Transmission Power Control for ToF Accuracy
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Solution Overview
Problem
Indoor navigation and positioning using time-of-flight (ToF) protocols face challenges due to unwanted link adaptation and high error vector magnitude (EVM) in wireless networks, which degrades measurement quality, especially in non-line of sight scenarios, requiring accurate power control to optimize EVM for effective channel estimation.
Innovation Solution
Implementing a Transmission Power Control protocol that determines the maximum allowed EVM through a responder or initiator determined method using an updated FTM messaging protocol, calculating the optimal transmit power based on received signal strength to maintain a low EVM, thereby enhancing the accuracy of fine timing measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If higher transmit power is used to increase Wi-Fi coverage, then coverage area is improved, but measurement quality of ToF ranging degrades due to non-linear power amplifier operation
Solution Approach 1:
The patent changes the EVM parameter from high to low to ensure the power amplifier operates in a linear range, thereby improving ToF measurement quality while maintaining adequate Wi-Fi coverage through optimized power control
2Reliability
If link adaptation is implemented to optimize communication reliability, then bit error rate is reduced, but ToF measurement accuracy degrades due to varying transmission conditions
Solution Approach 1:
The patent extracts link adaptation from the ToF measurement process, applying it only to data transmission phases while keeping ToF measurements at fixed power levels to ensure measurement consistency and accuracy
3Reliability
If lower MCS is used to transmit short packets in ToF protocol, then transmission robustness is improved, but EVM tolerance increases allowing higher power transmission that degrades channel estimation
Solution Approach 1:
The patent changes the EVM parameter to be lower than what standard permits for lower MCS, constraining power amplifier operation to linear range and thereby improving channel estimation quality and ToF measurement accuracy
Data Source
AI summary
Embodiments of a communication station and method for transmission power control for Time-of-Flight (ToF) measurements in a wireless network are generally described herein. A protocol for fine timing measurements (FTMs) optimizes location performance rather than Wi-Fi coverage area and bit error rate by limiting an allowed maximum power and hence, EVM. A user equipment (UE) comprises a transceiver configured to receive, from an initiating station, a fine timing measurement request (FTMR) message at a maximum transmit power and lowest modulation and coding scheme (MCS), measure a relative received signal strength (RSSI) for the received FTMR message, determine a maximum transmit power, where the maximum transmit power is proportional to the measured RSSI; and transmit, to the initiating station, a fine timing measurement 1 (FTM1) message at the determined maximum transmit power and received lowest MCS.