車間光通訊通道不對稱性之分析

Characterizing Link Asymmetry in Vehicle-to-Vehicle Visible Light Communications

曾華彥(Hua-Yen Tseng)

指導教授 ： 蔡欣穆

國立臺灣大學/電機資訊學院/資訊工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01181

摘要

近年來光通訊被大量地應用於車間通訊上，因為比起射頻(RFbased)
可見光可以更有效地解決車間通訊的幾個挑戰，像是精準車間定位、建置成本的問題。利用車上本身的LED 頭燈及尾燈作為傳輸端，光電二極管作為接收端，即使在高密度的車流狀況，車間可見光通訊還是具有高穩定性，可以有效地識別傳輸端所傳送的消息，並且具有低成本的特性。在本論文中，我們提出了一個車間可見光通訊特有的問題: 通訊通道不對稱性，其被定義為在接收與傳送的通道有嚴重不對等的問題。為證實此問題，我們利用實車上LED 頭燈和尾燈進行實際測量，並且利用厘米級精度的雷達收集實際車流資料，綜合分析這些數據，我們得到了通道接收功率差的實驗分佈。我們的研究結果表明: 在80% 的情況下，我們的車輛使用頭燈的接收功率是22dB 或比相鄰車輛的尾燈傳輸接收功率更高，在這個狀況下，僅8.1% 有小於10dB 的接收功率差。這表明通訊通道不對稱性的問題是非常嚴重，在車間可見光通訊的系統設計或協議設計是需要被重視，進而避免封包流量嚴重下降的問題。

關鍵字

車間可見光通訊 ； 可見光通訊 ； 車間通訊 ； 通道不對稱性

並列摘要

Recently, it has been found that Vehicular Visible Light Communications (V2LC) can effectively address several challenges faced by conventional Radio-Frequency-based (RF-based) vehicular communications. Utilizing the LED headlamps and taillights as the transmitter and a photodiode as the receiver, V2LC has high reliability even in high vehicle density scenarios, can effectively identify the transmitter of a received message, and has low cost. In this paper, we identify a new problem unique to V2LC – link asymmetry, which is defined as significant difference in incoming and outgoing links and perform the first experimental work to characterize the problem. To this end, we performed extensive optical radiation pattern measurements with off-the-shelf LED headlamps and taillights. We also collected a number of vehicle mobility traces with 2-dimensional locations with centimeter-level accuracy as well as vehicle bearing. Combining these data, we performed an analytical study to obtain an experimental distribution of received power difference of the links in opposite directions. Our results show that in 80% of the cases the received power of the outgoing link using the headlamp of our vehicle is 22 dB or more than the received power of the incoming link using the neighboring vehicle’s taillight, and only 8.1% of the cases have less than 10-dB received power difference. This suggests that the link asymmetry problem is very severe in V2LC and new system design or protocol design consideration is required to prevent significant throughput degradation.

並列關鍵字

Vehicular Visible Light Communication (V2LC) ； Visible Light Communications (VLC) ； Vehicle-to-Vehicle (V2V) Communications ； Asymmetrical Links

參考文獻

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