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Distance Measurements Using a Two-Tone Wireless Signal and a Digital Receiver

IP.com Disclosure Number: IPCOM000008850D
Publication Date: 2002-Jul-17
Document File: 4 page(s) / 135K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses a wireless transmitter and receiver to measure the physical distance between the transmitter and the receiver. Benefits include inexpensive RF hardware that measures distance or relative location more accurately than existing technologies (such as GPS).

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Distance Measurements Using a Two-Tone Wireless Signal and a Digital Receiver

Disclosed is a method that uses a wireless transmitter and receiver to measure the physical distance between the transmitter and the receiver. Benefits include inexpensive RF hardware that measures distance or relative location more accurately than existing technologies (such as GPS).

Background

Currently, GPS receivers are costly (approximately $100 each), and these receivers only enable an accuracy of ~100 meters.  Also the GPS solution is very sensitive to channel conditions, thereby reducing the accuracy of the solution.

General Description

Transmitter Description

The transmitter consists of a simple RF circuit, where a two-tone signal is generated (see 

Figure 1). The transmitter consists of two oscillators, a phase comparator, two switches, a mixer, and an antenna. The oscillator Fc is the carrier signal and the oscillator Fmod is the modifier signal. These two signals are fed into the phase comparator, which compares the phase of the two input signals. When the signals are in phase, the phase comparator closes the switch to allow the signals to propagate to the mixer and antenna. When the signal phases are not in sync, the switch is opened blocking transmission of the signals to the mixer and the antenna. The mixer combines the two in-phase signals and the antenna transmits the signals.

Receiver Description

The receiver consists of simple RF and digital logic. The receiver demodulates the two-tone signal acquired from the transmitter, and calculates the distance information from the phase change between the two signals (see Figure 2). The receiver consists of an antenna, a down converter, an A/D converter, and a signal processor. The antenna receives the two-tone signal from the transmitter. This received signal is propagated to the down converter. The down converter (a single-stage mixer and a low pass filter in Figure 2) converts the signal from the carrier frequency (Fc) to a local intermediate frequency (Fif). The Fif is chosen such that the sample rate of the A/D converter is at least four times the highest frequency of the down converted signal. The A/D converter chan...