Acoustic Suppression via Ancillary RF Link Distance Estimation
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Solution Overview
Problem
In group communication systems, collocated transmitter and receiver devices often experience feedback loops that result in undesirable acoustic howling, particularly in public safety scenarios where critical information can be lost or delayed due to this issue.
Innovation Solution
The implementation of an ancillary RF link between devices to estimate their distance and adjust the gain of either the transmitter or receiver to reduce the feedback loop's gain below 0 dB, preventing howling by calculating and adjusting the total gain using techniques like RSS, TOA, and AOA, and modifying amplifier and attenuator settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gain of the feedback loop is increased to improve audio signal transmission, then the audio communication quality is improved, but acoustic howling occurs due to feedback between collocated transmitter and receiver
Solution Approach 1:
The system performs preliminary actions by estimating the distance between transmitter and receiver using RF signal characteristics (RSS, TOA, AOA) before audio transmission begins. Based on this pre-assessment, the system proactively adjusts the feedback loop gain to prevent howling from occurring in the first place, rather than reacting after howling is detected
Solution Approach 2:
The system dynamically changes the gain parameter of the feedback loop based on the estimated distance between devices. When devices are collocated (short distance), the gain is reduced to prevent howling. When devices are farther apart, the gain can be increased for better audio quality. This continuous parameter adjustment resolves the contradiction between maintaining high gain for quality and low gain for preventing howling
2Object-generated harmful factors
If the gain is reduced to eliminate howling, then acoustic feedback is suppressed, but audio signal strength and communication quality deteriorate
Solution Approach 1:
The system applies different gain settings to different spatial locations or device configurations. When devices are collocated (harmful feedback scenario), low gain is applied locally to suppress howling. When devices are separated (normal operation scenario), high gain is applied to maintain audio signal strength. This localized quality adjustment ensures optimal performance for each specific situation
Solution Approach 2:
The system makes the gain dynamic rather than static, continuously adjusting it based on real-time distance estimates from RF measurements. As devices move closer or farther apart, the gain automatically transitions between low and high states, maintaining both feedback suppression and signal strength as conditions change
3Object-generated harmful factors
If distance estimation and gain adjustment mechanisms are implemented, then howling is prevented, but device complexity increases
Solution Approach 1:
The system uses multi-functionality by employing the RF communication infrastructure for dual purposes: primary audio data transmission and secondary distance estimation for feedback suppression. The same RF channel and signal processing capabilities are reused to extract distance information (via RSS, TOA, or AOA measurements), eliminating the need for separate dedicated distance measurement hardware and reducing overall system complexity
Solution Approach 2:
The system performs self-service by using its own transmitted RF signals to estimate distance between devices. The transmitter's own signal characteristics (received strength, time of arrival, or angle of arrival at the receiver) provide the distance information needed for gain adjustment, without requiring external reference signals or additional measurement infrastructure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively reduces or eliminates howling in collocated transmitter-receiver pairs, ensuring clear communication by maintaining the total gain below 0 dB, even in mission-critical situations, by continuously adjusting gain components based on changing parameters.
Implementation Method 1
estimate the distance between these devices
Implementation Method 2
communications over the ancillary RF link
Implementation Method 3
the microphone on the transmitter may pick up the audio signal that has been transmitted by the transmitter and reproduced by a loudspeaker on the receiver. Under certain conditions, the resulting feedback loop can reinforce itself to create an undesirable acoustic signal, herein referred to as 'howling.'
Data Source
AI summary
Methods and systems are described in which the feedback between a transmitter and collocated receiver is reduced so that the overall feedback loop gain is less than 0 dB. Audio is transmitted from the transmitter to the receiver through a primary RF link while RSSI or TOA information to determine the separation between the end devices is exchanged using an ancillary RF link. The total loop gain is calculated using the gain of each end device and the separation. If the distance is less than a threshold distance, the gain of one or more components in the transmitter and/or receiver is reduced.