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The United States' Global Positioning System (GPS), having reached Fully Operational Capability on July 17, 1995[1] completed its original design goals. However, additional advances in technology and new demands on the existing system led to the effort to "modernize" the GPS system. Announcements from the Vice President and the White House in 1998 heralded the beginning of these changes and in 2000, the U.S. Congress reaffirmed the effort; referred to it as GPS III. The Global Positioning System (GPS), is currently the only fully-functional Global Navigation Satellite System (GNSS). ...
July 17 is the 198th day (199th in leap years) of the year in the Gregorian calendar, with 167 days remaining. ...
1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ...
The project involves new ground stations and new satellites, with additional navigation signals for both civilian and military users, and aims to improve the accuracy and availability for all users. A goal of 2013 has been established with incentives offered to the contractors if they can complete it by 2011.
New Navigation Signals
Civilian L2 (L2C) One of the first announcements was the addition of a new civilian-use signal, to be transmitted on a frequency other than L1 frequency used for the existing GPS Coarse Acquisition (C/A) signal. Ultimately, this became the L2C signal; so called because it is broadcast on the L2 frequency (1227.6 MHz). It is transmitted by all Block IIR-M and later design satellites. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...
The L2C signal is tasked with providing improving accuracy of navigation, providing an easy to track signal, and acting as a redundant signal in case of localized interference.
The immediate effect of having two civilian frequencies being transmitted from one satellite is the ability to directly measure, and therefore remove, the ionospheric delay error for that satellite. Without such a measurement, a GPS receiver must use a generic model or receive ionospheric corrections from another source (such as a Satellite Based Augmentation System). Advances in technology for both the GPS satellites and the GPS receivers have made ionospheric delay the largest source of error in the C/A signal. A receiver capable of performing this measurement is referred to as a dual frequency receiver. Augmentation of a Global Navigation Satellite System (GNSS) is a method of improving system attributes such as accuracy, reliability, and availability through the integrated of external information into the calculation process. ...
Technical Details - L2C contains two distinct PRN sequences:
- CM (for Civilian Moderate length code) is 10,230 bits long, repeating every 20 mS.
- CL (for Civilian Long length code) is 767,250 bits long, repeating every 1500 mS.
- Each signal is transmitted at 511,500 bits per second (bps), however they are multiplexed to form a 1,023,000 bps signal.
- CM is modulated with a 25 bps navigation message with forward error correction, where-as CL is a data-less sequence (it does not contain additional modulated data).
- The long, data-less CL sequence provides for approximately 24dB greater correlation protection (~250 times stronger) than L1 C/A.
- L2C has 2.7 dB greater data recovery, and 0.7 dB greater carrier-tracking.
- The transmission power is 2.3 dB weaker.
- In a single frequency application, L2C has a 65% more ionospheric error than L1.
Defined in IS-GPS-200D BPS can stand for: The Bogomolnyi Prasad Sommerfield bound The British Psychological Society The British Pharmacological Society The Biophysical Society The additives BioPsychoSymmetrie therapy, an holistic oriented therapy Bits per second (more usually bps) Basis points one one-hundredth of a percentage point Business Planning and Simulation Battle Programmer...
In telecommunications, multiplexing (MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ...
For the musical use of modulation, see modulation (music). ...
Military (M-code) A major component of the modernization process, a new military signal called M-code was designed to further improve the anti-jamming and secure access of the military GPS signals. The M-code is transmitted in the same L1 and L2 frequencies already in use by the previous military code, the P(Y) code. The new signal is shaped to place most of its energy at the edges (away from the existing P(Y) and C/A carriers).
Unlike the P(Y) code, the M-code is designed to be autonomous; meaning that a user can calculate their position using only the M-code signal. Users of the P(Y) code must typically first lock onto the C/A code and then transfer to lock onto the P(y)-code.
In a major departure from previous GPS designs, the M-code is intended to be broadcast from a high-gain directional antenna, in addition to a full-Earth antenna. This directional antenna's signal, called a spot beam, is intended to be aimed at a specific region (several hundred kilometers in diameter) and increase the local signal strength by 20 dB, or approximately 64 times stronger. A side effect of having two antennas is that the GPS satellite will appear to be two GPS satellites occupying the same position to those inside the spot beam.
While the full-Earth M-code signal is available on the Block IIR-M satellites, the spot beam antennas will not be deployed until the Block III satellites are deployed, tentatively in 2013.
- Satellite will transmit two distinct signals from two antennas; one for whole earth coverage, one in a spot beam.
- modulation is binary offset carrier
- 24MHz bandwidth
- its uses a new MNAV navigational message, which is packetized instead of framed, allowing for very flexible data payloads
- There are four effective data channels; different data can be sent on each frequency, and on each antenna.
- it can include FEC and error detection
- the spot beam is ~20 db more powerful than the earth coverage beam
- MCODE Power: –158 dBW / –138 dBW.
Safety of Life (L5) Civilian use signal, broadcast on the L5 frequency (1176.45 MHz). Planned to be available with first GPS IIF launch (2008). - Improves signal structure for enhanced performance
- Higher power than L1/L2 signal (~3db, or twice as powerful)
- Wider bandwidth = 10x processing gain
- Longer spreading codes (10x C/A)
- Aeronautical Radionavigation Services band
WRC-2000 added space signal component to this aeronautical band so aviation community can manage interference to L5 more effectively than L2
Defined in IS-GPS-705
New Civilian L1 (L1C) Civilian use signal, broadcast on the L1 frequency (1575.42 MHz), which currently contains the C/A signal used by all current GPS users. The L1C will be available with first Block III launch, currently scheduled for 2013. - Implementation will provide C/A code to ensure backward compatibility
- Assured of 1.5 dB increase in minimum C/A code power to mitigate any noise floor increase
- Data-less signal component pilot carrier improves tracking
- Enables greater civil interoperability with Galileo L1
Defined in IS-GPS-800
Block III satellites' improvements Block IIF power levels: MCODE: –158 dBW / –138 dBW. L1 and L2: –157 dBW for the C/A code signal and –160 dBW for the Y code signal. L5 will be –154 dBW. - Researchers from Aerospace confirmed that the most efficient means to generate the high-power M-code signal would entail a departure from full-Earth coverage, characteristic of all the user downlink signals up until that point. Instead, a high-gain antenna would be used to produce a directional spot beam (several hundred kilometers in diameter)... Originally, this proposal was considered as a retrofit to the planned Block IIF satellites. Upon closer inspection, program managers realized that the addition of a large deployable antenna, combined with the changes that would be needed in the operational control segment, presented too great a challenge for the existing system design
Sources - ^ http://www.navcen.uscg.gov/gps/geninfo/global.htm
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