An Ultrasonic Object Detection Applying the ID Based on Spread Spectrum Technique for a Vehicle

Abstract

When an ultrasonic sensor generates an ultrasonic wave and detects an obstacle from a reflected wave, a signal transmitted by other ultrasonic sensors would be interference. In this paper, to overcome the interference, a transducer transmits a signal with a unique ID modulated. The interference is ignored by verifying that the reflected signal includes its ID. The ID verification process uses a correlation between the received signal and the ID. Therefore, the ID is selected from orthogonal codes with good cross-correlation. Long code has the advantage of being more robust to interference. However, the reflected wave from nearby obstacles might return before the transmission ends. Therefore, the 7-bit Barker code is applied for near obstacle detection and a 31-bit Gold code is used for distant obstacle detection. The modulation technique is DQPSK, which is available in a narrow bandwidth and has a simple receiver structure. In ID recognition based on correlation, a near–far problem occurs due to a large amplitude difference between the received wave and interference. The addition of a zero-crossing detector solves this problem. The hardware is implemented based on the algorithm proposed in this paper. The simulation showed a detection rate of at least 90% and the the result of the real measurement represented a detection rate of 97.3% at 0.5 m and 94.5% at 2 m.

Low-Cost Ultrasonic Range Improvements for an Assistive Device

“…This means it has a more than detection rate greater than 98% and a Bit Error Rate (BER) close to 0.01, which better than other studies [ 17 , 18 ] also using DPSK modulation and transmission over the air.…”

“…To distinguish this phase change, a 180-degree change is used in order to maximize code detection. In [ 18 ], a similar schema is explained but with a very complicated and expensive hardware that is quite difficult to implement in an actual application.…”

“…For step 1, the micro controller generates a 40 kHz signal codified with DPSK information. It is easy to modulate analog signal as in [ 18 ]; however, a high-speed digital analog converter is expensive. Therefore, an analog modulation should be made using only digital available signals.…”

“…A phase modulation is included in the ultrasonic wave in order to detect the origin of the data echo without increasing the price. This ultrasonic phase modulation has been also studied and tested [ 17 , 18 ], however, using complex and expensive devices that can not be included in a low-cost ETA category.…”

A High Spatiotemporal Resolution Ultrasonic Ranging Technique With Multiplexing Capability

“…Binary PRN sequences are a set of special ascertained vectors with outstanding autocorrelation and cross-correlation properties i.e., orthogonality, such as Barker codes [38], Zadoff-Chu sequences [39], Gold Codes [29], Kasami codes [30], maximum length sequences [40] and Golay codes [41] to name a few. The excellent autocorrelation properties of these sequences provide an opportunity to accurately and precisely distinguish the positions of correlation peaks.…”