Determination of chip rate and center frequency for a spread spectrum acoustic ranging system

Spread spectrum systems are commonly used for ranging. Perhaps the most pervasive system is GPS. Because such a system relies on a high frequency signal, the receiver must have an unobstructed view of the sky. There are situations in which one cannot use GPS, such as in an orchard or indoors. This paper suggests that ranging can be achieved by applying the spread spectrum technique to sound waves rather than RF. In using air as the medium, there are many different factors that must be considered in deciding what the appropriate chip rate and center frequency should be. The speed of sound is much slower than RF. It changes significantly with a change in temperature. There are Doppler shift effects. The available bandwidth relative to center frequency is enormous when compared to RF. The attenuation of the higher frequencies is very dramatic for sound. This paper considers these factors and others in determining an appropriate chip rate and center frequency for acoustic ranging. Low frequencies in sound are attenuated much less than high frequency signals and to capitalize on this it was found that a center frequency of zero hertz and a relatively low chip rate of 100 chips/sec would be suitable.