Overview

In sections 1.4, 2.5, and 3.9 we discussed the effects that Doppler shifts have on our CDMA signal. Most people are vaguely familiar with the Doppler effect (named after Johann Christian Doppler, and his train full of blaring trumpeters circa 1845) as it applies to slow-moving sound waves. Many tend to relate the effect to their everyday experiences, as when a speeding train or automobile sounds its horn as it passes. However, they may not see the relation to signals which travel at the speed of light (i.e., our RF signal). The effect has two primary causes: the finite velocity at which the waves propagate (whether sound or RF waves); and our perception of pitch based on the length of time between each cycle of the horn's wail in other words, the wavelength of the signal. Since acoustic waves and RF signals alike travel at a finite speed, it takes a finite amount of time for each successive wave peak to travel from the source to the observer. If, however, either the source or the observer is in motion, the time it takes for each wave peak to get to the observer is either increased (when they are moving apart) or decreased (when they are moving closer together). In effect, the relative motion between source and observer either increases the perceived wavelength (moving apart) or compresses it (approaching each other). Mathematically:

F _obs = F _src x (v + V)/v ...