2 research outputs found
Physical Layer Security in Cooperative NOMA Hybrid VLC/RF Systems
Integrating visible light communication (VLC) and radio-frequency (RF)
networks can improve the performance of communication systems in terms of
coverage and data rates. However, adding RF links to VLC networks weakens the
secrecy performance due to the broadcast and ubiquitous nature of RF links.
This paper studies the physical layer security (PLS) in cooperative
non-orthogonal multiple access (CoNOMA) hybrid VLC/RF systems. Consider a VLC
system, where two entrusted users close to a VLC access point (AP) help an
out-of-coverage legitimate user using RF signals in the presence of an
eavesdropper. The AP transmits data to both entrusted users and the legitimate
user using the principle of NOMA, where the entrusted users harvest energy from
the received light intensity, decode the legitimate user's message, forward it
using a RF link, and then decode their messages. It is required to maximize the
secrecy rate at the legitimate user under quality-of-service (QoS) constraints
using beamforming and DC-bias and power allocation. Different solutions are
proposed for both active and passive eavesdropper cases, using semidefinite
relaxation, zero-forcing, beamforming, and jamming. Numerical results compare
between the different proposed approaches and show how the proposed approaches
contribute in improving the secrecy performance of the proposed model
User Pairing, Link Selection and Power Allocation for Cooperative NOMA Hybrid VLC/RF Systems
Despite the promising high-data rate features of visible light communications
(VLC), they still suffer from unbalanced services due to blockages and channel
fluctuation among users. This paper introduces and evaluates a new transmission
scheme which adopts cooperative non-orthogonal multiple access (Co-NOMA) in
hybrid VLC/radio-frequency (RF) systems, so as to improve both system sum-rate
and fairness. Consider a network consisting of one VLC access point (AP) and
multiple strong and weak users, where each weak user is paired with a strong
user. Each weak user can be served either directly by the VLC AP, or via the
strong user which converts light information received through the VLC link, and
forwards the information to the weak user via the RF link. The paper then
maximizes a network-wide weighted sum-rate, so as to jointly determine the
strong-weak user-pairs, the serving link of each weak user (i.e., either direct
VLC or hybrid VLC/RF), and the power of each user message, subject to user
connectivity and transmit power constraints. The paper tackles such a
mixed-integer non-convex optimization problem using an iterative approach.
Simulations show that the proposed scheme significantly improves the VLC
network performance (i.e., sum-rate and fairness) as compared to the
conventional NOMA scheme