urban environments due to the impact on GNSS measurements of non-line-of-sight (NLOS) signals and multipath effects. Here we propose a loosely coupled GNSS/IMU integration time synchronization error modeling and compensation algorithm to tackle this problem in the context of urban vehicle navigation. In the algorithm, the time synchronization error is augmented as a state variable in the Robust Extended Kalman Filter (REKF), with the robustness factor threshold being dynamically adjusted based on the time synchronization error. Furthermore, we have designed a system time synchronization detection scheme based on two detection factors, with the aim of achieving high-precision GNSS/IMU time synchronization in complex urban environments. Experimental results show that the proposed algorithm synchronizes data time to the millisecond level in urban positioning environments. This represents an improvement of more than 90% in time synchronization precision compared to the traditional EKF-based time synchronization algorithm, and an improvement of more than 60% compared to the REKF-based time synchronization algorithm. Furthermore, compared to the EKF-based GNSS/IMU fusion algorithm, the proposed algorithm enhances the accuracy of the determination of both position and velocity in the horizontal and 3D directions by more than 50% and heading accuracy by 85%.

The accuracy of time synchronization can be significantly increased by enhancing the performance of atomic clocks. Future-generation time-frequency loads will be equipped with the latest ultrahigh-precision atomic clocks (with a day stability better than 10−17) and will leverage advantages of the space environment such as microgravity and low interference to operate a new generation of high-performance time-frequency payloads on low-orbit spacecraft. Moreover, using the high-precision time-frequency system of ground stations, low-time-delay high-performance time-frequency transmission networks, which have the potential to achieve ultrahigh-precision time synchronization, will be constructed. By considering full link error terms above the picosecond level, this paper proposes a new space-to-ground microwave two-way time synchronization method for scenarios involving low-orbit spacecraft and ground stations. Using the theoretical principles and practical application scenarios related to this method, a theoretical and simulation verification platform was developed to research the impact of the attitude, phase center calibration, and orbit determination errors on the single-frequency two-way time synchronization method. The effectiveness of this new method was verified. The results showed that when the attitude error is less than 72 arc seconds (0.02°), the phase center calibration error is less than 1 mm, and the precision orbit determination (POD) error is less than 10 cm (three-axis). After disregarding nonlink error terms such as equipment noise, this method can attain a space-to-ground time synchronization accuracy of better than 1.5 ps, and the time deviation (TDEV) of the transfer link is better than 0.7 ps @ 100 s, which results in ultrahigh-precision space-to-ground time synchronization.

Time synchronization plays an important role in the performance of wireless sensor networks. It can enhance the throughput and the lifetime of the network by improving the energy-efficiency, the freshness of collected data and reducing the network traffic and message conflicts. Due to the constraints on sensor nodes’ energy resources and the vulnerability of the distributed infrastructure of wireless networks, an efficient, scalable and accurate time synchronization protocol is desirable. This paper presents an accurate reactive protocol, named HRTS, that synchronizes the sensor nodes’ clock based on the node’s demand. It minimizes the synchronization region dynamically to the set of nodes which request synchronization. HRTS improves the accuracy of the synchronization procedure by measuring time parameters accurately and removing delays accordingly. Compared with the conventional time synchronization protocols like PCTS and TPSN, HRTS also reduces energy consumption by decreasing the traffic overheads especially when the network is not very dense.

The ever-increasing number of WSN deployments based on a large number of battery-powered, low-cost sensor nodes, which are limited in their computing and power resources, puts the focus of WSN time synchronization research on three major aspects, i.e., accuracy, energy consumption and computational complexity. In the literature, the latter two aspects have not received much attention compared to the accuracy of WSN time synchronization. Especially in multi-hop WSNs, intermediate gateway nodes are overloaded with tasks for not only relaying messages but also a variety of computations for their offspring nodes as well as themselves. Therefore, not only minimizing the energy consumption but also lowering the computational complexity while maintaining the synchronization accuracy is crucial to the design of time synchronization schemes for resource-constrained sensor nodes. In this paper, focusing on the three aspects of WSN time synchronization, we introduce a framework of reverse asymmetric time synchronization for resource-constrained multi-hop WSNs and propose a beaconless energy-efficient time synchronization scheme based on reverse one-way message dissemination. Experimental results with a WSN testbed based on TelosB motes running TinyOS demonstrate that the proposed scheme conserves up to 95% energy consumption compared to the flooding time synchronization protocol while achieving microsecond-level synchronization accuracy.