Contribution to COBS synchronization with PTP IEEE std. 1588

Pallares, Oriol; Cadena-Munoz, Javier; Carreras, Normandino; Toma, Daniel Mihai; Río, Joaquín Del

doi:10.1109/oceans-bergen.2013.6607958

Cited by 4 publications

(9 citation statements)

References 4 publications

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“…According to [51,52] in order to estimate the Hurst exponent of a time series ( denotes vector of [ 1] data set), we should execute the following process.…”

Section: F Calculationmentioning

confidence: 99%

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Maximum Likelihood Estimation of Clock Skew in IEEE 1588 with Fractional Gaussian Noise

Levy

Pinchas

2015

Mathematical Problems in Engineering

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To support system-wide synchronization accuracy and precision in the sub-microsecond range without using GPS technique, the precise time protocol (PTP) standard IEEE-1588 v2 is chosen. Recently, a new clock skew estimation technique was proposed for the slave based on a dual slave clock method that assumes that the packet delay variation (PDV) in the Ethernet network is a constant delay. However, papers dealing with the Ethernet network have shown that this PDV is a long range dependency (LRD) process which may be modeled as a fractional Gaussian noise (fGn) with Hurst exponent (H) in the range of0.5<H<1. In this paper, we propose a new clock skew estimator based on the maximum likelihood (ML) technique and derive an approximated expression for the Cramer-Rao lower bound (CRLB) both valid for the case where the PDV is modeled as fGn (0.5<H<1). Simulation results indicate that our new clock skew method outperforms the dual slave clock approach and that the simulated mean square error (MSE) obtained by our new proposed clock skew estimator approaches asymptotically the developed CRLB.

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“…According to [51,52] in order to estimate the Hurst exponent of a time series ( denotes vector of [ 1] data set), we should execute the following process.…”

Section: F Calculationmentioning

confidence: 99%

“…Recently, the topic of synchronization in network nodes has attracted significant attention for a number of applications [1][2][3][4][5][6][7][8][9][10]. In many cases the global positioning system (GPS) is used to synchronize frequency and time accuracy in the sub-microsecond range.…”

Section: Introductionmentioning

confidence: 99%

Maximum Likelihood Estimation of Clock Skew in IEEE 1588 with Fractional Gaussian Noise

Levy

Pinchas

2015

Mathematical Problems in Engineering

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“…Moreover, the moored OBS has been validated with the cabled seismometer station of OBSEA [ 16 ] which detected the same seismic event as illustrated in Figure 13 . This cabled seismometer station is based on the Trillium 120P/PA broadband seismometer together with the Taurus data logger provided by Nanometrics Inc, and a GPS emulator developed with a Stellaris microcontroller [ 4 ].…”

Section: Resultsmentioning

confidence: 99%

“…The design consists of a seafloor OBS with a broadband sensor unit and a surface buoy connected to a cable with an intermediate buoy ( Figure 1 ). The validation of this prototype seismic system was done, comparing the data with the existing OBSEA seismometer [ 4 ]. The seismic system continuously transmits data to a controller in the surface buoy, at a rate of 1000 bps through an inductive link provided by two inductive modems [ 10 ] attached to the mooring line as illustrated in Figure 1 .…”

Section: Standalone Broadband Ocean Bottom Systemmentioning

confidence: 99%

“…Monitoring the regional seismic events in real time makes it possible to achieve fast estimation of actual earthquake scales, since the measured seismicity directly gives us the true size of the earthquake. In the last decade, various technologies have been proposed and tested to address this challenge, such as cabled Ocean Bottom Seismometers (OBSs) [ 1 , 2 , 3 , 4 ], OBSs acoustically linked to surface buoys or surface vehicles [ 5 , 6 ] and free-floating buoys [ 7 ]. Although a permanent array of wired OBSs can be considered as the best technology for seismic surveys, having practically unlimited power and data transmission bandwidth, it is very expensive to implement and its deployment is restricted to the locations where such cable observatories can be deployed.…”

Section: Introductionmentioning

confidence: 99%

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Real-Time Seismic Data from the Bottom Sea

Roset

Trullols

Artero-Delgado

et al. 2018

Sensors

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An anchored marine seismometer, acquiring real-time seismic data, has been built and tested. The system consists of an underwater seismometer, a surface buoy, and a mooring line that connects them. Inductive communication through the mooring line provides an inexpensive, reliable, and flexible solution. Prior to the deployment the dynamics of the system have been simulated numerically in order to find optimal materials, cables, buoys, and connections under critical marine conditions. The seismometer used is a high sensitivity triaxial broadband geophone able to measure low vibrational signals produced by the underwater seismic events. The power to operate the surface buoy is provided by solar panels. Additional batteries are needed for the underwater unit. In this paper we also present the first results and an earthquake detection of a prototype system that demonstrates the feasibility of this concept. The seismometer transmits continuous data at a rate of 1000 bps to a controller equipped with a radio link in the surface buoy. A GPS receiver on the surface buoy has been configured to perform accurate timestamps on the seismic data, which makes it possible to integrate the seismic data from these marine seismometers into the existing seismic network.

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Time synchronization in underwater acoustic sensor networks

Pallarés Valls

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This thesis deals with the development of a time synchronization algorithm for underwater sensor networks. The ease of deployment and maintenance of wireless networks leaded this research to the use of an acoustic communication sensor network to share a common base time between all nodes. Acoustic signals are well adapted to the underwater medium but experience very challenging impairments such as Doppler, extensive multi-paths and low transmission speed that can nevertheless be corrected at the reception side. Several acoustic waveforms can be invoked to transmit digital data through the underwater medium, without loss of generality, in this study is considered Orthogonal Frequency- Division Multiplexing (OFDM) communication scheme to exchange data between wireless underwater nodes containing sensor time references. This communication link will be used among others to carry time stamp message required for network synchronization. Time synchronization is a critical piece of infrastructure of any distributed system. UWSN make extensive use of synchronized time for many services provided by a distributed network. In UWSN, Global Positioning System (GPS) signals are not available and synchronization systems are mostly based on acoustic communication. Owing to high latency of the underwater acoustic transmission channel with respect to cabled or radio network makes the use of conventional synchronization protocols even more challenging underwater. Many time synchronization algorithms for underwater wireless sensor networks (UWSN) can be found in literature, such as TSHL, D-SYNC, DA-Sync. but only a few of them take into account all the water channel challenges, such as low available bandwidth, long propagation delays and sensor node mobility. To solve this problem, in this research a further development of the existing time synchronization protocols found in literature is driven. To perform time synchronization we apply Precision Time Protocol (PTP) std. IEEE 1588, which is capable to synchronize two clocks with a precision below hundreds of nanoseconds in a point to point cabled Ethernet Network, and DA-Sync protocol, which is a bidirectional message exchange based method between a master clock and an slave one, and refines its time synchronization parameters by using medium kinematic models. In cabled synchronization systems, such as PTP, time stamps are acquired in physical layer (PHY) in order to achieve maximum precision, avoiding indeterministic time like Operating System (OS) time slots or medium access protocols. Analogously, it happens in acoustic communication, time stamps are extracted from a large acquisition window, and the improvement of these time stamps is treated in this thesis. Contrary to cable networks, the low celerity of wave sound makes underwater acoustic communications system very sensitive to Doppler effect, yielding to non-uniform frequency scaling represented by compression or dilatation of the time axis. This frequency scaling can be induced by two factors: motion (sensor mobility, channel variation, etc...) and clock skew receiver between transmitter and receiver. Actually, in order to address this problem, some systems uses expensive inertial sensors for compensating Doppler scaling due to motion and temperature compensated low drift clocks. So in this thesis is evaluated the Doppler scaling caused by motion and skew in order to correct it. Finally, several tests in the laboratory, test tank, and at sea are performed in order to check the performance of acoustic communication and time synchronization. Results show a correct behavior of hardware and software, and also validate the performance of the time synchronization applied to acoustic UWSN. La sincronización temporal es una pieza clave de cualquier sistema distribuido. Las redes de sensores submarinas hacen uso de los sistemas de sincronización entre nodos para diversos servicios disponibles en cualquier red distribuida. Cabe mencionar que en las redes submarinas, las señales GPS (Global Positioning System) no están disponibles para la referencia temporal, y los sistemas de sincronización se tienen que basar principalmente en comunicaciones acústicas. Además, debido a la alta latencia de dichas redes, la portabilidad de protocolos de sincronización cableados o terrestres, es prácticamente imposible debido a las grandes diferencias de velocidades de propagación de las ondas electromagnéticas frente a las acústicas en el medio marino. Las señales acústicas se adecúan bien al medio submarino, pero presentan una serie de inconvenientes como el efecto Doppler, largas trayectorias multi-camino, además de una velocidad de transmisión baja, que han de ser corregidos en el equipo receptor. Se ha elegido el uso de "Orhtogonal Frequency-Division Multiplexing" (OFDM) como esquema de comunicaciones para el intercambio de datos entre nodos inalámbricos que tienen las bases temporales de cada uno de sus sensores. Este link de comunicaciones será usado, entre otros, para propagar los marcajes de tiempos entre mensajes necesarios para la sincronización de la red. En la literatura se pueden encontrar varios sistemas de sincronización para redes de sensores submarinas basadas en comunicación acústica como TSHL, D-SYNC, DA-Sync, pero sólo unos pocos tienen en cuenta toda la problemática del medio marino, como el bajo ancho de banda, los largos tiempos de propagación, o la movilidad de los sensores. Para resolver esta problemática de la sincronización temporal se ha empleado como referencia "Precision Time Protocol" (PTP) std. IEEE 1588, el cual es capaz de sincronizar dos relojes en una red cableada punto a punto con una precisión por debajo de los centenares de nanosegundos. Además se han empleado sistemas de mejora de la precisión temporal basados en ecuaciones cinemáticas de los nodos, tal y como se presenta en el estudio DA-Sync. En el protocolo PTP, los marcajes de tiempo se realizan en la capa física con el propósito de lograr la mayor precisión posible, ya que de este modo se evitan incertidumbres debidas a las temporizaciones de los sistemas operativos, o los algoritmos de acceso al medio. Análogamente, en esta tesis se presenta un sistema de marcaje de tiempos que extrae mediante hardware el marcaje temporal del inicio de la adquisición de datos. Difiriendo de las redes cableadas, la baja velocidad de propagación de las ondas acústicas en el medio marino hace que la comunicación sea altamente sensible al efecto Doppler, resultando en escalados frecuenciales no uniformes, que afectan a la base temporal dilatándola o comprimiéndola. Este escalado de frecuencia puede deberse a dos factores: movimiento (movimiento de sensores, variaciones del canal, etc.) o derivas del reloj de un nodo frente a otro nodo. Actualmente, para resolver este problema, algunos sistemas utilizan sistemas inerciales muy costosos para estimar el movimiento del sensor y relojes compensados por temperatura. En esta tesis se ha utilizado la información del canal respecto al escalado Doppler, además de las ecuaciones cinemáticas de primer orden, para estimar la movilidad y la deriva de los relojes. Finalmente, varios tests en laboratorio, tanque de agua, y experimentación en el mar son presentados para verificar el correcto funcionamiento de ambos sistemas de comunicación y sincronización. Los resultados validan el funcionamiento de todos los algoritmos software y del hardware, además de verificar el funcionamiento del sistema de sincronización aplicado a redes de sensores submarinas con comunicación acústica.

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Contribution to COBS synchronization with PTP IEEE std. 1588

Cited by 4 publications

References 4 publications

Maximum Likelihood Estimation of Clock Skew in IEEE 1588 with Fractional Gaussian Noise

Maximum Likelihood Estimation of Clock Skew in IEEE 1588 with Fractional Gaussian Noise

Real-Time Seismic Data from the Bottom Sea

Time synchronization in underwater acoustic sensor networks

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