The document discusses wireless connectivity through Visible Light Communications (VLC) as an alternative to Wi-Fi, highlighting its advantages such as faster data rates, enhanced security, and environmentally friendly attributes. It also addresses challenges in VLC implementation, including signal shadowing and modulation techniques, while presenting potential applications like indoor GPS and smart lighting systems. Overall, VLC is positioned as a promising solution to meet the growing demand for reliable high-speed internet access.

1. Mohammad Noshad
Wireless Connectivity Through
Lighting: Potential and Limitations
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2. 2
Outline
 Motivation
 Introduction to Visible Light Communications (VLC)
 Applications
 Challenges
 Modulation and Coding Techniques
 Networking in VLC Systems

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 Wi-Fi is the technology that provides wireless internet access.
 It is very popular
 Current frequency bands for Wi-Fi (IEEE 802.11)
 2.4, 5, or 60 (mm-wave) GHz
Wi-Fi Technology
Introduction Applications Challenges Modulation & Coding VLC Networks

4. What is Wrong with Wi-Fi?
 Throughput limitation of Wi-Fi
 The data-rate in Wi-Fi systems (2.4 and 5 GHz bands) is limited to 600 Mb/s
 This speed is divided among all users
 Supports limited number of users in crowded areas
 Each Wi-Fi access point can support limited number of users
 Limited bandwidth reuse
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5. What is Wrong with Wi-Fi?
 Wi-Fi signals passes through the walls
 It has low security against eavesdropping
 Need password for security
 Currently there is no wireless internet access in some buildings because of the
security concerns
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6. What is Wrong with Wi-Fi?
 Wi-Fi can cause interference on sensitive devices
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 There is national RF quite zone
Introduction Applications Challenges Modulation & Coding VLC Networks

7. What is Wrong with Wi-Fi?
 There is an increasing health concern due to exposure to Wi-Fi:
 Your body is exposed to Wi-Fi 24/7
 It passes through the skin – might be risky for neural system
 It is a concern for children and pregnant women
 Germany, Australia, France and some schools in Canada and US have banned
Wi-Fi use at schools
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Other Alternative: Optical Communications
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9. Other Alternative: Optical Communications
 Faster than other forms of communications
 Backbone of modern telecommunications
 Wireless optical communications has many applications
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10. White Light LEDs
 LED lamps are becoming popular because of their low energy
consumption and longevity
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11.  Goal: Use the lighting system also for communications
 Transmission requires energy, yet energy is already going from infrastructure
to user in the form of light.
Visible Light Communications (VLC)
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 LEDs are good candidates for VLC
 Low cost
 High-Speed
 Safe for eye
 Two technologies in white LEDs
 Phosphor-based
 Cheap
 Trichromatic
 High-speed
 Color control
Visible Light Communications (VLC)
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Applications and Potentials

14. Advantages
Advantages of VLC
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Introduction Applications Challenges Modulation & Coding VLC Networks
 Safe for human body
 High security
 Can provide high-speed connection (1 Gb/s)
 No interference on RF signals
 Environmentally “green”
 Can providing accurate (~1 mm) indoor positioning system
(indoor GPS)

15. Indoor Wireless Networks
 Home
 Office
 Library
 Airplane
 Hospital
 Convention Center
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16. Future VLC Products
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VLC-enabled LED bulbs and LED panels
Introduction Applications Challenges Modulation & Coding VLC Networks

17. Future VLC Products
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VLC-enabled floor-lamps and desk lamps can be easily bought from the
market and installed.
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VLC modems will be used to connect users to the VLC network
Future VLC Products
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 VLC models will be integrated into smart-phones
 Small modems will be presented to the marked for older
smartphones to stablish connection.
Future VLC Products
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20. Another Cool Application
 Car to Car Communication
 Intelligent Traffic System
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Visible Light Positioning
 Signals transmitted by LEDs
can be used to estimate the
position of a receiver relative
to the LEDs
 Receiver receives signals from
one or more lights
 Required accuracy depends on
application
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Visible Light Positioning
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VLC Opens Other Potential Applications
 Users are connected to lights
 Lighting features can be simply controlled from the mobile device
 Dim the lights
 Control hue of the light
 Smart lighting is much easier with VLC
 There are photodetectors on the user device and on the luminaries
 Photodetectors sense the intensity of the light
 The lights can control the illumination level automatically
 Internet of things can be developed on VLC networks
 All the electronic devices can connect to access-points using their LEDs
 Access-points know the location of all devices
Introduction Applications Challenges Modulation & Coding VLC Networks

24. Another Cool Application
 Car to Car Communication through headlights and taillights
 Intelligent Traffic System
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Challenges

26. Shadowing
 Shadowing is when the direct path from user to luminary is blocked
 Channel estimation
 Equalizer is needed to decrease inter-symbol interference (ISI) effect
 Channel estimation is required to implement optimum equalizer
 We plan to use position of users to estimate channel response
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27. Connectivity
Users should stay connected when they move
There are overlaps between the coverage of luminaries
(This is due to lighting standards)
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28. Uplink Connection
 Visible light is used for downlink
It is not desirable to use white light for uplink
There are two options:
 Infrared
 Dimmed white light
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29. Lighting Standards
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 The illumination should satisfy some standards
 There is a required level of light for each
environment
The distribution of light should be uniform
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30. Dimming Control
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 Dimming is a feature required in modern lighting systems
 The level of the light should be controllable by the user
Introduction Applications Challenges Modulation & Coding VLC Networks

31. Background Light
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 Strong background light can affect the performance of the system
 The system should operate when it is exposed to extreme Sun
light
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32. Other Challenges
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 Dimming is a feature required
in modern lighting systems
 The level of the light should
be controllable by the user
 The system should operate
when it is exposed to extreme
Sun light
Background light (direct Sun exposure)
Dimming
 The illumination should satisfy
some standards
 There is a required level of
light for each environment
 The distribution of light should
be uniform
Lighting Standards
 We address all of these by modulation and coding

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Modulation and Coding

34.  In VLC systems, peak and average powers are given
Modulations for VLC Systems
Time
OpticalPower
Peak Power
Average Power
 Peak to average power ratio (PAPR) is fixed
 This is determined by dimming level
 Adaptive modulation techniques are needed
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 LEDs are the main sources
 Modulations that can be used are different from RF
systems
 Two families of modulations are used:
 Pulsed techniques:
 On-off keying (OOK),
 Pulse amplitude modulation (PAM)
 Pulse position modulation (PPM)
 Subcarrier techniques:
 Orthogonal frequency division multiplexing (OFDM)
 Hadamard Coded Modulation (HCM)
Modulations for VLC Systems
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Orthogonal Frequency Division Multiplexing (OFDM)
 Special version of subcarrier modulation where all the
subcarrier frequencies are orthogonal
 Efficiently utilizes the available bandwidth
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 Original OFDM cannot be used in incoherent optical systems
 It generates complex-valued signals
 Incoherent optical sources can only transmit positive real signals
 Modified forms of OFDM
OFDM for Optical Systems
 Asymmetrically Clipped Optical (ACO) OFDM
 Apply Hermitian symmetry
 Modulate only half of the data
 DC-biased Optical (DCO) OFDM
 Apply Hermitian symmetry to make signal real
 Add a DC bias and clip the negative part
rate of ≈1/2
rate of ≈ 1/4
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OFDM for Optical Systems
Optical
Peak Power
Optical wireless system model
 Clipping the OFDM signal at 0 and Pmax adds a clipping noise
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OFDM for Optical Systems
 Consider two systems:
1) Optical wireless communications requiring high average
power levels, such as VLC systems
2) Optical systems with unconstrained energy usage
 OFDM does not work well in these two cases
Low average power
High average power
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OFDM signal generation
Why not use another orthogonal basis function?
Hadamard matrix is an option
Add a vector to make
signals positiveEach component of u is
M-ary PAM modulated
Hadamard Coded Modulation (HCM): An Alternative for OFDM
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HCM Trnasmitter
 Can be implemented with fast Walsh-Hadamard transform (FWHT)
 FWHT has the same complexity as FFT: O(N logN)
Introduction Applications Challenges Modulation & Coding VLC Networks
M. Noshad, M. Brandt-Pearce, IEEE Global Communications Conference, Dec 2014

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HCM Receiver
 Receiver is implemented using inverse FWHT (IFWHT)
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HCM versus OFDM
BER of HCM vs ACO-OFDM and DCO-OFDM
Can we shift HCM to the left?
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Improving Energy Efficiency
 The first row of Hadamard matrix is all ones
 Adding or removing a DC value has no effect on (N-1) of the columns
 We use only N-1 rows of Hadamard to modulate the data
 Send (x – min x) instead of x
 Then we can reduce the energy of transmitted signals
 New technique is named DR-reduced (DCR) HCM
0
u2
u1
u3
u4
u5
u6
u7
Introduction Applications Challenges Modulation & Coding VLC Networks
M. Noshad, M. Brandt-Pearce, IEEE Transactions on Communications, Feb 2016.

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Improving Energy Efficiency
Motivation Past Research Existing Solutions Proposed Techniques Results
HCM signal DCR-HCM signal
DC part
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DCR-HCM vs HCM
Probability mass function for HCM and DCR-HCM
M. Noshad, M. Brandt-Pearce
HCM DCR-HCM
HCM generates large signals with higher probability
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BER of HCM and DCR-HCM vs ACO-OFDM and DCO-OFDM
Spectral efficiency = 1
HCM versus OFDM
Introduction Applications Challenges Modulation & Coding VLC Networks
M. Noshad, M. Brandt-Pearce, IEEE Transactions on Communications, Feb 2016.

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HCM versus OFDM
Maximum achievable SNR versus the spectral efficiency for HCM, DCR-HCM,
ACO-OFDM and DCO-OFDM.
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VLC Networks

50. VLC Networks
 Providing network access for large number of users is essential is
VLC systems
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51. Multiuser VLC Networks
 LEDs are used in VLC networks
 Frequency-domain processing may be expensive and
complicated
 They are nonlinear
 Time-based modulations, specially pulsed techniques, are
preferred
 Current Solutions for Multiuser Support
 Time division multiple access
 Code division multiple access
 Spatial division multiple access
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52. Solutions for Multiuser Support
 Time division multiple access
 Low data-rate
 Inflexible data-rates
 Does not support dimming
 Code division multiple access
 Spatial division multiple access
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53. Solutions for Multiuser Support
 Time division multiple access
 Code division multiple access
 Time spreading codes are preferred
 Optical orthogonal codes (OOC)
 Are designed for fiber-optic communications
 Codes have the same length and weight
 Cross-correlation is equal or smaller than 1
 For fixed number of users it is hard to control dimming
 Spatial division multiple access 53
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54. Solutions for Multiuser Support
 Time division multiple access
 Code division multiple access
 Spatial division multiple access
 Uses narrow optical beams
 The area is divided into sub-spaces
 Face problem when two users are in one sector
 It needs to be used with another multiple access technique
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55. Conclusions
 Wi-Fi cannot satisfy the increasing demand for high-speed internet
access
 VLC is strong contender for future wireless networks
 Modulation and networking techniques need to be adapted to VLC
systems because of their constraints
 There is still much to be done on the networking aspects of VLC
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56. Questions?
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