臺灣大學: 電機工程學研究所張帆人呂宜璋Lu, I-ChangI-ChangLu2013-03-272018-07-062013-03-272018-07-062012http://ntur.lib.ntu.edu.tw//handle/246246/253890工程實務上為了測量物體之間的遠近，可以使用雷射測距儀或超音波測距儀。雷射測距儀一般來說精度高、速度快、價錢卻較昂貴。超音波感測器具有構造簡單、體積小、費用低等優點，普遍使用在機器人避障，車用倒車系統，工廠加工自動化檢測，油桶液位量測等方面。 傳統的超音波測距儀使用脈衝回聲(pulse-echo)方式來量測距離，計算信號從發射到接收的時間TOF(time-of-flight)，之後將聲速與其TOF一半的時間相乘得到量測距離。 本文使用PRN code(Pseudo Random Noise code)與BPSK(Binary Phase Shift Keying)調變方法，增加SNR特性，有效抵抗雜訊，並增加超音波測距儀的最大量測距離，在模擬上使用IQ通道解調變與複數解調變兩種不同的方式，比較其自相關函數圖，驗證結果合乎預期。 考量市面上常見的超音波感測器的工作頻率，以及超音波在空氣中衰減的速度與頻率成正比的特性，軟體模擬選擇40KHz做為載波的信號、320KHz的取樣頻率，並在發射端產生120dB的傳送信號。BPSK用途的PRN code為長度1023個chip，PRN code的載波頻率為4KHz。並在50dB的背景雜訊下，量測距離約為20公尺。To get the distance information is an interesting and important topic. Laser rangefinders and ultrasonic rangefinders are two typical instruments for this purpose. In general, the advantages of laser rangefinder include long range, fast and accurate. However, the prices of laser rangefinders are more expensive than those of ultrasonic rangefinders. The advantages of ultrasonic rangefinders are simple, small and cheap. They have been widely used in cars or robots to detect obstacles within close range. Other applications are oil level measurement, medical imaging and so on. Traditionally, a short ultrasonic burst is transmitted from the transmitter in ultrasonic sensor. When there is an object in the path, some of transmitted ultrasonic wave is reflected. The receiver then can detect this echo. The signal’s time of flight (TOF) from the sending terminal to the receiving terminal being multiplied by the speed of the ultrasonic in the air, the distance between them can be calculated. This article discusses a ranging algorithm based on direct sequence spread spectrum (DSSS) approach, which contains the ideas of pseudo-random noise code (PRN code) and binary phase shift keying (BPSK). The time of flight is obtained by the peak finding of the correlation results between the echoed and transmitted signals. The process gain makes the peak appears even if the echoed signals are buried in the background noises. In order to improve the signal-to-noise ratio (SNR), we use I-Q channel demodulation and complex variable demodulation method. The algorithm is verified by software simulations. For the designed ultrasonic ranging system, we use sound pressure level (SPL) to represent sound propagation amplitude in the air. The SPL of transmission signal is 120 dB, and the SPL of background noise 50 dB. The frequency of the ultrasonic wave (i.e. carrier frequency) is 40 KHz. The carrier is modulated by BPSK with PRN code of 1023 chips. The chipping rate of PRN code is 4 KHz. In order to compute the correlation operation, the sampling rate used is 320 KHz. The simulation results show that the maximum distance estimated is approximately 20 meters in the two-way ranging scheme.1790281 bytesapplication/pdfen-US超音波測距直接序列展頻二元相位反轉調變同調解調變複數解調變ultrasonic rangingDSSSBPSKIQ channel demodulationcomplex demodulationthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/253890/1/ntu-101-R99921055-1.pdf