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.

Shape from focus enables microscopic 3D sensing by combining it with a microscope system. However, edge bleeding artifacts of estimated depth easily occur in this environment. Therefore, this study analyzed artifacts and proposed a method to reduce edge bleeding artifacts. As a result of the analysis, the artifact factors are the depth of field of the lens, object texture, brightness difference between layers, and the slope of the object. Additionally, to reduce artifacts, a weighted focus measure value method was proposed based on the asymmetry of local brightness in artifacts. The proposed reduction method was evaluated through simulation and implementation. Edge bleeding artifact reduction rates of up to 60% were shown in various focus measure operators. The proposed method can be used with postprocessing algorithms and reduces edge bleeding artifacts.

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.

다수의 초음파 센서가 공존하는 환경에서 다른 초음파 센서에서 송신한 초음파 신호에 의해 혼선이 발생하고 그에 따른 측정 오차가 발생하는 문제가 발생한다. 이러한 문제를 해결하기 위해 초음파 센서별로 ID 코드를 부여하여 ID 코드에 따라 변조된 초음파를 송신하는 코드 분할(Code division) 방식이 개시되고 있다. 그러나 코드 분할 방식만으로 초음파 센서의 혼선을 방지하기 위해 측정 환경 내의 초음파 센서의 수가 많아질수록 코드의 직교성을 보장하기 위한 ID 코드가 매우 길어져야 했다. 본 논문에서 상기 온오프 변조 방식의 코드 분할 방식의 문제점을 해결하기 위한 위상 정보를 활용하여 같은 위상값을 가지는 신호의 집합으로 분리하는 방식의 위상 정보 기반 온오프 복조기를 제안한다. 제안하는 온오프 복조기를 사용한 코드 분할 수행 시 기존 방법 대비 짧은 ID 코드로도 높은 수신률을 달성한다.

최근 자율주행 자동차를 비롯한 무인 로봇 기술이 발달됨에 따라 초음파를 이용한 송수신 장치의 사용량이 증가하고 있다. 초음파 송수신 장치는 고주파 대역의 음파를 송수신하여 사물과의 거리를 측정한다. 초음파 송수신 장치를 동시에 여럿 사용할 시 장치 간 혼선이 발생하기에, 다양한 변조 방법을 이용하여 이를 방지한다. 하지만 각각의 특징에 따른 도플러 효과의 영향을 받아 복조 과정에서 오류가 발생한다. 처프 신호로 CDMA(Code-Division Multiple Access)를 수행할 경우 전송시간이 길어지며, 특정 환경에서만 사용할 수 있다. 본 논문에서는 초음파 CDMA에서의 도플러 효과를 극복하기 위한 chirp-OOK(chirp-OnOffKeying) 혼합 변조 방법을 제안한다. 또한 제안한 혼합 변조 방법의 성능을 일반적인 OOK 방법 그리고 Teodoro의 처프 기반의 도플러 보상 방법과 비교 분석하였다. 제안한 chirp-OOK 혼합 변조 방법은 상대 속도에 상관없이 안정적이고 정확한 성능을 보였다.

Ultrasonic sensors are inexpensive and can take measurements with high accuracy, even with simple hardware configurations, so they are used in various fields. When multiple ultrasonic sensors exist in the measurement space, crosstalk occurs due to other nodes, which causes measurement errors. Crosstalk includes not only receiving homogeneous signals from other nodes, but also overlap by other signals, and interference by heterogeneous signals. This paper proposes a method that uses frequency sweep keying modulation to be robust against overlap and a faster region-based convolutional neural networks (R-CNN)-based 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 a 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 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 performs better than the existing methods and is expected to be used in various applications.