Wireless Ranging Protocol Using Fine Timing Measurement
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Solution Overview
Problem
Current methods for measuring range between wireless stations in indoor environments, such as those used for positioning, often require multiple messages and can increase congestion, leading to measurement errors and inefficiencies.
Innovation Solution
The method involves exchanging fine timing measurement (FTM) messages between wireless stations, where each message includes fields indicating the time of transmission and receipt of previous messages, allowing for accurate range computation with fewer messages and reduced wireless medium usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple messages are exchanged for range measurement, then measurement accuracy is improved, but wireless medium congestion increases and measurement errors increase
Solution Approach 1:
The patent applies preliminary action by pre-synchronizing clocks between wireless stations before range measurement. The initiating station transmits a synchronization frame containing timestamp information, and the responding station adjusts its clock based on this information. This preliminary clock synchronization eliminates the need for multiple measurement messages, as the time of flight can be directly calculated from the synchronized clocks, thereby reducing wireless medium congestion while maintaining measurement accuracy.
2Measurement precision
If multiple messages are exchanged for range measurement, then measurement accuracy is improved, but measurement errors increase
Solution Approach 1:
The patent performs preliminary clock synchronization before range measurement to eliminate timing offsets that cause measurement errors. By synchronizing clocks in advance using synchronization frames with timestamp information, the system ensures that subsequent range calculations based on time of flight are accurate without requiring multiple redundant measurement messages, thus reducing measurement errors while maintaining precision.
Solution Approach 2:
The patent implements feedback mechanisms where the responding station sends acknowledgment frames containing timestamp information back to the initiating station. This feedback allows the initiating station to verify the synchronization accuracy and calculate range measurements with higher reliability. The feedback loop ensures that timing information is validated and corrected if necessary, reducing measurement errors.
3Measurement precision
If more FTM messages are transmitted, then range measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent reduces power consumption by performing preliminary clock synchronization that enables single-message or minimal-message range measurement. Instead of transmitting multiple FTM messages to achieve the required measurement precision, the synchronized clocks allow the system to calculate range from limited timestamp information, significantly reducing the number of transmissions and associated power consumption while maintaining measurement precision.
4Device complexity
If clock synchronization is not performed, then device complexity is reduced, but measurement accuracy deteriorates
Solution Approach 1:
The patent implements a relatively simple preliminary clock synchronization mechanism using standardized synchronization frames with timestamp fields. This approach adds minimal complexity to the devices while dramatically improving measurement accuracy. The synchronization is performed once before measurements, eliminating the need for complex continuous synchronization mechanisms, thus achieving good measurement precision with acceptable device complexity.
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AI summary
A method at a responding wireless device, STA, a responding STA and a non-transitory storage medium for storing instructions to perform said method, the method comprising: receiving (602) a fine timing measurement, FTM, request message from an initiating STA; and transmitting (604) at least a subsequent FTM message to the initiating STA in response to the FTM request message, the subsequent FTM message comprising at least one field indicating a time of transmission of a previous FTM message and a time of receipt of an acknowledgement message transmitted in response to receipt of the previous FTM, the at least one field comprising a common portion indicative of most significant portions of the time of transmission of the previous FTM message and the time of receipt of the acknowledgement message, a first fractional portion indicative of the time of transmission of the previous FTM message and a second fraction portion indicative of the time of receipt of the acknowledgement message.