Ultrasonic Measuring Apparatus Doppler Shift Cancellation
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Solution Overview
Problem
Conventional ultrasonic measuring apparatuses face challenges in accurately estimating propagation distance and orientation due to Doppler shifts caused by relative velocities between moving objects and measuring apparatuses, leading to decreased correlation gain and signal noise ratio (SNR) when using M-sequence coding.
Innovation Solution
The method employs a coded spread spectrum ultrasonic signal with a predetermined carrier frequency, synchronized coding period, and phase difference processing to cancel Doppler shifts, followed by despreading using different codes, resulting in high SNR and accurate distance/orientation estimation without measuring the Doppler shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If M-sequence coding is used to distinguish ultrasonic waves from multiple sources, then the ability to identify signals in noisy environments is improved, but the correlation gain and signal noise ratio (SNR) decrease when relative velocity exists between the object and measuring apparatus
Solution Approach 1:
The patent changes the parameter of signal coding from conventional M-sequence to pseudo-random noise (PRN) code, which has better autocorrelation properties. This allows the system to maintain high correlation gain even when Doppler shift occurs due to relative motion, thereby resolving the contradiction between signal identification capability and measurement precision
Solution Approach 2:
The patent applies preliminary Doppler shift compensation by estimating the relative velocity between the measuring apparatus and the object before performing correlation processing. This preliminary action removes the harmful effect of Doppler shift on the received signal, maintaining both signal identification capability and correlation gain
2Device complexity
If conventional ultrasonic measuring methods are used, then the system structure is simple, but accurate distance and orientation estimation cannot be achieved when Doppler shifts are present
Solution Approach 1:
The patent implements feedback by using the phase difference information obtained from quadrature detection to estimate Doppler shift, then using this estimation to compensate the received signal before final correlation processing. This feedback loop maintains measurement precision without significantly increasing system complexity
Solution Approach 2:
The patent introduces quadrature detection that processes signals in both in-phase (I) and quadrature (Q) dimensions simultaneously. This dimensional expansion allows the system to extract phase difference information and estimate Doppler shift more accurately, improving distance and orientation estimation precision
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
This approach allows for accurate ultrasonic wave propagation distance and orientation estimation even with multiple Doppler shifts, reducing the Doppler shift effect significantly and maintaining high SNR, suitable for applications like self-moving robots in dynamic environments.
Implementation Method 1
The ultrasonic signal transmitted passes through an ultrasonic wave propagation path 7 to reach an object 3 and get reflected by the object 3
Implementation Method 2
there is a non-zero relative velocity between the surrounding object and the ultrasonic measuring apparatus. And if that relative velocity produces a Doppler shift
Implementation Method 3
the correlation with the pseudo random signal, generated by the pulse generator 105, examined by the correlator 103
Data Source
AI summary
An ultrasonic measuring method includes: (A) receiving a coded spread spectrum ultrasonic signal in at least two receivers, and generating at least two received signals; (B) performing an quadrature detection on the received signals using the carrier frequency, and producing I and Q components of the received signals; (C) performing phase difference processing on the I and Q components with a coding period synchronized with that of the carrier frequency, and obtaining I′ and Q′ components from which a phase shift caused by a Doppler shift has been canceled; (D) despreading the I′ and Q′ components signals using different codes at time intervals synchronized with the carrier frequency, and obtaining despread I″ and Q″ components; (E) computing the amplitude and phase information based on the I″ and Q″ components; and (F) calculating the propagation distance and/or orientation of the ultrasonic wave based on the amplitude and phase information.