IEEE Consumer Electronics Magazine - July 2018 - 58

DSE is a lightweight encryption
scheme designed for smart-grid
wireless communication.
transmitted data from these devices using the Li-Fi communication technique. We used the red-green-blue (RGB) color
code scheme to communicate with multiple devices simultaneously. In the case of the outdoor environment, which depends
on the availability of LED sources, we used hybrid (Li-Fi/
Wi-Fi) communication techniques. In the city's intelligent network infrastructure, all of the controllers are interconnected in
a distributed network so that each IoT device in the intelligent
urban network can communicate effectively with high availability and shorter response time. Depending on the local
environment and the available energy source, we will choose
the existing proposed energy-harvesting techniques to
empower the smart devices in a smart city [11].

Li-Fi COmmuniCatiOn mODuLatiOn sCheme
Figure 2 shows the block diagram for the communication
between smart devices and the controller. When the smart
devices want to communicate with the controller, they first
encrypt the data using the dynamic secret-based encryption
(DSE) scheme. DSE is a lightweight encryption scheme
designed for smart-grid wireless communication [12]. After
that, the device will send the encrypted data to the data frame
creator and modulation block, which will then create and
encode the data frame and subsequently pass through the
modulation phase. Once modulated, data are transformed into
the LED array frame block, wherein (and using the LED driver) an RGB LED emits LED rays to communicate with the
controller, integrated by a photodetector to receive the data
frame from intelligent devices. By demodulating and decoding the data frames, the data frame passes through the data

decryption block to obtain the data transmitted to the controller. It performs similar operations while sending communications from the controller to the smart devices. To enable
multiaccess bidirectional communication between the smart
devices and the controller, we present the hybrid communications modulation scheme as described in this section. We
leveraged the strength of multiaccess transmission for VLC
by using a mobile phone as proposed by Chen et al. [13].
The hybrid modulation scheme for Li-Fi uses the code
division multiple access (CDMA) technique and color-shift
keying (CSK) scheme simultaneously. CDMA allows multiaccess, while the CSK scheme helps avoid single-color interference and enhances the Li-Fi capacity to access the
network. Using the orthogonal spreading-codes technique,
each smart device is assigned its own modulation code and
magnitude levels represented by the R, G, and B colors.
At the transceiver end, we can assume that device number 1
has encrypted data [R, G, B] = [120, 20, 0] and modulation
code = [−1, −1, 1, 1, 1, −1], and that device number 2 has
encrypted data [R, G, B] = [100, 50, 0] and modulation code =
[1, −1, −1, 1, 1, 1]. We explain the process by using green as
an example. The other two colors (i.e., red and blue) are processed in a similar manner. The green magnitude of device
number 1 and device number 2 is 20 and 50, respectively,
spread by the individual device modulation code; the spread
signal becomes [−20, −20, 20, 20, 20, −20] and [50, −50, −50,
50, 50, 50] using the f ^ DED ih function in
f ^ DED ih = DED i C M # N ,

where DED i is the encrypted data of device number 1 and
C M # N is a matrix of modulation code of all of the devices. M
is the number of devices (i.e., rows) and N is the length of the
modulation code (i.e., columns). Each row of C M # N matrix
denotes the value of the modulation code of each device.
To produce the total green magnitude signal, we use the
g ^ R h function in (2) and get the transmitting data output

Device 1

RGB
LED
Data Frame
Creation
and
Modulation

Data
Encryption

LED Array
Frame

Device n

Controller

Data
Decryption

Demodulation
of Data Frame

figurE 2. A block diagram for the communication between the smart devices and the controller.
58 IEEE Consumer Electronics Magazine

july 2018

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Photo
Detector

Table of Contents for the Digital Edition of IEEE Consumer Electronics Magazine - July 2018