RF chnl, # GC, Launched, Operation begins, Operation ends, Life-time (months), Satellite health status, Comments. In almanac, In ephemeris (UTC).

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GLONASS Time. There are many efforts underway to improve the GLONASS accuracy. The stability of the satellites' onboard clocks has improved from 5 x.

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RF chnl, # GC, Launched, Operation begins, Operation ends, Life-time (months), Satellite health status, Comments. In almanac, In ephemeris (UTC).

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GLONASS Time. There are many efforts underway to improve the GLONASS accuracy. The stability of the satellites' onboard clocks has improved from 5 x.

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The accuracy of calculated offset between SV timescale and GLONASS Time β. 5β,6 ns (rms). Page 2. c. Location of corrections in broadcast messages: L1/L2. -.

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Offset of GLONASS time from UTC (SU) [Coordinated Universal Time Russia]. Almanac of all other GLONASS satellites. βThe Earth was absolutely round I.

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GLONASS is a global navigation satellite system, providing real time position and velocity determination for military and civilian users. The satellites are located.

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Offset of GLONASS time from UTC (SU) [Coordinated Universal Time Russia]. Almanac of all other GLONASS satellites. βThe Earth was absolutely round I.

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RF chnl, # GC, Launched, Operation begins, Operation ends, Life-time (months), Satellite health status, Comments. In almanac, In ephemeris (UTC).

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GNSS Time Formats. Constellation. GPS. GLONASS. BEIDOU. GALILEO. Launchβ. First launch Fully operational First launch Fully operational.

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By the end of , 6 combined links are used for UTC computation. The conclusion obtained in this study is applicable in these two types of receivers. At present few authors work on this topic [ 23 ] and as yet there is not a good enough solution to be able to use in UTC time transfer. We may have two explanations for this conflicted result. The residual influence of the IGS ionosphere correction used in this study might be one of such factors. If the biases are physically caused by the GLN signal frequencies alone, they should be constant with time, isotropically equivalent, and independent of receivers and baselines. This conclusion meant that in principle the GLN CV time transfer technique could be used directly as GPS without the need of the frequency bias corrections for the computation of UTC; that is, comparing the gain and the complexity of the computation, it is not worth to make the frequency bias corrections in the monthly UTC computation. The coexisting multitechniques strategy has led to a rapid increase in the level of redundancy in the UTC data bank, with new techniques being added all the time. Table 4 lists the results obtained for the five baselines of different distances. A time link technique can be used in UTC only when it is calibrated, and its short- and long-term stabilities are proven. As we assume the frequency biases are receiver dependent hence constant with time, we can apply these values obtained from the SU-PTB GLN data for the period to correct the corresponding data for and as well Figure 6 a shows the time link SU-PTB , and Figure 6 b illustrates the time deviations before and after correction for the frequency biases on the same baseline on Figure 6 c shows that of , one year after Not as seen for the baseline OP-PTB, Figures 6 b and 6 c show no obvious improvement in the time deviation for averaging time of hours. The discussion in the following focuses on introducing the weighted combination. It is expected that application of the frequency bias corrections to the raw GLN measurements should lead to a significant reduction in noise level and improvement in the short-term stability of the link. Further study is required. Figure 10 shows the comparisons of the corresponding time deviations. We gave some examples of the links based on a combination of two fully independent techniques to be used in UTC time transfer [ 21 ]. Table 9 summarizes the availability of the GNSS and TW facilities at some of the national laboratories contributing to UTC, where at least two time and frequency transfer techniques are equipped. Table 1 listed the satellites in order of the frequency codes. In addition, PPP relies on the Earth geocentric reference and related quantities, such as the geocentric coordinates of the satellites in space and of the antenna centres of the receivers on the ground, and the processing is complex.{/INSERTKEYS}{/PARAGRAPH} As discussed previously, cf. We use the data sets of UTC , , and as well as a month long-term data set β Similarly, taking PPP as reference, the standard deviations are 1. However, earlier GLN studies [ 1 β 9 ] remained at an experimental stage because there were only a few operationalGLN timing receivers, the GLN constellation was incomplete, and there were unsolved technical issues; among them the major difficulty was of the multiple GLN frequency biases. What is important is not the size of the bias but whether or not it depends significantly on the GLN frequency, the receiver, and time. Observing the relation between the biases and the frequencies, Table 2 b and the corresponding Figure 4 show the values in the increasing order of the nominal frequencies. Other open issues are the use of the carrier phase, the calibrations, and the raw data recording. This would indicate that the biases vary with the frequency codes but the satellites. The time deviation is an indicator of the time stability in a link. Similar results were obtained in more recent tests using TTS receivers [ 19 ]. We briefly outline our considerations for the coming future studies at the BIPM. For averaging times of beyond 20 hours, the three time deviation curves converge. We have a couple of TTS4 receiver data recently and start to study them. {PARAGRAPH}{INSERTKEYS}We then outline various considerations for future developments, including the uses of P-codes and carrier-phase information. Again, we cannot exclude the effects of other frequency-dependent factor s including the impact of the temperature variations. However further investigation is required. In the following study we use GPS as reference. In this study, we investigate the receivers available at present in the UTC time transfer. It is important to establish whether the biases are well below the measurement noise and are therefore negligible, or alternatively if a calibration or correction is needed for each frequency in a GLN CV time link. Early studies based on certain physical considerations and on first-generation GLN receivers, for example, 3S Navigation, addressed the question of so-called frequency biases disturbing the CV time transfer [ 3 , 4 ] and suggested a precorrection to each GLN frequency for the data to be used for UTC computation. Considering the gain in applying the frequency bias corrections is not significant and the complexity of the computation is, it has been decided [ 12 ] not to use these corrections in the computation of UTC. Our main interest is the influence of the so-called frequency biases on the CV time links. We also estimated the so-called frequency biases using other references such as P3 and TW, and the results are almost the same as those listed in Table 2 ; that is, the standard deviation is mainly due to the noise in L1C. On the other side, the differences between the PRNs using the same frequency are mostly less than 0. The and data are separated by 4 months and and by 12 months. Would there exist other frequency dependent or independent factors, in addition to the receiver only dependent ones, that affect the frequency biases? The standard deviations of the smoothing residuals for the months , , , and are listed in Table 6. TTS-4 and Septentrio receivers are not investigated in this study. We do not know the exact reason at present. The number of common points of the comparison N is typically about , with the exception of for PRN In Tables 2 a and 2 b and Figure 4 , it is seen that the standard deviation of the frequency bias cf. Even if we apply them to correct the frequency biases, such small values will be masked by the measurement noise and other frequency dependant biases. However, this was not observed in our previous investigations using the 3S Navigation receivers [ 6 ] nor in recent evaluations using the latest TTS-3 receivers [ 19 ]. All three laboratories are equipped with TTS-3 receivers. Comparing the time deviations estimated before and after the bias corrections, it is seen in Figures 5 b and 5 c that after correction the little knolls at about hour averaging time in the uncorrected plot disappear. The possible use of P3-code clearly merits further investigation. The Mean is the mean value of the of the different PRNs using the same frequency. The ionosphere influence is location, direction, and frequency dependent. The first point has been fully discussed in earlier studies, such as [ 4 β 6 ]. Similar to Figure 5 b , an improvement in the time transfer stability is observed for the averaging time of 2 to 3 hours. Since January combined solutions have therefore been applied in UTC generation. In contrast to PPP, we are investigating a different approach, namely, the postcombination. Let us by the way point out that receiver dependent must lead to baseline dependent because the baseline is composed of a pair of receivers. In the following discussions, because the short-term measurement noise of the L1C time link is about 0. Eight satellites are equally distributed in each plane. We used the frequency bias corrections listed in Table 2 a , based on the data, to correct the raw data of , , and for the same baseline, OP-PTB. We currently use the IAC ephemeride products and the IGS ionosphere maps to compute the precise orbit and ionosphere corrections. This numerical evaluation based on two CV links does not prove the existence of the impact of the biases which are bigger than the measurement noise and depend on the GLN frequencies. All the data were collected using the same type of receivers TTS The same conclusion holds for the long-term variations in their calibrations cf. Knowing the measurement uncertainties of TW and of GPS PPP and the simplicity of the combination computation, the gain here is hence conservative and the operation is worthy. If the frequency biases are constant for that baseline, they should be applicable to the raw data of other periods. The standard deviation obtained with the L1C code is statistically no bigger than that using the P-codes, and indeed for long distances, the L1C code results are slightly better than those of the P-codes. The frequency-bias corrections obtained from might not be really or completely caused by the frequency-bias but, at least partially, by some other frequency dependent biases. We first compute the code and CP separately and then to combine the code and CP solutions. The frequency biases should therefore be universal and could be corrected for in the UTC time transfer. The combination thus leads to an improvement in the short-term stability for averaging times of up to 1 day. The standard deviation of the smoothing residuals is also an index of the gains. The tendency to use multitechniques for UTC time transfer is unavoidable. For this baseline, it seems the frequency biases are statistically not baseline dependent. The results show a gain in time transfer quality for an averaging time of hours. The situation has greatly improved in recent years. In GLN time transfer today: 1 Common View CV is still advantageous in cancelling the influence of the satellite clock and reducing the orbit and atmosphere delay uncertainties; 2 the state of the art of using the P-codes shows no obvious advantages over that of the L1C code, as unexpected biases and noises would degrade the quality of the P-code data. To guarantee the accuracy and robustness of UTC generation, a multitechnique strategy for UTC time transfer is indispensable. There seems to be no obvious correlation between the amplitudes of the biases and the nominal frequencies. In consequence, the time deviation of the one month data set is slightly improved for averaging times within one day. Given the of 1. Although measurements are typically provided by the receivers, the P1 and P2 codes are primarily not intended for civil use [ 18 ]. The P-codes are of higher quality than the C-code, and logically one would thus expect them to have obvious advantages in time transfer. According to previous studies, we assume first that the frequency biases exist and are physically caused by the GLN frequencies, significantly receiver dependent, and are constant. Figure 5 c is the comparison of the time deviations of the data one year after with and without the bias corrections. Assuming the trajectory of the GLN satellite is on average symmetric around the observers, hours correspond to the half-time of the observable passage of the satellite. The result is given in Table 3. In total 11 coded frequencies are emitted by 1 or 2 satellites each. The first satellite was launched on 12 October , and the constellation was completed in , although until recent years it has not always been well maintained. The previous results do not fully support the previous studies summarized in the beginning of Section 2. One difficulty with the PPP is the ambiguity of the carrier-phase information.