應用二進制頻率鍵移調變於壓電元件的超音波通訊

Abstract

近年來，大眾愈發重視車輛行駛時的安全性及舒適便利度，環保節能議題亦漸漸普及於社會中，搭載車用行動通訊網路的智慧車概念因而興起；車廠將感測器、雷達、攝影機等裝置安裝於智慧車以輔助駕駛；此類裝置可提供功能如：安全防護系統、自動駕駛、即時導航資訊等。 車用行動通訊網路中涵蓋數種通訊方式，例如倒車雷達系統應用超音波通訊。聲學通訊優點為成本低、相容性高；且與無線電波相比，對人體健康影響小；在近距離資料傳輸的範疇中逐漸受重視，若結合無線電波通訊，更可解決頻寬小的問題。 本研究目的為應用二進制頻率鍵移調變於超音波壓電元件中，建構一套通訊系統，不僅能偵測訊號，且含有編碼資訊；未來可整合至倒車雷達系統，一旦車距變小，如塞車或排隊，則系統會自動分享相關資訊；例如前方發生車禍或有拋錨事故，則車間會彼此傳遞此訊息。本研究首先測量超音波壓電元件性質，並建構出元件性質的方程式模型；另外，比較各種不同編碼、解碼方式，確保通訊過程的錯誤率最低；最後分析不同距離與位元週期的字元錯誤率。 實驗結果顯示，當品質因數越低時，元件改變頻率時的反應時間越短；位元傳輸速率高的情況之下，不歸零-L編碼方式及濾波型頻率鍵移調變檢測法解碼方式在位元錯誤率的表現較為理想；由於壓電元件的阻尼效應，傳輸訊號首尾的位元錯誤率偏高，資料傳輸時應挑選適當編碼方式組成訊息位元組，降低此效應的影響。感測器距離為30cm時，位元間隔0.15msec以上可達成中文字元錯誤率0.19%，英文字元錯誤率0%；距離45cm時，位元間隔0.2msec以上可達成錯誤率0%；距離為60cm時，位元間隔0.43msec以上始可達成錯誤率0%。

In recent years, security, comfort and convenience driving experience have become increasingly important. This trend as well as issues of energy saving and environmental protection, result in the popularity of intelligent vehicles with vehicular ad-hoc network. The vehicle manufacturers install transducers, radars and cameras on intelligent vehicles, which operate many functions such as safety system, auto-driving system, and instantaneous navigation. Vehicular ad-hoc network includes several different ways of communication. For example, parking sensors apply ultrasonic communication. The advantage of acoustic communication system is low cost, high system compatibility, less influence on human health compared to radio waves. As a result, such system has increasing importance in the technique of short-distance data transmission. If we combine the acoustic communication system with other wireless communication systems via radio waves, the problem of narrow band can be solved, and a good communication quality can be achieved. The purpose of this research is to establish a communication system that not only detects the signals but also has the ability to transmit information. The system applies binary frequency shift keying to piezoelectric transducers. In the future, we can integrate it in vehicular ad-hoc network system. Once the distance between two adjacent vehicles becomes too short such as getting stuck in a traffic jam or waiting in the queue, vehicles will automatically share the relevant information. For example, vehicles will notify one another when car accidents or breakdowns happened. This research will, first, measure the basic characteristics of ultrasonic piezoelectric transducers and construct the model based on them. In addition, we compare different methods of encoding and decoding so as to ensure the lowest error rate during transmission. Last, we analyze the data error rate of different distances. According to the experiment results, the lower the quality factor of the piezoelectric transducer, the shorter the response time of alternating frequency. Under the circumstance of high bits transmission rate, NRZ-L and filter-type FSK demodulators deliver better performance in the bit error rate. Due to the damping effect of transducers, the bit error rate of first bit and last bit is much higher than that of other bits. Therefore, the data should be encoded via an adequate method to avoid damping effect during transmission. When the distance between two transducers is 30cm, we can achieve 0.19% bit error rate of Chinese characters and 0% of the rate of English words by setting bit duration as 0.15msec. When the distance between two transducers is 45cm, 0% bit error rate of both Chinese characters and English words can be achieved by setting bit duration as 0.2msec. However, if the distance between two transducers is 60cm, we have to set bit duration as 0.43msec to attain 0% bit error rate of both Chinese characters and English words.