Frequency Sweep Keying CDMA for Reducing Ultrasonic Crosstalk

Abstract

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.

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

“…Frequency sweep keying [31] modulates by sweeping the frequency in an increasing or decreasing direction around the center frequency using a general high-Q ultrasonic transducer. Figure 1 shows codes '1' and '0' on a spectrogram modulated using frequency sweep keying.…”

“…In CDMA, modulation/demodulation methods include on-off keying (OOK) [28], phase shift keying (PSK) [29], frequency shift keying (FSK) [30], and frequency sweep keying [31]. Several papers have combined these methods with ultrasound systems to solve the multiple access problem.…”

“…However, when using a general narrow-band transducer, the transmission and reception signal strength are weak due to the band limiting, making application difficult. The modulation method described in [31], which was previously studied by our research team, sweeps the frequency in the direction of the increase or decrease around the center frequency. Demodulation is performed by correlating the received signal and the reference bit mask in the spectrogram.…”