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Visible Light Communication Visible Light Communication A Major Qualifying Project Report, completed in partial fulfillment of the requirements for the degree of Bachelor of Science at Worcester Polytechnic Institute By Shridhar Ambady Megan Bredes Calvin Nguyen Submission Date: March 26, 2015 Advised by: Professor Lifeng Lai Abstract With increasing demands for faster and more secure wireless communications, there is a pressing need for a new medium of wireless communication as the radio spectrum is already crowded. Visible light is a medium that can address both of these needs. It is a relatively new technology with great potential. This project was completed to develop a working visible light communication system and demonstrate the transmission capabilities of such a system. This year’s team set a goal to surpass the previous year’s team in transmission speed, range, and size. Of these goals, transmission speed and range were both achieved, while the transmission of a large audio file was deemed not possible based off the difficulties the team encountered while processing large amounts of data. ii This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review. iii Acknowledgements We express our deepest gratitude to Professor Lifeng Lai, our MQP advisor for devoting his time and effort to making this project possible. With his helpful feedback and suggestions on tackling problems that have arisen during the duration of the project, we are grateful to have him advise the MQP. We also express our thanks to last year's team that worked on the original VLC project as well as the creators of the works that were cited in this report. iv Table of Contents Executive Summary .................................................................................................................................... viii 1 Introduction ............................................................................................................................................... 1 1.1 Motivations ......................................................................................................................................... 1 1.2 Visible Light Communications ............................................................................................................. 3 1.2.1 History .......................................................................................................................................... 4 1.3 Possible Applications .......................................................................................................................... 7 1.3.1 Drawbacks of VLC ......................................................................................................................... 8 1.4 Goals and Features.............................................................................................................................. 9 2 Design Approach ...................................................................................................................................... 11 2.1 Component Selection ........................................................................................................................ 11 2.1.1 Analog Parts ............................................................................................................................... 11 2.1.2 Digital Parts ................................................................................................................................ 17 2.2 Analog Design.................................................................................................................................... 25 2.2.1 Transmitter ................................................................................................................................ 25 2.2.2 Receiver ...................................................................................................................................... 28 2.2.3 Design Verification ..................................................................................................................... 31 2.3 Digital Design .................................................................................................................................... 34 2.3.1 Transmitter ................................................................................................................................ 34 2.3.2 Receiver ...................................................................................................................................... 37 3 Results and Conclusions ........................................................................................................................... 41 3.1 Analog Results ................................................................................................................................... 41 3.2 Digital results .................................................................................................................................... 43 3.2.1 Transmitting Text ....................................................................................................................... 44 3.2.2 Transmitting an MP3 File ........................................................................................................... 44 3.3 Overall Conclusions ........................................................................................................................... 49 3.4 Future Recommendations ................................................................................................................ 50 References .................................................................................................................................................. 51 Appendix A: Parts List ................................................................................................................................. 52 Appendix B: Matlab Code ........................................................................................................................... 53 receiver.m ............................................................................................................................................... 53 match_filter.m ........................................................................................................................................ 54 downsample.m ....................................................................................................................................... 55 v Appendix C: C# Code ................................................................................................................................... 56 Appendix D: MCU C code ............................................................................................................................ 58 Transmitter Code .................................................................................................................................... 58 Receiver Code ......................................................................................................................................... 59 Table of Figures Figure 1: Frequency Allocations in the United States ................................................................................... 2 Figure 2: RONJA system attempting to transmit through heavy fog ............................................................ 4 Figure 3: 500 Mbps White LEDs .................................................................................................................... 5 Figure 4: VLC System design from 2013 ........................................................................................................ 7 Figure 5: Transmitter Circuit Diagram......................................................................................................... 26 Figure 6: Transmitter - Final Design ............................................................................................................ 27 Figure 7: Old Receiver Circuit Diagram ....................................................................................................... 28 Figure 8: Receiver Final Design ................................................................................................................... 30 Figure 9: Receiver Circuit - Final Design ...................................................................................................... 31 Figure 10: Photodiode Output before Op-Amp .......................................................................................... 32 Figure 11: Photodiode Output after Op-Amp ............................................................................................. 32 Figure 12: Bad Output ................................................................................................................................. 33 Figure 13: Good Output .............................................................................................................................. 33 Figure 14: C# Transmitter Program GUI ...................................................................................................... 35 Figure 15: Op-amp output from 1200 bits/sec 'U' Signal at 1 foot ............................................................. 42 Figure 16: Op-amp output from 1200 bits/sec audio signal at 1 foot .......................................................
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