Clock synchronization Research Papers - Academia.edu (original) (raw)

This paper examines the timekeeping environments of several orbital and aircraft flight scenarios for application to the next generation architecture of positioning, navigation, timing, and communications. The model for timekeeping and... more

This paper examines the timekeeping environments of several orbital and aircraft flight scenarios for application to the next generation architecture of positioning, navigation, timing, and communications. The model for timekeeping and time dissemination is illustrated by clocks onboard the International Space Station, a Molniya satellite, and a geostationary satellite. A mathematical simulator has been formulated to model aircraft flight test and satellite scenarios. In addition, a time transfer simulator integrated into the Formation Flying Testbed at the NASA Goddard Space Flight Center is being developed. Real-time hardware performance parameters, environmental factors, orbital perturbations, and the effects of special and general relativity are modeled in this simulator for the testing and evaluation of timekeeping and time dissemination algorithms.

Recent technological advances have accelerated a renaissance in usage of non-geostationary (non-GSO) communication satellites in provision of various services domestically and globally. Early ventures into communication satellites have... more

Recent technological advances have accelerated a renaissance in usage of non-geostationary (non-GSO) communication satellites in provision of various services domestically and globally. Early ventures into communication satellites have used satellites in low Earth orbits. The main reasons for this mode of operation were that the booster technology was not available to lift satellites into a higher orbit, the satellite technology was not sufficiently mature to achieve higher performance such as power generation and signal bandwidth. Also, there was a problem with reliability due to operation in hostile space environment. After that early stage, more than 30 years the most dominant domain of communication using satellites has been in circular geostationary equatorial Earth synchronous orbit. As the satellite system technology developed, it became possible to provide services by the use of satellites in various orbital regimes like low Earth orbit (LEO at about 1000 km altitude), mediu...

Cryptography helps solve many computer and communication problems, including clock synchronization, where a group of nodes wants to agree on a theoretically unique clock in the system with the presence of malicious nodes trying to prevent... more

Cryptography helps solve many computer and communication problems, including clock synchronization, where a group of nodes wants to agree on a theoretically unique clock in the system with the presence of malicious nodes trying to prevent the process of convergence; so we will need a set of mechanisms, including encryption. Many synchronization techniques suffer from high power consumption or vulnerability to attack or difficulty of implementation. In this article, we propose a synchronization protocol that contains two parts. The first part uses a lightweight linear scheme to encrypt clock messages to fend off certain types of attacks such as message manipulation. This scheme is suitable for Wireless sensor networks (WSNs) with negligible encryption and decryption time. The second part is the process of calculating the clock based on a very simple consensus algorithm. The study of the proposed protocol has shown very satisfactory results.

A stitchable clock mesh, a dual operation mode method, and a master clock stratum are provided for a 3D chip stack. The stitchable clock mesh includes at least one clock mesh, on each of the two or more strata, having a plurality of... more

A stitchable clock mesh, a dual operation mode method, and a master clock stratum are provided for a 3D chip stack. The stitchable clock mesh includes at least one clock mesh, on each of the two or more strata, having a plurality of sectors for providing a global clock signal. The stitchable clock mesh further includes mesh data sensors, on each of the two or more strata, for collecting mesh data for the at least one mesh. The mesh data includes measured functional data and measured performance data for a current system configuration. The stitchable clock mesh further includes mesh segmentation and joining circuitry for selectively performing a segmentation operation or a joining operation on the least one mesh or one or more portions thereof responsive to the mesh data and the current system configuration selectable from a plurality of system target configurations.

This paper gives brief introduction about clock synchronization in wireless mobile ad-hoc networks. Here we will discuss about the clock synchronization problem and scalability of MANETs. Also we will discuss about the major scopes for... more

This paper gives brief introduction about clock synchronization in wireless mobile ad-hoc networks. Here we will discuss about the clock synchronization problem and scalability of MANETs. Also we will discuss about the major scopes for synchronization in MANETs. We will discuss various algorithms proposed as solutions for the problem of clock synchronization in MANETs. Here we will discuss about TSF (timing synchronization function), MASP (Modified automatic self-timing procedure). At last we will compare the results for the throughput, end to end delay and energy parameters which are very important for the efficient utilization of the wireless adhoc networks.

Wireless Sensor Network (WSNs) have become a new information collection and monitoring solution for a variety of application. In WSN, sensor nodes have strong hardware and software restriction in terms of processing power, memory... more

Wireless Sensor Network (WSNs) have become a new information collection and monitoring solution for a variety of application. In WSN, sensor nodes have strong hardware and software restriction in terms of processing power, memory capability, power supply and communication throughput. Due to these restrictions, fault may occur in sensor. This paper presents a distance based fault detection (DBFD) method for wireless sensor network using the average of confidence level and sensed data of sensor node. Simulation results show that sensor nodes with permanent faults and without fault which was judged as faulty are identified with high accuracy for a wide range of fault rate, and keep false alarm rate for different levels of sensor fault model and also correct nodes are identified by accuracy. Keywords-wireless sensor networks; sensor nodes; communication throughput; distance based fault detection; confidence level; I. INTRODUCTION A sensor network is composed of a large number of sensor ...

Sensor networks for infrastructure monitoring systems require battery-operated sensing nodes with a lifetime of 10 years, a standardized technology, and low engineering costs. Receiver-initiated transmission and coordinated sampled... more

Sensor networks for infrastructure monitoring systems require battery-operated sensing nodes with a lifetime of 10 years, a standardized technology, and low engineering costs. Receiver-initiated transmission and coordinated sampled listening are promising power-saving communication methods that can be used for infrastructure monitoring. First, we compared receiver-initiated transmission and coordinated sampled listening from the viewpoint of power consumption and communication success probability. The results of the comparison showed that if we can continue coordinated sampled listening synchronous communication mode, we can satisfy the low power consumption performance required for infrastructure monitoring. However, coordinated sampled listening synchronous communication cannot be maintained for a longer period owing to performance variations of the clock crystal oscillator (CXO). We solved this problem by developing energy efficient system-media access control protocol (NES MAC),...

This article gives a brief critical examination of the special theory of relativity and a similar Newtonian framework to the first order of the v/c ratio, focusing on the phenomena of aberration, Fresnel dragging, and the Doppler effect.... more

This article gives a brief critical examination of the special theory of relativity and a similar Newtonian framework to the first order of the v/c ratio, focusing on the phenomena of aberration, Fresnel dragging, and the Doppler effect. It will show that both frameworks yield the same equations modeling these phenomena within the first order limit. This is done at a level understandable to anyone with a working knowledge of calculus so that the underlying ideas do not get lost in abstruse mathematical formulations.

Distributed Embedded Systems (DESs) carrying out critical tasks must be highly reliable and hard in real-time. Moreover, to operate in dynamic operational contexts in an effective and efficient manner, they must also be adaptive.... more

Distributed Embedded Systems (DESs) carrying out critical tasks must be highly reliable and hard in real-time. Moreover, to operate in dynamic operational contexts in an effective and efficient manner, they must also be adaptive. Adaptivity is particularly interesting from a dependability perspective, as it can be used to develop dynamic fault tolerance mechanisms, which, in combination with static ones, make it possible to provide better and more efficient fault tolerance. However, constructing a DES with such complexity presents many challenges. This is because all the mechanisms that support fault tolerance, real-time, and adaptivity must be designed to operate in a coordinated manner. This paper presents the Dynamic Fault Tolerance for Flexible Time-Triggered Ethernet (DFT4FTT), a self-reconfigurable infrastructure for implementing highly reliable adaptive DES. Here, we describe the design of its hardware and software architecture and the main set of mechanisms, with a focus on ...

Einstein’s “universal constant” speed of light has been the keystone in derivations of the Lorentz transformation up to the present time. This assumed universal constant is discretionary within the empirical/time-averaged unequal two-way... more

Einstein’s “universal constant” speed of light has been the keystone in derivations of the Lorentz transformation up to the present time. This assumed universal constant is discretionary within the empirical/time-averaged unequal two-way speeds of light. Einstein’s (assumed) universal constant may accordingly be replaced by the (empirical) two-way universal constant. (i.e., c becomes c+ and c- in all moving IRFs). Here the Lorentz transformation is operationally derived given (unequal) two-way light-speeds in the moving frame. The two-way transformation exhibits space-time details in the moving frame that are absent in the overarching one-way transformation. Time continuity during the (operational) derivation is one such detail, where any one-way transformation sets-aside (e.g., atomic clock) tracking or following how the moving IRF state is achieved, whereas the procedure is explicit in the two-way light-speeds transformation. Einstein’s same-motion transformation plays a key role in the (novel) derivation. This mathematical development within the IRF system reveals extreme photonic behavior—in particular, the development admits or allows assumed near-infinite incoming light-speed—that helps, together with the Hubble expansion, to explain ongoing challenges—e.g., the dark sector.