LiFi − High Speed Wireless Networking Using Nano-Metre Waves

Professor Harald Haas

http://www.lifi.eng.ed.ac.uk/

Twitter: @dlarah15

Sensors

Connectivity

Data/Signal processing

Big data / data analytics / AI

Action / Apps / Robotics

SMART-X Environments,

e.g., manufacturing, cities, homes, cars, bodies..

Ener

gy h

arve

stin

g Connectivity

Senses

Nervous System

Brain

Nervous System

Arms, Legs, Voice

Spectrum Crunch

Winzer, Neilson, “From Scaling Disparities to IntegratedParallelism: A Decathlon for a Decade, IEE/OSA JLT, 2017

In 20 years (6G?), this means × 12,000 bandwidth500 MHz used for WiFi in 5 GHz band will need to become 6 THz

RF is only 0.3 THz!!20 times shortfall!

The small cell concept

T. Cogalan and H. Haas, “Why Would 5G Need Optical Wireless Communications?,” PIMRC, October 2017.

Hitting physical limits in cellular RF communications

5

Source: MSR, Stadium Tech Report, Q1/2016

“… under-seat deployments are now winning favorin all sorts of arenas for their ability to use human bodiesto help build a more dense network …”

The electromagnetic spectrum

Z. Wang, D. Tsonev, S. Videv and H. Haas, "On the Design of a Solar-Panel Receiver for Optical Wireless Communications With Simultaneous Energy Harvesting," JSAC, vol. 33, no. 8, pp. 1612-1623, Aug. 2015

Taxonomy

Range

Transmission speeds

Communication Mode

Duplex mode

Ultra high ≥ 100 Gbps

High ≥ 10 Mbps

Medium range ≥ 10 cm < 100 m

Short range < 10 cm

Long range ≥ 100 m

Mobile, multiuser access and seamless handover

SimplexFull-duplex

Low < 10 Mbps

Static point-to-point (cable replacement)

Mobile point-to-point

Half-duplex

Very high ≥ 1 Gbps

Very Low < 1 Mbps

Non-linearity effects

1. Amplitude distortion

2. Upper clipping

3. Lower clipping

Intensity modulation(IM) of the optical carrier

Elgala, H., Mesleh, R., and Haas, H., "Indoor Broadcasting via White LEDs and OFDM", IEEE Trans. Consum. Electron., vol. 55, no. 3, pp. 1127 – 1134, Aug. 2009

BER performance

Creating unipolar OFDM signals at the expense of spectrum efficiency

o Generate two copies of a bipolar OFDM frame.o Reverse the signs in the second copy.o Remove all negative samples.o Concept known in literature as U-OFDM or as Flip-OFDM.

Unipolar / flip OFDMo Spectral efficiency is halved.

o M-QAM DCO-OFDM should be compared to M2-QAM U-OFDM.

o U-OFDM quickly loses energy efficiency with increasing spectral efficiency.

o The same problem is observed in ACO-OFDM and PAM-DMT.Bipolar OFDM

U-OFDM

Bipolar Frame 1

Bipolar Frame 1

Bipolar Frame 1

Positive Frame 1

NegativeFrame 1

Positive Frame 2

Negative Frame 2

Positive Frame 3

Negative Frame 3

N. Fernando, Y. Hong and E. Viterbo, "Flip-OFDM for Unipolar Communication Systems," IEEE Transactions on Communications, vol. 60, no. 12, pp. 3726-3733, Dec/ 2012.

D. Tsonev, S. Sinanovic and H. Haas, "Novel Unipolar Orthogonal Frequency Division Multiplexing (U-OFDM) for Optical Wireless," Vehicular Technology Conference (VTC Spring), Yokohama, 2012

Avoiding spectrum efficiency loss in unipolar OFDM

+

+U-OFDM Depth 3

U-OFDM Depth 2

U-OFDM Depth1

P11N11P12N12P13N13P14N14

P21P21N21N21P22P22N22N22

P31P31P31P31N31N31N31N31

Maximum Depth 1 2 3 4 5 6 7

Additional spectral efficiency [%]

50 75 87.5 93.8 96.9 98.4 99.2

o Subtraction removes interference from additional streams.

D. Tsonev, S. Videv and H. Haas, "Unlocking Spectral Efficiency in Intensity Modulation and Direct Detection Systems," JSAC, vol. 33, no. 9, pp. 1758-1770, Sept. 2015.

Electrical energy efficiency

))}I(V()E{V(elec ttP =

o Voltage over LED probed

and captured with the

Oscilloscope

o Bandwidth = 20 MHz

o Constant bit loading

o Pre-equalization

LED technologies / data rates

LEDtechnology

Data rate / Gbps

RGB LEDPhosphor coated blue LED

GaN micro LED micro LED

0.1

1

10

100

RGB laser LEDs

Tsonev, et al., "Towards a 100 Gb/s visible light wireless access network," Opt. Express 23, 1627-1637 (2015)

1

8 Gbps

15 GbpsMohamed Sufyan Islim, et al., “Towards 10 Gb/s OFDM-based Visible Light Communication using a GaN Violet micro-LED”, Photonics Research, 2017

LiFi ASICsTransmitter LiFi MIMO ASICReceiver LiFi MIMO ASIC

A. V. N. Jalajakumari et al., "High-Speed Integrated Digital to Light Converter for Short Range Visible Light Communication," in IEEE Photonics Technology Letters, vol. 29, no. 1, pp. 118-121, 2017

Taking the 3 gigabit/s hurdle

Tsonev, D, et al., “A 3-Gb/s Single-LED OFDM-based Wireless VLC Link Using a Gallium Nitride μLED,” Photonics Technology Letters, vol. 26, no. 7, pp. 637 - 640, 2014

Misconception number one: LoS

1.1 Gbps @ 10 m

10 m1.1 Gbps

Misconception: Interference from sunlight

M. S. Islim, M. Safari, S. Videv, and H. Haas, “A Proof-of-Concept of Outdoor Visible Light Communications in the presence of Sunlight”, in LED professional Symposium - Expo 2016, Bregenz (Austria), 20-22 September, 2016

Misconception: Interference from sunlight

M. S. Islim, M. Safari, S. Videv, and H. Haas, “A Proof-of-Concept of Outdoor Visible Light Communications in the presence of Sunlight”, in LED professional Symposium - Expo 2016, Bregenz (Austria), 20-22 September, 2016

Dark Room Sunlight Irradiance

Sunlight + Blue Filter

S866

4-50

K[1

9.6

mm

2 ]

Average SNR [dB] 17.57 12.42 16.64

SNR degradation compared to Dark Room 0% 29.33% 5.32%

Data rate @ BER< 3.8e-3 [Mbps] 416.44 313.35 396.71

Degradation of data rates compared to Dark Room. 0% 24.8% 4.7%

S866

4-05

K[0

.19

mm

2 ]

Average SNR [dB] 18.58 16.42 17.36

SNR degradation compared to Dark Room 0% 11.6% 1.7%

Data rate @ BER< 3.8e-3 [Mbps] 1139.26 1015 1122.34

Degradation of data rates compared to Dark Room. 0% 10.9% 1.5%

LiFi attocell networking

Haas, H., “High-speed wireless networking using visible light, SPIE Newsroom, Online: http://spie.org/x93593.xml (invited)Haas, H., Wang, Y., and Yin, E., “What is LiFi?”, Journal of Lightwave Technology, vol. 3, iss. 8, April 2016 (invited)Tsonev, D.; Videv, S.; and Haas, H.; “Light fidelity (Li-Fi): towards all-optical networking,” Proc. SPIE 9007, Broadband Access

Communication Technologies VIII, 900702, 1 Feb. 2014

Rx FOV 85° - with lighting constraint

16 January, 201827

0.76 b/s/Hz/m2

Rx FOV 45° - without lighting constraint

16 January, 201828

2.24 b/s/Hz/m2

LiFi attocell networking• Each light fixture

serves as an access point (AP), and serves multiple users.

• Four types of deployment scenarios:

• (a) HEX; • (b) Square;• (c) HCPP; • (d) PPP.

C. Chen, et al., "Downlink Performance of Optical Attocell Networks," in JLT, 2016

Area data rate results

Haas, et al., “What is LiFi”, JLT, 34 (6), 1533-1544, 2016

Joint transmission in VLC

C. Chen, et al., "Fractional Frequency Reuse in DCO-OFDM-Based Optical Attocell Networks," in Journal of Lightwave Technology, vol. 33, no. 19, pp. 3986-4000, Oct.1, 1 2015.

Simulation SetupRoom size 16 m x 9 m

x3 m

Modulation bandwidth

20 MHz

Number of atto-cells

13

Number of users 40

Benchmark systems:

- Universal frequency reuse system ( reuse factor = 1 )

- Static reuse partitioning system ( reuse factor = 3 )

Simulated proposed system:

- Joint transmission with frequency plan 1

- Joint transmission with frequency plan 2

Simulation results – full frequency reuse

Simulation results – joint transmission

The ‘LiFi’ disruptionThe advent of LED lighting has shifted the business metric of the lighting world from $/bulb to $/lux. The additional energy management allows for building optimisation.

Added communications and the increasing desire for infrastructure data means a convergence to $/bit.

IEEE 802.11 LC Study Group

2018 20212017 20202019

Pre-standarddevices available

802.11 ballot& standardpublishing

802.11study group

802.11 topicinterest group

Creation ofLiFi alliance

Alliance PoCsand interop testing

802.11 standard

drafts

802.11task

group

IEEE 802.11 Study Group

LiFi is real...

Source: telecoms.com Source: 123rf.com

Electromagnetic spectrum is continuum → Move from cm-Wave to mm-Wave to nm-Wave !!