Enhancing physical layer security in wireless networks with cooperative approaches
View/ Open
Liu2016 latex.zip (10.39Mb)
Date
29/11/2016Author
Liu, Weigang
Metadata
Abstract
Motivated by recent developments in wireless communication, this thesis aims to
characterize the secrecy performance in several types of typical wireless networks.
Advanced techniques are designed and evaluated to enhance physical layer security in
these networks with realistic assumptions, such as signal propagation loss, random node
distribution and non-instantaneous channel state information (CSI).
The first part of the thesis investigates secret communication through relay-assisted
cognitive interference channel. The primary and secondary base stations (PBS and SBS)
communicate with the primary and secondary receivers (PR and SR) respectively in the
presence of multiple eavesdroppers. The SBS is allowed to transmit simultaneously with
the PBS over the same spectrum instead of waiting for an idle channel. To improve
security, cognitive relays transmit cooperative jamming (CJ) signals to create additional
interferences in the direction of the eavesdroppers. Two CJ schemes are proposed to
improve the secrecy rate of cognitive interference channels depending on the structure of
cooperative relays. In the scheme where the multiple-antenna relay transmits weighted
jamming signals, the combined approach of CJ and beamforming is investigated. In
the scheme with multiple relays transmitting weighted jamming signals, the combined
approach of CJ and relay selection is analyzed. Numerical results show that both these
two schemes are effective in improving physical layer security of cognitive interference
channel.
In the second part, the focus is shifted to physical layer security in a random wireless
network where both legitimate and eavesdropping nodes are randomly distributed. Three
scenarios are analyzed to investigate the impact of various factors on security. In
scenario one, the basic scheme is studied without a protected zone and interference. The
probability distribution function (PDF) of channel gain with both fading and path loss
has been derived and further applied to derive secrecy connectivity and ergodic secrecy
capacity. In the second scenario, we studied using a protected zone surrounding the source
node to enhance security where interference is absent. Both the cases that eavesdroppers
are aware and unaware of the protected zone boundary are investigated. Based on the
above scenarios, further deployment of the protected zones at legitimate receivers is
designed to convert detrimental interference into a beneficial factor. Numerical results
are investigated to check the reliability of the PDF for reciprocal of channel gain and to
analyze the impact of protected zones on secrecy performance.
In the third part, physical layer security in the downlink transmission of cellular network
is studied. To model the repulsive property of the cellular network planning, we assume
that the base stations (BSs) follow the Mat´ern hard-core point process (HCPP), while
the eavesdroppers are deployed as an independent Poisson point process (PPP). The
distribution function of the distances from a typical point to the nodes of the HCPP is
derived. The noise-limited and interference-limited cellular networks are investigated
by applying the fractional frequency reuse (FFR) in the system. For the noise-limited
network, we derive the secrecy outage probability with two different strategies, i.e. the
best BS serve and the nearest BS serve, by analyzing the statistics of channel gains. For
the interference-limited network with the nearest BS serve, two transmission schemes are
analyzed, i.e., transmission with and without the FFR. Numerical results reveal that both
the schemes of transmitting with the best BS and the application of the FFR are beneficial
for physical layer security in the downlink cellular networks, while the improvement due