Secrecy Outage Probability Analysis for Visible
Light Communications with SWIPT and Random
Terminals
Yu Qiu
∗
, Jin-Yuan Wang
†
, Sheng-Hong Lin
†
, Jun-Bo Wang
∗
, and Min Lin
†
∗
National Mobile Communications Research Laboratory, Southeast University, Nanjing 211111, China.
†
College of Telecommunications and Information Engineering, Nanjing University of Posts and Telecommunications,
Nanjing 210003, China.
E-mail: jywang@njupt.edu.cn
Abstract—This paper investigates the physical-layer data se-
cure transmission for indoor visible light communications (VL-
C) with simultaneous wireless information and power transfer
(SWIPT) and random terminals. A typical indoor VLC system
including one transmitter, one desired information receiver and
one energy receiver is considered. The two receivers are randomly
deployed on the floor, and the random channel characteristics is
analyzed. Based on the possibility that the energy receiver is a
passive information eavesdropper, the secrecy outage probability
(SOP) is employed to evaluate the system performance. A closed-
from expression for the lower bound of the SOP is obtained. For
the derived lower bound of SOP, the theoretical results match
the simulation results very well, which indicates that the derived
lower bound can be used to evaluate the secrecy performance.
Moreover, the gap between the results of the lower bound and
the exact simulation results is also small, which verifies the
correctness of the analysis method to obtain the lower bound.
I. INTRODUCTION
As a complementary technology to radio frequency (RF)
wireless communication, the indoor visible light communica-
tion (VLC) has received more and more attention. VLC is a
promising technology for lighting and information transmis-
sion in indoor environments. Due to the advantages of having
no electromagnetic spectrum regulation and being harmless to
human body, VLC will play a vital role in the future fifth
generation (5G) wireless communications.
In indoor VLC, a light emitting diode (LED) is used as
a light source. As long as the user is illuminated by the
LED, it can receive information from the source. This brings
legitimate users with a security risk of data transmission.
Recently, physical layer (PHY) security has been proposed
as an effective way to guarantee the security of information
theory. In [1], the secrecy capacity for the single input single
output (SISO) VLC is analyzed. For multiuser VLC, the
secrecy outage probability (SOP) and the ergodic secrecy rate
(ESR) are derived in [2]. To improve the PHY security, a
channel determined subcarrier shifting scheme is proposed in
[3] for orthogonal frequency division multiplexing (OFDM)
based VLC. In [4], a chaos based PHY security method
is introduced for the OFDM based VLC systems with the
capacity against known/chosen plaintext attacks. In [5], secure
transmission for VLC with random terminals is discussed, but
ref. [5] ignores the two constraints of optical signals. Note
that only information transmission is considered in [1] - [5],
energy harvesting in VLC system is not discussed.
In addition, as it is known, many mobile terminals in indoor
VLC are energy-limited (e.g., sensor nodes for monitoring
temperature and humidity), which are typically powered by
batteries. To prolong the network lifetime, it is necessary to
recharge the batteries in time, which incurs very high costs
to do this tedious work. A good solution is to harvest energy
from the environment to charge these terminals [6]. Recently,
simultaneous wireless information and power transfer (SWIP-
T) has become a new research area, which employs the same
emitted signal to transfer both energy and information. In [7],
practical SWIPT receiver architectures with a time switch (TS)
were proposed, and [8] perform SWIPT with energy harvesting
(EH) and information decoding (ID) separated using two
circuits based on a dynamic power splitting (DPS) scheme.
In [9], a new architecture integrating information decoding
and energy harvesting on one circuit was designed and rate-
energy tradeoff was analysed. However, few akin research has
discussed the indoor VLC SWIPT. For indoor VLC, it has a
natural advantage to harvest light energy, because the emitted
light of the LEDs can be effectively used by the users. In [10],
a sum rate maximizing problem for indoor VLC with SWIPT
is investigated. Note that the secure transmission in [10] is not
considered.
As is known, secure transmission and green communication
are the future development goals of communication. It is
practical to consider secure data transfer in indoor VLC
SWIPT system. To the best of our knowledge, this issue has
not been investigated yet. In this paper, we consider a VLC
SWIPT system with a transmitter (i.e., Alice), an information
receiver (i.e., Bob), and an energy harvester (i.e., Eve), in
which Eve may play as a passive eavesdropper. The main
contributions of the paper are listed as follows:
• For VLC with spatially random terminals, the random
channel characteristics is analyzed. In this paper, Bob and
Eve are uniformly distributed on the floor. Based on the
random characteristics, the probability density function