Robustness enhancements of time-of-flight measurements in a CDMA ultrasonic channel of an opto-acoustic indoor positioning system using MEMS microphones

Oberdorfer, Martin; Esslinger, Dominik; Benz, Gregor; Sawodny, Oliver; Tarín, Cristina

doi:10.1109/ius46767.2020.9251546

Cited by 5 publications

(3 citation statements)

References 14 publications

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“…When using multiple narrowband ultrasonic transducers, the number of ultrasonic transducers must increase with the number of modes. The third method, code division multiple access (CDMA), ensures orthogonality by assigning different codes to each node [23][24][25][26][27]. It is a commonly used method in ultrasound and is also called coded ultrasound or multi-code ultrasound.…”

Section: Introductionmentioning

confidence: 99%

Improved Frequency Sweep Keying CDMA Using Faster R-CNN for Extended Ultrasonic Crosstalk Reduction

Park,

Baek

2023

Sensors

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Ultrasonic sensors are inexpensive and provide highly accurate measurements, even with simple hardware configurations, facilitating their use in various fields. When multiple ultrasonic sensors exist in the measurement space, crosstalk occurs due to other nodes, which leads to incorrect measurements. Crosstalk includes not only receiving homogeneous signals from other nodes, but also overlapping by other signals and interference by heterogeneous signals. This paper proposes using frequency sweep keying modulation to provide robustness against overlap and a faster region-based convolutional neural network (R-CNN) demodulator to reduce the interference caused by heterogeneous signals. The demodulator works by training Faster R-CNN with the spectrograms of various received signals and classifying the received signals using Faster R-CNN. Experiments implementing an ultrasonic crosstalk environment showed that, compared to on–off keying (OOK), phase-shift keying (PSK), and frequency-shift keying (FSK), the proposed method can implement CDMA even with shorter codes and is robust against overlap. Compared to correlation-based frequency sweep keying, the time-of-flight error was reduced by approximately 75%. While the existing demodulators did not consider heterogeneous signals, the proposed method ignored approximately 99% of the OOK and PSK signals and approximately 79% of the FSK signals. The proposed method performed better than the existing methods and is expected to be used in various applications.

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Section: Introductionmentioning

confidence: 99%

Improved Frequency Sweep Keying CDMA Using Faster R-CNN for Extended Ultrasonic Crosstalk Reduction

Park,

Baek

2023

Sensors

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“…CDMA is a method to assign orthogonality between signals by assigning different ID codes to each node [23][24][25][26]. In the single-node ultrasound system, the coded ultrasonic method has been used to improve the measurement distance and TOF measurement accuracy because of the improved signal-to-noise ratio (SNR) of the received signal [27,28].…”

Section: Introductionmentioning

confidence: 99%

Frequency Sweep Keying CDMA for Reducing Ultrasonic Crosstalk

Park

Baek

2022

Sensors

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Various sensors are embedded in automobiles to implement intelligent safety technologies such as autonomous driving and front–rear collision avoidance technology. In particular, ultrasonic sensors have been used in the past because they have an accuracy of centimeters to sub-centimeters in air despite their low cost and low hardware complexity. Recently, the crosstalk problem between ultrasonic sensors has been raised because the number of ultrasonic sensors in the unit space has increased as the number of vehicles increases. Various studies have been conducted to solve the crosstalk, but a demodulation error occurs when signals overlap. Therefore, in this paper, we propose a method that is robust to ultrasonic signal overlap, is robust even at shorter code length, and has reduced time of flight (TOF) error compared to the existing method by applying frequency sweep keying modulation based on code division multiple access (CDMA). As a result of the experiment, the code was detected accurately regardless of the overlap ratio of the two signals, and it was robust even in situations where the power of the two signals was different. In addition, it shows an accurate TOF estimation even if the ID code length is shorter than the existing on–off-keying, frequency shift keying, and phase shift keying methods.

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“…These studies showed that 1-D OCDMA could extend the ToF measurement distance and potentially support faster scanning rate and better angular resolution than the conventional pulsed-ToF methods. Besides LiDAR applications, Oberdorfer, et al [17] applied 1-D binary-phase-shift-keyed (BPSK) CDMA to enhance crosstalk robustness in ultrasonic ToF measurements of an optoacoustic indoor positioning system.…”

Section: Introductionmentioning

confidence: 99%

2-D Optical-CDMA Modulation With Hard-Limiting for Automotive Time-of-Flight LiDAR

Yang

Lin

et al. 2021

IEEE Photonics J.

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In this proof-of-principle paper, the application of 2-D optical code-division multiple-access (OCDMA) modulation to long-range automotive time-of-flight (ToF) light detection and ranging (LiDAR) is studied. The regulations and physical constraints that govern the design parameters are reviewed. Using 2-D carrier-hopping prime codes (CHPCs), the modulation model and a novel 2-D hard-limiting decoder are designed and validated with OptiSystem TM simulations. Based on the design parameters, the 2-D CHPCs have six times as many distinct sequences (for sensor identification) as 1-D code sequences. Analytical and simulation studies show that the proposed 2-D OCDMA modulation model can eliminate the near-far (power) problem and support more LiDAR sensors with distinctive ToF tags, greater interference robustness for more simultaneous ToF measurements, and better performance than the 1-D counterparts. The simulation results show that the 2-D model can support four times as many simultaneous emitting sensors without false detections as the 1-D model. In summary, the 2-D OCDMA modulation has more benefits and is more cost efficient overall, even though it is more complex.

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Robustness enhancements of time-of-flight measurements in a CDMA ultrasonic channel of an opto-acoustic indoor positioning system using MEMS microphones

Cited by 5 publications

References 14 publications

Improved Frequency Sweep Keying CDMA Using Faster R-CNN for Extended Ultrasonic Crosstalk Reduction

Improved Frequency Sweep Keying CDMA Using Faster R-CNN for Extended Ultrasonic Crosstalk Reduction

Frequency Sweep Keying CDMA for Reducing Ultrasonic Crosstalk

2-D Optical-CDMA Modulation With Hard-Limiting for Automotive Time-of-Flight LiDAR

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