WLAN Multi-Carrier CTS Frames for Indoor Location Finding
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Solution Overview
Problem
Existing wireless localization methods, such as GPS and cellular network triangulation, are unreliable and inaccurate indoors and in crowded urban environments, and require association with access points to estimate angles of departure.
Innovation Solution
A method that involves detecting a beacon from a station with multiple antennas, transmitting a request-to-send (RTS) frame using a multi-carrier modulation scheme, and receiving a clear-to-send (CTS) frame to estimate angles of departure and other properties without establishing an association with the access point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If GPS or cellular network triangulation is used for location finding, then location coordinates can be derived, but the method works poorly indoors and in crowded urban environments
Solution Approach 1:
The patent uses WLAN access points as intermediary elements for location determination. Instead of relying directly on GPS satellites or cellular towers, the system mediates location finding through local WLAN infrastructure (access points and stations) that are more reliably available indoors and in urban environments. The multi-carrier CTS frames from multiple access points serve as intermediary signals for triangulating the mobile station's position.
2Measurement precision
If association with access points is established to estimate angles of departure, then location accuracy improves, but the process becomes more complex and time-consuming
Solution Approach 1:
The patent performs preliminary actions by having access points continuously transmit multi-carrier CTS frames as part of their normal WLAN operation. This preliminary transmission of directional signals means that when a mobile station needs location determination, the necessary angle-of-departure information is already available from recently received CTS frames, eliminating the need for complex association procedures specifically for location purposes.
Solution Approach 2:
The patent makes the WLAN infrastructure universal by using the existing RTS/CTS mechanism for both its original purpose (carrier sensing and collision avoidance) and for location determination. The same CTS frames used for medium access control are also used for angle-of-departure estimation, eliminating the need for separate dedicated location-finding protocols or association procedures.
3Reliability
If traditional RTS/CTS mechanism is used, then carrier sensing and collision avoidance are achieved, but no location information can be derived
Solution Approach 1:
The patent merges two previously separate functions into a single integrated system. The RTS/CTS mechanism simultaneously performs both carrier sensing/collision avoidance (its traditional function) and location determination (new function). By encoding angle-of-departure information in the multi-carrier CTS frames and having mobile stations process these frames for both MAC protocol compliance and location calculation, the system combines networking and localization into one unified process.
Data Source
AI summary
A method for communication includes detecting, at a first station in a wireless network, a beacon transmitted over the wireless network by a second station having multiple antennas. In response to the beacon, a request-to-send (RTS) frame is transmitted over the wireless network using a multi-carrier modulation scheme from the first station to the second station. The first station receives a clear-to-send (CTS) frame transmitted over the wireless network, in response to the RTS frame, by the second station via the multiple antennas using the multi-carrier modulation scheme, and estimates a property of the first station based on the received CTS frame.