METHOD FOR ESTIMATING JOINTLY TIME-OF-ARRIVAL OF SIGNALS AND TERMINAL LOCATION

• US 20080032708A1
• Filed: 08/01/2007
• Published: 02/07/2008
• Est. Priority Date: 08/03/2006
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Chong, Chia-Chin, Guvenc, Ismail
• Granted Patent: US 7,574,221 B2
• Time in Patent Office: Days
• US Class Current: 455/456.2
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/0273 using multipath or indirect path propagation signals in position determination
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• 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

A method that estimates jointly and iteratively the first arriving path of a received signal and a mobile terminal location uses a residual location error. The method may include setting a ranging threshold to reduce residual location error. The method iteratively estimates the first arriving path of the received signals and mobile terminal location, with the estimate of mobile terminal location improving the estimate of the first arriving path, and vice versa. Initially, a peak selection method determines a rough time-of-arrival (TOA) for a signal received at each of a number of different fixed terminals. An estimate of the location of the mobile unit is then provided (e.g., based on a least-squares (LS) triangulation). If the residual error is unsatisfactory, the TOAs are refined, using a search-back algorithm, which searches back from the strongest paths of the received signals. The new TOAs are used to refine the estimate of the location of the mobile terminal. In addition, the parameters of the search-back algorithm (e.g., a search-back threshold, timing windows) may be modified for greater accuracy in the estimated first path. The first arriving path estimate and the location estimate are iterated until convergence (e.g., the residuals are within a tolerance) or until a termination condition is reached, usually controlled by the thresholds setting.

Claims

1. A method for estimating the location of a mobile unit based on signals received from a plurality of fixed terminals, comprising:

(a) at each fixed terminal, determining a time-of-arrival for the signal received at the fixed terminal;

(b) based on the times-of-arrival determined at the fixed terminals, providing an estimate of the location of the mobile unit; and

(c) determining if the estimate of the location of the mobile unit is accurate within a predetermined threshold using residuals each representing an error relating the estimate of the location of the mobile unit with the known positions of the fixed terminals.

2. A method as in claim 1, further comprising:

when the estimate of the location of the mobile unit is accurate within the predetermined threshold, adopting the estimate of the location of the mobile unit; and

when the estimate of the location of the mobile unit is not accurate within the predetermined threshold, modifying the times-of-arrival, and repeating (b) and (c).

3. A method as in claim 1, where modifying the times-of-arrival comprises estimating each time-of-arrival based on a search-back algorithm.

4. A method as in claim 3, wherein the search-back algorithm compares the signal strength of the received signal at each fixed terminal against a search-back parameter threshold.

5. A method as in claim 4 wherein the search-back parameter threshold depends on information derived from a determination of whether or not the signal received at the fixed terminal is line-of-sight.

6. A method as in claim 1, wherein the search-back parameter threshold depends on the predetermined threshold used in determining the accuracy of the estimate of the location of the mobile unit.

7. A method as in claim 6, wherein the search-back algorithm provides a time corresponding to a given sample as the time-of-arrival when the given sample is greater than the search-back parameter threshold and all samples preceding the given sample are less than the search-back parameter threshold.

8. A method as in claim 1, wherein the times-of-arrivals of signals received at three or more fixed terminals are used in the estimate of the location of the mobile unit.

9. A method as in claim 8, successive estimates of the location of the mobile unit are provided using times-of-arrivals of different groups of fixed terminals, each group having three or more fixed terminals.

10. A method as in claim 1, wherein the time-of-arrival for the signal received at each fixed terminal is initially provided as the time-of-arrival of the strongest signal component.

11. A method as in claim 10, wherein the strongest signal component is detected using a peak detector.

12. A method as in claim 11, wherein the peak detector detects the energy in a signal output from a matched filter or an energy detector.