A reference device determines its distance from a communication device by first using a training process to determine a calibrated time delay for the communication device when the communication device is at a known distance from the reference device. The calibrated time delay is a steady state internal processing delay for the communication device. Subsequently, when the reference device is at an unknown distance from the communication device, the reference device determines the unknown distance using the previously determined calibrated time delay along with a measured signal travel time at the unknown distance.