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GLONASS Services
| GLONASS | |
|---|---|
| Title | GLONASS Services |
| Author(s) | GMV |
| Level | Basic |
| Year of Publication | 2011 |
Equivalent to the Standard Positioning Service (SPS) and the Precise Positioning Service (PPS) of GPS, GLONASS provides a standard precision (SP) navigation signal and a high precision (HP) navigation signal. These signals are sometimes also referred to as Channel of Standard Accuracy (CSA) and Channel of High Accuracy (CHA), respectively.
Standard Precision Service (SP)
Originally, the Standard Precision signal was transmitted only on L1, whereas the High Accuracy code was transmitted both on L1 and L2. The modernization of GLONASS began with the launch of second generation of satellites, GLONASS-M. Since that moment on, a second civil signal on L2 band is transmitted, allowing user to cancel out the inospheric refraction. Currently, with the first GLONASS-K sent into orbit, a third civil signal on L3 band is available for civilian users (for more information, please refer to GLONASS Space Segment).
The Standard Precision signals is generated by the Modulo-2 addition of the following three binary signals:
- PR ranging code transmitted at 511 kbps.
- Navigation message transmitted at 50 bps, and 100 Hz auxiliary meander sequence.
Given sequences are used for modulation of carriers in L1 and L2 sub-bands when generating standard accuracy signals. PR ranging code is a sequence of maximum length of shift register with a period 1 millisecond and bit rate 511 kbps. PR ranging code is sampled at the output of 7th stage of the 9-stage shift register. The initialization vector to generate this sequence is (111111111). The first character of the PR ranging code is the first character in the group 111111100, and it is repeated every 1 millisecond. The generating polynomial, which corresponds to the 9-stage shift register, is G(X) = 1 + X5 + X9.
High Precision Service (HP)
The High Precision signal is broadcast in phase quadrature with the SP signal, effectively sharing the same carrier wave as the SP signal, but with a ten times higher bandwidth (5.11 Mbps) than the SP signal.[1] Contrary to GPS, GLONASS is not degraded artificially by the system operators. Neither there are plans to introduce such measures in future. A-S is the additional encrypting of the P-code, thus denying the non-military user access to this source of precise range measurements. Like with S/A, there is no such technique employed by GLONASS, nor is it planned to introduce anything like it in future. The GLONASS P-code never was published by the system operators, but it was made known to the scientific community. This means, the GLONASS P-code is fully available. This enables the user to employ dual-frequency measurements for correction of ionospheric effects. This provides a further improvement in obtainable positioning accuracy. However, along with the P-code not being published by the system operators, it neither was officially released for use outside the Russian Armed Forces. Instead, they reserve the right to alter the code in future. This keeps a number of potential users and receiver manufacturers from actually implementing the GLONASS P-code.
Military Signal Access to India
Under an agreement with India signed in January 2004, Russian Space Agency (RSA) committed to make the system operational with 24 satellites by 2010. A constellation of 18 GLONASS satellites not only provide full coverage to Russian they also cover India. [2] During a December 2005 summit between Indian Prime Minister Manmohan Singh and Russian President Vladimir Putin, it was agreed that India would share some of the development costs of the GLONASS-K series. On December 21, 2010, during the visit of Russian President Dmitry Medvedev to India, Russia and India signed an agreement to share high precision signals from the Global Navigation Satellite System (GLONASS). [3] India is the first country that has been given access to the military signal.