US-12618934-B2 - Methods and systems for validating locations

US12618934B2US 12618934 B2US12618934 B2US 12618934B2US-12618934-B2

Abstract

This invention relates to methods and systems for determining whether a reference point in a location system has changed used measurement residuals determined from an exchange of messages between reference points. In one embodiment a method of determining whether the location of a first one of a plurality of reference points used in a location system has changed is provided. The reference points each have a known initial position and the method includes the steps of: sending a wireless message between a second reference point and the first reference point and recording the times of sending and receipt of the wireless message; estimating, from the recorded times, an estimated distance between the first reference point and the second reference point; comparing the estimated distance to the actual distance between the known initial positions of the first and second reference points to determine a measurement residual; and determining, using the measurement residual, whether the location of the first reference point has changed.

Inventors

James Aweya
Nawaf ALMOOSA

Assignees

Khalifa University of Science and Technology
BRITISH TELECOMMUNICATIONS PLC
EMIRATES TELECOMMUNICATIONS CORPORATION

Dates

Publication Date: 20260505
Application Date: 20201207

Claims (20)

1 . A method of determining whether the location of a first one of a plurality of reference points used in a location system has changed, the reference points each having a known initial position, the method including the steps of: sending a wireless message between a second reference point and the first reference point and recording the times of sending and receipt of the wireless message; estimating, from the recorded times, an estimated distance between the first reference point and the second reference point; comparing the estimated distance to the actual distance between the known initial positions of the first and second reference points to determine a measurement residual; and determining, using the measurement residual, whether the location of the first reference point has changed; wherein the step of determining includes comparing the measurement residual or residuals to a pre-determined measurement residual for a message sent between the first and second reference points when they are at their initial positions.
2 . The method of claim 1 wherein the steps of sending, estimating and comparing are performed a plurality of times and the step of determining uses all of the determined measurement residuals.
3 . The method of claim 2 wherein the step of determining uses an average of the determined measurement residuals.
4 . The method of claim 3 , wherein the step of determining includes: comparing the measurement residual or residuals to a pre-determined measurement residual for a message sent between the first and second reference points when they are at their initial positions; and comparing the average of the determined measurement residuals to an average of a plurality of pre-determined measurement residuals for a plurality of messages sent between the first and second reference points when they are at their initial positions.
5 . The method of claim 1 wherein the location of the first reference point is determined to have changed if the measurement residual or residuals differs from the pre-determined measurement residual by more than a pre-determined amount.
6 . The method of claim 1 , further including the steps of: sending a wireless message between a plurality of other reference points and the first reference point and recording the times of sending and receipt of the wireless message; and for each of the plurality of other reference points: estimating, from the recorded times, an estimated distance between the first reference point and the other reference point; comparing the estimated distance to the actual distance between the known initial positions of the first reference point and the other reference point to determine a measurement residual, wherein the step of determining uses all of the determined measurement residuals.
7 . The method of claim 1 wherein the step of determining includes estimating the entropy of the measurement residual or residuals.
8 . The method of claim 7 further including the step of estimating the entropy of a plurality of pre-determined measurement residuals for a plurality of messages sent between the first and second reference points when they are at their initial positions.
9 . The method of claim 7 wherein the location of the first reference point is determined to have changed if the entropy of the measurement residual or residuals differs from the entropy of the plurality pre-determined measurement residuals by more than a pre-determined amount.
10 . The method of claim 1 wherein the steps are performed with each of the plurality of reference points as the first reference point.
11 . The method of claim 1 wherein the steps of sending, estimating, comparing and determining are performed periodically while the location system is operational.
12 . A method of determining the location of a mobile device, the method including the mobile device exchanging wireless messages with a plurality of reference points having known initial positions and determining the location of the mobile device from the timing of the sending and receiving of said messages, wherein the method further includes determining whether the location of any of the reference points has changed using a method according to claim 1 .
13 . The method of claim 12 wherein, when determining the location of the mobile device, the method does not use any reference point whose location is determined to have changed.
14 . A location system having a plurality of reference points each having a known initial position and arranged to exchange wireless messages with a mobile device to determine the location of the mobile device, the system including a processor which is arranged to: estimate from the recorded times of sending and receipt of a wireless message between a second reference point and a first reference point, an estimated distance between the first reference point and the second reference point; compare the estimated distance to the actual distance between the known initial positions of the first and second reference points to determine a measurement residual; and determine, using the measurement residual, whether the location of the first reference point has changed; wherein the processor is arranged to determine whether the location of the first reference point has changed by comparing the measurement residual or residuals to a pre-determined measurement residual for a message sent between the first and second reference points when they are at their initial positions.
15 . The location system of claim 14 wherein, if the location of the first reference point is determined to have changed, the system is arranged not to use that reference point in subsequent location determinations.
16 . The location system of claim 15 wherein the processor is arranged to perform the steps of estimating and comparing a plurality of times and to use all of the determined measurement residuals in determining whether the location of the first reference point has changed.
17 . The location system of claim 16 wherein the processor is arranged to determine whether the location of the first reference point has changed using an average of the determined measurement residuals.
18 . The location system of claim 17 , wherein the processor is arranged to determine whether the location of the first reference point has changed by: comparing the measurement residual or residuals to a pre-determined measurement residual for a message sent between the first and second reference points when they are at their initial positions; and comparing the average of the determined measurement residuals to an average of a plurality of pre-determined measurement residuals for a plurality of messages sent between the first and second reference points when they are at their initial positions.
19 . The location system of claim 14 wherein the processor is arranged to determine that the location of the first reference point if the measurement residual or residuals differs from the pre-determined measurement residual by more than a pre-determined amount.
20 . The location system of claim 14 , wherein the processor is further arranged to: for each of a plurality of other reference points in the system: estimate, from the recorded times of sending and receipt of wireless messages sent between the other reference point and the first reference point, an estimated distance between the first reference point and the other reference point; compare the estimated distance to the actual distance between the known initial positions of the first reference point and the other reference point to determine a measurement residual, and to determine whether the location of the first reference point has changed using all of the determined measurement residuals.

Description

RELATED APPLICATIONS This application claims priority to and all benefits of International Application No. PCT/GB2020/053134, filed on Dec. 7, 2020 for METHODS AND SYSTEMS FOR VALIDATING LOCATIONS, the entire disclosure of which is fully incorporated herein by reference. FIELD OF THE INVENTION The present invention relates to methods and systems for validating locations. It is particularly, but not exclusively, concerned with methods and systems for validating the location of access points, in particular reference access points in wireless networks such as WLANs. BACKGROUND OF THE INVENTION The Global Positioning System (GPS) is a widely available and almost indispensable service that provides location information used in many applications, such as navigation and emergency location services (e.g. E911). It is not hard to see that the applications of GPS and other similar Global Navigation Satellite Systems (GNSS) (for example the Russian GLONASS, the European Union's Galileo, and the Chinese Beidou) will continue to grow. Although being a very useful and indispensable service, GPS, however, does have a number of limitations, particularly for indoor applications. GPS receivers typically do not work well or at all indoors because the weak signals that are transmitted from the satellites are blocked by the building structures the receiver are located in. Furthermore, even in the outdoor environment, particularly in city centers with skyscrapers and very tall buildings, the satellite signals can be blocked by the surrounding environment because it obstructs the view between the GPS receiver and the geostationary satellites (so-called “urban canyons”). For these reasons and others, location techniques that can operate in the indoor environment (using, for example, wireless Local Area Network (WLAN) technologies) are sought after to complement the services provided by GPS. Location systems based on WiFi (IEEE 802.11) are generating a lot of interest in the industry mainly due to the ubiquity of WiFi and its presence in almost all aspects of our daily lives (in schools, hospitals, shopping malls, offices, factories, airports, etc.). This has made the need for location systems based on WiFi a pressing issue and an active area of research both in the industry and academia. The indoor environment itself presents significant challenges to localization. The location system has to address very tough challenges like NLOS and multipath propagation errors to provide accurate location estimates. Similar to GPS, there are numerous applications for indoor location systems (i.e., location based services). Some applications include indoor navigation, location-based security, printer finding based on one's location, location-based information access and sharing, people tracking, asset tracking and management, and location-based games. Indoor location can also be combined with a Radio Frequency Identification (RFID) reader and asset tagging to achieve some of the applications above. The location of an RFID reader can be determined and the reader in turn can be used to scan RFID tags. For example, in automated inventory systems, the automatically located wireless RFID reader records into the inventory database any tag that it scans. The location system infers the location of an RFID tag by estimating the location of the reader and makes entries into the database the items it scans. The most common localization techniques are Receiver Signal Strength Indicator (RSSI), Time Difference of Arrival (TDOA), Time of Arrival (TOA), and Angle of Arrival (AOA). All these techniques have two main components, a measurement block and a location computation block. The measurement block performs the functions of: measuring distance from signal power loss between a transmitter and receiver in RSSI; measuring distance between a transmitter and receiver using a two-way ranging protocol or time synchronized transmitter and receiver in TOA; measuring time/range differences between a number of receivers receiving a signal sent from a transmitter in TDOA; or measuring angle of arrival of a signal at a receiver sent from a transmitter in AOA. The location computation block uses the measurement block data to obtain a location estimate. The positions of the reference points used in the location estimates of clients is a key requirement in location systems and has to be known at all times the system is operational. This is because accurate localization depends heavily on how accurate the positions of the reference points are known. Errors due to inaccurate recording of the positions of the reference points translate directly into an error in the location estimates. This error is an additional error on top of the other sources of error such as NLOS and multipath propagation errors, as well as computational errors that may occur in the location computation algorithm. The location computation algorithm is the component in the location system that computes the