Update on Global Navigation Satellite Systems

Synth

I received an email today with a summary of the current status of various GPS systems. It was in a pdf, so I copied the text out.

Update on Global Navigation Satellite Systems (GNSS)

Global navigation satellite systems (GNSS) remain the system of choice for positioning or navigating in the offshore market and have been used since the introduction of GPS in the early 1990s. Significant technological change in this area is anticipated over the next decade. The purpose of this information note is to provide an update on the current status of the various satellite navigation constellations and augmentation services available to users and to highlight some of the expected technical changes.

1 GPS
The offshore industry was an early adopter of the now extensively used Global Positioning System (GPS). Since the first satellite launch in 1978 the system has become an important tool in the exploration and development of oil and gas fields.
At present the GPS constellation consists of 31 operational satellites with the next launch scheduled for 20 December 2007. The GPS system, which until recently utilised the C/A and P-Code ranging signals modulated on to the L1 and L2 carrier frequencies in order to allow position determination, is undergoing modernisation.
The following sections will provide a brief overview of the changes to GPS.

1.1 L1C
The current C/A-code available on L1 is used by many GPS users but in contrast with the modernised L2 and L5 signals, C/A has deficiencies:
♦ No pilot carrier;
♦ No forward error control (FEC);
♦ Less precise message structure;
♦ Short 1023 chip code (relatively poor correlation performance).
The signal is designed to be interoperable with Galileo and the draft specification is available with final approval expected by the end of 2007. The main design criterion for the new L1C (L-one-C) is to provide a robust new signal to benefit all users and applications. The main attributes of the signal are:
♦ signal acquisition and tracking;
♦ code and carrier measurements;
♦ spreading code correlation performance;
♦ data demodulation, both speed and threshold.
L1C will be available on all GPS III satellites with first launch planned for 2013.

1.2 L2C
This civilian signal will be included on all GPS IIR-M plus future satellites. Currently four such satellites are available to users with the next launch scheduled for 20 December 2007. The principal advantage is the fact that L2C is superior to L1 in terms of cross-correlation, threshold tracking and data recovery performance which will allow more robust tracking of the L2 signal. New user hardware will be required in order to use the new L2C signal. The remaining four Block IIR-M satellites are scheduled for launch during 2008.

1.3 L5
A completely new civil signal is to be included on all Block IIF satellites which will transmit at 1176.45MHz. The signal will have increased bandwidth and power compared with the existing L1 signal and modernised L2 signal. No military code is to be included on the L5 signal, which will be available on the Block IIF and Block III satellites.

1.4 GPS IIF
The last generation of the Block II satellites is the IIF satellites with the first satellite now undergoing testing. Launch is scheduled for late 2008 or early 2009 once all the Block IIR-M satellites have been launched. The IIF satellites have the following characteristics:
♦ 12 Satellites built by Boeing;
♦ 2 Rubidium + 1 Caesium clock ;
♦ 12 year design life;
♦ Launch options: Atlas V or Delta IV;
♦ SPS signals: L1C/A, L2C, L5;
♦ PPS signals: L1-L2P(Y), L1-L2MSV1.

1.5 GPS III
The next generation satellites to follow on from the Block II satellites are the Block III satellites due for launch from 2013. These will have the following features:
♦ Increased accuracy;
♦ Increased A/J power(up to 20 dB);
♦ Signal integrity;
♦ Search and rescue;
♦ Common signals with Galileo (L1C).

1.6 Ground Segment
As part of the GPS modernisation programme, the ground segment has undergone various upgrades to ensure the ground infrastructure is compatible for the new signals. This involved replacing the legacy operations control segment. The phased transition was successfully completed on 14 September 2007; system performance was maintained during and after transition.

1.7 S/A (Selective Availability) Capability
On 18 September 2007 the President of the United States accepted the Department of Defense recommendation to “end procurement of Global Positioning System (GPS) satellites that have the capability to intentionally degrade the accuracy of civil signals”. This means that GPS III will not have any S/A capability.

2 GLONASS
The Russian equivalent to GPS currently has 12 operational satellites in orbit. The most recent launch of a GLONASS satellite was on 26 October 2007; the next launch is scheduled for 25 December 2007, with a further seven launched during 2008 such that by the end of next year the GLONASS constellation will consist of 18 operational satellites.
Ambitious plans for modernising the GLONASS constellation have been announced and include:
♦ Continuous global navigation by 2010
– 24 satellites in constellation;
♦ Ground control segment modernisation
– Monitoring station network extension (Russia)
– System time scale improvement
– Monitoring network outside Russia;
♦ Signal modernisation
– Third civil signal at L3 (available on GLONASS-K satellite from 2009-2010)
– New interoperable signals at L1 and L5 based on CDMA (as opposed to FDMA);
♦ Interoperability with GPS and future GALILEO
– Geodesy reference frame
– Time system.

3 Galileo
The European Galileo system is still moving forward, although the speed of this has been slowed by discussions over the proposed public/private partnership funding of the system.
Technically, the programme is still moving forward with the Giove-A satellite launched in December 2005 securing the Galileo frequency filings. Giove-B is undergoing testing with launch anticipated in early 2008 which will prove the full navigation payload. This will be followed in 2009 with the launch of the first of four in-orbit validation satellites.
The latest consensus is that Galileo will be fully operational from 2013 provided everything proceeds as scheduled. At present there are no contracts in place for the build of the remaining satellites required to complete the constellation; this could result in further project slippage.

4 Other Systems

4.1 COMPASS
On 14 April 2007, the Chinese launched their first satellite as part of the plan to provide navigation and positioning on a global basis. Their constellation is named COMPASS (or Beidou II) and their current plan is for 30 medium earth orbit satellites and five geostationary satellites. There is little information publicly available at present; however, Stamford University and Septentrio Satellite Navigation have managed to decode the signals transmitted by the first COMPASS satellite.

4.1.1 Beidou
The existing Chinese Beidou satellite system comprises a constellation of four geostationary satellites intended to have two-way communications and permit the user to determine a position. This system was considered experimental and a precursor to the COMPASS (or Beidou II) system.

4.2 Japan
In Japan the QZSS system will provide regional satellite coverage transmitting on the L1-L2-L5 frequencies designed to work with GPS. Satellite coverage is designed so that at least one satellite out of the three satellites in the QZSS constellation can be observed in Japan at an elevation angle greater than 60º. It is expected that the first satellite will be launched in 2009.

4.3 India
The Indian Regional Navigation Satellite System (IRNSS) is scheduled to have first launch in 2009/2010. IRNSS is designed to be a constellation of three geostationary and four orbiting satellites, and the Indians anticipate completion of the system by 2011-2012.

5 Augmentation Systems
There are various augmentation systems delivering corrections to users via satellite for use over regional areas. These systems are normally referred to as satellite based augmentation systems (SBAS).

5.1 WAAS
The Wide Area Augmentation System is operating over North America. It currently comprises 38 reference stations, three master stations, four ground Earth stations, two geostationary satellites and two operational control centres. The reference stations include additional stations in Alaska, Canada and Mexico which have been added to the system to extend WAAS coverage.
The progress of the various phases of the WAAS programme can be summarised thus:
♦ Phase I – Initial operating capability (IOC) – completed July 2003;
♦ Phase II – Full LPV (localised performance with vertical) performance – expected completion September 2008;
♦ Phase III – Full LPV-200 performance – planned for 2009-2013;
♦ Phase IV – Dual frequency operations – planned for 2014-2028.

5.2 EGNOS
The European Geostationary Overlay Service is currently in initial operation phase with full operational qualification planned for 2008. The structure for service provision is under preparation with certification and service introduction scheduled for 2009. The system will offer three services: an open service, safety of life service and a commercial service.
Information note IMCA S 03/05 briefed Offshore Survey Division members on EGNOS. That note remains available to Offshore Survey Division members via the members-only website or on request to Marine Division members.

5.3 MSAS
The MSAS system providing coverage in the Far East is progressing with two geostationary satellites (MTSAT) in orbit. These satellites were launched in 2005 and 2006 with operational test and evaluation ongoing since launch. MSAS IOC was scheduled for 27 September 2007.

5.4 Gagan
The Indian GAGAN (GPS Aided Geo Augmented Navigation) system is an SBAS designed to provide a seamless navigation facility in the region and be fully interoperable with other such systems. The system will comprise 16 reference stations, three master control centres, and three Earth uplink stations. It is expected that the GAGAN system will be operational by 2008. Three geostationary satellite are expected with the first payload deployed onboard GSAT-4 with two satellites to follow in Q4 2008 and Q1 2009.

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