Time Sync Research Articles

Enhancement of Precise Underwater Object Localization

AbstractUnderwater communication applications extensively use localization services for object identification. Because of their significant impact on ocean exploration and monitoring, underwater wireless sensor networks (UWSN) are becoming increasingly popular, and acoustic communications have largely overtaken radio frequency broadcasts as the dominant means of communication. The two localization methods that are most frequently employed are those that estimate the angle of arrival and the time difference of arrival. The military and civilian sectors rely heavily on UWSN for object identification in the underwater environment. As a result, there is a need in UWSN for an accurate localization technique that accounts for dynamic nature of the underwater environment. Time and position data are the two key parameters to accurately define the position of an object. Moreover, due to climate change there is now a need to constrain energy consumption by UWSN to limit carbon emission to meet net‐zero target by 2050. To meet these challenges, we have developed an efficient localization algorithm for determining an object position based on the angle and distance of arrival of beacon signals. We have considered the factors like sensor nodes not being in time sync with each other and the fact that the speed of sound varies in water. Our simulation results show that the proposed approach can achieve great localization accuracy while accounting for temporal synchronization inaccuracies. When compared to existing localization approaches, the mean estimation error (MEE) (MEE) and energy consumption figures, the proposed approach outperforms them. The MEEs is shown to vary between 84.2154 and 93.8275 m for four trials, 61.2256 and 92.7956 m for eight trials, and 42.6584 and 119.5228 m for 12 trials. Comparatively, the distance‐based measurements show higher accuracy than the angle‐based measurements.

Energy Stimulated Time Synchronization for Energy Harvesting Wireless Networks

In this work, we develop a new energy-preserving time synchronization method, called the energy stimulated time sync (ESTS), for ultra-low-power wireless networks with energy harvesting capabilities. Compared with existing methods, ESTS does not rely on timestamp exchange but uses short energy tones to synchronize the nodes within the receiving range. ESTS is a centralized synchronization method based on a fully-passive wake-up radio (WuR) circuit, which can provide a variety of synchronization accuracy to meet different application requirements while consuming much lower energy than timestamp-based synchronization methods. We have implemented ESTS on Microchip ATmega256RFR2 system-on-chip (SoC). According to experiment results, ESTS can achieve an average of 5 ms and 70 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>s time precision for rough synchronization and fine synchronization, respectively. Moreover, the fully-passive WuR circuit consumes zero energy in the idle status. In the entire synchronization process, the rough synchronization only needs to be performed once, and the node consumes as low as 4 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>J of energy for each fine synchronization, making ESTS a promising solution for ultra-low-power wireless networks.

Integrating TimeSync Disturbance Detection and Repeat Forest Inventory to Predict Carbon Flux

Understanding change in forest carbon (C) is important for devising strategies to reduce emissions of greenhouse gases. National forest inventories (NFIs) are important to meet international accounting goals, but data are often incomplete going back in time, and the amount of time between remeasurements can make attribution of C flux to specific events difficult. The long time series of Landsat imagery provides spatially comprehensive, consistent information that can be used to fill the gaps in ground measurements with predictive models. To evaluate such models, we relate Landsat spectral changes and disturbance interpretations directly to C flux measured on NFI plots and compare the performance of models with and without ground-measured predictor variables. The study was conducted in the forests of southwest Oregon State, USA, a region of diverse forest types, disturbances, and landowner management objectives. Plot data consisted of 676 NFI plots with remeasured individual tree data over a mean interval (time 1 to time 2) of 10.0 years. We calculated change in live aboveground woody carbon (AWC), including separate components of growth, mortality, and harvest. We interpreted radiometrically corrected annual Landsat images with the TimeSync (TS) tool for a 90 m × 90 m area over each plot. Spectral time series were divided into segments of similar trajectories and classified as disturbance, recovery, or stability segments, with type of disturbance identified. We calculated a variety of values and segment changes from tasseled cap angle and distance (TCA and TCD) as potential predictor variables of C flux. Multiple linear regression was used to model AWC and net change in AWC from the TS change metrics. The TS attribution of disturbance matched the plot measurements 89% of the time regarding whether fire or harvest had occurred or not. The primary disagreement was due to plots that had been partially cut, mostly in vigorous stands where the net change in AWC over the measurement was positive in spite of cutting. The plot-measured AWC at time 2 was 86.0 ± 78.7 Mg C ha−1 (mean and standard deviation), and the change in AWC across all plots was 3.5 ± 33 Mg C ha−1 year−1. The best model for AWC based solely on TS and other mapped variables had an R2 = 0.52 (RMSE = 54.6 Mg C ha−1); applying this model at two time periods to estimate net change in AWC resulted in an R2 = 0.25 (RMSE = 28.3 Mg ha−1) and a mean error of −5.4 Mg ha−1. The best model for AWC at time 2 using plot measurements at time 1 and TS variables had an R2 = 0.95 (RSME = 17.0 Mg ha−1). The model for net change in AWC using the same data was identical except that, because the variable being estimated was smaller in magnitude, the R2 = 0.73. All models performed better at estimating net change in AWC on TS-disturbed plots than on TS-undisturbed plots. The TS discrimination of disturbance between fire and harvest was an important variable in the models because the magnitude of spectral change from fire was greater for a given change in AWC. Regional models without plot-level predictors produced erroneous predictions of net change in AWC for some of the forest types. Our study suggests that, in spite of the simplicity of applying a single carbon model to multiple image dates, the approach can produce inaccurate estimates of C flux. Although models built with plot-level predictors are necessarily constrained to making predictions at plot locations, they show promise for providing accurate updates or back-calculations of C flux assessments.

High-Reliability Sub-Nanosecond Network Time Synchronization Method Enabled by Double-Frequency Distributed Time Synchronization

Time synchronization is a long-standing challenge in distributed systems like indoor/outdoor positioning, coordinated multi-point in 4G/5G mobile communication, etc., which require nanosecond-level high-reliable time sync networks. At present, a widely adopted solution for time sync networks is the precision time protocol specified in IEEE 1588v2, which can provide sub-microsecond sync accuracy. In addition, a novel network time sync method called distributed time synchronization has also been proposed recently, which can achieve 50-ns-level accuracy and stronger survivability in metro, regional, and backbone networks. However, both of the above methods encounter difficulties in achieving nanosecond sync accuracy and network reliability simultaneously. In this paper, by analyzing the main factors influencing the degradation of time sync accuracy, we reveal that the finite clock resolution is a major barrier to achieving nanosecond-level time synchronization. In order to establish a low-cost, high-reliability, and sub-nanosecond-level time sync network, we propose a novel network time sync method called double-frequency distributed time synchronization (DF- DTS). By selecting two specific and distinct frequencies for the sending and receiving clocks of the nodes/devices being synchronized, the time sync errors induced by the finite clock resolution can be reduced by a statistical approach. We set up a theoretical model for the DF-DTS and analyze the time sync accuracy through both mathematical derivations and network simulations. Furthermore, we propose a failure-restoration mechanism to enhance the reliability of DF-DTS networks by improving the time sync accuracy under failures and reducing the failure recovery time. Finally, we conduct both point- to-point and network time sync experiments to validate the proposed DF-DTS method. The results demonstrate that DF-DTS can achieve sub-nanosecond-level sync accuracy that is 1-2 orders of magnitude higher than the clock resolution in a prototype four-node DF-DTS network. Moreover, a network simulation under failure cases is conducted, and the results show that our method has significant advantages in both time sync accuracy and recovery time in the failure-restoration process compared to IEEE 1588v2.

Application of Non-Linear Gaussian Regression-Based Adaptive Clock Synchronization Technique for Wireless Sensor Network in Agriculture

Efficient and low power utilizing clock synchronization is a challenging task for a wireless-sensor network (WSN). Therefore, it is crucial to design a light weight clock synchronization protocols for these networks. An adaptive clock offset prediction model for WSN is proposed in this paper that exchanges fewer synchronization messages to improve the accuracy and efficiency. Timing information required is collected by setting a small WSN set up to investigate the soil condition to control the irrigation in agriculture. The networks investigate soils moisture, temperature, humidity, and pressure content along with the sensors clock offset. First, the prediction model perceives the existing sensor clock offset to observe the clock characteristics and delay. Then, a Gaussian function is applied for adjusting the parameters weight of the observed value in the prediction model. The system results demonstrate that the proposed adaptive non-linear Gaussian regression synchronization model utilizes 20% less energy as consumed by time sync protocol for sensor-network and reference broadcast synchronization Protocol. It also reduces the synchronization error with respect to root-mean-square error (RMSE) by 24.85% as compared to linear prediction synchronization with RMSE 28.72% in terms of accuracy.

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.

The Design and Implement for Transceiver of WIA-PA

In this paper, the system scheme and system architecture for transceiver of WIA-PA are presented. The low-IF topology and direct up conversion method are employed, corresponding to receiver part and transmitter part. And in the baseband part, differential and correlation demodulate received signals, as well as time sync, frequency offset calibrate and frame sync operations are designed for solvation the problem of real radio environmental effects. The chip implements using 0.18μm CMOS process has small chip area and low power consumption. The minimum sensitivity of receiver is less than-85dBm for 1% PER (packet error rate), which is better than the required sensitivity for specification.

The Development of Self-Test Box for Magneto Telluric Recorder

MT method is one of the hottest points of geophysics. The higher quality original data, the better result MT method done, so some high reliability and better functional observe system is urgent demand. The instrument usually need self-test in field, in order to make sure of the reliability of the observe system. This paper introduced a kind of self-test box including GPS, DTCXO, MCU, FPGA and DDS, and relate single chip, FPGA and the upper user control software. After several field surveys, the generator of sinusoid signal, pulse signal and pseudo-random signal also clarifies the effectiveness of the self-test box, taking into account of time sync and pseudo-random signal processing.

Time Synchronization in Wireless Sensor Networks: A Survey

Time synchronization is a critical piece of infrastructure for any distributed system. Wireless sensor networks have emerged as an important and promising research area in the recent years. Time synchronization is important for many sensor network applications that require very precise mapping of gathered sensor data with the time of the events, for example, in tracking and vehicular surveillance. It also plays an important role in energy conservation in MAC layer protocols. The paper studies different existing methods, protocols, significant time parameters (clock drift, clock speed, synchronization errors, and topologies) to achieve accurate synchronization in a sensor network. The studied Synchronization protocols include conventional time sync protocols (RBS, Timing-sync Protocol for Sensor Networks -TPSN, FTSP), and other application specific approaches such as all node-based approach, a diffusion-based method and group sync approaches aiming at providing network-wide time. The goal for writing this paper is to study most common existing time synchronization approaches and stress the need of a new class of secure-time synchronization protocol that is scalable, topology independent, fast convergent, energy efficient, less latent and less application dependent in a heterogeneous hostile environment. Our survey provides a valuable framework by which protocol designers can compare new and existing synchronization protocols from various metric discussed in the paper. So, we are hopeful that this paper will serve a complete one-stop investigation to study the characteristics of existing time synchronization protocols and its implementation mechanism in a Sensor network environment.

“A little bit more mysterious…”: Ambience and Art in the Dark

“A little bit more mysterious…”: Ambience and Art in the Dark

FireFly: a cross-layer platform for real-time embedded wireless networks

We propose a cross-layer approach with tightly-coupled time synchronization for real-time support and predictable lifetime in battery-operated sensor networks. Our design spans a sensor hardware platform with hardware-based global time synchronization, a TDMA link layer protocol with collision-free multi-hop support and node scheduling algorithms for maximum concurrency and streaming. Our dual-radio sensor platform, FireFly, features an IEEE 802.15.4 transceiver and supports global time synchronization indoors by using an AM radio carrier-current method and an atomic clock receiver for outdoors. A TDMA-based link protocol, RT-Link, leverages the hardware for fixed and mobile nodes with a near-optimal and predictable node lifetime of over 2 years. It outperforms comparable sensor network link protocols such as B-MAC and S-MAC in terms of end-to-end latency and throughput and node lifetime across all duty cycle ratios. Operating over RT-Link is MAX, a scheduling framework which offers optimal transmission concurrency and bandwidth management for networks with regular structure. Through analysis and experiments we show that global time sync is a robust, economical and scalable alternative to in-band software-based techniques. To illustrate the capabilities and flexibility of our platform, we describe our experiences with two-way voice streaming over multiple hops. We have deployed a 42-node network with sub-100 μs synchronization accuracy in the NIOSH experimental coal mine for people-tracking and voice communication.

The relativistic effects in localization of gamma-burst sources

The paper discusses influence of relativistic effects in gamma-burst propagation and the time sync. It is shown that the phenomenon of gamma-source aberration, while using the localization algorithm based on the estimates of gamma-burst arrival time instants should be regarded as relativistic effect. Criterions are derived which determine whether it is necessary to account for the relativistic effects, depending on the localization accuracy.

An Analysis and Demonstration of Clock Synchronization by VLBI

A prototype of a semi-real time system for synchronizing the Deep Space Net station clocks by radio interferometry was successfully demonstrated on August 30, 1972. The system utilized an approximate maximum likelihood estimation procedure for processing the data, thereby achieving essentially optimum time sync estimates for a given amount of data, or equivalently, minimizing the amount of data required for reliable estimation. Synchronization accuracies as good as 100 ns rms were achieved between Deep Space Stations 11 and 12, both at Goldstone, Calif. The accuracy can be improved by increasing the system bandwidth until the fundamental limitations due to baseline and source position uncertainties and atmospheric effects are reached. These limitations are under 10 ns for transcontinental baselines.