International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / Researchers at the National Wind Technology Center have identified a need to acquire data on the rotor of an operating wind turbine at precisely the same time as other data is acquired on the ground or a non-rotating part of the wind turbine. The researchers will analyze that combined data with statistical and correlation techniques to clearly establish phase information and loading paths and insights into the structural loading of wind turbines. A data acquisition unit has been developed to acquire the data from the rotating system at precise universal times specified by the user. The unit utilizes commercial data acquisition hardware, spread-spectrum radio modems, and a Global Positioning System receiver; and a custom-built programmable logic device. A prototype of the system is now operational, and initial field deployment is anticipated this summer.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / In this paper, we develop a method for achieving high precision of time and frequency synchronization among multiple base stations in GPS system. We first describe the basic theory of timing and frequency checking, and then analyze several error sources which influence the precision of time and frequency synchronization. Furthermore, we derive explicit formula for calculating the precision of time and frequency. Tested results have indicated that our method can indeed achieve very high time and frequency precision.

Time synchronization in wireless sensor networks (WSNs) is essential and significant for maintaining data consistency, coordination, and performing other fundamental operations, such as power management, security, and localization. Energy efficiency is the main concern in designing time synchronization protocols for WSNs because of the limited and generally nonrechargeable power resources. In this dissertation, the problem of time synchronization is studied in three different aspects to achieve energy efficient time synchronization in WSNs. First, a family of novel joint clock offset and skew estimators, based on the classical two-way message exchange model, is developed for time synchronization in WSNs. The proposed joint clock offset and skew correction mechanisms significantly increase the period of time synchronization, which is a critical factor in the over-all energy consumption required for global network synchronization. Moreover, the Cramer-Rao bounds for the maximum likelihood estimators are derived under two different delay assumptions. These analytical metrics serve as good benchmarks for the experimental results thus far reported. Second, this dissertation proposes a new time synchronization protocol, called the Pairwise Broadcast Synchronization (PBS), which aims at minimizing the number of message transmissions and implicitly the energy consumption necessary for global synchronization of WSNs. A novel approach for time synchronization is adopted in PBS, where a group of sensor nodes are synchronized by only overhearing the timing messages of a pair of sensor nodes. PBS requires a far smaller number of timing messages than other well-known protocols and incurs no loss in synchronization accuracy. Moreover, for densely deployed WSNs, PBS presents significant energy saving. Finally, this dissertation introduces a novel adaptive time synchronization protocol, named the Adaptive Multi-hop Timing Synchronization (AMTS). According to the current network status, AMTS optimizes crucial network parameters considering the energy efficiency of time synchronization. AMTS exhibits significant benefits in terms of energy-efficiency, and can be applied to various types of sensor network applications having different requirements.

Time-synchronization in wireless ad-hoc sensor networks is a crucial piece of infrastructure. Thus, it is a fundamental design problem to have a good clock syn- chronization amongst the nodes of wireless ad-hoc sensor networks. Motivated by this fact, in this thesis, the joint maximum likelihood (JML) estimator for relative clock phase offset and skew under the exponential noise model for the reference broadcast synchronization protocol is formulated and found via a direct algorithm. The Gibbs Sampler is also proposed for joint estimation of relative clock phase offset and skew, and shown to provide superior performance compared to the JML-estimator. Lower and upper bounds for the mean-square errors (MSE) of the JML-estimator and the Gibbs Sampler are introduced in terms of the MSE of the uniform minimum variance unbiased estimator and the conventional best linear unbiased estimator, respectively. The suitability of the Gibbs Sampler for estimating additional unknown parameters is shown by applying it to the problem in which synchronization of clock drift is also needed.

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / A Flight Test Instrumentation (FTI) system may consist of equipment that either supports PTPv1 (IEEE 1588 Std 2002) or PTPv2 (IEEE 1588 Std 2008). The challenge in such time distributed system is the poor compatibility between the two PTP protocol versions. This paper describes how to combine the PTP versions in the same network with minimum or no manual configuration.

There is a growing interest in autonomous driving systems that can safely rely on multiple sensors including GNSS, IMU, Radar and LiDAR to navigate with high accuracy, integrity, continuity, and availability in complex urban environments. Many existing data sets, collected with multi-sensor platforms, focus on validating different variations of visual localization algorithms like SLAM, place recognition, object detection and visual odometry that help navigate in sky-obstructed and GNSS-denied environments. However, GNSS still plays a vital role in providing the most assured navigation solution. In this thesis, we develop a robust system intended for collecting data sets that will support the design of tightly integrated navigation algorithms and the analysis of integrity risk using GNSS coupled with IMU, Radar, and LiDAR in challenging automotive environments. GNSS pseudorange, doppler, and carrier phase and IMU acceleration and angular velocities are measurements that the system is specifically designed to collect for sensor-fusion algorithm refinement. In addition, time synchronization between sensors is crucial in data sets validating tightly integrated navigation, especially in applications with high dynamics. However, there is no widely accepted accurate and stable method for synchronizing clocks between different sensor types. We implement a common-clock synchronization and a hardware-trigger clock synchronization between multiple sensors. We then collect a preliminary data set to compare the accuracy and stability of sensor time-tagging using a GNSS-receiver-generated hardware trigger versus using a local-clock ROS-based time stamping. We evaluate the impact of these synchronization methods on mapping accuracy performance. / Master of Science / There is a growing interest in vehicles that can drive themselves without human intervention. Typically, these vehicles must rely on different types of sensors that perceive the environment in different ways and complement each other to navigate complex environments. Many algorithms have been developed to use the measurements from these sensors to accurately determine the vehicle position, velocity and orientation with high accuracy. Many existing data sets intended to validate these algorithms focus on sensors that use visual perception to navigate. In this thesis, we develop a robust data collection system to support (a) the validation of innovative navigation system design that make full use of complementary sensor properties and (b) the quantification of how much trust we can put into the navigation solution. In addition, tight integration of these sensors requires accurate timing of the measurements across multiple sensors. However, there is no widely accepted method of synchronizing clocks between multiple sensor types. We implement a first method in which all sensor information is time-stamped using a common clock, and a second method in which one sensor sends a pulse to another to synchronize their two clocks. To compare the accuracy and stability of these synchronization methods, we collect a preliminary data set.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / One of the problems for manufacturers and users of flight test data acquisition equipment, is to guarantee synchronization between multiple units acquiring data on the vehicle. Past solutions have involved proprietary interconnects and multiple wire installations increasing weight and complexity and reducing inter-operation of units. This problem has become particularly important given the trend towards commercial busses, especially Ethernet, as a system interconnect. The IEEE1588 standard offers a way to transmitting time accurately over Ethernet. This paper discusses the standard, how it might be implemented, and examines the issues involved in adopting this standard for flight test data acquisition. A particular implementation that results in a synchronized four-wire Ethernet based distributed data acquisition system is discussed in section 3.

Efficient algorithms for time synchronization, including compensation for clock drift, are essential in order to obtain reliable fusion of data samples from multiple wireless sensor nodes. This paper evaluates the performance of algorithms based on three different approaches; one that synchronizes the local clocks on the sensor nodes, and a second that uses a single clock on the receiving node (e.g. a mobile phone), and a third that uses broadcast messages. The performances of the synchronization algorithms are evaluated in wireless personal area networks, especially Bluetooth piconets and ZigBee/IEEE 802.15.4 networks. A new approach for compensation of clock drift and a realtime implementation of single node synchronization from the mobile phone are presented and tested. Finally, applications of data fusion and time synchronization are shown in two different use cases; a kayaking sports case, and monitoring of heart and respiration of prematurely born infants. / <p>QC 20130605</p>

Time Domain Reflectometer (TDR) measures the electrical length of a cable from the applied end to the location of an impedance change. An impedance change causes a portion of the applied signal to reflect back based on the value of its reflection coefficient. The time of flight (TOF) between the applied and reflected wave is computed and multiplied with previously determined signal propagation velocity to determine the location of the impedance change. We intentionally open terminate the output end of the cable which makes the reflection coefficient be maximum (=1) to measure its electrical length. Conventional TDRs designed for testing integrity of long cables use various closed pulse shaped test signals i.e. the half sine wave and the Gaussian pulse, that disperse (change shape) and change velocity while propagation along the cable. Quoting Dr. Leon Brillouin’s comments on electromagnetic energy propagation [10], “in a vacuum, all waves (e.g. frequencies) propagate at the same velocity, hence withoutdistortion, whereas in a dispersive lossy media, except for an infinitely long sinusoidal waveform, distortion will occur due to frequency dependent velocity.” This signal distortion generally degrades the accuracy of the measurement of the signal’s TOF. We discuss here an Enhanced Resolution Time Domain Reflectometer (e-TDR). The enhanced resolution is due to a newly discovered signal called SPEEDY DELIVERY (SD) by Dr. Robert Flake at The University of Texas at Austin (US PATENT 6,441,695 B1 issued in August 27, 2002). This SD signal has a propagation velocity that is a programmable constant and this signal preserves its shape during propagation through dispersive lossy media (DLM). This signal behavior allows us to use ‘e-TDR’ in applications where remotely located signals need to be synchronized or asynchronized precisely. Potential applications include signal based synchronization of devices like sensors connected in a network. Since the cable carrying data from sensors at discrete and remote locations to a collecting center have different electrical lengths, it is necessary to precisely offset the timestamp of the incoming signal from these sensors to allow accurate data fusion. Our prototype is capable of synchronizing signals 1,200 ft (~ 400 m) apart with sub-nanosecond resolution. / text

abstract: This research work describes the design of a fault current limiter (FCL) using digital logic and a microcontroller based data acquisition system for an ultra fast pilot protection system. These systems have been designed according to the requirements of the Future Renewable Electric Energy Delivery and Management (FREEDM) system (or loop), a 1 MW green energy hub. The FREEDM loop merges advanced power electronics technology with information tech-nology to form an efficient power grid that can be integrated with the existing power system. With the addition of loads to the FREEDM system, the level of fault current rises because of increased energy flow to supply the loads, and this requires the design of a limiter which can limit this current to a level which the existing switchgear can interrupt. The FCL limits the fault current to around three times the rated current. Fast switching Insulated-gate bipolar transistor (IGBT) with its gate control logic implements a switching strategy which enables this operation. A complete simulation of the system was built on Simulink and it was verified that the FCL limits the fault current to 1000 A compared to more than 3000 A fault current in the non-existence of a FCL. This setting is made user-defined. In FREEDM system, there is a need to interrupt a fault faster or make intelligent deci-sions relating to fault events, to ensure maximum availability of power to the loads connected to the system. This necessitates fast acquisition of data which is performed by the designed data acquisition system. The microcontroller acquires the data from a current transformer (CT). Mea-surements are made at different points in the FREEDM system and merged together, to input it to the intelligent protection algorithm that has been developed by another student on the project. The algorithm will generate a tripping signal in the event of a fault. The developed hardware and the programmed software to accomplish data acquisition and transmission are presented here. The designed FCL ensures that the existing switchgear equipments need not be replaced thus aiding future power system expansion. The developed data acquisition system enables fast fault sensing in protection schemes improving its reliability. / Dissertation/Thesis / M.S. Electrical Engineering 2011