127 research outputs found
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Advanced interference management techniques for future generation cellular networks
The demand for mobile wireless network resources is constantly on the rise, pushing
for new communication technologies that are able to support unprecedented
rates. In this thesis we address the issue by considering advanced interference
management techniques to exploit the available resources more efficiently under
relaxed channel state information (CSI) assumptions. While the initial studies
focus on current half-duplex (HD) technology, we then move on to full-duplex
(FD) communication due to its inherent potential to improve spectral efficiency.
Work in this thesis is divided into four main parts as follows.
In the first part, we focus on the two-cell two-user-per-cell interference broadcast
channel (IBC) and consider the use of topological interference management
(TIM) to manage inter-cell interference in an alternating connectivity scenario.
Within this context we derive novel outer bounds on the achievable degrees of freedom
(DoF) for different system configurations, namely, single-input single-output
(SISO), multiple-input single-output (MISO) and multiple-input multiple-output
(MIMO) systems. Additionally, we propose new transmission schemes based on
joint coding across states that exploit global topological information at the transmitter
to increase achievable DoF. Results show that when a single state has a
probability of occurrence equal to one, the derived bounds are tight with up to
a twofold increase in achievable DoF for the best case scenario. Additionally,
when all alternating connectivity states are equiprobable: the SISO system gains
11/16 DoF, achieving 96:4% of the derived outer bound; while the MISO/MIMO
scenario has a gain of 1/2 DoF, achieving the outer bound itself.
In the second part, we consider a general G-cell K-user-per-cell MIMO IBC
and analyse the performance of linear interference alignment (IA) under imperfect
CSI. Having imperfect channel knowledge impacts the effectiveness of the IA
beamformers, and leads to a significant amount of residual leakage interference.
Understanding the extent of this impact is a fundamental step towards obtaining
a performance characterisation that is more relevant to practical scenarios. The
CSI error model used is highly versatile, allowing the error to be treated either
as a function of the signal-to-noise ratio (SNR) or as independent of it. Based
on this error model, we derive a novel upper bound on the asymptotic mean
sum rate loss and quantify the DoF loss due to imperfect CSI. Furthermore,
we propose a new version of the maximum signal-to-interference plus noise ratio
(Max-SINR) algorithm which takes into account statistical knowledge of the CSI
error in order to improve performance over the naive counterpart in the presence
of CSI mismatch.
In the third part, we shift our attention to FD systems and consider weighted
sum rate (WSR) maximisation for multi-user multi-cell networks where FD base-stations
(BSs) communicate with HD downlink (DL) and uplink (UL) users. Since
WSR problems are non-convex we transform them into weighted minimum mean
squared error (WMMSE) ones that are proven to converge. Our analysis is first
carried out for perfect CSI and then expanded to cater for imperfect CSI under
two types of error models, namely, a norm-bounded error model and a stochastic
error model. Additionally, we propose an algorithm that maximises the total DL
rate subject to each UL user achieving a desired target rate. Results show that
the use of FD BSs provides significant gains in achievable rate over the use of HD
BSs, with a gain of 1:92 for the best case scenario under perfect CSI. They also
demonstrate the robust performance of the imperfect CSI designs, and confirm
that FD outperforms HD even under CSI mismatch conditions.
Finally, the fourth part considers the use of linear IA to manage interference
in a multi-user multi-cell network with FD BSs and HD users under imperfect
CSI. The number of interference links present in such a system is considerably
greater than that present in the HD network counterpart; thus, understanding
the impact of residual leakage interference on performance is even more important
for FD enabled networks. Using the same generalised CSI error model from the
second part, we study the performance of IA by characterising the sum rate and
DoF losses incurred due to imperfect CSI. Additionally, we propose two novel IA
algorithms applicable to this network; the first one is based on minimising the
mean squared error (MMSE), while the second is based on Max-SINR. The proposed
algorithms exploit statistical knowledge of the CSI error variance in order
to improve performance. Moreover, they are shown to be equivalent under certain
conditions, even though the MMSE based one has lower computational complexity.
Furthermore for the multi-cell case, we also derive the proper condition for
IA feasibility
Hybrid Processing Design for Multipair Massive MIMO Relaying with Channel Spatial Correlation
Massive multiple-input multiple-output (MIMO) avails of simple transceiver
design which can tackle many drawbacks of relay systems in terms of complicated
signal processing, latency, and noise amplification. However, the cost and
circuit complexity of having one radio frequency (RF) chain dedicated to each
antenna element are prohibitive in practice. In this paper, we address this
critical issue in amplify-and-forward (AF) relay systems using a hybrid analog
and digital (A/D) transceiver structure. More specifically, leveraging the
channel long-term properties, we design the analog beamformer which aims to
minimize the channel estimation error and remain invariant over a long
timescale. Then, the beamforming is completed by simple digital signal
processing, i.e., maximum ratio combining/maximum ratio transmission (MRC/MRT)
or zero-forcing (ZF) in the baseband domain. We present analytical bounds on
the achievable spectral efficiency taking into account the spatial correlation
and imperfect channel state information at the relay station. Our analytical
results reveal that the hybrid A/D structure with ZF digital processor exploits
spatial correlation and offers a higher spectral efficiency compared to the
hybrid A/D structure with MRC/MRT scheme. Our numerical results showcase that
the hybrid A/D beamforming design captures nearly 95% of the spectral
efficiency of a fully digital AF relaying topology even by removing half of the
RF chains. It is also shown that the hybrid A/D structure is robust to coarse
quantization, and even with 2-bit resolution, the system can achieve more than
93% of the spectral efficiency offered by the same hybrid A/D topology with
infinite resolution phase shifters.Comment: 17 pages, 13 figures, to appear in IEEE Transactions on
Communication
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