Visible Light Wireless Communications and Its Fundamental Study 2005 Toshihiko Komine Copyright c  2006 by Toshihiko Komine All rights reserved Contents Abstract 1 1 General Introduction 2 1.1 Historical Overview of Visible Light Wireless Communication . . . 2 1.2 Difference between Visible Light Wireless Communication and Other Wireless Communications . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Conventional Optical Wireless Communication Systems . . . . . . 5 1.3.1 IrDA links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.2 Physical layer for IEEE 802.11 . . . . . . . . . . . . . . . . . . 8 1.4 Purpose and Position of This Study . . . . . . . . . . . . . . . . . . . 9 1.4.1 Outline of the Dissertation . . . . . . . . . . . . . . . . . . . . 10 1.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2 Basic Knowledge for Indoor Optical Wireless Communication 15 2.1 Intensity Modulation and Direct Detection Channels . . . . . . . . . 15 2.2 Channel Direct Current Gains . . . . . . . . . . . . . . . . . . . . . . 17 2.3 Electrical SNR and BER . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3 Characteristics of White LED 21 3.1 Basic Properties of LED Light . . . . . . . . . . . . . . . . . . . . . . 22 3.2 Radiation Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.3 Luminous Intensity and Optical Output Power . . . . . . . . . . . . 23 3.4 Total Luminous Flux . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 4 Proposal of Indoor Visible Light Wireless Communication Systems uti- lizing White LED Lighting Equipment and Their Performance Evaluation for Lighting Design 29 4.1 Proposal of New LED Lighting Equipments with Function of Wire- less Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . 29 4.1.1 Visible Light Wireless Data Transmission Lighting Equipment 30 i 4.1.2 Radiation Pattern and Illuminance Distribution of LED Light- ing Equipments . . . . . . . . . . . . . . . . . . . . . . . . . . 33 4.1.3 Received Optical Power for Data Transmission . . . . . . . . 33 4.1.4 Propagation Delay by Wide Surface Area of Lighting Equip- ment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.1.5 BER Performance of Proposal Systems . . . . . . . . . . . . . 38 4.2 Influence of Multiple Lighting Equipments that Transmit Different Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 5 Various New Proposals in Indoor Environment 44 5.1 Basic Study on Communication Performance in Various Indoor Models 45 5.1.1 Lighting Design in Indoor Environment Based on Lighting Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 5.1.2 Illuminance Distribution Based on Lighting Engineering . . 46 5.1.3 Proposed Lighting Equipment Diversity System . . . . . . . 49 5.1.4 Received Optical Power . . . . . . . . . . . . . . . . . . . . . 49 5.1.5 Propagation Delay by Plural Lighting Equipments . . . . . . 51 5.1.6 BER Performance . . . . . . . . . . . . . . . . . . . . . . . . . 53 5.2 Effective Lighting System to Shadowing and Its Performance Eval- uation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 5.2.1 Influence of Intersymbol Interference by Lighting Equipment Diversity System . . . . . . . . . . . . . . . . . . . . . . . . . 57 5.2.2 Effect of Shadowing . . . . . . . . . . . . . . . . . . . . . . . 58 5.3 Proposal of Adaptive Equalization for Visible Light Wireless Com- munication System that has Mobility . . . . . . . . . . . . . . . . . . 65 5.3.1 System Description . . . . . . . . . . . . . . . . . . . . . . . . 65 5.3.2 Mean Square Error . . . . . . . . . . . . . . . . . . . . . . . . 68 5.3.3 BER Performance . . . . . . . . . . . . . . . . . . . . . . . . . 68 5.3.4 Training Sequence Interval . . . . . . . . . . . . . . . . . . . 70 5.3.5 Tolerance Properties to Shadowing . . . . . . . . . . . . . . . 71 5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 5.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 6 Integrated System of Visible Light Wireless Communication and Power Line Communication for Improvement of Convenience and User-Friendliness 76 6.1 System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 6.2 Narrowband Power Line Noise . . . . . . . . . . . . . . . . . . . . . 78 6.3 Performance Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.3.1 Flicker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 6.3.2 BER Performance . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.3.3 Communication Area . . . . . . . . . . . . . . . . . . . . . . 81 ii 6.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 6.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 7 Conclusion 85 7.1 Conclusion From Chapter 4 . . . . . . . . . . . . . . . . . . . . . . . 86 7.2 Conclusion From Chapter 5 . . . . . . . . . . . . . . . . . . . . . . . 86 7.3 Conclusion From Chapter 6 . . . . . . . . . . . . . . . . . . . . . . . 87 7.4 Future Indoor Visible Light Wireless Communications . . . . . . . . 87 Acknowledgments 89 List of Papers 90 Transaction Papers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 International Conferences . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Technical Reports and Other Presentations . . . . . . . . . . . . . . . . . 92 iii List of Figures 1.1 Photophone. (Lucent Technologies, Bell Labs Innovations) . . . . . 3 1.2 An example of an IrDA. . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3 The IrDA protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.4 IrDA optical geometry. . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.5 An example of an IEEE 802.11 network with infrared transmission. 8 1.6 PPM signals at 1 and 2 Mbit/s. . . . . . . . . . . . . . . . . . . . . . . 9 1.7 Outline of the dissertation. . . . . . . . . . . . . . . . . . . . . . . . . 11 2.1 Modeling link as a baseband filter, time-invariant system having impulse response h(t), with signal-independent, additive noise N(t). The photodetector has responsivity R. . . . . . . . . . . . . . . . . . 16 2.2 Calculation for channel DC gain. . . . . . . . . . . . . . . . . . . . . 18 3.1 Spectral luminous efficiency functions as defined by the CIE. . . . . 23 3.2 Measuring method of radiation pattern. . . . . . . . . . . . . . . . . 23 3.3 Radiation pattern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.4 Measuring method of optical output power and luminous intensity. 24 3.5 Luminous intensity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.6 Optical output power. . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.7 Semiangle at half power and luminous intensity on optical axis. . . 27 4.1 A proposed system image. . . . . . . . . . . . . . . . . . . . . . . . . 30 4.2 L-PPM system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 4.3 Symbol timing controller. . . . . . . . . . . . . . . . . . . . . . . . . 32 4.4 Radiation pattern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 4.5 Illuminance distribution at each height between the light equipment and the receiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 4.6 Calculation of illuminance. . . . . . . . . . . . . . . . . . . . . . . . . 35 4.7 Received optical power of the general lighting. . . . . . . . . . . . . 36 4.8 Received optical power of the downlight. . . . . . . . . . . . . . . . 36 4.9 Received optical power. . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.10 Received optical power vs. electrical SNR. . . . . . . . . . . . . . . . 37 4.11 RMS delay spread at H=3.0 m. . . . . . . . . . . . . . . . . . . . . . 38 4.12 Mean delay time at H=3.0 m. . . . . . . . . . . . . . . . . . . . . . . 38 iv 4.13 BER performance of the general lighting. . . . . . . . . . . . . . . . 39 4.14 BER performance of the downlight. . . . . . . . . . . . . . . . . . . . 39 4.15 Illuminance and BER performance of the general lighting at H=3.0 m. 40 4.16 Illuminance and BER performance of the downlight at H=3.0 m. . . 40 4.17 Influence of multiple lighting equipments. . . . . . . . . . . . . . . 41 4.18 BER performance by plural lighting equipments at H=3.0 m. (Non tracking, FOV 90 deg.) . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.19 DUR and distance between lighting equipments. (Non tracking, FOV 90 deg.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 5.1 Proposed lighting equipment diversity system. . . . . . . . . . . . . 45 5.2 Position of Lighting Equipments. . . . . . . . . . . . . . . . . . . . . 46 5.3 Number of reflection. (Model A) . . . . . . . . . . . . . . . . . . . . 47 5.4 Illuminance distribution. . . . . . . . . . . . . . . . . . . . . . . . . . 48 5.5 The lighting equipment diversity system. . . . . . . . . . . . . . . . 49 5.6 Received optical power distribution. . . . . . . . . . . . . . . . . . . 50 5.7 Impulse response at (0.3, 2.1, 0.85). . . . . . . . . . . . . . . . . . . . 51 5.8 RMS delay spread. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 5.9 Influence of each noise variance at corner of the room (Model A: (0.1, 0.1, 0.85)). Modulation scheme is 2-PPM. . . . . . . . . . . . . . 54 5.10 BER Distribution at 500 Mbit/s. . . . . . . . . . . . . . . . . . . . . . 55 5.11 BER Distribution at 800 Mbit/s. . . . . . . . . . . . . . . . . . . . . . 56 5.12 Outage Area Rate at each model. . . . . . . . . . . . . . . . . . . . . 57 5.13 Position of the each lighting equipment. . . . . . . . . . . . . . . . . 58 5.14 Outage area rate at each modulation scheme. . . . . . . . . . . . . . 59 5.15 A model of the human body as pedestrian. . . . . . . . . . . . . . . 59 5.16 Outage call duration rate. . . . . . . . . . . . . . . . . . . . . . . . . 60 5.17 Outage call duration rate vs. mean density of pedestrians: bit rate is 100 Mbit/s, and the offered load is 4 erl. . . . . . . . . . . . . . . . 61 5.18 Outage call duration rate vs. mean density of pedestrians: bit rate is 500 Mbit/s, and the offered load is 4 erl. . . . . . . . . . . . . . . . 61 5.19 Outage call duration rate vs. offered load: bit rate is 100 Mbit/s, and the mean density of pedestrians is 0.05 m −2 . . . . . . . . . . . . . . . 62 5.20 Outage call duration rate vs. offered load: bit rate is 500 Mbit/s, and the mean density of pedestrians is 0.05 m −2 . . . . . . . . . . . . . . . 62 5.21 Blocking rate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.22 Outage call duration rate vs. offered load: bit rate is 100 Mbit/s, the mean density of pedestrian is 0.05 m −2 . . . . . . . . . . . . . . . . . . 64 5.23 Outage call duration rate vs. offered load: bit rate is 500 Mbit/s, the mean density of pedestrian is 0.05 m −2 . . . . . . . . . . . . . . . . . . 64 5.24 FIR equalizer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5.25 Decision feedback equalizer. . . . . . . . . . . . . . . . . . . . . . . . 66 v 5.26 Mean square error. Received optical power is -5.55 dBm/cm 2 , loop number is 1000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 5.27 BER distribution without DFE. Data rate is 500 Mbit/s. . . . . . . . . 69 5.28 BER distribution with DFE. Data rate is 500 Mbit/s. FF tap is 4, FB tap is 2, step parameter is 0.01, training sequence is 10000 bits. . . 69 5.29 BER distribution without DFE. Data rate is 800 Mbit/s. . . . . . . . . 69 5.30 BER distribution with DFE. Data rate is 800 Mbit/s. FF tap is 4, FB tap is 2, step parameter is 0.01, training sequence is 10000 bits. . . 69 5.31 Outage area rate versus data rate. Step parameter is 0.01, length of training sequence is 10000 bits. . . . . . . . . . . . . . . . . . . . . . 70 5.32 Distance between position X and Y versus BER by channel estima- tion. FF tap is 4, FB tap is 2, Step parameter is 0.01, length of training sequence is 10000 bits. . . . . . . . . . . . . . . . . . . . . . . . . . . 70 5.33 Outage call duration rate vs. mean density of pedestrians: bit rate is 500 Mbit/s, and the offered load is 4 erl. . . . . . . . . . . . . . . . 71 5.34 Blocking rate performance at 500 Mbit/s. . . . . . . . . . . . . . . . . 72 6.1 Proposed system model. . . . . . . . . . . . . . . . . . . . . . . . . . 77 6.2 Waveform on power line. . . . . . . . . . . . . . . . . . . . . . . . . 77 6.3 Snap-shot of generated noise waveforms. . . . . . . . . . . . . . . . 79 6.4 Integrated OFDM-QPSK System. . . . . . . . . . . . . . . . . . . . . 80 6.5 Maximum relative voltage change. Data rate is 27.3 kbit/s (1 carrier), 54.6 kbit/s (2 carriers), 109.2 kbit/s (4 carriers) and 218.4 kbit/s (8 carriers). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.6 The BER performance of the proposed integrated system. . . . . . . 82 6.7 BER of whole system vs. number of carrier. SNR pl is 16 dB. Data rate is 27.3 kbit/s (1 carrier), 54.6 kbit/s (2 carriers), 109.2 kbit/s (4 carriers) and 218.4 kbit/s (8 carriers). . . . . . . . . . . . . . . . . . . 82 6.8 Numerical analysis condition. . . . . . . . . . . . . . . . . . . . . . . 83 6.9 Horizontal distance vs. SNR vl . Data rate is 27.3 kbit/s (1 carrier), 54.6 kbit/s (2 carriers), 109.2 kbit/s (4 carriers) and 218.4 kbit/s (8 carriers). 84 vi List of Tables 1.1 Comparison between radio, infrared, and visible light system for indoor wireless communication. . . . . . . . . . . . . . . . . . . . . 5 1.2 Signaling rate and pulse duration specifications of IrDA 1.4. . . . . 7 3.1 Results of measurements. . . . . . . . . . . . . . . . . . . . . . . . . 26 3.2 Semiangle at half power and luminous intensity on optical axis. . . 27 4.1 Design parameters of LED lighting equipments. . . . . . . . . . . . 31 4.2 SNR calculation parameters. . . . . . . . . . . . . . . . . . . . . . . . 35 5.1 Three typical models of visible light wireless environment. . . . . . 45 5.2 Simulation parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . 53 5.3 Simulation conditions for influence of shadowing. . . . . . . . . . . 60 6.1 Noise parameters on power line. . . . . . . . . . . . . . . . . . . . . 79 6.2 Simulation parameter for the integrated system. . . . . . . . . . . . 80 6.3 Parameters for SNR calculation. . . . . . . . . . . . . . . . . . . . . . 83 vii Abstract In 1990’s, white LEDs (Light Emitting Diodes) have been invented for various uses and subsequently investigated. Compared with conventional lighting devices, the white LED has lower power consumption, lower voltage, longer lifetime, smaller size, faster response, and cooler operation. The white LED will eventually replace incandescent or fluorescent lights in offices and homes. In this dissertation, an indoor visible light wireless communication system uti- lizing white LED lighting equipment is proposed. In this system, these devices are used not only for illuminating rooms but also for a wireless optical commu- nication system. This dual function of LED, for lighting and communication, is creating many new and interesting applications. The function is based on the fast switching of LEDs and the modulation of the visible light waves for free-space communications. The system has large power compared with infrared wireless communication system. Based on lighting engineering, their communication per- formances are evaluated. Then, various new communication schemes in indoor visible light environment are proposed and discussed. A diversity technique is proposed so that shadowing problem may be alleviated. Moreover, to overcome the intersymbol interference caused by optical path difference between lighting equipments, an adaptive equal- izer is proposed and discussed. The effectual interval of training sequence for channel estimation alleviates the influence of shadowing. Finally, an integrated system of visible light wireless communication and power line communication for improvement of convenience and user friendliness is pro- posed. This system can also be considered as a very economical integration be- tween power line communication and wireless communication. In this system, there is no necessity to lay a new communication cable in a ceiling. And, by screwing the electric bulb into a socket, the data transmission becomes possible. From these proposals, it is found that the idea of the proposed systems is very promising for future high speed wireless networks and the visible light wireless communication can be one choice for an indoor optical wireless data transmission system. . Historical Overview of Visible Light Wireless Communication . . . 2 1.2 Difference between Visible Light Wireless Communication and Other Wireless Communications. Integrated System of Visible Light Wireless Communication and Power Line Communication Easy wiring in ceiling for visible light wireless communication Expectation