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ISBN: 978-1-119-33138-4

CONTENTS

Preface

1 Introduction to Visible Light Communications

1.1 History
1.2 Advantages and applications
1.3 Overview of modulation and signal processing
1.4 Standards
References

2 Visible Light Communications: Channel and Capacity

2.1 LED characteristics
2.2 LED lighting constraints
2.3 Photodiode characteristics
2.4 Propagation links
2.5 Noise in VLC systems
2.6 Channel capacity
2.7 Conclusion
References

3 Single Carrier/Carrierless Modulation and Coding

3.1 Pulse amplitude modulation
3.2 Pulse position modulation
3.3 Carrierless amplitude phase modulation
3.4 Modulation and coding schemes for dimmable VLC
3.5 Conclusion
References

4 Multicarrier Modulation

4.1 Optical OFDM for visible light communications
4.2 Performance enhancement for optical OFDM
4.3 Spectrum- and power- efficient optical OFDM
4.4 Optical OFDM under lighting constraints
4.5 Conclusion
References

5 Multicolor Modulation

5.1 Color shift keying
5.2 CSK with coded modulation
5.3 Wavelength division multiplexing with predistorion
5.4 Conclusion
References

6 Optical MIMO

6.1 Non-imaging optical MIMO techniques
6.2 Imaging optical MIMO techniques
6.3 Multiuser precoding techniques
6.4 Optical MIMO-OFDM
6.5 Conclusion
References

7 Signal Processing and Optimization

7.1 Sum-rate maximization for the multi-chip based VLC system
7.2 Heterogeneous VLC-WiFi optimization
7.3 Signal estimation and modulation design for VLC with SDGN
7.4 Conclusion
References

8 Optical Camera Communication: Fundamentals

8.1 Why OCC
8.2 OCC applications: beyond imaging
8.3 Fundamentals of OCC
8.4 Capacity bounds for OCC
8.5 Outage capacity for OCC with misalignment
8.6 Conclusion
References

9 Optical Camera Communication: Modulation and System Design

9.1 Coding and decoding
9.2 Modulation schemes
9.3 System impairment factors
9.4 Synchronization in OCC
9.5 OCC system experimental platform
9.6 Conclusion
References

10 Index

IEEE PRESS SERIES ON DIGITAL AND MOBILE COMMUNICATION

EULA

List of Illustrations

Chapter 2

Figure 2.1 Different LED types.
Figure 2.2 P-N junction under an equilibrium condition.
Figure 2.3 P-N junction under forward bias.
Figure 2.4 VPPM signal with 25 percent pulse width.
Figure 2.5 CIE 1931 xy color coordinates, where x and y are the chromaticity values. The outer curve is the spectral locus with wavelengths shown in nm. The three-digit values refer to the center wavelength of the seven bands defined in the IEEE 802.15.7 standard.
Figure 2.6 Classifications of the propagation links [15].
Figure 2.7 Illustrations of m-simplex and its outer parallel body.
Figure 2.8 Two-dimensional cube with its outer parallel body and sphere packing.
Figure 2.9 Comparison of free-space optical intensity channel capacity bounds when both peak-power and average-power constraints are applied with α = 0.1.
Figure 2.10 Comparison of free-space optical intensity channel capacity bounds when both peak-power and average-power constraints are applied with α ∈ [1/2, 1].
Figure 2.11 Comparison of free-space optical intensity channel capacity bounds when only the average-power constraint is applied.
Figure 2.12 Comparison of Poisson channel capacity bounds when both peak-power and average-power constraints are applied.
Figure 2.13 Comparison of Poisson channel capacity bounds when only the average-power constraint is applied.
Figure 2.14 Comparison of improved free-space optical intensity channel capacity bounds when both peak-power and average-power constraints are applied with ς = 1.
Figure 2.15 Comparison of improved free-space optical intensity channel capacity bounds when only the average-power constraint is applied with ς = 1.

Chapter 3

Figure 3.1 A PAM-SCFDE VLC system.
Figure 3.2 Illustration of 4-SPAM modulation scheme with two LEDs.
Figure 3.3 Illustration of 2-grouped modulation with a 9-LED squared array.
Figure 3.4 Transmitted waveforms for 2-PPM and 4-PPM.
Figure 3.5 L-PPM system with chip-rate zero-forcing decision-feedback equalizer.
Figure 3.6 L-PPM system with symbol-rate zero-forcing decision-feedback equalizer.
Figure 3.7 Examples of modified PPM schemes.
Figure 3.8 Diagram of CAP transceiver.
Figure 3.9 Diagram of CAP as a multirate transmultiplexer.
Figure 3.10 PAPR at CCDF=10^{− 5} for PAM and CAP.
Figure 3.11 Diagram of 3D-CAP as a multirate transmultiplexer.
Figure 3.12 The solved three signals using the minimax optimization algorithm.
Figure 3.13 Visible light communications with dimming control.
Figure 3.14 An example of the compensation scheme for OOK.

Chapter 4

Figure 4.1 The block diagram of DCO-OFDM transceiver for visible light communications.
Figure 4.2 Three different optical OFDM signals: DCO-OFDM (left-column plots), ACO-OFDM (center-column plots) and PAM-DMT (right-column plots).
Figure 4.3 Unipolar optical OFDM signal encoding.
Figure 4.4 Performance comparison of DCO-OFDM, ACO-OFDM, PAM-DMT and U-OFDM schemes.
Figure 4.5 LED nonlinear transfer characteristic and DC bias setting for DCO-OFDM signal.
Figure 4.6 Performance comparison of static and dynamic DC bias and scaling factor optimization.
Figure 4.7 The block diagram of BICM-ID scheme for clipped DCO-OFDM in visible light communications.
Figure 4.8 Three cases of recoverable upper-clipping in RoC added ACO-OFDM scheme.
Figure 4.9 Block diagram of the transmitter for ADO-OFDM (top and middle branches) and HACO-OFDM (bottom and middle branches).
Figure 4.10 Block diagram of the iterative receiver for HACO-OFDM.
Figure 4.11 BER performance comparison of the conventional and iterative receivers for HACO-OFDM (Case 1 with power allocation factor η = 0.3942).
Figure 4.12 BER performance comparison of the conventional and iterative receivers for HACO-OFDM (Case 2 with power allocation factor η = 0.2650).
Figure 4.13 eU-OFDM transmitter with 3 modulation depths.
Figure 4.14 Examples of Layer 1, Layer 2 and Layer 3 ACO-OFDM signals with 16 subcarriers.
Figure 4.15 Block diagram of LACO-OFDM transmitter with L layers.
Figure 4.16 Spectral efficiency comparison of LACO-OFDM and ACO-OFDM.
Figure 4.17 BER performance of LACO-OFDM with 16QAM and 4 layers.
Figure 4.18 BER performance comparison of LACO-OFDM, ACO-OFDM and HACO-OFDM.
Figure 4.19 PWM signal with different pulse widths for dimming control.
Figure 4.20 Variable optical OFDM for visible light communications with dimming control.
Figure 4.21 RPO-OFDM signal waveform with different PWM signals.
Figure 4.22 An example of AHO-OFDM signal with dimming level d = 70%.
Figure 4.23 Optical dimming level d as a function of , , and .
Figure 4.24 Performance comparison of AHO-OFDM, DCO-OFDM and HACO-OFDM for a target BER of 2 × 10^{− 3} under different dimming levels.

Chapter 5

Figure 5.1 Diagram of CSK transmitter.
Figure 5.2 Centers of the seven color bands on xy color coordinates.
Figure 5.3 Constellations of 4-CSK, 8-CSK, and 16-CSK provided by IEEE 802.15.7 standard.
Figure 5.4 Diagram of CSK receiver with color calibration.
Figure 5.5 Constellations of 4-CSK, 8-CSK, and 16-CSK for QLED.
Figure 5.6 Diagram of MAP-based soft detection for coded CSK system.
Figure 5.7 Diagram of three-stage CSK system with MAP-based soft detection and URC precoder.
Figure 5.8 VLC system with RGB-type white LEDs.
Figure 5.9 BER performance comparison of the RGB-type LED based VLC system with and without the predistortion module, where the convolutional code with the soft-decision Viterbi decoder is used.
Figure 5.10 BER performance comparison of the RGB-type LED based VLC systems with and without the predistortion module, where the LDPC code with the BP decoder is used.
Figure 5.11 BER performance comparison of the RGB-type LED based VLC systems with and without the predistortion module, where the turbo code with the BCJR decoder is used.

Chapter 6

Figure 6.1 Non-imaging optical MIMO VLC system.
Figure 6.2 Examples of optical MIMO encoding.
Figure 6.3 Performance comparison of RC, SMP and OSM for non-imaging VLC system with spectral efficiency of 4 bit/s/Hz, where all the LEDs have equal power.
Figure 6.4 Performance comparison of RC, SMP and OSM for 4 × 4 non-imaging VLC system with spectral efficiency of 4 bit/s/Hz and different power imbalance factors.
Figure 6.5 Imaging optical MIMO VLC system.
Figure 6.6 An example of the image on the receiver array.
Figure 6.7 Examples of images on the detector array.
Figure 6.8 Illustration of MU-MIMO VLC system.
Figure 6.9 Diagram of the MU-MIMO VLC transmitter.
Figure 6.10 System throughput comparison between equal power allocation and optimal power allocation.
Figure 6.11 System throughput comparison when the number of LEDs no less than that of PDs.
Figure 6.12 System throughput comparison when the constraint about the number of LEDs and PDs is not satisfied.
Figure 6.13 MU-MIMO-OFDM VLC transmitter with N_r users, N_t LED units and N subcarriers.
Figure 6.14 Average spectral efficiency of DCO-OFDM-based MU-MIMO VLC system with different average emitted optical power and DC bias.
Figure 6.15 Average spectral efficiency comparison of ACO-OFDM-based and DCO-OFDM-based MU-MIMO VLC systems with different average emitted optical power.

Chapter 7

Figure 7.1 Block diagram of the multi-chip LED based VLC system.
Figure 7.2 MacAdam ellipses in CIE 1931 color space chromaticity diagram with 10 times the actual size in MacAdam’ experiment.
Figure 7.3 Maximum sum-rate for different luminous fluxes when CCT= 5000 K.
Figure 7.4 Percentages of three light components to achieve the maximum sum-rate for different luminous fluxes when CCT= 5000 K.
Figure 7.5 Comparison between different steps of MacAdam ellipse under different luminous fluxes when CCT= 5000 K.
Figure 7.6 Maximum achievable sum-rate comparison for different CCT values under chromaticity constraint based on MacAdam ellipse.
Figure 7.7 Illustration of the heterogeneous VLC-WiFi system.
Figure 7.8 Illustration of transition rates for (a) 0 < b < B, (b) b = 0 and (c) b = B.
Figure 7.9 Impact of γ₂ on the system performance for four schemes.
Figure 7.10 Impact of handover delay τ on the system performance for four schemes.
Figure 7.11 VLC system with square-root signaling.
Figure 7.12 SER performance of the optimal signaling against thermal noise variance.
Figure 7.13 SER performance of the optimal signaling against shot noise variance.
Figure 7.14 SER performance of the optimal signaling against the APPR.

Chapter 8

Figure 8.1 The diagram of the transceiver for optical camera communication (OCC) [4].
Figure 8.2 Color filter arrays in image sensor.
Figure 8.3 The application of OCC in intelligent transportation system.
Figure 8.4 The application of OCC in screen-camera communication.
Figure 8.5 The imaging system pipeline.
Figure 8.6 The structure of a CMOS image sensor.
Figure 8.7 Readout architectures of interline transfer of different image sensors [26].
Figure 8.8 2D MTF for the image sensor detector with different shape active areas.
Figure 8.9 Schematic of a CMOS pixel sensor.
Figure 8.10 PFN noise for CCD and CMOS image sensors.
Figure 8.11 The diagram of the photosensor model.
Figure 8.12 System diagram of correlated double sampling.
Figure 8.13 SNR in OCC with different pixel size areas.
Figure 8.14 SNR in OCC with different integration time.
Figure 8.15 SNR in OCC with different block size.
Figure 8.16 The equivalent system model for CMOS image sensor based OCC.
Figure 8.17 Diffraction-limited optical subsystem.
Figure 8.18 Geometrical model of CMOS image sensor by Ibrahima Djite [39].
Figure 8.19 Detector and beam footprint for transmitters with misalignment and inter-pixel-interference in the pixel based detector plane.
Figure 8.20 Capacity-achieving distribution for signal-dependent noise channel (P = 4, A = 10, ς²₁σ² = 100ς₂²σ²).
Figure 8.21 Capacity bounds for OCC.
Figure 8.22 Non-imaging MIMO receivers.
Figure 8.23 Diagram of the imaging optical MIMO system.

Chapter 9

Figure 9.1 Illustrative diagram for an optical channel with a mapper [4].
Figure 9.2 Schematic block diagram for MLC and mapper [4].
Figure 9.3 Schematic block diagram for multi-stage decoders (MSD) [4].
Figure 9.4 Mapping function over to induce p(0) = 7/8 and p(A) = 1/8.
Figure 9.5 System model for the single encoding and mapping scheme.
Figure 9.6 The factor graph for joint demapping and decoding.
Figure 9.7 The cutoff frequencies of the human eye and the camera.
Figure 9.8 The example of UFSOOK pattern and UPSOOK pattern [8].
Figure 9.9 An example of the 4-UPSPAM signal and the data frame structure.
Figure 9.10 Timing chart for the rolling shutter image sensor.
Figure 9.11 Data decoding using the rolling shutter scheme.
Figure 9.12 OOK, FSK and CSK modulation using the rolling shutter effect.
Figure 9.13 Illustration of an imaging optical MIMO communication system.
Figure 9.14 Block diagram of a spatial OFDM system [27].
Figure 9.15 Block diagram of a spatial WPDM system.
Figure 9.16 Illustration of the linear misalignment between transmitted and received frames [27].
Figure 9.17 Illustration of a received pixel depending on four transmitted pixels.
Figure 9.18 Constellation of SACO-OFDM impaired by linear misalignment.
Figure 9.19 Attenuation versus subcarrier index and fraction of misalignment.
Figure 9.20 Illustration of a received frame with geometry perspective distortion.
Figure 9.21 Received constellation for SACO-OFDM and Gaussian PSF due to blur effect with σ = 0.35.
Figure 9.22 Illustration of imaging optical MIMO system using an optical lens.
Figure 9.23 The ICI gain and received constellation for spatial OFDM in the presence of vignetting.
Figure 9.24 Diagram of decision feedback equalization in spatial frequency domain.
Figure 9.25 The transmitted and received signal amplitudes across different frequencies due to the blur effect.
Figure 9.26 Mismatched frame rates between transmitter-receiver pairs (inter-frame intervals are omitted).
Figure 9.27 Per-frame tracking bar pattern.
Figure 9.28 The architecture of eIRA-Raptor coding and joint iterative decoding.
Figure 9.29 The CIM-MIMO OCC transceiver diagram.
Figure 9.30 Observed nonideal issues in CIM-MIMO OCC design.
Figure 9.31 The joint nonlinearity and crosstalk effect between red-green-blue channels.
Figure 9.32 The spatial frame layout and packet format for each LED.
Figure 9.33 LED array and symbol detection.
Figure 9.34 The 3D 64-CIM constellation at the receiver.
Figure 9.35 The OCC experimental platform.
Figure 9.36 BER performance of CIM-MIMO OCC systems.

Preface

This book presents the state-of-the-art of visible light communication (VLC) focusing on the modulation and signal processing aspects. VLC has many advantages, such as wide unregulated bandwidth, high security and low cost over its traditional radio frequency counterpart. It has attracted increasing attention from both academia and industry, and is considered as a promising complementary technology in the fifth generation (5G) wireless communications and beyond, especially in indoor applications. This book provides, for the first time a systematical and advanced treatment of modulation and signal processing for VLC and optical camera communication (OCC) systems. Example designs are presented and the analysis of their performance is detailed. In addition, the book includes a bibliography of current research literature and patents in this area.

Visible Light Communications: Modulation and Signal Processing endeavors to provide topics from VLC models to extensive coverage of the latest modulation and signal processing techniques for VLC systems. Major features of this book include a practical guide to design of VLC systems under lighting constraints, and the combination of the theoretical rigor and practical examples in present OCC systems.

Although it contains some introductory materials, this book is intended to serve as a useful tool and a reference book for communication and signal processing professionals, such as engineers, designers, and developers with VLC-related projects. For university undergraduates majoring in communication and signal processing, this book can be used as a supplementary tool in their design projects. Graduate students and researchers working in the field of modern communications will also find this book interest and valuable. The book is organized as follows.

Chapter 1 provides an overview of the history of VLC, its advantages, applications, related modulation and signal processing techniques, and standardization progresses.

Chapter 2 investigates optical channel models and channel capacity subject to lighting constraints from light emitting diode (LED), where chromaticity control, dimming control, and flicker mitigation are also discussed. The link characteristics including shadowing, direct versus indirect lighting and natural light are introduced. Typical optical channel models are addressed in detail. In addition, channel capacity under different lighting constraints is derived to achieve tight upper and lower bounds.

Chapter 3 reviews carrierless, single carrier modulations and some coding schemes for VLC systems. Modulation and coding techniques for dimming control and flicker mitigation are also introduced to satisfy illumination requirements.

Chapter 4 briefly reviews conventional optical orthogonal frequency division multiplexing (OFDM) schemes and then focuses on recent developments on optical OFDM including performance enhancement, spectrum- and power-efficient optical OFDM, and optical OFDM under lighting constraints. Comprehensive comparisons of the existing and proposed modulation techniques are provided as well.

Chapter 5 discusses multicolor modulation schemes under illumination requirements. The LED colorimetry is introduced as a measure for illumination quality, and various modulation schemes are explored to support both communication and high-quality illumination.

Chapter 6 explains optical multiple-input multiple-output (MIMO) techniques for imaging and non-imaging VLC systems, including modern optical MIMO, optical spatial modulation, optical space shift keying, and optical MIMO-OFDM. Furthermore, multiuser precoding techniques for VLC systems are also introduced under lighting constraints.

Chapter 7 addresses the signal processing and optimization issues for VLC systems including pre- and post-equalization, interference mitigation, and capacity maximization. The hybrid visible light communication and wireless fidelity (VLC-WiFi) system is also introduced to provide better coverage, and the system optimization problem is formulated and solved.

Chapter 8 introduces OCC fundamentals. It describes a typical OCC link, from the optical signal source, propagation path, to optical lens, filters, pixelated image sensors, and the receiver. Different noise models such as ambient noise, temporal noise and fixed pattern noise are also addressed. Inter-pixel interference in the active pixel sensor, optical crosstalk due to diffraction and light diffusion, and the distortion due to perspective are introduced.

Chapter 9 discusses OCC modulation schemes and system design aspects. It also introduces various system impairment factors and mitigation techniques, including tracking and coding techniques to achieve synchronization. The off-line and real-time prototypes as well as the potential applications of smartphone cameras are illustrated.

This work was supported by National Key Basic Research Program of China under Grant No. 2013CB329200.

The authors also wish to thank Mr. Rui Jiang at Tsinghua University, China for his contributions to Chapter 2, and Mr. Jiandong Tan at Tsinghua University, China for his help with writing Chapter 4.

The authors are indebted to anonymous reviewers for their detailed and insightful constructive comments, as well as many researchers for their published works serving as rich reference sources in the book. The help provided by Mary Hatcher and other staff members from John Wiley & Sons is most appreciated.

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IEEE Press Editorial Board
Tariq Samad, Editor in Chief

Giancarlo Fortino	Don Heirman	Linda Shafer
Dmitry Goldgof	Xiaoou Li	Mohammad Shahidehpour
Ekram Hossain	Jeffrey Nanzer	Saeid Nahavandi
Andreas Molisch	Ray Perez	Zidong Wang