GPS Signal Fundamental 10.23MHZ L, carrier phase C/A code P code Navigation 157542MHz103MH|10.23MH S0BPS Ly carrier phase P code 1201260Nz 10.23MHZ OBPS 電 Principles of the Global Positioning System 20053-181(1 Two codes are used for the satellite clock readings both characterized by a pseudorandom noise (PRN) sequence Code Type frequency Repeated time coarse/acquisition f10 everv millisecond lear/access(C/A) precision(or protected) once every 266.4 code (p-code) W-code encrypt the P-code to transmitted in 30 the Y-code, f 20 seconds Y-code Encrypted by W-code Principles of the Global Positioning System 2005-3-18
6 Principles of the Global Positioning System 2005-3-18 11 11 GPS Signal Fundamental frequency 10.23MHz L1 carrier phase 1575.42MHz L2 carrier phase 1227.60MHz C/A code 1.023MHz P code 10.23MHz P code 10.23MHz Navigation message 50BPS Navigation message 50BPS ×154 ×120 ÷10 ÷204600 Principles of the Global Positioning System 2005-3-18 12 Two codes are used for the satellite clock readings, both characterized by a pseudorandom noise (PRN) sequence
Component Frequency(MH) Fundamental Frequency fo=10.23 Carrier li 1546=157542(190cm) Carrier l2 120=122760(244cm) P-Cod =10.23 C/A-Code J10=1023 W-Code f20=0.5115 Navigation message f204600=50X106 The unmodulated carriers by Li(t)=acos(it) The C/A-code is placed on the Li carrier in phase quadrature (i.e, 90 offset)with the P-code 電 Principles of the Global Positioning System 2005-3-18(13 A Random code? The Pseudo random Code(PrC)or Pseudo random Noise code, PRN, is a fundamental part of GPS Physically it's just a very complicated digital code, or in other words, a complicated sequence of "on"and"off pulses. The signal is so complicated that it almost looks like random electrical noise. Hence the name "Pseudo- Random Principles of the Global Positioning System 2005-3-181414
7 Principles of the Global Positioning System 2005-3-18 13 Principles of the Global Positioning System 2005-3-18 14 14 A Random Code? The Pseudo Random Code (PRC) or Pseudo Random Noise code, PRN, is a fundamental part of GPS. Physically it's just a very complicated digital code, or in other words, a complicated sequence of "on" and "off" pulses. The signal is so complicated that it almost looks like random electrical noise. Hence the name "PseudoRandom
A Random code? Since each satellite has its own unique Pseudo- Random Code, this complexity also guarantees that the receiver won,'t accidentally pick up another satellite's So all the satellites can use the same frequency without jamming each other. And it makes it more difficult for a hostile force to jam the system In fact the Pseudo Random Code gives the dod a way to control access to the system 電 Principles of the Global Positioning System 20053181515 a Random code? Another reason for the complexity of the Pseudo Random Code, is crucial to making GPS economical The codes make it possible to use information theory to "amplify"the GPS signal And that's why GPS receivers don' t need big satellite dishes to receive the gPs signals Principles of the Global Positioning System 2005-3-181616
8 Principles of the Global Positioning System 2005-3-18 15 15 A Random Code? ¾ Since each satellite has its own unique PseudoRandom Code, this complexity also guarantees that the receiver won't accidentally pick up another satellite's signal. ¾ So all the satellites can use the same frequency without jamming each other. And it makes it more difficult for a hostile force to jam the system. ¾ In fact the Pseudo Random Code gives the DoD a way to control access to the system. Principles of the Global Positioning System 2005-3-18 16 16 A Random Code? ¾ Another reason for the complexity of the Pseudo Random Code, is crucial to making GPS economical. ¾ The codes make it possible to use information theory to “amplify” the GPS signal. And that's why GPS receivers don't need big satellite dishes to receive the GPS signals