Time Synchronization Problem Research Articles

Measuring the shape of randomly arriving pulses shorter than the acquisition step

In this paper we have developed and tested a novel method for measuring precisely the shape of pulses shorter than the acquisition step, which is effective for random delays of the input pulses with respect to the start pulse of the analogue-to-digital converter (ADC). The method is based on conversion of the short pulses to be measured into longer damped oscillations and their correct acquisition (sampling) with saving the pulse information, rearranging of the sampled oscillations with respect to some reference time instant to form a finer-discretization high-precision oscillation, and retrieving the pulse shape by inverse algorithms. We demonstrated experimentally the good performance (5–7% rms error) of this method (by using 20 MHz/8 bits ADC) when measuring the shape of randomly arriving pulses, shorter than the ADC sampling step (50 ns), with an equivalent sampling frequency up to 2 GHz (0.5 ns equivalent sampling step). The resolving of shapes in a pulse pair with an inter-pulse delay shorter than the ADC sampling interval has also been demonstrated. The limiting equivalent sampling frequency is estimated to be up to 500 GHz. This method can be effectively applied for creation of some novel short-pulse measuring techniques, avoiding the problem of time synchronization to the start pulses in lidar and radar, nuclear experiments, tomography, communications, etc.

Time synchronization in sensor networks: a survey

Time synchronization is an important issue in multihop ad hoc wireless networks such as sensor networks. Many applications of sensor networks need local clocks of sensor nodes to be synchronized, requiring various degrees of precision. Some intrinsic properties of sensor networks, such as limited resources of energy, storage, computation, and bandwidth, combined with potentially high density of nodes make traditional synchronization methods unsuitable for these networks. Hence, there has been an increasing research focus on designing synchronization algorithms specifically for sensor networks. This article reviews the time synchronization problem and the need for synchronization in sensor networks, then presents in detail the basic synchronization methods explicitly designed and proposed for sensor networks.

Efficient three-party key exchange using smart cards

In this paper, we propose a novel three-party key exchange scheme using smart cards. The main merits of our scheme include: (1) there is no need for verification, passwords or shared keys table in the trusted server; (2) users can freely choose and change their own passwords, (3) the communication and computation cost is very low; (4) two users can authenticate each other by the trusted server; (5) it generates a session key agreed between two users; (6) it is a nonce-based scheme which does not have a serious time-synchronization problem.

Time synchronization in a local area network

In this article we examine the problem of synchronizing the time-of-day clock in one node of an automation network system with a reference clock. The emphasis of this article is on switched, highly loaded networks, where unpredictable delays introduce excessive synchronization noise. PC clocks are accurate enough when connected within a network, but a new requirement is for them to be synchronized, which means that they should show the same time at the same instant. The most prominent time-synchronization method is the network time protocol proposed by Mills and Internet engineering task force group. A complete solution of the high-precision time-synchronization problem must reduce the randomness associated with the RTOS. The methods discussed in this article can help determine the frequency and time offset of a local time-of-day clock. The next challenge is to construct a local time-of-day clock and apply the synchronization information to it.

Efficient password authenticated key agreement using smart cards

The smart-card based remote user authentication and key agreement scheme is a very practical solution to create a secure distributed computer environment. In this paper, we propose a novel user authentication and key agreement scheme with much less computational cost and more functionality. The main merits include: (1) the scheme needs no verification table; (2) users can freely choose their own passwords; (3) the communication and computation cost is very low; (4) users and servers can authenticate each other; and (5) it generates a session key agreed by the user and the server. Also, our proposed scheme is a nonce-based scheme which does not have a serious time-synchronization problem.

Efficient multi-server password authenticated key agreement using smart cards

Remote user authentication and key agreement scheme using smart cards is a very practical solution to validate the eligibility of a remote user and provide secure communication later. Also, due to fast progress of networks and information technology, most of provided services are in multi-server environments. In this paper, we propose a novel user authentication and key agreement scheme using smart cards for multi-server environments with much less computational cost and more functionality. The major merits include: (1) users only need to register at the registration centre once and can use permitted services in eligible servers; (2) the scheme does not need a verification table: (3) users can freely choose their passwords; (4) the computation and communication cost is very low; (5) servers and users can authenticate each other; (6) it generates a session key agreed by the user and the server; and (7) it is a nonce-bayed scheme which does not have a serious time-synchronization problem.

Detection and Elimination of Time Synchronization Problems for the GERESS Array by Correlating Microseismic Noise

The German Experimental Seismic System, known as the GERESS array, is identified in Annex 1 of the Protocol to the Comprehensive Nuclear Test-Ban Treaty (CTBT) as a primary seismic station (PS 19). Since its construction and commissioning in 1991, the performance of this array has been hampered by incidental occurrences of timing problems involving the loss of time synchronization for as many as a few array elements. During GSETT-3 (Conference of Disarmament Group of Scientific Experts Technical Test-3) and since the establishment of the Vienna International Data Centre (IDC), the array has contributed data to the CTBT monitoring system. Beginning in 1997, the German National Data Center (NDC) at the Federal Institute for Geosciences and Natural Resources (BGR) started to archive these data on CD-ROM and makes them available via Auto-DRM, notwithstanding the fact that the data may be time-corrupted. Instances have been found when up to five array elements were unsynchronized, which may lead to inconsistent array processing results. Up to now the detection and elimination of such timing errors was considered an unsolvable problem. This would certainly be true if the GERESS array were a single- (or three-) component station. However, an array provides the chance to use waveform correlation of coherent signals, as is usually provided by teleseismic events of significant magnitude, where timing differences are easily identified and measured. These large teleseismic events, unfortunately, are not frequent enough to be used on a regular and continuous basis. The only continuously available signal observed at a seismic station is microseismic noise, which, thus, is usually considered an obstacle to seismological investigations. In this study, however, we present results that this ocean-generated seismic signal can be favorably used in waveform correlation as a constant source of sufficient seismic energy. Scanning several years of GERESS waveform data allowed us …

INTEGRATION OF GPS AND AN INERTIAL SYSTEM FOR PRECISE SURVEYING APPLICATIONS

This report studies the possibility of combining GPS and INS techniques for precise kinematic position determination. A Kalman filter is written for the integration of single frequency GPS phase and local level INS data and some fundamental problems such as fixing cycle slips or complete losses of lock, and time and space synchronisations are investigated. It is shown that the time synchronization problem can be completely solved in post-processing and that total losses of lock for up to 30 s on all satellites can expect to be recovered. Additionally it is shown that carrying out a zero velocity update during loss of lock can increase this time to at least 70 s.

An Adaptive Receiver Approach to the Time Synchronization Problem

In this paper, a frequency shift keying (FSK) system that adapts to unknown signal arrival times is defined and analyzed. The adaptive receiver extracts information concerning the signal arrival times directly from the information bearing signals and uses these measurements in a structure known to be optimum for the case of perfect measurements. The system error rate is derived and plotted as a function of the received SNR, the size of the signal alphabet, and the quality of the delay measurements.

Time resolved Schlieren and interferometer studies of a low pressure discharge

Time resolved Schlieren and interferometer studies of an air discharge at pressures between 0.4 and 4 mmHg, using a single-shot sub-microsecond light source, are described with special reference to the problem of time synchronization. The information which can be obtained from each of these measurements is discussed and the limitations and relative merits considered. It is shown how the information derived from these experiments helps towards an understanding of the behaviour of the discharge.