LiFi in streetlights

Presented by
Nikhil K. Kuriakose
MBCET,
Trivandrum.

 Introduction
 LiFi in Streetlights
 System Design & Simulation
 Prototype Description
 Advantages & Applications
 Conclusion
 References
14/10/2016 Dept. of Electronics & Communication, MBCET 2
LiFi integrated in streetlights

 LiFi (‘Light Fidelity’) is one of the prominent emerging technologies in
today’s world
 Radio spectrum is getting more congested each minute, leading to
alternate transmission techniques
 Using LiFi, speed of data transmission is greatly increased; upto
28 Gigabytes per second, which is 100 times faster than Wifi !
14/10/2016 3Dept. of Electronics & Communication, MBCET

 Light based WiFi
 Light is used instead of radio waves to transmit information
 Transmitter fitted with LED lamps act like WiFi modems
 Provides illumination as well as data communication

 Capacity
Spectrum is 10,000 times greater than that of radio frequency
 Efficiency
Highly efficient since LED consumes less energy
 Availability
Light waves available everywhere
 Security
Cannot penetrate through walls, hence data cannot be intercepted

 Formed by streetlight as transmitter and mobile phone camera as
receiver.
 Streetlights receive data via PLC & modulate the information through LED
bulb
 The light is received by the smartphone through a photodiode integrated
in it’s camera
 Uplink is via Bluetooth, ZigBee or WiFi

714/10/2016 Dept. of Electronics & Communication, MBCET
Fig 1. LiFi network in a smart city

The system design and simulation consists of two processes:
I. Simulation of the Modulator
II. Simulation of the Transmitting Channel

I. Simulation of Modulator
 Each of the blocks that make up the LiFi transmitter and receiver are
simulated in MATLAB
 The modulation schemes used are on-off-keying (OOK) and variable
pulse position modulation (VPPM).
 Reed Solomon (RS) encoders and Convolutional encoders (CC) are used
so as to correct channel errors and improve the link reliability.

 An interleaver is included to avoid burst errors
 RLL (Run Length Limited) encoders are used to balance the DC level of
the output
 The RLL encoders used here are Manchester and 4B6B encoders

Fig 2. Block diagram of Modulator

 The bit error rate (BER) is plotted after addition of AWGN (Additive White
Gaussian Noise).
 It is observed that the operating mode that has the lowest data rate
presents the best performance because of the high protection.
 SNR = 10 dB is chosen to illustrate the effect on an image transmission
using our simulated LiFi system.
 Also, if a SNR = 15 dB is chosen, a level of BER and image quality are
acceptable for all modes of operation.

Fig 3. Performance plot (BER vs. SNR)

Fig 4. The quality of the image clearly shows the effect of coding

II. Simulation of Transmitting Channel
 The transmitting medium (in this case, air), is an essential factor that
affects the LiFi reception
 Some of the factors that affect reception include ambient light, Line Of
Sight (LOS), Field Of View (FOV), height of the streetlight, etc
 Analysis is carried out by taking the impulse response of the channel,
which is then used to analyze and combat the effects of channel
distortions

 For analysis, the link is considered to have LOS between the streetlight
and mobile phone
 There may be scattering effects due to reflections from objects. These
reflections are considered in the simulation process
 The channel response is given by
h(t; S, R) = h(k) (t; S, R)
where
S, R  position of transmitter and receiver respectively
k  reflection order

 To calculate the kth reflection, we use the formula:
h (k) (t; S, R) = h (0) (t; S, {r, n, π/ 2, dr 2 }) ⊗ h k−1 (t; {r, n, 1}, R)
where
h (0)  channel response for zeroth order reflection
n  mode number, which specifies directionality of the source

Fig 5. Channel response h(t; S, R)

 From the graph, it is observed that the reflections do not create any
problems for detection because the direct beam is much stronger than
others
 The predominance of LOS beam between transmitter and receiver is
clearly observed

I. Transmitter
 Transmitter and receiver have been implemented on two separate
FPGAs
 The transmitter front-end, (the streetlight), is comprised of a Spartan
3E-xc3s500E FPGA, acting as the LiFi modulator
 It also includes the LED driver circuit and a commercial high power
white LED as the light emitting source

 The data stream received from PLC is delivered via an Ethernet port to the
FPGA and encoded
 Then the modulated signal is fed to the LED driver circuit, which acts in
switching mode, varying the current of the streetlight LED

II. Receiver
 The FPGA used in the receiver has a larger memory, in order to store
the performance measurements
 The receiver front-end, at the phone’s camera, is equipped with a
Spartan 6-xc6slx16 FPGA
 An external circuit has been designed and implemented to capture the
signal using an LDR (light-dependent resistor)

 This digital signal is then delivered to the demodulator FPGA, which works
in the reverse manner of the modulator
Fig 6. Set up and prototype receiver

Fig 7. LiFi Hardware Architecture

 Data rate greater than 28 Gigabytes per second; theoretically allowing HD
movies to be downloaded in 10 seconds
 LiFi is expected to be ten times cheaper than Wi-Fi
 Useful in electromagnetic sensitive areas such as in aircraft cabins,
hospitals and nuclear power plants without causing electromagnetic
interference
 Potential downsides are short range, low reliability and high installation
costs

 LED lightbulbs, or in this case our streetlamps, can be potentially
converted into a wireless router just by adding a small microchip.
 It’s even more secure than WiFi, because light can’t permeate walls –
meaning potential hackers are unable to access your session.
 The latest crop of smartphones are LiFi enabled, and can connect through
the use of their camera sensors. Older models and non-LiFi enabled
products will have to use a dongle until LiFi connectivity comes pre-
equipped in devices.
 The LiFi industry is estimated to be worth around Rs. 5 Lakh Crores by
2021.

1. D.V. Gibson, G. Kozmetsky and R.W Smilor, "The technopolis Phenomenon: Smart
Cities Fast SystemsGlobal Networks", Rowman and Little-field, 1992.
2. A. Zanella, N. Bui,A. Castellani, L.Vangelista and M. Zorzi, "Internet ofThings for
Smart Cities", IEEEJournal Internet ofThings, vol. 1, pp. 22-32, Feb. 2014.
3. C. Doukas and F. Antonelli, "A full end-to-end as a service for smart city
applications", IEEE 10th International Conference onWireless and Mobile Computing
Networking and Communications (WiMob), pp. 181-186.
4. J.Vucic and K.D. Langer, "High-SpeedVisible Light Communications: State-of-
art", Optical Fiber Communication Conference (OFC' 12).
References

LiFi in streetlights

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