Transmit Power Control for Null Data Packets in WLAN Ranging
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Solution Overview
Problem
Current wireless local area network (WLAN) technologies face challenges in accurately determining distances between devices, especially when using null data packets (NDPs), due to signal distortion caused by power amplifiers operating in non-linear regions, which affects the signal-to-interference-plus-noise ratio (SINR) at high transmit powers.
Innovation Solution
The method involves generating frames with indications of transmit power for NDPs, allowing communication devices to calculate pathloss and adjust transmit power to optimize SINR, by including a physical layer (PHY) header and omitting the PHY data portion, and using these calculations to select appropriate transmit powers for subsequent NDPs during ranging measurement exchanges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high transmit power is used for NDP transmission to improve SINR, then signal quality improves, but power amplifier distortion increases causing signal degradation
Solution Approach 1:
The system dynamically adjusts the transmit power of NDPs based on measured pathloss from previous transmissions. The transmit power is not fixed but adapts according to channel conditions and distance, allowing the system to operate at optimal power levels that avoid power amplifier distortion while maintaining adequate SINR for accurate time of flight measurements
Solution Approach 2:
The system implements a feedback mechanism where devices exchange information about received signal power and calculate pathloss. This feedback is used to determine appropriate transmit power levels for subsequent NDP transmissions, creating a closed-loop control system that prevents distortion by avoiding excessive power levels
2Measurement precision
If transmit power is increased to improve distance measurement accuracy, then measurement precision improves, but signal distortion increases reducing measurement accuracy
Solution Approach 1:
The transmit power is dynamically adjusted based on the calculated pathloss from previous exchanges. This dynamic adjustment ensures that NDPs are transmitted at the minimum necessary power to achieve accurate measurements without causing distortion that would degrade measurement precision
Solution Approach 2:
The system changes the transmit power parameter based on measured channel conditions. By adjusting this key parameter according to pathloss calculations, the system optimizes the balance between achieving sufficient signal strength for accurate timing measurements and avoiding the distortion that occurs at excessively high power levels
Data Source
AI summary
A first communication device generates a frame that includes an indication of a transmit power corresponding to one or more null data packets (NDPs) separate from the frame to permit a second communication device to determine a pathloss between the first communication device and the second communication device based on a received power of the one or more NDPs at the second communication device. The first communication device transmits the frame as part of a ranging measurement exchange. As part of one or more ranging measurement exchanges, the first communication device transmits the one or more NDPs in accordance with the transmit power indicated in the frame.