Enhanced time of arrival method
First Claim
1. A method for improving accuracy of a radio location system based on time-of-arrival at a receiver using direct-sequence spread-spectrum modulation for time stamping a received radio broadcast, comprising the steps of:
- determining a time position of a correlation peak of the received radio broadcast;
estimating from the correlation peak a leading edge of a correlation function;
collecting a multiplicity of correlation envelope samples of the leading edge of the correlation function, each of said multiplicity of correlation envelope samples separated by a portion of a chip time; and
calculating slope information from the leading edge of the correlation function for increasing resolution and accuracy of a time-of-arrival reading.
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Accused Products
Abstract
A method for improving a radio location system based on time-of-arrival. Time-of-arrival radio location systems are limited in ultimate accuracy by signal-to-noise ratio and by the time varying multipath environment in which they must operate. These systems time stamp some feature of an arriving signal, from a transmitter, in order to calculate a range or a hyperbolic line-of-position. Some feature of the received signal must be identified which can provide repeatable readings, in order for a time-of-arrival system to be reliable. The present invention teaches techniques which maintain a high signal-to-noise ratio while identifying a feature of the received signal which is least affected by multipath. The technique uses correlation peak/envelope information to estimate the leading edge of the correlation function, then enhances discrete samples at the leading edge of the correlation function to yield high signal-to-noise ratio readings. The present invention can reduce required transmitted bandwidth, increase system resolution and accuracy by twenty to one, and maintain high message traffic throughput.
79 Citations
41 Claims
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1. A method for improving accuracy of a radio location system based on time-of-arrival at a receiver using direct-sequence spread-spectrum modulation for time stamping a received radio broadcast, comprising the steps of:
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determining a time position of a correlation peak of the received radio broadcast; estimating from the correlation peak a leading edge of a correlation function; collecting a multiplicity of correlation envelope samples of the leading edge of the correlation function, each of said multiplicity of correlation envelope samples separated by a portion of a chip time; and calculating slope information from the leading edge of the correlation function for increasing resolution and accuracy of a time-of-arrival reading. - View Dependent Claims (2, 3, 4, 5, 31, 37)
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6. A method for locating radio units based on time-of-arrival at a receiver using direct sequence spread spectrum to time stamp incoming radio broadcasts, the method comprising the steps of:
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receiving a signal; reducing a bandwidth of the receiver for enhancing signal-to-noise ratio; measuring a leading edge of a correlation function; comparing the leading edge to a level at least equaling a sum of an auto-correlation code noise and estimated background noise; time stamping a first arriving signal, using the leading edge of the correlation function, responsive to the leading edge exceeding the sum; and remeasuring, responsive to the leading edge not exceeding the sum, a leading edge of the correlation function. - View Dependent Claims (10, 36)
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7. A method for locating radio units based on time-of-arrival at a receiver using direct sequence spread spectrum to time stamp incoming radio broadcasts, the method comprising the steps of:
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receiving a signal; measuring a leading edge of a correlation function; comparing the leading edge to a level at least equaling a sum of an auto-correlation code noise and estimated background noise; time stamping a first arriving signal, using the leading edge of the correlation function, responsive to the leading edge exceeding the sum; remeasuring, responsive to the leading edge not exceeding the sum, a leading edge of the correlation function; collecting a multiplicity of samples at the leading edge of the correlation function; deriving slope information from the multiplicity of samples; and enhancing resolution, using the slope information, of a time-of-arrival time stamp. - View Dependent Claims (9, 11, 38)
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8. A method for locating radio units based on time-of-arrival at a receiver using direct sequence spread spectrum to time stamp incoming radio broadcasts, the method comprising the steps of:
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receiving a signal; reducing a bandwidth of the receiver for enhancing signal-to-noise ratio; measuring a leading edge of a correlation function; comparing the leading edge to a level at least equaling a sum of an auto-correlation code noise and estimated background noise; time stamping a first arriving signal, using the leading edge of the correlation function, responsive to the leading edge exceeding the sum; remeasuring, responsive to the leading edge not exceeding the sum, a leading edge of the correlation function; collecting a multiplicity of samples at the leading edge of the correlation function; deriving slope information from the multiplicity of samples; and enhancing resolution, using the slope information, of a time-of-arrival time stamp.
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12. A method for locating radio units based on time-of-arrival at a receiver using direct sequence spread spectrum to time stamp incoming radio broadcasts, the method comprising the steps of:
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receiving a signal; estimating a leading edge of a correlation function from an aspect of the correlation function; and realigning a chip code temporal position to the leading edge of the correlation function; and time stamping a first arriving signal using at least one sample from the estimated leading edge of the correlation function. - View Dependent Claims (13, 14, 15, 16, 17, 18, 39, 40, 41)
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19. A method for improving accuracy of a radio location system based on time-of-arrival at a receiver using direct sequence spread spectrum to time stamp a received radio broadcast, the method comprising the steps of:
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receiving a signal; determining a time position of a correlation peak; estimating, using the correlation peak, a leading edge of a correlation function; moving a chip code position backward by at least one chip time; moving the chip code position forward by sub-chip increments until at least one of a correlation envelope reading exceeds a preset margin and a preset number of samples are taken; and time stamping the chip code position to represent a time-of-arrival of the signal. - View Dependent Claims (20, 21, 25, 26)
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22. A method for improving accuracy of a radio location system based on time-of-arrival at a receiver using direct sequence spread spectrum to time stamp the received radio broadcast, the method comprising the steps of:
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receiving a signal; determining a time position of a correlation peak; estimating, using the correlation peak, a leading edge of a correlation function; moving a chip code position backward by approximately one chip time; enhancing signal-to-noise ratio by at least one of reducing a bandwidth of the receiver and increasing an integration time; moving the chip code position, at least one of forward and backward, by sub-chip multiples, for verifying the chip code position occurs prior to the leading edge of the correlation function; moving the chip position forward by sub-chip increments until at least one of a correlation envelope reading exceeds a preset margin and a preset number of samples are taken; and time stamping the chip code position to represent time-of-arrival of the signal. - View Dependent Claims (23)
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24. A method for improving accuracy of a radio location system based on time-of-arrival using direct sequence spread spectrum to time stamp a signal received as a radio broadcast, the method comprising the steps of:
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determining a time position of a correlation peak; estimating, using the correlation peak, a leading edge of a correlation function; moving a chip code position backward by less than one chip time; moving the chip code position backward by sub-chip increments until a correlation envelope decreases by at least one of a preset margin and an auto-correlation noise floor; and time stamping the chip code position to represent time-of-arrival of the signal. - View Dependent Claims (30, 35)
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27. A method for improving a radio location system based on time-of-arrival, using spread spectrum to time stamp a received radio broadcast, the method comprising the steps of:
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receiving a signal; determining a time position of a correlation peak; estimating, using the correlation peak, a leading edge of a correlation function; moving a chip code position backwards by less than one chip time; moving the chip code position at least one of forward and backward; measuring a resulting change in at least one of signal strength, quieting output, and lock detect, as a first reading; moving the chip code position by at least one of forward and backward; measuring a resulting change in at least one of signal strength, quieting output, and lock detect, as a second reading; and calculating, using the first reading and the second reading, a slope for increasing the resolution of a time-of-flight radio location system. - View Dependent Claims (28, 29)
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32. A method for improving a radio location system based on time-of-arrival using direct sequence spread spectrum to time stamp the received radio broadcast, the method comprising the steps of:
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receiving a signal; determining a time position of a correlation peak; estimating, using the correlation peak, a leading edge of a correlation function; moving a chip code position backward by at least one chip time from the correlation peak; moving the chip code position forward by a portion of a chip time; and time stamping, responsive to a correlation envelope exceeding a preset margin, the chip code position representative of a time-of-arrival of the signal. - View Dependent Claims (33, 34)
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Specification