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Hybrid System for Train Tracking and Monitoring Model
Published in Tanuja Patgar, Devi CS Kavitha, On-Board Design Models and Algorithm for Communication Based Train Control and Tracking System, 2022
Tanuja Patgar, Devi CS Kavitha
The GPS utilizing system of many satellites was invented for purpose of navigation but developed and maintained by the US Department of Defense (DoD). It became fully operational globally in 1993. A total of 24 operational satellites were used initially, distributed 12 over six orbits in properly geometrically spaced slots. The satellites orbit around the earth about 20,200 km above the earth’s surface with approximately 12-hour periods. Each satellite transmits a radio signal containing navigation parameter to estimate its position, velocity and time information. GPS signals mainly consist of radiofrequency carrier, unique Pseudo-Random Noise code (PRN) and binary navigation message. The PRN code is a sequence of 1’s and 0’s multiplied with binary navigation message and modulated with carrier frequency 1605.32 MHz and 1328.40 MHz to form the transmitted signal. The GPS receiver acquires the transmitted signal information and performs data processing.
Time Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
All GPS satellites broadcast on the L1 (1.57542 GHz) and L2 (1.2276 GHz) carrier frequencies, with satellites launched after May 2010 also utilizing the L5 carrier at 1.17645 GHz. The satellites are identified by a unique spread-spectrum waveform, called a pseudorandom noise (PRN) code, which it transmits on each carrier. There are two types of PRN codes. The first type is a coarse acquisition (C/A) code with a chip rate of 1.023 megabits/s. The second type is a precision (P) code with a chip rate of 10.230 megabits/s. The C/A code is broadcast on L1, and the P code is broadcast on both L1 and L2. A 50 bit/s data message is also broadcast on both carriers [16–18]. Dual-frequency timing receivers have become more common as of 2010, but most timing devices receive only L1. Nearly all GPS timing receivers can simultaneously track at least eight satellites.
Alternative sources of navigation and traffic flow data
Published in Lawrence A. Klein, ITS Sensors and Architectures for Traffic Management and Connected Vehicles, 2017
In normal operation, GPS receivers deduce their position by calculating their distance from several satellites at once. Each satellite carries an atomic clock and broadcasts its location, the time, and a signature pattern of 1023 plus and minus signs known as a pseudorandom noise (PRN) code. These codes identify a signal as originating from, for instance, satellite A versus satellite B, which is necessary because all GPS satellites broadcast civilian signals on the same frequency. The PRN code patterns also repeat over time, and their distinctive arrangements of pluses and minuses enable GPS receivers to use them to determine the signal transmission delay between a satellite and the receiver. A receiver uses these delays, along with the satellite positions and time stamps, to triangulate its precise location. To get a good fix, a receiver must receive signals from four or more satellites at a time—it can figure coordinates based on just three, but it needs the fourth to synchronize its inexpensive, drift-prone clock with the constellation's precise atomic clocks.
A Comprehensive Survey on GNSS Interferences and the Application of Neural Networks for Anti-jamming
Published in IETE Journal of Research, 2021
Kambham Jacob Silva Lorraine, Madhu Ramarakula
The GNSS satellites broadcast the navigation message at 50 bit/s, which is modulated onto the Pseudorandom Noise (PRN) code; usually C/A code. For GPS, the C/A code is 1023 chips in length with a chipping rate of 1.023 MHz. Then, using Binary Phase Shift Keying (BPSK), the resulting signal is modulated onto the carrier. The broadcasted GNSS signal is represented as where s(t) represents the GNSS signal, denotes the power of the signal, d(t) is navigation data, c(t) is spreading code (C/A code), ⊕ symbolizes exclusive or, and represents the carrier frequency and carrier phase.