Time, its scales and part in satellite navigation systems. Czas, jego skale i udział w Nawigacyjnych Systemach Satelitarnych


 Marilynn Stokes
 3 years ago
 Views:
Transcription
1 Scientific Journals Maritime University of Szczecin Zeszyty Naukowe Akademia Morska w Szczecinie 2010, 20(92) pp , 20(92) s Time, its scales and part in satellite navigation systems Czas, jego skale i udział w Nawigacyjnych Systemach Satelitarnych Jacek Januszewski Gdynia Maritime University, Faculty of Navigation, Ship Operation Department Akademia Morska w Gdyni, Wydział Nawigacyjny, Katedra Nawigacji Gdynia, al. Jana Pawła II 3, Key words: timescales, time dilution of coefficient (TDOP), timesystems Abstract There are different scales related to time; actually two the most important timescales are the TAI (Time Atomic International) and the UTC (Universal Time Coordinated). In addition to these times Satellite Navigation Systems (SNS) have developed their own system time: GPS Time (GPST), the GLONASS System Time (GLONASSST) and the Galileo System Time (GST). The sources, the generation and the relation between all these times and timescales are described in this paper. Additionally the time dilution of precision (TDOP) coefficient and the data concerning the time transmitted in navigation messages by satellites of different SNS will be presented. Słowa kluczowe: skale czasu, współczynnik dokładności pozycji użytkownika (TDOP), systemy czasu Abstrakt Z czasem związane są różne skale, ale dwie najważniejsze z nich to TAI (Międzynarodowa Skala Atomowa) i UTC (Czas Uniwersalny Skoordynowany). Nawigacyjne Systemy Satelitarne (NSS) stworzyły jednak własne skale czasu: GPST czas systemu GPS, GLONASSST czas systemu GLONASS i GST czas systemu Galileo. W artykule omówiono źródła, pochodzenie i relacje zachodzące między wszystkimi ww. czasami i skalami. Dodatkowo opisano współczynnik dokładności pozycji użytkownika TDOP oraz te parametry dotyczące czasu, które są przekazywane w depeszach nawigacyjnych satelitów poszczególnych systemów. Introduction Time is a component of the measuring system (e.g. satellite navigation system) used to sequence events, to compare the events and the intervals between them (e.g. time of signal propagation between satellite and terrestrial receiver), and to quantify the motions of objects. The use of atomic properties for time measurements was born in 1955 when the first cesium beam frequency standard began regular operation in the United Kingdom [1]. As nowadays the satellite position fix is based on pseudorange measurements (apparent transit time of the signal from a satellite to the receiver), the knowledge of all used universal and atomic time scales and the relation between them is very important for all users of Satellite Navigation Systems (SNS). This transit time is defined as the difference between signal reception time, as determined by the receiver clock, and the transmission time at the satellite, as market on the signal. SNS is also a timing system, that is, it can be used for time synchronization. Universal and Atomic Time scales Two basic groups of time scales are of importance in satellite navigation systems: Universal Time, connected with the diurnal rotation of Earth. The timedependent orientation of Earth with respect to the inertial space is required in order to relate the Earthbased observations to a spacefixed reference frame. UT is a modern continuation of Greenwich Mean Time (GMT); 52 Scientific Journals 20(92)
2 Time, its scales and part in satellite navigation systems Atomic Time, related to phenomena in nuclear physics. The precise measurement of signal travel times, e.g. pseudorange in satellite navigation systems, requires a uniform and easily accessible time scale with high resolution. The third basic groups of time scales, Ephemeris (Terrestrial) Time, important in satellite geodesy, in particular, is derived from the orbital motion of celestial bodies around the Sun. All these time scales are based on the observation of uniform and repetitive astronomical or physical phenomena. Universal Time (UT) family Before the acceptance of atomic scales astronomical time scales were used for everyday timekeeping. Although astronomical times are no longer the best measure of time, they continue to play a role in current research. These time scales are still used today, but mostly for applications related to astronomy. UT is witness to the Earth s rotation, whilst serving also to establish Coordinated Universal Time (UTC). They are based on mean solar time. The mean solar second provides the basis for Universal Time (UT). We can distinct three principal variations of UT [2, 3]: UT0, the original mean solar time scale, based on the rotation of the Earth on its axis; UT1, the principal form of UT, the most widely used astronomical time scale, it is an improved version of UT0 with corrections added for polar motion. UT1 is the same everywhere on Earth. The correction from UT0 to UT1 is at most about s. The current version of UT1 (since 2003, namely sometimes UT1R) is exactly what is needed for geophysical investigations. It permits evaluation of the length of the day with a precision that revels changes due to storm systems and changes in ocean currents. UT1 drifts with respect to atomic time. This is on the order of several milliseconds per day and can accumulate to 1 second in a 1 year period; UT2, a smoothed version of UT1 by adding an empirical formula to remove the effect of the annual seasonal variations in the rotation of the Earth. It is mostly of historic interest and rarely used anymore. Atomic Time family Atomic time scales are derived from groups of commercial and laboratory cesium standards which generate time intervals, based on the definition of the International System of Units (SI). The definition of the second atomic time scale, related to Cesium 133 atom, has been worked by the 13 th Conference of the International Committee of Weights and Measures BIPM (Bureau International des Poids et Mesures) in Paris, We can put the question why in this definition the number of the periods of the radiation is equal 9,192,631,770? Because it corresponded exactly with the previous definition of the second, the ephemeris second. In practice, atomic time scale are derived from groups of commercial and laboratory cesium standards which generate time intervals, based on the definition of the SI second. The time scale based on atomic standards is called International Atomic Time (TAI). TAI is a uniform time scale based on the atomic second, which is defined as the fundamental unit of time in the International System of Units. TAI is the continuation of time scales which began with the first cesium atomic clock in 1955 which is not tied to the earth s rotation on its axis or its revolution around the Sun. TAI is computed as the weighted mean of individual clocks. Therefore TAI is a statistically formed common time scale for international use. TAI is referred to as a paper time scale since it is not kept by a physical clock. The value all existing atomic time scales was equal to that of UT2 on January 1, 1958, but that date was before highprecision international coordination of time had begun. The name TAI was officially proposed in 1970 and adopted in Due to the deceleration of Earth s rotation the difference between TAI and UT scales is increasing. The difference between TAI and UT1, for some selected dates, is presented in the table 1. We must say that large size of these differences stems from the fact that the unit of the SI second was adopted from the length of the ephemeris second. The latter was derived from the mean duration of the solar day between 1756 and 1895, when Earth s rotation was faster than today [4]. Nowadays there are two different time scales and two seconds definitions, universal and atomic, while one time scale is required only. This new scale must provide both a highly uniform time unit and the best possible adaptation to UT1, and hence to Earth rotation. Table 1. The difference TAI UT1 for selected dates [4] Tabela 1. Różnica między TAI i UT1 w wybranych dniach [4] Difference [s] Date +6.1 January 1, January 1, January 1, January 1, January 1, January 1, 2003 Zeszyty Naukowe 20(92) 53
3 Jacek Januszewski That s why, in January 1, 1972, a compromise time scale, Universal Time Coordinated (UTC), was introduced. UTC has been run according to the guidelines in Recommendation ITU R TF of the International Telecommunication Union (ITU) [1]. The definition of the UTC second is the same as that for atomic time, and is based on the cesium atom. UTC is now the scale for public time throughout the world. We can say that this is the new GMT. The acronym UTC is an EnglishFrench mixture for Coordinated Universal Time (CUT) in English or Temps Universal Coordonne (TUC) in French. It was internationally agreed to write Universal Coordinated Time as UTC, rather than CUT or TUC, making it language independent. UTC was set to agree with UT1 at 00 hours on January 1, At first the two time scales were kept close by introducing 0.1 second steps in UTC, as needed. Since 1972, changes in the Earth s spin rate have been accommodated by introducing leap second (p. 1.3) in UTC. This time is thus obtained by periodically adding or subtracting one second from TAI in order to build up a reference time that follows the Earth s rotation. That s why nowadays UTC and TAI differ by an integer number n of seconds: UTC = TAI n (1 s) (1) On 1 January 1972, TAI UTC was equal to 10 s. At the time of this writing (February 2010) the difference between TAI and UTC was: TAI UTC = +34 s (2) UTC is generated after the fact on the basis of the times kept by about 250 cesium clocks and hydrogen masers located at about 65 different laboratories located around the world. In the United States, UTC estimates are generated by the National Institute of Standards & Technology (NIST), Boulder, Colorado, and the United States Naval Observatory (USNO), Washington, D.C. Both institutions are charged with supplying time and frequency to the U.S. government and BIPM. Their UTC estimates are referred as UTC (USNO) and UTC (NIST). Other countries have similar institutional arrangement to their national time standards, which serve as the basis for realtime estimates of UTC. It takes BIPM about a month to collect and process the data to generate TAI and UTC. A monthly bulletin from BIPM reports the time difference that existed between each of the contributing clocks and UTC [5]. Differences between TAI and UTC since 1 January, 1972 (from the beginning of UTC) to the time of this writing is given in the table 2. Table 2. Difference Δt between TAI and UTC in years (in seconds) Tabela 2. Różnica Δt między TAI a UTC w latach (w sekundach) From to Δt From to Δt The USNO determines and distributes the timing and astronomical data required for accurate navigation and fundamental astronomy, and maintains a UTC time scale that is (by mutual agreement) within 100 ns of UTC(NIST) [3, 5]. In different countries around the world, local time is attached to UTC corrected by a whole number of hours. This is sometimes stipulated by written law (e.g. in France). Legal institutions sometimes prefer to use the national approximation to UTC, e.g. in Germany. There are countries where UTC is not legally recognised, although it is actually used, since no other time scale is readily available [1]. The still widespread use of the acronym GMT is not correct when it is intended to refer to UTC, as it is the case when expressing the time in general usage. After steering corrections, TAI is known from the values of TAI UTC(k) at standard dates. Each laboratory k has a master clock which supplies an approximation UTC(k) to UTC. This clock serves as a reference for all local dating procedures. BIPM publishes the values of UTC UTC(k) every month in its Circular T, available by electronic mail. Apart from this, by tracking GPS and GLONASS satellites for time comparisons, values of UTC GPS time and UTC GLONASS time are provided with similar uncertainties to those in UTC UTC(k). Time signal emissions conform as closely as possible to UTC. An ITU recommendation fixes a tolerance of 1 ms. In reality, the discrepancy is much smaller than this. It is also recommended 54 Scientific Journals 20(92)
4 Time, its scales and part in satellite navigation systems that the carrier frequency be tuned to the TAI frequency, with relative frequency offset less than [1]. Leap seconds A leap second is a second added to UTC time scale to keep the difference between UT1 and UTC to within ± 0.9 second. The introduction of one positive or negative leap second must be made at the end of a UTC month, preferably at the end of December or June, otherwise at the end of March or September. The first leap second was inserted on June 30 th, Since then, they have occurred at an average rate of less than one per year. All 24 leap seconds were positive, 9 were inserted on June 30 th, 15 on December 31 st. In February 2010 the 5 last leap seconds were added on December 31 st, 1995, June 30 th, 1997, December 31 st, 1998, December 31 st, 2005 and December 31 st, Dates for leap seconds are fixed by the International Earth Rotation Service (IERS) and announced at least 8 weeks beforehand. The announcement appears in IERS s Bulletin C. This bulletin is updated every six months, either to announce a time steep in UTC, or to confirm that there will be no time step at the next possible date. The probability that negative leap second will be needed is almost zero. Leap seconds are primarily for the benefit of astronomers: they keep UTC synchronized with the orbits of the stars and planets. If there were no leap seconds, then in about years from now, the sun would seem to be rising an hour late [6]. Information about the leap seconds can be found at the U.S. Naval Observatory Web site, usno.navy.mil. The current value of UT1 UTC is called the DUT1 correction (DUT1 = ± N 0.1 seconds, where N is a digit between 1 and 8) and is obtained from Time Section of the BIPM. The resolution of the DUT1 correction is 0.1 s, and represents an average value for an extended range of dates. Values of DUT1 and their application date are provided one month beforehand by the IERS and they are the same for all emissions. DUT1 corrections are broadcast among other things by the stations of NIST, as WWV, WWVH, and WWVB. The corrections values of DUT1 at 0000UTC of the selected days can be found in the vol. 2 of ALRS [7], e.g. on Mars 15, 2007 DUT1 was 0.1 s, on June 14, 2007 it was 0.2 s. The knowledge of these corrections allows the user to correct the value of disseminated UTC. Satellite navigation systems time scales While most clocks in the world are synchronized to UTC, the atomic clocks on the satellites are set to own SNS time. GPS System Time (GPST) GPS uses its own particular, continuous time scale GPS System Time (GPST). It differs from UTC by a nearly integer number of seconds: GPS time UTC = n s C t (3) where: n is an integer number, and the correction term C t is in the order of several nanoseconds. GPS system is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections which are periodically added to UTC. GPST is specified to be maintained to within one microsecond modulo integral seconds, and for the past ten years it has been maintained to within ( 25 ns) of this goal [8]. GPST is steered to UTC(USNO) on a daily basis. Over last several years GPST was kept within a few tens of ns from UTC(USNO) and TAI (modulo 1 second) [9]. GPST and UTC(USNO) were coincident at 0 h January 6, As at this moment the difference between TAI and UTC was 19 seconds, GPST remains at a constant offset with TAI: TAI GPS time = 19 seconds (4) At the time of this writing (February 2010) the difference between GPST and UTC was 15 seconds. Therefore the reception of GPS signals provides realtime access to TAI and UTC with uncertainties below 1 microsecond [4]. The GPST is also a paper time scale; it is based on statistically processed readings from the atomic clocks in the satellites and at various ground control segment components. This time, defined by the Control Segment, is generated from all the atomic clocks of the system, including those in the satellites. The GPS satellites have rubidium (Rb) and cesium (Cs) atomic clocks onboard (today s satellites block IIa have 2 Cs + 2 Rb, blocks IIR and IIR M have 3 Rb). These are kept within a millisecond of the master clocks at the GPS master control station. The largest unit used in stating GPS time is one week, defined as seconds where seconds is at Saturday / Sunday midnight GPS Time. Each week at this time, the week number increments by one, and the seconds into week resets to 0. Zeszyty Naukowe 20(92) 55
5 Jacek Januszewski Therefore as opposed to the year, month, and day format of the Gregorian calendar, the GPS date is expressed as a week number (WN) and a day of week number. The WN is transmitted as a tenbit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1024 weeks (2 10 = 1024). GPS week zero started at 00:00:00 UTC (00:00:19 TAI) on January 6, 1980, and WN became zero again for the first time at 23:59:47 UTC on August 21, 1999 (00:00:19 TAI on August 22, 1999). At this moment the difference between TAI and UTC was 32 seconds. The number of days passed since August 21, 1999, divided by 7 gives the WN, e.g. week 512 is from 15th to 21st June. In navigation message the data concerning time are transmitted in the first two and the last two subframes. Ephemeris parameters in subframe 1 contain estimated group delay differential (eightbit information about clock correction term) and four additional satellite clock correction parameters. Ephemeris parameters in subframe 2 contain reference time ephemeris. The almanac data provided in subframes 4 and 5 contain data time also, reference time almanac (time of applicability) and two satellite clock correction parameters. The 8 parameters providing the translation of GPST to UTC time are in page 18 of subframe 4 [10]. All these parameters time permit to calculate the GPST of transmission from the satellite, which will be used for calculation of its position and time of signal propagation from satellite to the user. The problem of keeping precise time and synchronizing clocks that are separated by considerable distances is an old one. The Transit, the first SNS, as terrestrial radionavigation systems (e.g. Loran C) were capable of time transfer with an accuracy level of about 1 milisecond. With the current techniques, GPS can distribute time with an accuracy of about 30 ns, and can compare remote clocks with an accuracy of about 5 ns [5]. GLONASS System Time (GLONASSST) GLONASS time, base on an atomic time scale similar to GPS, is strongly liked to the National time scale of Russian Federation UTC(SU) which is maintained by the Main Metrological Center of the Russian Time and Frequency service at Mendeleevo in the Moscow region. On other hand GLONASS system itself is the most powerful and accurate mean of UTC(SU) dissemination through out Russia and the world. That s why one of requirements of GLONASS updates is to keep UTC UTC(SU) difference within 10 ns [11]. Unlike the GPS time scale, GLONASS system time currently implements leap seconds, like UTC, and it has a constant offset of three hours (difference Moscow time to Greenwich time). This time is generated and controlled by the GLONASS Central Synchronizer, based on a set of hydrogen masers. The relation between UTC and GLONASSSTS is: UTC = GLONASS time + τ c 3 h (5) The discrepancy, τ c, comes from the different clock ensembles used and is communicated to the GLONASS users in frame 5 of the GLONASS navigation message [4]. GLONASS time is maintained within 1 ms, and typically better than 1 microsecond (μs) of UTC(SU) by the control segment with the remaining portion of the offset broadcast in the navigation message [12]. All GLONASS satellites use cesium atomic clocks. In navigation message the data concerning time are transmitted in the immediate data which include time marks and synchronization difference between satellite clock and GLONASS time, and in the nonimmediate data which include raw clock corrections to the GLONASS time and the GLONASS time correction relative to UTC(SU). Galileo System Time (GST) Galileo System Time (GST), modulo 1 second, is planned to be steered to a prediction taken from a number of UTC laboratories obtained through an external Galileo time service provider. GST is specified to be kept to within 50 ns (95%) of TAI over any 1 year time interval. The offset between TAI and GST will be known with a maximum uncertainty of 28% (2 sigma), assuming the estimation of TAI six weeks in advance. Users equipped with a Galileo timing receiver will be able to predict UTC to 30 ns for 95% of any 24 hours operation [13]. The GST is produced only with terrestrial clocks available in the two redundant Precise Time Facilities (PTF) of Galileo. PTF will host an active H maser (with necessary hotspares) and an ensemble of Cesium clocks, and steer the maser output to TAI. This steered time scale will serve as a physical representation of GST. Galileo will use a continuous reference time, like GPS. The first test Galileo satellite GIOVE A has on board rubidium atomic clock, the second satellite GIOVE B operates on hydrogen maser atomic clock, for the first time in history. The GST is optimized in order to achieve a very good shortterm stability required for the functions 56 Scientific Journals 20(92)
6 Time, its scales and part in satellite navigation systems associated with navigation. The use of satellite clocks, as in GPST, has two important aspects: the internal satellite clock s frequency drift and the inherent measurement error associated with satellite clocks. Both aspects would have had the effect of decreasing GST accuracy. Therefore, for meteorological aspects, comparisons with clocks external to Galileo will be used [14]. In Galileo navigation message the data concerning time are transmitted in each subframe, clock correction and GST status in the page 1, GST in the pages 2 and 3, GST UTC conversion, GST GPS conversion and Time of Week (TOW) in the page 4. Translation of SNS time to UTC/TAI UTC is obtained from GPS receiver, and in the future from Galileo receiver, by adding the integral number of leap seconds and fine UTC / TAI correction information contained in the navigation data. In order to provide an estimate of UTC from GPS, the navigation message broadcast by each GPS satellite includes estimates of the time difference between GPST and UTC(USNO) modulo one second, and its rate. The navigation message also includes the wholesecond difference between the two time scales due to leap seconds. These parameters allow a receiver clock to calculate an accurate estimate UTC(USNO). We know the time kept by a user s receiver clock, t u, and we want to generate UTC, t UTC. The latter can be defined from the following equation: t UTC = t u Δt u Δt UTC (6) where: Δt u is the receiver clock bias relative to GPST, and Δt UTC is the bias between GPST, t GPS, and UTC(USNO), t UTC. A GPS navigation receiver computes Δt u in order to schedule measurements, to time tag position estimates, and to timealign the measurements for precise relative positioning. The bias Δt UTC is equal: Δt UTC = t GPS t UTC (7) The USNO monitors Δt UTC and provides this information to the Control Segment. Its value can be computed at any instant (defined in GPST) from: Δt UTC = A 0 + A 1 (t GPS t 0U ) + Δt LS (8) where: A 0 and A 1 are constant and first order terms of polynomial, t 0U is reference time for UTC data, and Δt LS is the number of leap seconds added to UTC since 1980 (15 seconds as of 1 January 2009). The values of all these four parameters (A 0, A 1, t 0U and Δt LS ) are broadcast by each GPS satellite in its navigation message (page 18 of subframe 4). The time t GPS is equal: t GPS = t S Δt S (9) where t S is the time kept by a satellite clock, and Δt S is the satellite clock offset defined by: Δt S = α f0 + α f1 (t t 0c ) + α f2 (t t 0c ) 2 + Δt r (10) where: t 0c is the reference epoch, α f0 is the clock offset, α f1 is the fractional frequency offset, and α f2 is the fractional frequency drift. All these four parameters are broadcast by each GPS satellite in its navigation message (subframe 10), Δt r is the relativistic term calculated from other data. The rms error in estimation of Δt S and Δt UTC is currently estimated to be about respectively, 5 and 10 ns. As navigation receiver can estimate the receiver clock bias with a rms error of about 25 ns, the total error in direct time distribution from GPS is about 25 ns. Telecommunications applications typically require synchronization of multiple nodes with an accuracy of 100 ns, or better. Such synchronization can be achieved by setting up a GPS antenna at a fixed, surveyed location at each node, and determining time independently. With antenna position known, a GPS receiver can determine precise time by tracking one satellite only [5]. Time Dilution of Precision (TDOP) coefficient Dilution of Precision (DOP) terms represent the impact of the geometric scattering of the satellites, with respect to the receiver s position, on the position error, and hence on the accuracy of the positioning. There is a linear relation between DOP values and the resulting position accuracy for a given pseudorange error value σ UERE. We can distinct five DOP coefficients in common use which are useful to characterize the accuracy of various components of the position / time solution. One of these coefficients is TDOP (Time DOP) which value is defined by the quotient of the square root of the element of the covariance matrix and the speed of the radio wave. In some treatments, DOP is equal to the mentioned above square root only. In this case the variable c t b represents a range equivalent of the time bias error and σ ctb defined by the product TDOP σ UERE is its standard deviation [5, 8]. Zeszyty Naukowe 20(92) 57
7 Jacek Januszewski From among all DOP coefficients which depends on user s latitude, the least value has TDOP at equator. For a nominal GPS constellation (24 satellites fully operational), if all satellites are in view, TDOP coefficient can be less than 0.8 [15]. Satellite navigation system receivers time Satellite navigation systems receivers display the time in 12 hour or 24 hour notation, and the default setting is 24 hour notation. AM or PM is shown when 12 hour notation is selected. The time and date are in UTC or in Local Time (LT). The first time signalized by the receiver is UTC, but this receiver can also display LT. That s why the hour and minute, unlike second, can be changed by the user by entering a time difference from UTC. Some SNS receivers can show the time depending on season of the year, as summer time or winter time. Time synchronization related errors As any pseudo range error leads to user s position error we can also take into account synchronization errors. The problem of synchronization has to be clearly distinguished from those of precision or stability. Synchronization is related to the fact that all the SNS components deal with a common timescale. This is of primary importance when carrying out time measurements in the GNSS fields. We must remember the fact that 1 ns is equivalent to 30 cm. The synchronization of satellites clocks to GPS time is obtained from the navigation message. The problem of receiver synchronization must be carried out on a frequent time base [14]. Interoperability Interoperability of satellite navigation systems, as GPS, GLONASS and Galileo, and satellite based augmentation systems, as EGNOS and WASS can be defined as ability of each of these systems having independent control loop to operate jointly with other systems without interfering each other on condition that signal frequency ranges, coordinate reference frames and time reference frame coincide as much possible. Both GPST and GST are real time versions of the various UTC(k) laboratories they reflect. If the offset between these times is made available to user, interoperability is ensured. The GPS Galileo time offset will be easily determined or received by the user receiver. The U.S. and EU have agreed to have their satellites broadcast the GPS Galileo time offset in the future. The accuracy of this time offset modulo 1 second is specified to be less than 5 ns with 2sigma confidence interval over any 24 hour period. Once Galileo is operational (2015 or later), it is anticipated by many that most users will use a combined GPS and Galileo PNT (positioning, navigation, timing) service. There are two options for obtaining the GPS Galileo time offset [13]: the user is able to determine this offset in the position and navigation processing at the cost of one additional satellite tracked (fifth satellite when determining a three dimensional position); the offset could be measured by transitional time transfer techniques (e.g. two way, common way) or precisely estimated in near real time at the monitor station of both systems using a integrated GPS / Galileo receiver. Nowadays the difference between GPS time and GLONASS time is known with accuracy 30 ns, in the future 2 6 ns [7, 16]. When using GPS and GLONASS systems jointly, the difference in system time depends on the clocks from both systems and has to be taken into account. GPS Galileo Time Offset GPS Time and GST will be generated independently from each other. The residual offset between GST and GPS Time will be probably in the order of tens of nanoseconds. This GPS Galileo time offset (GGTO) will cause a bias between GPS and Galileo measurements taken by integrated receivers of these two systems. This will lead to an additional error in the user s navigation solution. A similar effect will appear when users correct pseudorange measurements to UTC using the broadcast offsets between GPS and Galileo reference time scales and UTC. At user level, GGTO can be estimated from GPS and Galileo measurements as an additional unknown in the user navigation solution. This would increase the dimension of the estimation problem, requiring at least five, and no four, measurements (pseudoranges) to be available to calculate user 3D position, time offset, and GGTO. At system level, GGTO can be determined by the GPS and Galileo ground segments, then predicted for the near future, and finally broadcast in the navigation messages to all users. Therefore the users can correct their observations with the received GGTO value and proceed with the classical navigation solution with four parameters; i.e. 3D position and time offset [9]. 58 Scientific Journals 20(92)
8 Time, its scales and part in satellite navigation systems Conclusions All time systems of GPS, GLONASS, and Galileo are based on UTC, but using individual realizations of UTC. Spending one satellite s observations enables a SNS receiver itself to solve for the time offset between two different satellite systems; typically the internal navigation system time (e.g. GPST, GLONASS System Time) is only used as a part of the navigation solution and is not considered as standard time product; with the current techniques, GPS system can distribute time with an accuracy of about 30 ns, and can compare remote clocks with an accuracy of about 5 ns; the GPS time is a paper time scale (computations performed at the Master Control Station), while Galileo System time is physically produced at Galileo Precise Timing Facility (PTF); the tendency is that most of modern navigation professional GPS equipment uses GPS time as the time base. Therefore, the translation from GPS time to UTC time may no longer be needed in modern receiver; GPS Galileo time offset (GGTO) can be determined at user level in the user receivers (at least five measurements are required) and at system level by GPS and Galileo systems and broadcast in the navigation message of both systems. Reference 1. AUDIN C., GUINOT B.: The Measurements of TimeTime, Frequency and the Atomic Clock, Cambridge University Press, Cambridge SEEBER G.: Satellite Geodesy, de Gruyter, Berlin / New York MISRA P., ENGE P.: Global Positioning System Signals, Measurements, and Performances, Ganga Jamuna Press, Lincoln VAN DIGGELEN F.: A GPS: Assisted GPS, GNSS, and SBAS, Artech House, Boston / London Admiralty List of Radio Signals. The United Kingdom Hydrographic Office, 2009, 10, vol KAPLAN E.D., HEGARTY C.J.: Understanding GPS Principles and Applications, Artech House, Boston / London MOUDRAK A. et al.: Interoperability on Time GPS Galileo Offset Will Bias Position, GPS World, 2005, Vol. 16, No BAOYEN TSUI J.: Fundamentals of Global Positioning System Receivers, John Wiley & Son Inc. New Jersey HAHN J., POWERS E.: GPS and Galileo Timing Operability, Global Navigation Satellite System Conference, Rotterdam SAMANA N.: Global Positioning, Technologies and Performance, John Wiley & Son Inc. New Jersey GROVES P.D.: Principles of GNSS, Inertial, and Multisensor integrated navigation systems, Artech House, Boston / London HEIN G.W. et al.: Envisioning a Future GNSS System of Systems, Part 2 Inside GNSS, 2007, Vol. 2, No. 2. Zeszyty Naukowe 20(92) 59
Best Practices for Leap Second Event Occurring on 30 June 2015
Best Practices for Leap Second Event Occurring on 30 June 2015 26 May 2015 Sponsored by the National Cybersecurity and Communications Integration Center in coordination with the United States Naval Observatory,
More informationSATELLITE TIMETRANSFER: RECENT DEVELOPMENTS AND PROJECTS
SATELLITE TIMETRANSFER: RECENT DEVELOPMENTS AND PROJECTS W. LEWANDOWSKI 1 and J. NAWROCKI 2 1 Bureau International des Poids et Mesures, Sèvres, France email: wlewandowski@bipm.org 2 Astrogeodynamical
More informationBureau International des Poids et Mesures. GNSS and UTC. W. Lewandowski
GNSS and UTC W. Lewandowski ITUBIPM Workshop Future of International Time Scale Geneve, 1920 September 2013 Outline of presentation A historical note Time scales Navigation on seas Global Navigation
More informationInternational time scales Atomic standards
International time scales Atomic standards E.F. Arias International Committee for GNSS, 2 nd Meeting Meeting of GNSS experts Bangalore, 5 September 2007 OUTLINE International coordination for metrology;
More informationCHAPTER 18 TIME TIME IN NAVIGATION
CHAPTER 18 TIME TIME IN NAVIGATION 1800. Solar Time The Earth s rotation on its axis causes the Sun and other celestial bodies to appear to move across the sky from east to west each day. If a person located
More informationLocal Sidereal Time is the hour angle of the First Point of Aries, and is equal to the hour angle plus right ascension of any star.
1 CHAPTER 7 TIME In this chapter we briefly discuss the several time scales that are in use in astronomy, such as Universal Time, Mean Solar Time, Ephemeris Time, Terrestrial Dynamical Time, and the several
More informationThe BIPM, the Time Department and UTC
The BIPM, the Time Department and UTC Elisa Felicitas Arias Fundamentals for a time and frequency laboratory BIPM, 11 September 2012 BUREAU INTERNATIONAL DES POIDS ET MESURES The BIPM It has headquarters
More informationGNSS Parameters. Position estimation uncertainties
GNSS Parameters Position estimation uncertainties Petr Bureš, bures@fd.cvut.cz Faculty of transportation sciences Czech technical university in Prague Contents Satellite systems in general Accuracy Position
More information1. GLOBAL NAVIGATION SATELLITE SYSTEMS
1. GLOBAL NAVIGATION SATELLITE SYSTEMS The Global Navigation Satellite System (GNSS) is a constellation of satellites, transmitting signals for use in navigation and positioning applications, anywhere
More informationHANDBOOK. Measuring System DESIGN EDITORS PETER H. SYDENHAM RICHARD THORN ARTICLE OFFPRINT
HANDBOOK OF Measuring System DESIGN EDITORS PETER H. SYDENHAM RICHARD THORN ARTICLE OFFPRINT 200: Calibrations and Standards in Time Measurement Michael A. Lombardi National Institute of Standards and
More informationCDMA Technology : Pr. S. Flament www.greyc.fr/user/99. Pr. Dr. W. sk www.htwgkonstanz.de. On line Course on CDMA Technology
CDMA Technology : Pr. Dr. W. sk www.htwgkonstanz.de Pr. S. Flament www.greyc.fr/user/99 On line Course on CDMA Technology CDMA Technology : CDMA / DS : Principle of operation Generation of PN Spreading
More informationRemote Calibration of a GPS Timing Receiver to UTC(NIST) via the Internet*
Remote Calibration of a GPS Timing Receiver to UTC(NIST) via the Internet* Michael A. Lombardi and Andrew N. Novick National Institute of Standards and Technology Boulder, Colorado lombardi@boulder.nist.gov
More informationA NEW ALGORITHM FOR CLOCK WEIGHTS FOR THE SIM TIME SCALE
Simposio de Metrología 202 82 de Octubre, 202 A NEW ALGORITHM FOR CLOCK WEIGHTS FOR THE SIM TIME SCALE 2 J. M. López R, M.A. Lombardi, N. Diaz, E. de Carlos L. División de Tiempo y Frecuencia, Centro
More informationThe Role of GPS in Precise Time and Frequency Dissemination
The Role of GPS in Precise Time and Frequency Dissemination Known primarily as a navigation system, the global positioning system is also used to disseminate precise time, time intervals, and frequency.
More informationGünter Seeber. Satellite Geodesy 2nd completely revised and extended edition
Günter Seeber Satellite Geodesy 2nd completely revised and extended edition Walter de Gruyter Berlin New York 2003 Contents Preface Abbreviations vii xvii 1 Introduction 1 1.1 Subject of Satellite Geodesy...
More informationTime and Clocks. Time and Clocks. Time
Time and Clocks Time: we model the continuum of realtime as a directed timeline consisting of an infinite set {T} of instants with the following properties: {T} is an ordered set, i.e., if p and q are
More informationDistributed Systems Theory 6. Clock synchronization  logical vs. physical clocks. November 9, 2009
Distributed Systems Theory 6. Clock synchronization  logical vs. physical clocks November 9, 2009 1 Synchronization: single CPU sys vs. dist sys. Single CPU: DS: critical regions, mutual exclusion, and
More informationComputer Time Synchronization
Michael Lombardi Time and Frequency Division National Institute of Standards and Technology Computer Time Synchronization The personal computer revolution that began in the 1970's created a huge new group
More informationComputer Time Synchronization
Michael Lombardi Time and Frequency Division NIST email: lombardi@boulder.nist.gov Computer Time Synchronization The personal computer revolution that began in the 1970's created a huge new group of time
More informationPseudorange Estimation; Receiver Position Computation; Receiver Data Formats
Pseudorange Estimation; Receiver Position Computation; Receiver Data Formats GPS Signals And Receiver Technology MM15 Darius Plaušinaitis dpl@gps.aau.dk Today s Subjects Pseudorange estimation Receiver
More informationSatellite Posi+oning. Lecture 5: Satellite Orbits. Jan Johansson jan.johansson@chalmers.se Chalmers University of Technology, 2013
Lecture 5: Satellite Orbits Jan Johansson jan.johansson@chalmers.se Chalmers University of Technology, 2013 Geometry Satellite Plasma Posi+oning physics Antenna theory Geophysics Time and Frequency GNSS
More informationUSE OF GLONASS AT THE BIPM
1 st Annual Precise Time and Time Interval (PTTI) Meeting USE OF GLONASS AT THE BIPM W. Lewandowski and Z. Jiang Bureau International des Poids et Mesures Sèvres, France Abstract The Russian Navigation
More informationTHE STEERING OF A REAL TIME CLOCK TO UTC(NBS) AND TO UTC by
THE STEERNG OF A REAL TME CLOCK TO UTC(NBS) AND TO UTC by J. Levine and D.W. Allan Time and Frequency Division National nstitute of Standards and Technology Boulder, Colorado 833 ABSTRACT We describe the
More informationGPS and Time: Using Clocks in Space for Accurate Time on the Ground
GPS and Time: Using Clocks in Space for Accurate Time on the Ground Dr Bruce Warrington National Measurement Institute Time and frequency: the context Accurate time and frequency are essential to modern
More informationProgress on works related to the proposed redefinition of UTC WGD Task Group on timing references Contribution from BIPM
Progress on works related to the proposed redefinition of UTC WGD Task Group on timing references Contribution from BIPM E.F. Arias, W. Lewandowski Eighth Meeting of the International Committee on Global
More informationStatus, Development and Application
Federal Space Agency GLONASS GLONASS Status, Development and Application Sergey G. Revnivykh International Committee on Global Navigation Satellite Systems (ICG) Second Meeting, September 47, 2007, Bangalore,
More information30TH SPACE WING 45TH SPACE WING AIR ARMAMENT CENTER AIR FORCE FLIGHT TEST CENTER ARNOLD ENGINEERING DEVELOPMENT CENTER BARRY M.
DOCUMENT 21409 TELECOMMUNICATIONS AND TIMING GROUP DEFINITIONS OF FREQUENCY AND TIMING TERMS, SATELLITE NAVIGATION AND TIMING SYSTEMS AND THE BEHAVIOR AND ANALYSES OF PRECISION CRYSTAL AND ATOMIC FREQUENCY
More informationGPS/Galileo Interface to UTC Time Services UTC
GPS/Galileo Interface to UTC Time Services GSTTAI, UTCTAI CV, TWSTFT Time Service Provider UTC(k) UTC(k) UTCTAI UTC UTC(k) UTCTAI UTC(USNO) GPS TimeUTC(USNO), UTCTAI 4 GPS/Galileo Timekeeping Function
More informationGENERAL INFORMATION ON GNSS AUGMENTATION SYSTEMS
GENERAL INFORMATION ON GNSS AUGMENTATION SYSTEMS 1. INTRODUCTION Navigation technologies with precision approach and landing systems, for civilian and military purposes, enable aircrafts to perform their
More informationNIST Time and Frequency Services
NIST Special Publication 432, 2002 Edition NIST Time and Frequency Services Michael A. Lombardi NIST Special Publication 432 (Minor text revisions made in April 2003) NIST Time and Frequency Services
More informationMODULE 9 LECTURE NOTES 3 GLOBAL POSITIONING SYSTEM (GPS)
MODULE 9 LECTURE NOTES 3 GLOBAL POSITIONING SYSTEM (GPS) 1. Introduction Global positioning system (GPS) is also known as Navigation System with Time and Ranging Global Positioning System (NAVSTAR) GPS.
More informationTime and frequency distribution using satellites
INSTITUTE OF PHYSICS PUBLISHING Rep. Prog. Phys. 65 (2002) 1119 1164 REPORTS ON PROGRESS IN PHYSICS PII: S00344885(02)989670 Time and frequency distribution using satellites Judah Levine Time and Frequency
More informationInternational Global Navigation Satellite Systems Service
International Global Navigation Satellite Systems Service IGS MultiGNSS Experiment IGS MGEX Call for Participation www.igs.org Response to this Call for Participation in IGS MGEX via Web Form Submission
More informationModern Surveying Techniques. Prof. S. K. Ghosh. Department of Civil Engineering. Indian Institute of Technology, Roorkee
Modern Surveying Techniques Prof. S. K. Ghosh Department of Civil Engineering Indian Institute of Technology, Roorkee Lecture  3 GPS Positioning Methods The different types of GPS positioning methods
More informationEvaluating the Accuracy of Maxim RealTime Clocks (RTCs)
REALTIME CLOCKS Application Note 632: Aug 01, 2001 Evaluating the Accuracy of Maxim RealTime Clocks (RTCs) This app note describes methods for measuring the accuracy of the Maxim RealTime Clocks (RTCs)
More informationPost Processing Service
Post Processing Service The delay of propagation of the signal due to the ionosphere is the main source of generation of positioning errors. This problem can be bypassed using a dualfrequency receivers
More informationTime and Frequency Measurements Using the Global Positioning System (GPS)
Time and Frequency Measurements Using the Global Positioning System (GPS) Michael A. Lombardi, Lisa M. Nelson, Andrew N. Novick, and Victor S. Zhang National Institute of Standards and Technology Time
More informationAllen Goldstein NIST Synchrometrology Lab Gaithersburg, MD allen.goldstein@nist.gov
Time Synchronization in Electrical Power Transmission and Distribution Systems Allen Goldstein NIST Synchrometrology Lab Gaithersburg, MD allen.goldstein@nist.gov Abstract Synchronization of measurements
More informationREALTIME GPS MONITORING OF ATOMIC FREQUENCY STANDARDS IN THE CANADIAN ACTIVE CONTROL SYSTEM (CACS)
30th Annual Pmbe Time and Time Internal (PTTI) Meeting REALTIME GPS MONITORING OF ATOMIC FREQUENCY STANDARDS IN THE CANADIAN ACTIVE CONTROL SYSTEM (CACS) F. Lahaye, M. Caissy, J. Popelar Geodetic Survey
More informationClocks/timers, Time, and GPS
FYS3240 PCbased instrumentation and microcontrollers Clocks/timers, Time, and GPS Spring 2015 Lecture #11 Bekkeng, 22.12.2014 How good is a crystal oscillator (XO)? Interested in the longterm measurement
More informationThe IGS: A MultiGNSS Service
The IGS: A MultiGNSS Service Chris Rizos, Urs Hugentobler, Ruth Neilan IUGG IAG Structure International Union of Geodesy and Geophysics (IUGG) 65 Member Countries (Adhering Bodies), 8 Associations International
More informationFundamentals of Time and Frequency
17 Fundamentals of Time and Frequency Michael A. Lombardi National Institute of Standards and Technology 17.1 Introduction Coordinated Universal Time (UTC) 17.2 Time and Frequency Measurement Accuracy
More informationThe European Satellite Navigation Programmes EGNOS and Galileo
The European Satellite Navigation Programmes EGNOS and Galileo Olivier Crop European GNSS Agency (GSA) Paris, 17 March 2014 20 March, 2014 The European GNSS Programmes 2 Basics of Satellite Navigation
More information4 Precise Time and Frequency Transfer
4 Precise Time and Frequency Transfer 41 Basic Measurement Techniques on Time and Frequency Transfer One of the most significant features of time and frequency standards is that it can be compared at
More information.11 THE DAY. S it crosses the meridian at apparent noon. Before (ante) noon is thus a.m., while after (post) noon is p.m. FIGURE 7.
Confirming Pages UNIT 7 PA RT I The Time of Day From before recorded history, people have used events in the heavens to mark the passage of time. The day was the time interval from sunrise to sunrise,
More informationTime Facility for German Galileo Test Environment GATE J. Furthner, German Aerospace Center (DLR)
Time Facility for German Galileo Test Environment GATE J. Furthner, German Aerospace Center () Folie 1, GTFS 2005 > JF Content Overview of GATE Major Objectives of GATE GATE Field Service Area Functions
More informationBeiDou Navigation Satellite System Open Service
BeiDou Navigation Satellite System Open Service Performance Standard (Version 1.0) China Satellite Navigation Office December 2013 Foreword The space constellation of BeiDou Navigation Satellite System
More informationTime Calibrator. 2013 Fountain Computer Products
Time Calibrator Time Calibrator All rights reserved. No parts of this work may be reproduced in any form or by any means  graphic, electronic, or mechanical, including photocopying, recording, taping,
More informationEnabling RTKlike positioning offshore using the global VERIPOS GNSS network. Pieter Toor GNSS Technology Manager
Enabling RTKlike positioning offshore using the global VERIPOS GNSS network Pieter Toor GNSS Technology Manager Introduction PPP/RTK Positioning Techniques PPPAR Technology Presentation Overview PPPAR
More informationPRECISE EPHEMERIDES FOR GPS TIME TRANSFER
PRECISE EPHEMERIDES FOR GPS TIME TRANSFER W. Lewandowski Bureau International des Poids et Mesures Pavillon de Breteuil 92312 Sevres Cedex, France and M. A. Weiss United States Department of Commerce National
More informationGPS Global Positioning System
GPS Global Positioning System GPS Accuracy Error sources Differential correction GPS Accuracy levels TerraSync settings that affect accuracy of GPS measurements These topics will be covered in this slide
More informationRELATING TIME TO THE EARTH S VARIABLE ROTATION
32nd Annual Precise Time and Time Interval (PTTI) Meeting RELATING TIME TO THE EARTH S VARIABLE ROTATION H. Chadsey and D. McCarthy U.S. Naval Observatory Washington, DC 20392, USA Abstract With the beginning
More informationTime transfer through GPS
Indian Journal of Radio & Space Physics Vol. 36, August 2007, pp. 303312 Time transfer through GPS P Defraigne 1, P Banerjee 2 & W Lewandowski 3 1 Royal Observatory of Belgium, Ringlaan 3, B1180 Brussels,
More information2
1 2 3 4 5 The first number series on the data screen represents Latitude (prefixed with the letter L ). Latitude 0 is at the equator and increases to 90 North (suffix N ) at the North Pole and 90 South
More informationGlobal Positioning System
B. HofmannWellenhof, H. Lichtenegger, and J. Collins Global Positioning System Theory and Practice Third, revised edition SpringerVerlag Wien New York Contents Abbreviations Numerical constants xix xxiii
More informationMichael A. Lombardi. "Time Measurement." Copyright 2000 CRC Press LLC. <http://www.engnetbase.com>.
Michael A. Lombardi. "Time Measurement." Copyright 2000 CRC Press LLC. . Time Measurement Michael A. Lombardi National Institute of Standards and Technology 18.1 The Evolution
More informationGPS: A Primer. presented by Jim Pugh, GISP GIS Project Manager. 2007, EMH&T, Inc.
GPS: A Primer presented by Jim Pugh, GISP GIS Project Manager GPS: A Primer GPS = Global Positioning System 24 Satellites in Orbit around Earth Each Broadcasts precise time and known location Receivers
More informationGEOPHYSICAL EFFECTS ON SITE DISPLACEMENTS FOR PERMANENT GPS TRACKING STATIONS IN TAIWAN
GEOPHYSICAL EFFECTS ON SITE DISPLACEMENTS FOR PERMANENT GPS TRACKING STATIONS IN TAIWAN C. C. Chang Department of Surveying and Mapping Engineering Chung Cheng Institute of Technology Tahsi, Taoyuan 335,
More informationMath 215 Project (25 pts) : Using Linear Algebra to solve GPS problem
Due Thursday March 1, 2012 NAME(S): Math 215 Project (25 pts) : Using Linear Algebra to solve GPS problem 0.1 Introduction The age old question, Where in the world am I? can easily be solved nowadays by
More informationA Fortran program to calculate sunrise and sunset
A Fortran program to calculate sunrise and sunset Nicholas Moe 23 April 2007 1 Introduction This is a description of a program written in Fortran 90/95 to calculate the rise and set ties of the sun, accurate
More informationDouglas Adams The Hitchhikers Guide to the Galaxy
There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.
More informationMichael A. Lombardi. "Frequency Measurement." Copyright 2000 CRC Press LLC. <http://www.engnetbase.com>.
Michael A. Lombardi. "Frequency Measurement." Copyright 2000 CRC Press LLC. . Frequency Measurement Michael A. Lombardi National Institute of Standards and Technology 19.1 Overview
More informationGLONASS STATUS UPDATE
GLONASS STATUS UPDATE Y. Urlichich, G. Stupak, V. Dvorkin, and S. Karutin Federal Space Agency 53 Aviamotornay str. Moscow, 111250, Russia Tel: + 7 495 673 97 29, Fax: +7 495 673 28 15, Email: sergey.karutin@rniikp.ru
More informationGlobal Positioning System (GPS) Time Dissemination for RealTime Applications
RealTime systems, 12, 940 (1997) 1997 Kluwer Academic Publishers, Boston. Manufactured in The Netherlands. Global Positioning System (GPS) Time Dissemination for RealTime Applications PETER H. DANA
More informationPNT Evolution: Future Benefits and Policy Issues. Scott Pace Director, Space Policy Institute George Washington University Washington, D.C.
PNT Evolution: Future Benefits and Policy Issues Scott Pace Director, Space Policy Institute George Washington University Washington, D.C. 5 November 2009 GPS is a Critical Component of the Global Information
More informationIRIG SERIAL TIME CODE FORMATS
IRIG STANDARD 20098 TELECOMMUNICATIONS AND TIMING GROUP IRIG SERIAL TIME CODE FORMATS WHITE SANDS MISSILE RANGE KWAJALEIN MISSILE RANGE YUMA PROVING GROUND DUGWAY PROVING GROUND ABERDEEN TEST CENTER NATIONAL
More information[3] beautiful visualisation of the satellites positions by HSR / ICOM.
GPS (Introduction) NTM2, Rumc, GPS, 1 Terms NAVSTAR GPS ( Navigational Satellite Timing and Ranging  Global Positioning System) is a GNSS (Global Navigation Satellite System), developed by the USDoD
More informationTRANSPORT PROBLEMS 2007 PROBLEMY TRANSPORTU Tom 2 Zeszyt 2
TRANSPORT PROBLEMS 2007 PROBLEMY TRANSPORTU Tom 2 Zeszyt 2 ARKADIUSZ TYSZKO*, TOMASZ TEMLIN, STANISŁAW OSZCZAK University of Warmia and Mazury in Olsztyn Chair of Satellite Geodesy and Navigation Heweliusza
More informationGeneral GPS Antenna Information APPLICATION NOTE
General GPS Antenna Information APPLICATION NOTE General GPS Antenna Information Global Positioning System and Precise Time & Frequency The Global Positioning System (GPS) is a worldwide radionavigation
More informationDancing in the Dark: How GNSS Satellites Cross the Earth s Shadow
Dancing in the Dark: How GNSS Satellites Cross the Earth s Shadow F. Dilssner, T. Springer, G. Gienger, R. Zandbergen European Space Operations Centre (ESOC), Darmstadt 24 January 2011 Technische Universität
More informationCHAPTER 11 SATELLITE NAVIGATION
CHAPTER 11 SATELLITE NAVIGATION INTRODUCTION 1100. Development The idea that led to development of the satellite navigation systems dates back to 1957 and the first launch of an artificial satellite into
More informationRadio Technical Commission for Maritime Services. GPS Update. Bob Markle RTCM Arlington, VA USA. NMEA Convention & Expo 2010
Radio Technical Commission for Maritime Services GPS Update NMEA Convention & Expo 2010 Bob Markle RTCM Arlington, VA USA What is RTCM? International nonprofit scientific, professional and membership
More informationSynchronization in. Distributed Systems. Cooperation and Coordination in. Distributed Systems. Kinds of Synchronization.
Cooperation and Coordination in Distributed Systems Communication Mechanisms for the communication between processes Naming for searching communication partners Synchronization in Distributed Systems But...
More informationTransmission of SBAS corrections over IALA beacons
Input paper: 1 ENAV1813.20 Input paper for the following Committee(s): check as appropriate Purpose of paper: ARM ENG PAP Input ENAV VTS Information Agenda item 2 13 Technical Domain / Task Number 2 Author(s)
More informationTIME SERVICES IN A LAN. A Technical Brief from GarrettCom, Inc., for use with MNS6KSECURE version 14.1 and higher. August 2008
SYNCHRONIZING TIME SOURCES AND SETTING UP RELIABLE TIME SERVICES IN A LAN A Technical Brief from GarrettCom, Inc., for use with MNS6KSECURE version 14.1 and higher August 2008 SUMMARY Networks and devices
More informationLab 6: GPS Geology 202 Earth s Interior. Due Thursday, March 4, 2004, and remember to sign out your GPS unit
Lab 6: GPS Geology 202 Earth s Interior Due Thursday, March 4, 2004, and remember to sign out your GPS unit Introduction: Latitude and Longitude Any location on Earth is described by two numbersits latitude
More informationIRIGB Time Signal Distribution over Geostationary Satellites
IRIGB Time Signal Distribution over Geostationary Satellites Senol Gulgonul 1, Mesut Gokten 1, Thomas Meinerz 2, Erdem Demircioglu 3, and Nedim Sozbir 1 1 Turksat AS, Konya Yolu 40.km, Golbasi, Ankara,
More informationINTEGRITY AND CONTINUITY ANALYSIS OCTOBER TO DECEMBER 2013 QUARTERLY REPORT FROM GPS. Integrity and Continuity Analysis 08/01/14 08/01/14 08/01/14
INTEGRITY AND CONTINUITY ANALYSIS FROM GPS OCTOBER TO DECEMBER 2013 QUARTERLY REPORT Prepared by: M Pattinson (NSL) 08/01/14 Checked by: L Banfield (NSL) 08/01/14 Approved by: M Dumville (NSL) 08/01/14
More information43 Two Way Satellite Time and Frequency Transfer
43 Two Way Satellite Time and Frequency Transfer IMAE Michito, SUZUYAMA Tomonari, GOTOH Tadahiro, SHIBUYA Yasuhisa, NAKAGAWA Fumimaru, SHIMIZU Yoshiyuki, and KURIHARA Noriyuki Two Way Satellite Time and
More informationRTCM State Space Representation Messages, Status and Plans
RTCM State Space Representation Messages, Status and Plans Martin Schmitz Geo++ GmbH 30827 Garbsen Germany www.geopp.com Outline Introduction Observation Space/ State Space Representation Status of RTCM
More informationThe Evolution of the Global Navigation Satellite System (GNSS) Spectrum Use
The Evolution of the Global Navigation Satellite System (GNSS) Spectrum Use Spectrum Management 2012 National Spectrum Management Association Scott Pace (with thanks to Chris Hegerty, MITRE) Space Policy
More informationRobot Perception Continued
Robot Perception Continued 1 Visual Perception Visual Odometry Reconstruction Recognition CS 685 11 Range Sensing strategies Active range sensors Ultrasound Laser range sensor Slides adopted from Siegwart
More informationAn Empirical Approach for the Estimation of GPS Covariance Matrix of Observations
An Empirical Approach for the Estimation of GPS Covariance Matrix of Observations Rodrigo Leandro, University of New Brunswic Marcelo Santos, University of New Brunswic Karen Cove, University of New Brunswic
More informationSynchronization in Distributed Systems
Synchronization in Distributed Systems Chapter 4: Time and Synchronisation Page 1 1 Cooperation and Coordination in Distributed Systems Communication Mechanisms for the communication between processes
More informationTime, Day, Month, and the Moon
Time, Day, Month, and the Moon Announcements o First Homework will start on Tue Sept 20st; due on Thu, Sept 29th. o Accessible through SPARK Assigned Reading n Units 7 and 8 Goals for Today n To discuss
More informationA Century of Time Measurement: From Pendulum to Optical Clocks
A Century of Time Measurement: From Pendulum to Optical Clocks Michael Lombardi NIST Time and Frequency Division NCSLI 2011 Introduction For most of recorded history, the most accurate measurements of
More informationDelivering NIST Time to Financial Markets Via CommonView GPS Measurements
Delivering NIST Time to Financial Markets Via CommonView GPS Measurements Michael Lombardi NIST Time and Frequency Division lombardi@nist.gov 55 th CGSIC Meeting Timing Subcommittee Tampa, Florida September
More informationEDMONDS COMMUNITY COLLEGE ASTRONOMY 100 Winter Quarter 2007 Sample Test # 1
Instructor: L. M. Khandro EDMONDS COMMUNITY COLLEGE ASTRONOMY 100 Winter Quarter 2007 Sample Test # 1 1. An arc second is a measure of a. time interval between oscillations of a standard clock b. time
More informationMULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
Exam Name MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) Two fixed navigation beacons mark the approach lane to a star. The beacons are in line
More informationApplied Geomorphology. Lecture 4: Total Station & GPS Survey Methods
Applied Geomorphology Lecture 4: Total Station & GPS Survey Methods Total Station Electronic version of Alidade Accurate to ±3 ppm horizontal & vertical 3x106 (5000 feet) = 0.2 inches Total Station Advantages
More informationPTB S TIME AND FREQUENCY ACTIVITIES IN 2006: NEW DCF77 ELECTRONICS, NEW NTP SERVERS, AND CALIBRATION ACTIVITIES
Proc. 38th Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting, Reston, Virginia, USA, 57 Dec 2006, pp. 3747, 2007. PTB S TIME AND FREQUENCY ACTIVITIES IN 2006: NEW DCF77 ELECTRONICS,
More informationOn May 27, 2010, the U.S. Air. Satellite. Antenna Phase Center and Attitude Modeling
GPS IIF1 Satellite Antenna Phase Center and Attitude Modeling Florian Dilssner Logica/European Space Agency Calculating the distances between satellites and user equipment is a basic operation for GNSS
More informationSchool of Biotechnology
Physics reference slides Donatello Dolce Università di Camerino a.y. 2014/2015 mail: donatello.dolce@unicam.it School of Biotechnology Program and Aim Introduction to Physics Kinematics and Dynamics; Position
More informationIonospheric Research with the LOFAR Telescope
Ionospheric Research with the LOFAR Telescope Leszek P. Błaszkiewicz Faculty of Mathematics and Computer Science, UWM Olsztyn LOFAR  The LOw Frequency ARray The LOFAR interferometer consist of a large
More informationMaritime Integrated PNT System
Maritime Integrated PNT System Core element for safe ship navigation Evelin Engler und Thoralf Noack DLR Institut für Kommunikation und Navigation Folie 1 Maritime Integrated PNT System = overlay of satellite
More informationDevelopment of BeiDou Navigation Satellite System
The 7th Meeting of International Committee on GNSS Development of BeiDou Navigation Satellite System China Satellite Navigation Office November 5, 2012 Beijing, China Part Ⅰ Development Plan Part Ⅱ System
More informationGPS BLOCK IIF RUBIDIUM FREQUENCY STANDARD LIFE TEST
GPS BLOCK IIF RUBIDIUM FREQUENCY STANDARD LIFE TEST F. Vannicola, R. Beard, J. White, K. Senior, T. Kubik, D. Wilson U.S. Naval Research Laboratory 4555 Overlook Avenue, SW, Washington, DC 20375, USA Email:
More informationThe Role of Precise Timing in HighSpeed, LowLatency Trading
The Role of Precise Timing in HighSpeed, LowLatency Trading The race to zero nanoseconds Whether measuring network latency or comparing realtime trading data from different computers on the planet,
More informationBriefing Note: Evolution from LoranC to eloran
Briefing Note: Evolution from to Executive Summary This paper has been prepared by the Research and Radionavigation Directorate of the General Lighthouse Authorities of the United Kingdom and Ireland for
More informationBiDirectional DGPS for Range Safety Applications
BiDirectional DGPS for Range Safety Applications Ranjeet Shetty 234A, Avionics Engineering Center, Russ College of Engineering and Technology, Ohio University Advisor: Dr. Chris Bartone Outline Background
More information