cET 318 faith Lecture 1. Signal Structure 5. Satellite Signal Book: p 71-85 Dr Guoqing Zhou 1.1 Physical Fundamentals This attenuation is usually expressed in decibels (dB). By definition, an attenuation of n dB means signal propagation from the that the original field strength is decreased by ite to the user by means of factor of 10-0In electromagnetic waves. Such waves Physical quantities (alternating) electric force. Dimension Circular frequency The field strength decreases ith inereasing distance period from the transmitting source. conforms Speed of light are equivalent to multiples of 2r radians. Another unit for cycles per second (cps )is Hertz(Hz) of a moving emitter or a me eceived frequency is Doppler sh do g=「fd f(received)≠e( emitted by an amount Af which, apart from relativistic effects, is proportional to the radial velocity ve dp/dt p of the emitter with respect to Known: F=1.5GHz, c=3x10 km/s, D-20, 000km Question: cycles=?(10), Observable=?1 Dr. Guoqing Zhou 5. Satellite Signal CET 318 Book: p. 71-85 1. Signal Structure 1.1 Physical Fundamentals GPS signal propagation from the satellite to the user by means of electromagnetic waves. Such waves are generated by an oscillating (alternating) electric force. The propagation conforms to Maxwell's laws. The field strength decreases with increasing distance from the transmitting source. This attenuation is usually expressed in decibels (dB). By definition, an attenuation of n dB means that the original field strength is decreased by a factor of 10-0.1n. Speed of light c m/s period P s wavelength λ m/cycle Phase ϕ cycle Circular frequency f Cycle/s Quantity Symbol Dimension Physical quantities Integer cycles are equivalent to multiples of 2π radians. Another unit for cycles per second (cps ) is Hertz (Hz) Example: Known: F=1.5GHz, c=3x105 km/s, D=20,000km, Question: cycles=? (108), Observable=? λ π c P f = = 1 2 dt d f ϕ = ∫ = t t fdt 0 ϕ ∫ = = − = − t t c D fdt f t t f t 0 ( ) ( ) ϕ 0 By Phase In the case of a moving emitter or a moving receiver, the received frequency is Doppler shifted. fr (received) ≠ fe (emitted) by an amount ∆f which, apart from relativistic effects, is proportional to the radial velocity vρ = dρ/dt = ρ of the emitter with respect to the receiver