Require Time Synchronization Research Articles

Time synchronization for an emulated CAN device on a Multi-Processor System on Chip

The increasing number of applications implemented on modern vehicles leads to the use of multi-core platforms in the automotive field. As the number of I/O interfaces offered by these platforms is typically lower than the number of integrated applications, a solution is needed to provide access to the peripherals, such as the Controller Area Network (CAN), to all applications. Emulation and virtualization can be used to implement and share a CAN bus among multiple applications. Furthermore, cyber-physical automotive applications often require time synchronization. A time synchronization protocol on CAN has been recently introduced by AUTOSAR.In this article we present how multiple applications can share a CAN port, which can be on the local processor tile or on a remote tile. Each application can access a local time base, synchronized over CAN, using the AUTOSAR Application Programming Interface (API). We evaluate our approach with four emulation and virtualization examples, trading the number of applications per core with the speed of the software emulated CAN bus.

Nanosecond-level time synchronization of AERA using a beacon reference transmitter and commercial airplanes

Radio detection of cosmic-ray air showers requires time synchronization of detectors on a nanosecond level, especially for advanced reconstruction algorithms based on the wavefront curvature and for interferometric analysis approaches. At the Auger Engineering Radio Array, the distributed, autonomous detector stations are time-synchronized via the Global Positioning System which, however, does not provide sufficient timing accuracy. We thus employ a dedicated beacon reference transmitter to correct for event-by-event clock drifts in our offline data analysis. In an independent cross-check of this "beacon correction" using radio pulses emitted by commercial airplanes, we have shown that the combined timing accuracy of the two methods is better than 2 nanoseconds.

An Algorithm for Inter-Satellite Autonomous Time Synchronization and Ranging in the Beidou Navigation Satellite System

Aiming at the requirement of the autonomous time synchronization in BeiDou Navigation Satellite System (BDS), an algorithm for inter-satellite autonomous time synchronization and ranging is proposed. Based on the establishment of the inter-satellite link length model of the BDS, a series of simulation has been carried out through the use of STK (Satellite Tool Kit), which includes the simulation of the length changing rules, the length variation scale and its variation ratio. Based on these simulations, an analysis of the impact of satellite motion on the inter-satellite two-way time synchronization and range has been presented. In this algorithm, the inter-satellite clock-offset and range with minimal error are acquired by utilizing the combination of clock-offset fitting polynomial and range fitting polynomial based on the least square fitting of data generated from the inter-satellite two-way time synchronization. Empirical evaluation of the BDS simulation shows that our time synchronization error is 2ns, and ranging error is 2m under the condition of acceptable simulation error. With the application of the algorithm to the inter-satellite autonomous time synchronization and ranging, the high-accuracy measurement of inter-satellite clock-offset and range of BDS can be reached.

A Novel Time Synchronization Method for Dynamic Reconfigurable Bus

UM-BUS is a novel dynamically reconfigurable high-speed serial bus for embedded systems. It can achieve fault tolerance by detecting the channel status in real time and reconfigure dynamically at run-time. The bus supports direct interconnections between up to eight master nodes and multiple slave nodes. In order to solve the time synchronization problem among master nodes, this paper proposes a novel time synchronization method, which can meet the requirement of time precision in UM-BUS. In this proposed method, time is firstly broadcasted through time broadcast packets. Then, the transmission delay and time deviations via three handshakes during link self-checking and channel detection can be worked out referring to the IEEE 1588 protocol. Thereby, each node calibrates its own time according to the broadcasted time. The proposed method has been proved to meet the requirement of real-time time synchronization. The experimental results show that the synchronous precision can achieve a bias less than 20 ns.

A Deadline-Aware Scheduling and Forwarding Scheme in Wireless Sensor Networks.

Many applications in wireless sensor networks (WSNs) require energy consumption to be minimized and the data delivered to the sink within a specific delay. A usual solution for reducing energy consumption is duty cycling, in which nodes periodically switch between sleep and active states. By increasing the duty cycle interval, consumed energy can be reduced more. However, a large duty cycle interval causes a long end-to-end (E2E) packet delay. As a result, the requirement of a specific delay bound for packet delivery may not be satisfied. In this paper, we aim at maximizing the duty cycle while still guaranteeing that the packets arrive at the sink with the required probability, i.e., the required delay-constrained success ratio (DCSR) is achieved. In order to meet this objective, we propose a novel scheduling and forwarding scheme, namely the deadline-aware scheduling and forwarding (DASF) algorithm. In DASF, the E2E delay distribution with the given network model and parameters is estimated in order to determine the maximum duty cycle interval, with which the required DCSR is satisfied. Each node independently selects a wake-up time using the selected interval, and packets are forwarded to a node in the potential forwarding set, which is determined based on the distance between nodes and the sink. DASF does not require time synchronization between nodes, and a node does not need to maintain neighboring node information in advance. Simulation results show that the proposed scheme can satisfy a required delay-constrained success ratio and outperforms existing algorithms in terms of E2E delay and DCSR.

Precision time synchronization control method for smart grid based on wolf colony algorithm

Abstract In order to satisfy the high accuracy and high security requirements of time synchronization in smart grid, this paper has conducted a research on high-precision time synchronization control algorithm based on IEEE 1588 protocol. A slave clock model is built considering both phase offset and frequency drift. A novel approach using proportional–integral–derivative (PID) controller in cooperation with the wolf colony algorithm (WCA) is proposed to eliminate the offset of the slave clock with respect to the master clock. As a new swarm-intelligence algorithm, WCA is introduced for self-tuning the optimal parameters of the PID controller, which simulates the intelligent predatory behaviors and prey distribution rule of the wolf colony. The WCA-based PID control approach is compared with the method based on standard Particle Swarm Optimization (PSO) and Back-Propagation (BP) neural network. The experimental results show that the proposed WCA-based PID control approach in time synchronization for smart grid has higher precision, can adaptively adjust compensation and keep the master–slave clock synchronization effectively.

Secure Access Control Method for Wireless Sensor Networks

Wireless sensor networks (WSNs) contain a large number of resource-constrained and energy-limited sensor nodes that are generally deployed in an open environment. Those sensor nodes communicate with each other or with a base station via wireless channels. Therefore, secure access control is an important issue in WSNs because sensor nodes are susceptible to various malicious attacks during the authentication and key establishment phase and the new node addition phase. In this study, we propose a new access control method based on elliptic curve cryptography and the chameleon hash function. This method addresses the security problems in the existing research. It also has additional advantages since it does not require time synchronization between communication nodes, nor does it require node verification tables. In addition to our proposal, the correctness, security, resistance to possible attacks, and the performance of the proposed method are analyzed and evaluated. The results of our study demonstrate that the proposed method has an outstanding performance and fulfills all the requirements for secure communication in WSNs.

IEEE 1588 Time Synchronization Board in MTCA.4 Form Factor

Distributed data acquisition and control systems in large-scale scientific experiments, like e.g. ITER, require time synchronization with nanosecond precision. A protocol commonly used for that purpose is the Precise Timing Protocol (PTP), also known as IEEE 1588 standard. It uses the standard Ethernet signalling and protocols and allows obtaining timing accuracy of the order of tens of nanoseconds. The MTCA.4 is gradually becoming the platform of choice for building such systems. Currently there is no commercially available implementation of the PTP receiver on that platform. In this paper, we present a module in the MTCA.4 form factor supporting this standard. The module may be used as a timing receiver providing reference clocks in an MTCA.4 chassis, generating a Pulse Per Second (PPS) signal and allowing generation of triggers and timestamping of events on 8 configurable backplane lines and two front panel connectors. The module is based on the Xilinx Spartan 6 FPGA and thermally stabilized Voltage Controlled Oscillator controlled by the digital-to-analog converter. The board supports standalone operation, without the support from the host operating system, as the entire control algorithm is run on a Microblaze CPU implemented in the FPGA. The software support for the card includes the low-level API in the form of Linux driver, user-mode library, high-level API: ITER Nominal Device Support and EPICS IOC. The device has been tested in the ITER timing distribution network (TCN) with three cascaded PTP-enabled Hirschmann switches and a GPS reference clock source. An RMS synchronization accuracy, measured by direct comparison of the PPS signals, better than 20 ns has been obtained.

AFDA: Asynchronous Flipped Diversity ALOHA for Emerging Wireless Networks With Long and Heterogeneous Delay

The design of random media access control (MAC) protocol renews great attention for emerging challenged wireless environments, where the propagation delay is long, heterogeneous, and/or varying, such as satellite or underwater acoustic sensor networks. In these environments, the existing MAC solutions based on slotted transmissions, carrier sensing, or channel reservation by control packets are no longer favorable or even feasible. In this paper, we propose the asynchronous flipped diversity ALOHA (AFDA) to tackle the challenges based on a new diversity transmission scheme. Different from the existing diversity transmission schemes, each data packet and its flipped replica are transmitted back to back, and the zigzag decoding technique is adopted to resolve collisions. The performance of AFDA has been evaluated by analysis and simulations. The results show that, without time synchronization or handshaking requirements, the performance of AFDA is unaffected by the duration or variation of the propagation delay, and it substantially improves system performance in terms of throughput, packet loss ratio, and network admission region.

Fault Correspondence Analysis in Complex Electric Power Systems

Wide area measurement system (WAMS) mainly serves for the requirement of time synchronization in complex electric power systems. The analysis and control of power system mostly depends ...

An Efficient Real-Time Broadcast Authentication Scheme for Command and Control Messages

Broadcast (multicast) authentication is crucial for large and distributed systems, such as cyber-physical infrastructures (e.g., power-grid/smart-grid) and wireless networks (e.g., intervehicle networks, military ad hoc networks). These time-critical systems require real-time authentication of command and control messages in a highly efficient, secure, and scalable manner. However, existing solutions are either computationally costly (e.g., asymmetric cryptography) or unscalable/impractical (e.g., symmetric cryptography, one-time signatures, delayed key disclosure methods). In this paper, we develop a new broadcast authentication scheme that we call rapid authentication (RA), which is suitable for time-critical authentication of command and control messages in large and distributed systems. We exploit the semistructured nature of command and control messages to construct special digital signatures, which are computationally efficient both at the signer and verifier sides. We show that RA achieves several desirable properties that are not available in existing alternatives simultaneously: 1) fast signature generation and verification; 2) immediate verification; 3) constant size public key; 4) compact authenticating tag; 5) packet loss tolerance; 6) being free from time synchronization requirement; and 7) provable security.

Loop Assisted Synchronization-Free Localization for Underwater Acoustic Sensor Networks

Underwater acoustic sensor networks (UASNs) have attracted significant attention recently. Localization is one of the most important issues associated with UASNs. Most of the existing underwater localization algorithms require time synchronization. However, time synchronization is difficult to be achieved in the underwater networks. The beam width and three-dimensional direction of underwater acoustic sensor nodes are ignored by the existing underwater localization algorithms. This will increase the difficulty to avoid time synchronization. We develop a loop assisted synchronization-free localization to achieve synchronization-free localization algorithm when taking into account the beam width and direction of the underwater nodes. We propose link detection stage to get link state information (symmetry and length). In addition we introduce a loop-assisted localization method to solve the problem of asymmetric link ranging without time synchronization. Finally, we propose an intersections based location estimation mechanism for error problem in practical measurement and we improve the localization accuracy. The simulation results and experimental results verify the effectiveness and feasibility of the proposed work.

Distributed and Asynchronous Data Collection in Cognitive Radio Networks with Fairness Consideration

As a promising communication paradigm, Cognitive Radio Networks (CRNs) have paved a road for Secondary Users (SUs) to opportunistically exploit unused licensed spectrum without causing unacceptable interference to Primary Users (PUs). In this paper, we study the distributed data collection problem for asynchronous CRNs, which has not been addressed before. We study the Proper Carrier-sensing Range (PCR) for SUs. By working with this PCR, an SU can successfully conduct data transmission without disturbing the activities of PUs and other SUs. Subsequently, based on the PCR, we propose an Asynchronous Distributed Data Collection (ADDC) algorithm with fairness consideration for CRNs. ADDC collects a snapshot of data to the base station in a distributed manner without the time synchronization requirement. The algorithm is scalable and more practical compared with centralized and synchronized algorithms. Through comprehensive theoretical analysis, we show that ADDC is order-optimal in terms of delay and capacity, as long as an SU has a positive probability to access the spectrum. Furthermore, we extend ADDC to deal with the continuous data collection issue, and analyze the delay and capacity performances of ADDC for continuous data collection, which are also proven to be order-optimal. Finally, extensive simulation results indicate that ADDC can effectively accomplish a data collection task and significantly reduce data collection delay.

Partial discharge location in power cables using a double ended method based on time triggering with GPS

Partial discharge (PD) diagnostics is the most widely used tool to assess the insulation condition of insulated power cables which facilitates informed maintenance planning leading to extended service life of ageing assets. Time domain reflectometry (TDR) using a single ended or double ended approach is the most widely used method for locating PD sources. The success of the single ended method is dependent upon cable network design. However, by monitoring PDs at both ends of the cable, i.e. double-ended PD monitoring, higher accuracy of PD location can be achieved with a higher success rate. The double ended method is not widely used due to its complex system design, time synchronization and communication requirement between measurement units. This paper proposes a double ended PD location system which triggers on the predefined one pulse per second (1PPS) signal obtained from a global positioning systems (GPS) using novel time based triggering logic (TBTL) implemented in field programmable gate arrays (FPGA). This system ignores non-useable (not synchronized) data caused by flywheel 1PPS from GPS receiver due to any short-term loss of satellite signals which eventually reduces the PD location accuracy. Furthermore TBTL also ignores spurious triggering pulses radiated from noise sources within the substation. With the use of a communication link between two ends of the cable provided via mobile broadband together with TBTL, eliminated the acquisition of non-useable(not synchronized) data. Based on laboratory tests and on-site measurements PD location accuracy of less than ± 10 m can be achieved. The system design, laboratory tests and on-site measurements are discussed.

IEEE 1588 based time synchronization system for a seafloor observatory network

An IEEE 1588 based application scheme was proposed to achieve accurate time synchronization for a deep seafloor observatory network based on the communication topological structure of the Zhejiang University Experimental and Research Observatory. The principles of the network time protocol (NTP) and precision time protocol (PTP) were analyzed. The framework for time synchronization of the shore station, undersea junction box layer, and submarine science instrument layer was designed. NTP and PTP network signals were decoded by a PTP master clock on a shore station that receives signals from the Global Positioning System and the BeiDou Navigation Satellite System as reference time sources. These signals were remotely transmitted by a subsea optical-electrical composite cable through an Ethernet passive optical network. Accurate time was determined by time synchronization devices in each layer. Synchronization monitoring experiments performed within a laboratory environment indicated that the proposed system is valid and has the potential to realize microsecond accuracy to satisfy the time synchronization requirements of a high-precision seafloor observatory network.

High-Accuracy TDOA-Based Localization without Time Synchronization

Localization is of great importance in mobile and wireless network applications. Time Difference of Arrival (TDOA) is one of the widely used localization schemes, in which the target (source) emits a signal and a number of anchors (receivers) record the arriving time of the source signal. By calculating the time difference of different receivers, the location of the target is estimated. In such a scheme, receivers must be precisely time synchronized. But time synchronization adds computational cost, and brings errors which may lower localization accuracy. Previous studies have shown that existing time synchronization approaches using low-cost devices are insufficiently accurate, or even infeasible under high requirement for accuracy. In our scheme (called Whistle), several asynchronous receivers record a target signal and a successive signal that is generated artificially. By two-signal sensing and sample counting techniques, time synchronization requirement can be removed, while high time resolution can be achieved. This design fundamentally changes TDOA in the sense of releasing the synchronization requirement and avoiding many sources of errors caused by time synchronization. We implement Whistle on commercial off-the-shelf (COTS) cell phones with acoustic signal and perform simulations with UWB signal. Especially we use Whistle to localize nodes of large-scale wireless networks, and also achieve desirable results. The extensive real-world experiments and simulations show that Whistle can be widely used with good accuracy.

Beyond OFDM: Best-Effort Dynamic Spectrum Access Using Filterbank Multicarrier

Orthogonal frequency division multiplexing (OFDM), widely recommended for sharing the spectrum among different nodes in a dynamic spectrum access network, imposes tight timing and frequency synchronization requirements. We examine the use of filterbank multicarrier (FBMC), a somewhat lesser known and understood alternative, for dynamic spectrum access. FBMC promises very low out-of-band energy of each subcarrier signal when compared to OFDM. In order to fully understand and evaluate the promise of FBMC, we first examine the use of special pulse-shaping filters of the FBMC PHY layer in reliably transmitting data packets at a very high rate. Next, to understand the impact of FBMC beyond the PHY layer, we devise a distributed and adaptive medium access control (MAC) protocol that coordinates data packet traffic among the different nodes in the network in a best-effort manner. Using extensive simulations, we show that FBMC consistently achieves at least an order of magnitude performance improvement over OFDM in several aspects including packet transmission delays, channel access delays, and effective data transmission rate available to each node in static, indoor settings. Using measurements of power spectral density and high data rate transmissions from a transceiver that we build using our National Instruments hardware platform, we show that while FBMC can decode/distinguish all the received symbols without any errors, OFDM cannot. Finally, we also examine the use of FBMC in a vehicular network setup. We find that FBMC achieves an order of magnitude performance improvement over large distances in this setup as well. Furthermore, in the case of multihop vehicular networks, FBMC can achieve about 20 × smaller end-to-end data packet delivery delays and relatively low packet drop probabilities. In summary, FBMC offers a much higher performing alternative to OFDM for networks that dynamically share the spectrum among multiple nodes.

Measurement of Baseline and Orientation between Distributed Aerospace Platforms

Distributed platforms play an important role in aerospace remote sensing, radar navigation, and wireless communication applications. However, besides the requirement of high accurate time and frequency synchronization for coherent signal processing, the baseline between the transmitting platform and receiving platform and the orientation of platform towards each other during data recording must be measured in real time. In this paper, we propose an improved pulsed duplex microwave ranging approach, which allows determining the spatial baseline and orientation between distributed aerospace platforms by the proposed high-precision time-interval estimation method. This approach is novel in the sense that it cancels the effect of oscillator frequency synchronization errors due to separate oscillators that are used in the platforms. Several performance specifications are also discussed. The effectiveness of the approach is verified by simulation results.

Time synchronization over ethernet passive optical networks

Time synchronization is critical when using Ethernet passive optical networks as a mobile backhaul to support time-sensitive services. This article presents an overview of time synchronization methods over EPON. It outlines the requirements and challenges particular to the EPON link delay asymmetry, and presents the technical solution recently approved by IEEE. Performance analysis and prototype results demonstrate that this technical solution meets various time synchronization requirements. The article then reviews the major standard efforts on EPON time synchronization that employ this solution, IEEE Std 802.1ASTM-2011 Clause 13. With this standard in place, EPON can play its part in time distribution networks.

PKC Based Broadcast Authentication using Signature Amortization for WSNs

Public Key Cryptography (PKC) is widely used for broadcast authentication. Intensive use of PKC for broadcast authentication, however, is thought to be expensive to resource constrained sensor nodes. In this paper, we propose a novel PKC based broadcast authentication scheme using signature amortization for Wireless Sensor Networks (WSNs). The proposed scheme exploits only one Elliptic Curve Digital Signature Algorithm (ECDSA) signature to authenticate all broadcast messages. Thus, the overhead for the signature is amortized over all broadcast messages. Besides low overhead, the proposed scheme retains high security that is as strong as conventional PKC based broadcast authentication schemes. Moreover, the proposed scheme can achieve immediate authentication and does not require time synchronization. For the implementation of the proposed scheme, an efficient public key distribution protocol is also presented in this paper. Experimental results of a testbed show that the overhead for authenticating a broadcast message is reduced significantly.