4 research outputs found
On the Placement of RF Energy Harvesting Node in Wireless Networks with Secrecy Considerations
The potential dual use of radio-frequency (RF) signals for carrying energy and information brings an exciting opportunity for energy harvesting (EH) from ambient RF signals in wireless communication networks. To maximize the efficiency of harvesting wireless energy, it is desirable to have the EH node located close to the transmitter. However, when the transmitted information is confidential, the EH node should be regarded as a potential eavesdropper, and hence, it is preferred to have the EH node located far from the transmitter. Therefore, the placement of EH nodes in wireless networks becomes an interesting problem when secrecy is an important consideration. In this paper, we investigate the optimal placement of the EH node with physical-layer security considerations by formulating and solving two optimization problems. The first problem maximizes the average EH power subject to a secrecy outage constraint, while the second problem minimizes the secrecy outage probability subject to an EH constraint. Our results also demonstrate the tradeoff between secrecy and EH performances caused by the placement of the EH node
Wireless Physical Layer Security: Towards Practical Assumptions and Requirements
The current research on physical layer security is far from
implementations in practical networks, arguably due to
impractical assumptions in the literature and the limited
applicability of physical layer security. Aiming to reduce the
gap between theory and practice, this thesis focuses on wireless
physical layer security towards practical assumptions and
requirements.
In the first half of the thesis, we reduce the dependence of
physical layer security on impractical assumptions. The secrecy
enhancements and analysis based on impractical assumptions cannot
lead to any true guarantee of secrecy in practical networks. The
current study of physical layer security was often based on the
idealized assumption of perfect channel knowledge on both
legitimate users and eavesdroppers. We study the impact of
channel estimation errors on secure transmission designs. We
investigate the practical scenarios where both the transmitter
and the receiver have imperfect channel state information (CSI).
Our results show how the optimal transmission design and the
achievable throughput vary with the amount of knowledge on the
eavesdropper's channel. Apart from the assumption of perfect CSI,
the analysis of physical layer security often ideally assumed the
number of eavesdropper antennas to be known. We develop an
innovative approach to study secure communication systems without
knowing the number of eavesdropper antennas by introducing the
concept of spatial constraint into physical layer security. That
is, the eavesdropper is assumed to have a limited spatial region
to place (possibly an infinite number of) antennas. We show that
a non-zero secrecy rate is achievable with the help of a friendly
jammer, even if the eavesdropper places an infinite number of
antennas in its spatial region.
In the second half of the thesis, we improve the applicability of
physical layer security. The current physical layer security
techniques to achieve confidential broadcasting were limited to
application in single-cell systems. The primary challenge to
achieve confidential broadcasting in the multi-cell network is to
deal with not only the inter-cell but also the intra-cell
information leakage and interference. To tackle this challenge,
we design linear precoders performing confidential broadcasting
in multi-cell networks. We optimize the precoder designs to
maximize the secrecy sum rate with based on the large-system
analysis. Finally, we improve the applicability of physical layer
security from a fundamental aspect. The analysis of physical
layer security based on the existing secrecy metric was often not
applicable in practical networks. We propose new metrics for
evaluating the secrecy of transmissions over fading channels to
address the practical limitations of using existing secrecy
metrics for such evaluations. The first metric establishes a link
between the concept of secrecy outage and the eavesdropper's
ability to decode confidential messages. The second metric
provides an error-probability-based secrecy metric which is often
used for the practical implementation of secure wireless systems.
The third metric characterizes how much or how fast the
confidential information is leaked to the eavesdropper. We show
that the proposed secrecy metrics enable one to appropriately
design secure communication systems with different views on how
secrecy is measured