Method and system for determining position of mobile radio terminals

• US 6,009,334 A
• Filed: 11/26/1997
• Issued: 12/28/1999
• Est. Priority Date: 11/26/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Fischer, Sven, Lundqvist, Patrik, Grubeck, Hans
• Primary Examiner(s): Loomis, Paul
• Assistant Examiner(s): Corsaro, Nick
• Application Number:
  US08/978,960
• Time in Patent Office: 762 Days
• Field of Search: 455/427, 455/428, 455/456, 455/457, 455/423, 455/424, 455/446, 455/67.1, 455/67.6, 455/226.1, 342/387, 342/457
• US Class Current: 455/456.2
• CPC Class Codes: G01S 11/08 using synchronised clocks
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A method and apparatus are disclosed for determining more accurately, in a radio environment with time dispersion, the distance between a radio receiver and radio transmitter, by special processing of received radio signals that have been transmitted repeatedly from the same radio transmitter and are possibly subject to multipath propagation. The Time of Arrival (TOA) of the received radio signals is repeatedly estimated using channel power profiles. A TOA value near the minimum occurring TOA is selected wherein each estimated TOA is derived from incoherent integration of a randomly chosen number of the received bursts having the same known bit sequence, in order to eliminate the influence of noise.

Claims

1. A method for determining, in a radio environment with time dispersion, the distance between a radio transmitter and a radio receiver, comprising the steps of:

transmitting from said radio transmitter M samples of a signal;

receiving in said receiver said M samples together with multipath components and noise;

determining an estimated channel power profile for each of said M samples;

selecting a first set of N samples from said M samples;

performing incoherent integration for said estimated channel power profiles for said first set of N samples to form a first integrated signal;

if a quality level of said first integrated signal with respect to signal to noise is less than a predetermined threshold, selecting another sample from said M samples;

performing incoherent integration for said estimated channel power profiles for said first set of N samples and said another sample to form a second integrated signal;

if a quality level of said second integrated signal with respect to signal to noise is greater than or equal to said predetermined threshold, determining a time-of-arrival of a maximum level of said second integrated signal;

entering said time-of-arrival into a time-of-arrival versus frequency of occurrence array;

selecting a second set of N samples from said M samples;

repeating all of said performing through said entering steps for said second set of N samples; and

determining a minimum value estimated time-of-arrival from said array.

2. The method of claim 1, wherein the step of determining a minimum value estimated time-of-arrival from said array comprises reading out from said array a time value having a first predetermined number of all occurrences being higher time-of-arrival values, and a complement of said first predetermined number of all occurrences being lower time-of-arrival values.

3. The method of claim 2, wherein said first predetermined number is greater than 70%, and said second predetermined number is 100% minus said first predetermined number in percent.

4. The method of claim 1, wherein the receiving step comprises receiving said M samples separately in two independent radio receivers to form 2 times said M samples.

5. The method of claim 1, wherein said array comprises a matrix.

6. The method of claim 1, wherein a manual version of said entering step comprises entering said time-of-arrival into a time-of-arrival versus frequency of occurrence diagram.

7. A method for determining the distance between a mobile station and a base station in a mobile network, comprising the steps of:

transmitting from said mobile station a first plurality of signal samples;

receiving at said base station said first plurality of signal samples;

forming an estimated channel power profile value for each of said first plurality of signal samples;

selecting a second plurality of samples from each said estimated channel power profile value;

integrating said estimated channel power profile value for said second plurality of samples to form a first integrated channel power profile;

if a quality level of said first integrated channel power profile is less than a predetermined threshold value, selecting at least one additional sample from each said estimated channel power profile value;

integrating said estimated channel power profile for said second plurality of samples and said at least one additional sample to form a second integrated channel power profile;

if a quality level of said second integrated channel power profile is greater than or equal to said predetermined threshold value, determining a time-of-arrival for a maximum of said second integrated channel power profile;

entering said time-of-arrival into a time-of-arrival versus frequency of occurrence array;

selecting a third plurality of samples from each said estimated channel power profile value;

repeating said integrating through said entering steps for said third plurality of samples; and

determining a minimum time-of-arrival from said array.

8. The method of claim 7, wherein said integrating steps comprise incoherent integration.

9. The method of claim 7, wherein said minimum time-of-arrival represents a shortest distance between said mobile station and said base station.

10. The method of claim 7, wherein the step of determining a minimum time-of-arrival comprises reading out from said array a time value having a first number of all occurrences being higher time-of-arrival values, and a complement of said first number of all occurrences being lower time-of-arrival values.

11. The method of claim 10, wherein said first number is greater than 0.7, and said complement of said first number is 1 minus said first number.

12. A method for determining, in a radio environment with time dispersion, a distance between a radio transmitter and a radio receiver, comprising the steps of:

transmitting from said radio transmitter M samples of a signal;

receiving in said radio receiver said M samples together with multipath components and noise;

selecting a first set of N samples from said M samples to form a mathematical function of said N samples, varying the number for N iteratively such that said mathematical function of said N samples preserves time information and reduces said noise to a first predetermined value, said first predetermined value indicating a desired level of said signal relative to said noise;

creating additional sets of N samples from said M samples, by repeating said selecting step and starting each said repeating step with a different random and independent set of N samples, and terminating said repeating step when a number of said additional sets of N samples comprises a second predetermined value;

determining a time-of-arrival for each of said first set and said additional sets of N samples;

storing each said time-of-arrival in a time-of-arrival versus frequency of occurrence array; and

determining an estimated time-of-arrival from said time-of-arrival versus frequency of occurrence array.

13. A method for performing, in a radio environment with time dispersion and noise, a determination of an earliest time-of-arrival for a known received signal transmitted repetitively as M samples from a remote transmitter, said M samples subject to fading such that a time-of-arrival varies between at least two of said M samples, comprising the steps of:

selecting from among said M samples a first set of samples;

forming a mathematical function from said first set of samples to improve a signal-to-noise quality without destroying time-of-arrival information;

repeating said selecting and forming steps for additional sets of samples in addition to said first set of samples;

determining a time-of-arrival for each of said first set and said additional sets of samples; and

statistically processing each said time-of-arrival obtained from said determining step to obtain an estimate of said earliest time-of-arrival.

14. The method of claim 13, wherein said first set of samples and said additional sets of samples comprise an equal number of N samples.

15. The method of claim 13, wherein said first set of samples and said additional sets of samples comprise different numbers of samples.

16. The method of claim 13, wherein a number of samples used in said first set of samples and said additional sets of samples is selected to obtain a desired signal-to-noise quality for each of said first set of samples and said additional sets of samples.

17. The method of claim 13, wherein a number of samples used in said first set of samples and said additional sets of samples is selected to obtain a desired signal-to-noise quality defined by h/sigma.

18. A system for use in determining the distance between a mobile station and a base station in a mobile network, comprising:

a mobile transmitter for transmitting a first plurality of signal samples;

a base station receiver for receiving said first plurality of signal samples; and

a processor coupled to said base station receiver, said processor operable to;

form an estimated channel power profile value for each of said first plurality of signal samples;

select a second plurality of samples from each said estimated channel power profile value;

integrate said estimated channel power profile value for said second plurality of samples to form a first integrated channel power profile;

select at least one additional sample from each said estimated channel power profile value if a quality level of said first integrated channel power profile is less than a predetermined threshold value;

integrate said estimated channel power profile for said second plurality of samples and said at least one additional sample to form a second integrated channel power profile;

determine a time-of-arrival for a maximum signal amplitude of said second integrated channel power profile if a quality level of said second integrated channel power profile is greater than or equal to said predetermined threshold value;

enter said time-of-arrival into a time-of-arrival versus frequency of occurrence array;

select a third plurality of samples from each said estimated channel power profile value;

repeat the first integrate operation through the enter operation for said third plurality of samples; and

determine a minimum time-of-arrival from said array.