利用LED的閃爍傳達重要的訊息在物聯網 (Internet of Things) 中是一項很有用的功能，
而且只需透過配備於智慧型手機上的相機對閃爍的LED做解碼。
前代的技術只針對單個LED做解碼，
使得頻寬和回應時間都受到限制。
為了突破這些限制，
我們嘗試使用不同的方式對多個LED做解碼。
我們可以利用每個裝置上的單個LED閃爍訊息，
並藉由同時偵測多個裝置上的單顆LED，
使得相同時間內能獲得更多的訊息量。
我們也利用在一個裝置上配備多個LED來傳送單個訊息，
藉由同時偵測單個裝置上的多顆LED，
使得單個訊息的傳送時間大幅縮短。
實驗結果顯示，
藉由普遍配備於使用者身上的智慧型手機，
以及對多個LED解碼的技術，
可以真正的突破頻寬和回應時間的限制，
並達到頻寬的增加。

Use of blinking LED to convey useful status information to be decoded
by smartphone cameras has been shown to be a useful feature for end
users of devices in the Internet of Things (IoT). Previous techniques
have been limited to decoding of a single LED, which is limited in
bandwidth and response time. We propose to overcome these limitations
by exploring the use of multiple LEDs in different ways: decoding
multiple devices that output using their own single LED in parallel,
and decoding a single device that raises bandwidth by using multiple
LEDs to encode more information in a given time frame. Experimental
results show the practical limits achieved by a modern
smartphone-class device.

Abstract i
Contents i
Acknowledgments v
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Background and Related Work 3
2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Optical Wireless Sensor Networks . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.2 The Internet of Things . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2.1 Out-of-band Pairing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2.2 Visible Light Communication . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.3 Visual Tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 System Overview 9
3.1 System Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Encoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.1 Packetizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.2 Modulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.1 Control Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.2 Color Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.3 Demodulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.4 Depacketizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.5 Verification Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4 Communication Concepts 13
4.1 Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1.1 Single-LED Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1.2 Multi-LED Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2.1 Single-LED Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.2.2 Multi-LED Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.3 Error Correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5 Implementation 24
5.1 Encoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.1.1 Embedded System Platform . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.1.2 Signal Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.1.3 Programming API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1.4 Profile Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.2 Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.2.1 Image Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2.2 Signal Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6 Evaluation 33
6.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.2.1 Error Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.2.2 Transmission Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7 Conclusions and Future Work 41
7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

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