Per-Antenna RF Power Back-Off for SAR-Compliant Transmission Paths
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Solution Overview
Problem
Radio communication devices face challenges in controlling transmission power of multiple antennas to comply with specific absorption rate (SAR) limits, especially when human body parts are present, and require mechanisms to reduce RF radiation effectively while maintaining communication operations.
Innovation Solution
The implementation of a power back-off operation (PBO) and time back-off (TBO) mechanisms in radio communication devices, where transmission power is reduced or postponed based on human presence detection, using a designated interface to trigger these operations, even when the main processor is in a low power mode or unresponsive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If power back-off operation is applied to all antennas collectively, then SAR compliance is achieved, but communication performance deteriorates due to unnecessary power reduction on antennas not directed toward human body parts
Solution Approach 1:
The patent divides the antenna array into individual antenna elements, each with independent back-off control. The controller applies power back-off operation individually to each antenna based on its specific transmission direction and detected human body proximity, rather than uniformly reducing power across all antennas. This segmentation enables selective power reduction only for antennas directed toward human body parts, maintaining communication performance on other antennas.
Solution Approach 2:
The patent implements location-specific power back-off by determining the transmission direction of each antenna and detecting human body parts in those specific directions. The power back-off operation is applied locally to individual antennas based on their specific spatial relationship with detected human body parts, rather than applying a global power reduction to all antennas. This local quality approach ensures that only antennas with human body proximity in their transmission direction undergo power reduction.
2Ease of operation
If main processor controls power back-off operation, then coordinated power management is achieved, but system reliability deteriorates when main processor is in low power mode or unresponsive
Solution Approach 1:
The patent implements self-service by enabling the RF transmitter to autonomously perform power back-off operations without continuous main processor intervention. When the main processor is in low power mode or unresponsive, the RF transmitter can independently detect human body parts via the proximity sensor, determine which antennas require back-off based on transmission directions, and apply power reduction to those antennas. This self-service capability ensures SAR compliance continuity even when the main processor cannot provide control signals.
Solution Approach 2:
The patent prepares the RF transmitter in advance to handle SAR compliance independently by configuring it with the capability to detect human body parts and determine transmission directions. The RF transmitter is pre-equipped with the necessary sensors and control logic to autonomously execute power back-off operations when needed, rather than waiting for main processor instructions. This preliminary action ensures that the system can maintain SAR compliance even when the main processor is unavailable.
3Device complexity
If power back-off is applied uniformly to all antennas, then implementation complexity is reduced, but manufacturing precision deteriorates due to inability to account for individual antenna characteristics
Solution Approach 1:
The patent implements a universal controller that can perform multiple functions: detecting human body parts, determining transmission directions for each antenna, selecting which antennas require back-off, and applying power reduction. This multi-functional controller handles individual antenna characteristics through a unified control mechanism, avoiding the need for separate complex control systems for each antenna while still achieving precise individual power control when needed.
Data Source
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AI summary
A radio frequency (RF) transmitter may include: an interface configured to receive a signal representative of a detected presence by a proximity sensor configured to detect a presence in a vicinity of a plurality of antennas, a plurality of transmission paths, each transmission path is configured to provide an RF signal to a respective antenna of the plurality of antennas; a processing circuitry configured to: detect, responsive to a received signal representative of the detected presence, a change at a signal power reflected at each transmission path, and adjust transmit power of each antenna of at least one of the antennas based on a detected change at the respective transmission path.