Transmitter Power Control via Human Proximity Detection
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Solution Overview
Problem
Portable devices face challenges in accurately determining proximity to a human body to adjust transmitter output power and meet specific absorption rate (SAR) requirements, leading to potential excessive RF exposure or unnecessary power reduction in wireless communication scenarios.
Innovation Solution
A system combining image sensors and proximity sensors to detect the proximity of RF transmitter antennas to a human body, using real-time image recognition to differentiate between human and non-human objects, thereby adjusting transmitter output power to maintain SAR compliance without degrading wireless link performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the transmitter operates at maximum power to ensure optimal wireless link performance, then network range and communication quality are improved, but SAR exposure limits may be exceeded when the device is close to human body
Solution Approach 1:
The transmitter power is made dynamic rather than fixed at maximum. The system continuously monitors proximity sensor inputs and adjusts the transmitter power level in real-time based on the detected proximity to human body, transitioning between high power (when safe) and low power (when proximity detected) modes
Solution Approach 2:
The system implements feedback control by monitoring proximity sensor outputs and using this information to adjust transmitter power. The proximity sensor provides continuous feedback about the device's proximity to human body, and the transmitter controller uses this feedback to modulate power levels accordingly
2Object-affected harmful factors
If proximity sensors are used to detect human body proximity for SAR compliance, then RF exposure is controlled, but the system complexity increases due to additional sensor integration and processing
Solution Approach 1:
The proximity sensor is designed with multi-functionality, serving both SAR compliance monitoring and potential other device functions. The same sensor infrastructure (sensor, controller, and processing logic) is used to detect human body proximity for SAR purposes while also enabling other device operations such as display brightness adjustment or audio routing
3Reliability
If transmitter power is limited to meet SAR requirements, then RF exposure compliance is achieved, but wireless link performance and network range are reduced
Solution Approach 1:
The power limitation is applied locally and selectively only in the specific spatial region where human body proximity is detected, rather than applying a global power reduction. The system maintains full transmitter power in regions where no human body is detected, ensuring optimal wireless performance is preserved wherever safe
Data Source
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Figure 2
AI summary
A method for adjusting transmitter output power (PTX) comprises sensing, by a proximity sensor communicatively coupled to a transmitting device, whether an object is proximate to the transmitting device. The method further comprises analyzing an image from a camera to determine whether the transmitting device is proximate to a portion of a human body, when the proximity sensor senses the object proximate to the transmitting device. Further, the method comprises adjusting the PTX of an antenna operatively coupled to the transmitting device to be less than or equal to a SAR threshold output power (PSARMAX), when it is determined that the transmitting device is proximate to the portion of the human body or when it cannot be determined whether the transmitting device is proximate to a portion of a human body.