Patent ID: 7466219

Claim:
A communication device comprising: a transmitter that transmits a distance-calculation signal with which to calculate a distance to a partner communication device; a detector that receives the distance-calculation signal returned from the partner communication device and detects a phase difference between the distance-calculation signal when transmitted and the distance-calculation signal when received; a calculator that calculates the distance to the partner communication device based on the phase difference detected by the detector; a modulator that modulates the distance-calculation signal with a carrier wave of a first frequency; and a demodulator that demodulates the distance-calculation signal that has been modulated with a carrier wave of a second frequency higher than the first frequency and returned by the partner communication device after received from the modulator and demodulated by the partner communication device, wherein the modulator ASK-modulates the distance-calculation signal with the carrier wave of the first frequency, and wherein the demodulator demodulates the distance-calculation signal that has been FSK-modulated with the carrier wave of the second frequency and returned by the partner communication device.