Enhanced time of arrival method

DETAILED DESCRIPTION A general object of the invention is using the least amount of bandwidth possible to yield accurate time-of-arrival readings.
Another object of the invention is enhanced accuracy time-of-arrival readings with minimal transmitted message dwell time to allow the greatest number of simultaneous users on a radio location system.
An additional object of the invention is identifying and measuring a feature in a received signal which is least affected by multipath errors.
A further object of the invention is obtaining accurate time-of-arrival readings with low signal-to-noise ratio, minimum detectable signals.
A still further object of the invention is to provide enhanced time-of-arrival readings with resolution greater than the sub-chip step size searched.
According to the present invention, as embodied and broadly described herein, an enhanced time of arrival method for use with a radio location system is provided.
A receiver uses direct sequence spread-spectrum modulation to time stamp a received radio broadcast.
The receiver receives a spread-spectrum modulated signal from a transmitter.
The steps include determining, in the received spread-spectrum signal, a time position of a correlation peak and estimating, from the correlation peak, a leading edge of a correlation function.
The steps further include moving a receiver chip code position, corresponding to the estimated leading edge of the correlation function, backward by about one chip time, relative to the chips in the received spread-spectrum signal.
The receiver-chip-code position, relative to the chips in the received spread spectrum signal, is then moved forward by sub-chip increments until a correlation envelope reading exceeds a preset margin.
The method uses the leading edge of the correlation function, as determined by the receiver-chip-code position when the correlation envelope reading exceeds the preset margin, to time stamp an arriving signal.
The term "receiver-chip-code position" as used herein is the position of chips in a chip sequence generated at the receiver