Investigation on GEO satellite orbit determination based on CEI measurements of short baselines

Connected-Element Interferometry (CEI) is a technique for measuring the phase delay of difference of Time Of Arrival (TOA) of a downlink radio signal to two antennae on a short baseline. This technique can use an atomic clock for time-frequency transmission and achieve intermediate accuracy angular tracking. Owing to the relatively short length of the baseline, the passive reception mode, and near real-time operation, CEI can be used to continuously monitor the orbit variations of both cooperative and non-cooperative satellites. In this paper, a small-scale CEI system of two orthogonal baselines (75 m × 35 m) is investigated to track a Geostationary Earth Orbit (GEO) Television (TV) satellite at 110·5°E. The phases are extracted from correlation results. The results show that the Root Mean Square (RMS) of the phase fitting residuals, if not calibrated, is within 2° at night and up to 10° in the daytime. After applying the calibration signal, the RMS of the phase fitting residuals in the daytime decreases to the same level at night. Comparing the phase delay with the a priori phase delay using Two-Line-Element (TLE) data, the integer ambiguity is successfully resolved. Finally, a batch algorithm is used to estimate the orbit of the GEO satellite, and the orbit determination accuracy is evaluated using the precise orbits provided by the China National Time Service Centre (NTSC). The results show that the accuracies in the radial direction and the cross-track direction are less than 1 km, and the Three-Dimensional (3D) position accuracy reaches the 2 km order of magnitude.

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Long-Distance Time Transfer in Optical Fiber Networks Using a Cascaded Taming Technology

Mathematical Problems in Engineering ◽

10.1155/2021/8860028 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Ding Chen ◽

Jiangning Xu ◽

Yifeng Liang ◽

Shan Jiang ◽

Hongyang He

Keyword(s):

Optical Fiber ◽

High Precision ◽

Wavelength Division Multiplexing ◽

Time Synchronization ◽

Atomic Clock ◽

Process Time ◽

Long Distance ◽

Time Service ◽

Time Frequency ◽

Fiber Link

In order to meet the time service needs of high-precision, long-distance, and multinode optical network, this paper proposes a new time synchronization solution, which combines the wavelength division multiplexing (WDM) technology with cascaded taming clock technology. The WDM technology is used for time synchronization between each pair of master-slave nodes. In the system, there are two wavelengths on the fiber link between the master node and the slave node for transmitting signals. 1 plus per second (PPS) signal, time code signal, and 10 MHz signal are, respectively, and successively, sent to the optical fiber link. By solving the one-way delay through analysis of error contribution and link characteristics of the time transmission process, time synchronization of the master-slave nodes pair is achieved. Furthermore, the authors adopt cascaded taming clock technology to ensure accurate time synchronization of each node. A 700 km long-distance time-frequency synchronization system is constructed in the laboratory. The system uses a cesium atomic clock as the reference clock source and transmits the signals through 8 small rubidium atomic clocks (RB clocks) hierarchically. Results from the experiment show that the long-term time stability is 47.5 ps/104 s. The system’s structural characteristics and the experiment results meet the requirements to allow practical use of high-precision time synchronization in networks. This proposed solution can be applied in various civil, commercial, and military fields.

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Evaluation of C-Band Precise Orbit Determination of Geostationary Earth Orbit Satellites based on the Chinese Area Positioning System

Journal of Navigation ◽

10.1017/s0373463313000787 ◽

2013 ◽

Vol 67 (2) ◽

pp. 343-351 ◽

Cited By ~ 8

Author(s):

Cao Fen ◽

Yang XuHai ◽

Su MuDan ◽

Li ZhiGang ◽

Chen Liang ◽

...

Keyword(s):

Orbit Determination ◽

Precise Orbit Determination ◽

Earth Orbit ◽

Positioning System ◽

Time Service ◽

Geostationary Earth Orbit ◽

Precise Orbit ◽

Geo Satellite ◽

First Time ◽

Better Than

Geostationary Earth Orbit (GEO) satellites play a significant role in the space segment of the Chinese Area Navigation System. The C-Band transfer ranging method developed by the National Time Service Center (NTSC) has been widely used in the Chinese Area Positioning System (CAPS), with its advantages of separating satellite ranging from time synchronization and being unaffected by weather. The explicit ranging correction models for the C-Band transfer ranging method are introduced in detail in this article for the first time. Precise Orbit Determination (POD) using C-Band pseudo-range observation of GEO satellite 2010-001A in July 2012 has been conducted. The residual Root Mean Square (RMS) of each site and POD are analysed with orbit difference over overlaps of adjacent orbit arcs. Moreover, the orbit of the GEO satellite has been evaluated by Satellite Laser Ranging (SLR) data from both domestic and foreign SLR sites for the first time. The residual RMS of POD using C-Band observation is better than 0·1 m, and the orbit difference over overlaps of adjacent orbit arcs is better than 3 m. In addition, the residual RMS in line-of-sight for a SLR site in China are better than 1 m, while the RMS for the Yarragadee site in Australia is about 3·4 m. It has been shown that the GEO satellite orbit accords very well with the C-Band observation. Also, the distribution of CAPS stations affects the orbit precision. All sites in CAPS are now located in China with low and medium latitudes. The residual RMS of the SLR site in the southern hemisphere is larger than that of the site in China.

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Time-frequency analysis of VHF wave form for precise location of partial discharge in small-scale high voltage apparatuses

Proceedings of the 7th International Conference on Properties and Applications of Dielectric Materials (Cat. No.03CH37417) ◽

10.1109/icpadm.2003.1218422 ◽

2004 ◽

Author(s):

C.K. Lee ◽

Y. Muramoto ◽

N. Hozumi ◽

M. Nagao

Keyword(s):

Frequency Analysis ◽

High Voltage ◽

Partial Discharge ◽

Small Scale ◽

Wave Form ◽

Precise Location ◽

Time Frequency Analysis ◽

Time Frequency

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Modeling of Non-WSSUS Double-Rayleigh Fading Channels for Vehicular Communications

Wireless Communications and Mobile Computing ◽

10.1155/2017/6394653 ◽

2017 ◽

Vol 2017 ◽

pp. 1-15 ◽

Cited By ~ 4

Author(s):

Carlos A. Gutiérrez ◽

J. J. Jaime-Rodríguez ◽

J. M. Luna-Rivera ◽

Daniel U. Campos-Delgado ◽

Javier Vázquez Castillo

Keyword(s):

Fading Channels ◽

Communication Systems ◽

Rayleigh Fading ◽

Channel Model ◽

Closed Form Solution ◽

Multipath Fading ◽

Rayleigh Distribution ◽

Rayleigh Fading Channels ◽

Small Scale ◽

Time Frequency

This paper deals with the modeling of nonstationary time-frequency (TF) dispersive multipath fading channels for vehicle-to-vehicle (V2V) communication systems. As a main contribution, the paper presents a novel geometry-based statistical channel model that facilitates the analysis of the nonstationarities of V2V fading channels arising at a small-scale level due to the time-varying nature of the propagation delays. This new geometrical channel model has been formulated following the principles of plane wave propagation (PWP) and assuming that the transmitted signal reaches the receiver antenna through double interactions with multiple interfering objects (IOs) randomly located in the propagation area. As a consequence of such interactions, the first-order statistics of the channel model’s envelope are shown to follow a worse-than-Rayleigh distribution; specifically, they follow a double-Rayleigh distribution. General expressions are derived for the envelope and phase distributions, four-dimensional (4D) TF correlation function (TF-CF), and TF-dependent delay and Doppler profiles of the proposed channel model. Such expressions are valid regardless of the underlying geometry of the propagation area. Furthermore, a closed-form solution of the 4D TF-CF is presented for the particular case of the geometrical two-ring scattering model. The obtained results provide new theoretical insights into the correlation and spectral properties of small-scale nonstationary V2V double-Rayleigh fading channels.

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Total Electron Content (TEC) estimation over Pakistan from local GPS network using spherical harmonics

Annals of Geophysics ◽

10.4401/ag-8433 ◽

2021 ◽

Vol 64 (1) ◽

Author(s):

Maria Mehmood ◽

Sajid Saleem ◽

Renato Filjar ◽

Najam Naqvi ◽

Arslan Ahmed

Keyword(s):

Spherical Harmonics ◽

Orbit Determination ◽

Region Of Interest ◽

Local Model ◽

Small Scale ◽

Electron Content ◽

Total Electron ◽

Gps Network ◽

Spherical Harmonics Expansion ◽

The Impact

Many organizations allow GNSS users to access Global Ionosphere Maps (GIMS). However, the TEC estimates derived from GIMs are of insufficient quality to describe small-scale TEC variations over Pakistan. In this paper, the first local TEC map over Pakistan for the year 2019, derived from a regional GPS network, is presented. Spherical harmonics expansion is employed to estimate TEC with the spatial resolution of latitude 0.2° x longitude 0.2° and temporal resolution of 5 minutes. The impact of changing the degree/order of harmonics is assessed and it is determined that harmonic expansion up to 6 degrees is sufficient for estimating accurate TEC map for the region of interest. We have demonstrated that the TEC maps of Pakistan generated by local model conform better to the GIM by Center of Orbit Determination (CODE) (RMS = 5.83) as compared to International Reference Ionosphere (IRI-2016) (RMS = 7.18). We found that the TEC estimated by the local model shows a better correlation to measured TEC; CODE-GIM overestimated TEC, while IRI-2016 underestimates it. Moreover, it was observed that TEC peaks during noon (1100-0100 LT) and Equinox (April). The residuals of local TEC estimates with respect to TEC obtained from CODE- GIM indicate the inaccuracy of CODE-GIM over the region of Pakistan: highest deviation of TEC from local model with respect to CODE –GIM was observed in April (RMS = 8.73) and minimum in October (RMS = 2.78). We have also analyzed the performance of our maps in geomagnetically disturbed days. The research presented in this paper will contribute towards the ionosphere study over Pakistan, where limited research is available currently.

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