METHOD OF AND SYSTEM FOR ESTIMATING A TIME OF ARRIVAL OF A RADIO SIGNAL

• US 20030036390A1
• Filed: 12/21/1999
• Published: 02/20/2003
• Est. Priority Date: 01/09/1999
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: LOPES, LUIS, VILLIER, ERIC, LUDDEN, BRENDAN
• Granted Patent: US 6,675,018 B2
• Time in Patent Office: Days
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/0215 Interference
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

The invention relates to a method for estimating time of arrival of radio signals in particular as used for location determination. A known method of determining the location of a subscriber unit (401) calculates a number of ranges based on the distance from base stations (403,405,407) with known location. The ranges are calculated from time of arrival estimates of the signals from the different base stations but a significant source of error is the multipath signal components typical in for example cellular mobile communication systems. According to the invention, the effect of multipath is mitigated by selecting a subset of signals based on a time of arrival estimate of each of the signals. An averaged time of arrival estimate with improved accuracy is then determined from the selected subset. A typical use of the invention is for location determination in a cellular mobile communication system.

Claims

1. A method of estimating an average time of arrival of a radio signal comprising the steps of:

transmitting a plurality of radio signals from a transmitter to a receiver through a propagation channel;

estimating a time of arrival for each of a plurality of the radio signals received at the receiver;

selecting a subset of the plurality of the radio signals received at the receiver in response to the time of arrival estimates;

generating an averaged propagation channel estimate from the subset of radio signals; and

estimating an averaged time of arrival from the averaged propagation channel estimate.

2. A method of estimating an average time of arrival of a radio signal as claimed in claim 1 wherein the subset consists of the radio signals having an estimated time of arrival between a lower percentile and an upper percentile of the time of arrival estimates of the plurality of the radio signals received at the receiver.

3. A method of estimating an average time of arrival of a radio signal as claimed in claim 1 wherein the subset consists of a number of the radio signals having the closest time of arrival estimate to the time of arrival corresponding to a percentile of the time of arrival estimates of the plurality of the radio signals received at the receiver.

4. A method of estimating an average time of arrival of a radio signal as claimed in claim 2 wherein at least one of the percentiles is varied in response to at least one parameter chosen from the group of:

a) a variance of the time of arrival estimates;

b) a signal to noise ratio of at least one of the plurality of signals;

c) a previous averaged propagation channel estimate;

d) a propagation channel estimate of at least one of the plurality of signals;

e) an accuracy of the averaged time of arrival estimate; and

f) available computational resource.

5. A method of estimating an average time of arrival of a radio signal as claimed in claim 3 wherein the number of the radio signals in the subset is varied in response to a parameter chosen from the group of

a) a variance of the time of arrival estimates;

b) a signal to noise ratio of at least one of the plurality of signals;

c) a previous averaged propagation channel estimate;

d) a propagation channel estimate of at least one of the plurality of signals;

e) an accuracy of the averaged time of arrival estimate, and

f) available computational resource.

6. A method of estimating an average time of arrival of a radio signal as claimed in claim 5 wherein the step of generating an averaged propagation channel estimate from the subset of signals includes weighting each of the radio signals of the subset in response to a parameter chosen from the group of:

a) a signal to noise ratio of the signals;

b) an estimated propagation channel impulse response energy; and

c) the multipath propagation characteristics for the radio signals.

7. A method of estimating an average time of arrival of a radio signal as claimed in claim 1 wherein a propagation channel estimate for each signal of the subset is generated and the step of generating an averaged propagation channel estimate from the subset of signals includes averaging these propagation channel estimates.

8. A method of estimating an average time of arrival of a radio signal as claimed in claim 1 used in a cellular communication system.

9. A method of estimating a range between a transmitter and a receiver comprising the step of estimating an average time of arrival of a radio signal in accordance with claim 1.

10. A method of position determination comprising the step of estimating at least one range in accordance with claim 9.

11. A method of position determination as claimed in claim 10 wherein a plurality of ranges are estimated and the weighting of each range estimate is in response a distribution of the time of arrival estimates of the plurality of signals.

12. A method of position determination as claimed in claim 1 further comprising the step of determining a dominant source of error and wherein the selection of the subset of the plurality of the radio signals received at the receiver is also in response to the dominant source of error.

13. A system for estimating an average time of arrival of a radio signal comprising:

a receiver;

a transmitter transmitting a plurality of radio signals to the receiver through a radio propagation channel;

processor means for estimating a time of arrival for each of a plurality of the radio signals received at the receiver;

means for selecting a subset of the plurality of the radio signals received at the receiver in response to the time of arrival estimates;

means for generating an averaged propagation channel estimate from the subset of radio signals; and

means for estimating an averaged time of arrival from the averaged propagation channel estimate.