2 research outputs found
Physical Layer Security in Wireless Networks: Design and Enhancement.
PhDSecurity and privacy have become increasingly significant concerns in wireless communication
networks, due to the open nature of the wireless medium which makes the wireless
transmission vulnerable to eavesdropping and inimical attacking. The emergence and
development of decentralized and ad-hoc wireless networks pose great challenges to the
implementation of higher-layer key distribution and management in practice. Against
this background, physical layer security has emerged as an attractive approach for performing
secure transmission in a low complexity manner. This thesis concentrates on
physical layer security design and enhancement in wireless networks.
First, this thesis presents a new unifying framework to analyze the average secrecy
capacity and secrecy outage probability. Besides the exact average secrecy capacity
and secrecy outage probability, a new approach for analyzing the asymptotic behavior is
proposed to compute key performance parameters such as high signal-to-noise ratio slope,
power offset, secrecy diversity order, and secrecy array gain. Typical fading environments
such as two-wave with diffuse power and Nakagami-m are taken into account.
Second, an analytical framework of using antenna selection schemes to achieve secrecy
is provided. In particular, transmit antenna selection and generalized selection combining
are considered including its special cases of selection combining and maximal-ratio
combining.
Third, the fundamental questions surrounding the joint impact of power constraints on
the cognitive wiretap channel are addressed. Important design insights are revealed
regarding the interplay between two power constraints, namely the maximum transmit
at the secondary network and the peak interference power at the primary network.
Fourth, secure single carrier transmission is considered in the two-hop decode-andi
forward relay networks. A two-stage relay and destination selection is proposed to minimize
the eavesdropping and maximize the signal power of the link between the relay and
the destination. In two-hop amplify-and-forward untrusted relay networks, secrecy may
not be guaranteed even in the absence of external eavesdroppers. As such, cooperative
jamming with optimal power allocation is proposed to achieve non-zero secrecy rate.
Fifth and last, physical layer security in large-scale wireless sensor networks is introduced.
A stochastic geometry approach is adopted to model the positions of sensors, access
points, sinks, and eavesdroppers. Two scenarios are considered: i) the active sensors
transmit their sensing data to the access points, and ii) the active access points forward
the data to the sinks. Important insights are concluded
Joint Spatial and Spectrum Cooperation in Wireless Network.
PhDThe sky-rocketing growth of multimedia infotainment applications and broadband-hungry
mobile devices exacerbate the stringent demand for ultra high data rate and more spectrum resources. Along with it, the unbalanced temporal and geographical variations
of spectrum usage further inspires those spectral-efficient networks, namely, cognitive
radio and heterogeneous cellular networks (HCNs). This thesis focuses on the system
design and performance enhancement of cognitive radio (CR) and HCNs. Three different
aspects of performance improvement are considered, including link reliability of cognitive
radio networks (CNs), security enhancement of CNs, and energy efficiency improvement
of CNs and HCNs.
First, generalized selection combining (GSC) is proposed as an effective receiver design
for interference reduction and reliability improvement of CNs with outdated CSI. A uni-
ed way for deriving the distribution of received signal-to-noise ratio (SNR) is developed
in underlay spectrum sharing networks subject to interference from the primary trans-
mitter (PU-Tx) to the secondary receiver (SU-Rx), maximum transmit power constraint
at the secondary transmitter (SU-Tx), and peak interference power constraint at the
PU receiver (PU-Rx), is developed. Second, transmit antenna selection with receive
generalized selection combining (TAS/GSC) in multi-antenna relay-aided communica-
tion is introduced in CNs under Rayleigh fading and Nakagami-m fading. Based on
newly derived complex statistical properties of channel power gain of TAS/GSC, exact
ergodic capacity and high SNR ergodic capacity are derived over Nakagami-m fading.
Third, beamforming and arti cial noise generation (BF&AN) is introduced as a robust
scheme to enhance the secure transmission of large-scale spectrum sharing networks
with multiple randomly located eavesdroppers (Eves) modeled as homogeneous Poisson
Point Process (PPP). Stochastic geometry is applied to model and analyze the impact of
i
BF&AN on this complex network. Optimal power allocation factor for BF&AN which
maximizes the average secrecy rate is further studied under the outage probability con-
straint of primary network. Fourth, a new wireless energy harvesting protocol is proposed
for underlay cognitive relay networks with the energy-constrained SU-Txs. Exact and
asymptotic outage probability, delay-sensitive throughput, and delay-tolerant through-
put are derived to explore the tradeoff between the energy harvested from the PU-Txs
and the interference caused by the PU-Txs. Fifth, a harvest-then-transmit protocol is
proposed in K-tier HCNs with randomly located multiple-antenna base stations (BSs)
and single antenna mobile terminals (MTs) modeled as homogeneous PPP. The average
received power at MT, the uplink (UL) outage probability, and the UL average ergodic
rate are derived to demonstrate the intrinsic relationship between the energy harvested
from BSs in the downlink (DL) and the MT performance in the UL. Throughout the
thesis, it is shown that link reliability, secrecy performance, and energy efficiency of
CNs and HCNs can be signi cantly leveraged by taking advantage of multiple antennas,
relays, and wireless energy harvesting