47,413 research outputs found
Physical-Layer Security: Wide-band Communications & Role of Known Interference
Data security is of such paramount importance that security measures have been implemented across all layers of a communication network. One layer at which security has not been fully developed and studied is the physical layer, the lowest layer of the protocol stack. Towards establishing fundamental limits of secure communications at the physical layer, we address in this dissertation two main problems. First, we study secure communication in the wide-band regime, and second we study the role of known interference in secure communication.
The concept of channel capacity per unit cost was introduced by Verdu´ in 1990 to study the limits of cost-efficient wide-band communication. It was shown that orthogonal signaling can achieve the channel capacity per unit cost of memoryless stationary channels with a zero-cost input letter. The first part of this dissertation introduces the concept of secrecy capacity per unit cost to study cost-efficient wide- band secrecy communication. For degraded memoryless stationary wiretap channels, it is shown that an orthogonal coding scheme with randomized pulse position and constant pulse shape achieves the secrecy capacity per unit cost with a zero-cost input letter. For general memoryless stationary wiretap channels, the performance of orthogonal codes is studied, and the benefit of further randomizing the pulse shape is demonstrated via a simple example. Furthermore, the problem of secure communication in a MIMO setting is considered, and a single-letter expression for the secrecy capacity per unit cost is obtained for the MIMO wiretap channel.
Recently there has been a lot of success in using the deterministic approach to provide approximate characterization of Gaussian network capacity. The second part of this dissertation takes a deterministic view and revisits the problem of wiretap channel with side information. A precise characterization of the secrecy capacity is obtained for a linear deterministic model, which naturally suggests a coding scheme which we show to achieve the secrecy capacity of the degraded Gaussian model (dubbed as “secret writing on dirty paper”) to within half a bit. The success of this approach allowed its application to the problem of “secret key agreement via dirty paper coding”, where also a suggested coding scheme achieves the secret-key capacity to within half a bit
On the Throughput Cost of Physical Layer Security in Decentralized Wireless Networks
This paper studies the throughput of large-scale decentralized wireless
networks with physical layer security constraints. In particular, we are
interested in the question of how much throughput needs to be sacrificed for
achieving a certain level of security. We consider random networks where the
legitimate nodes and the eavesdroppers are distributed according to independent
two-dimensional Poisson point processes. The transmission capacity framework is
used to characterize the area spectral efficiency of secure transmissions with
constraints on both the quality of service (QoS) and the level of security.
This framework illustrates the dependence of the network throughput on key
system parameters, such as the densities of legitimate nodes and eavesdroppers,
as well as the QoS and security constraints. One important finding is that the
throughput cost of achieving a moderate level of security is quite low, while
throughput must be significantly sacrificed to realize a highly secure network.
We also study the use of a secrecy guard zone, which is shown to give a
significant improvement on the throughput of networks with high security
requirements.Comment: Accepted for publication in IEEE Transactions on Wireless
Communication
Secure Massive MIMO Communication with Low-resolution DACs
In this paper, we investigate secure transmission in a massive multiple-input
multiple-output (MIMO) system adopting low-resolution digital-to-analog
converters (DACs). Artificial noise (AN) is deliberately transmitted
simultaneously with the confidential signals to degrade the eavesdropper's
channel quality. By applying the Bussgang theorem, a DAC quantization model is
developed which facilitates the analysis of the asymptotic achievable secrecy
rate. Interestingly, for a fixed power allocation factor , low-resolution
DACs typically result in a secrecy rate loss, but in certain cases they provide
superior performance, e.g., at low signal-to-noise ratio (SNR). Specifically,
we derive a closed-form SNR threshold which determines whether low-resolution
or high-resolution DACs are preferable for improving the secrecy rate.
Furthermore, a closed-form expression for the optimal is derived. With
AN generated in the null-space of the user channel and the optimal ,
low-resolution DACs inevitably cause secrecy rate loss. On the other hand, for
random AN with the optimal , the secrecy rate is hardly affected by the
DAC resolution because the negative impact of the quantization noise can be
compensated for by reducing the AN power. All the derived analytical results
are verified by numerical simulations.Comment: 14 pages, 10 figure
Semantically Secure Lattice Codes for Compound MIMO Channels
We consider compound multi-input multi-output (MIMO) wiretap channels where
minimal channel state information at the transmitter (CSIT) is assumed. Code
construction is given for the special case of isotropic mutual information,
which serves as a conservative strategy for general cases. Using the flatness
factor for MIMO channels, we propose lattice codes universally achieving the
secrecy capacity of compound MIMO wiretap channels up to a constant gap
(measured in nats) that is equal to the number of transmit antennas. The
proposed approach improves upon existing works on secrecy coding for MIMO
wiretap channels from an error probability perspective, and establishes
information theoretic security (in fact semantic security). We also give an
algebraic construction to reduce the code design complexity, as well as the
decoding complexity of the legitimate receiver. Thanks to the algebraic
structures of number fields and division algebras, our code construction for
compound MIMO wiretap channels can be reduced to that for Gaussian wiretap
channels, up to some additional gap to secrecy capacity.Comment: IEEE Trans. Information Theory, to appea
Optimal Number of Transmit Antennas for Secrecy Enhancement in Massive MIMOME Channels
This paper studies the impact of transmit antenna selection on the secrecy
performance of massive MIMO wiretap channels. We consider a scenario in which a
multi-antenna transmitter selects a subset of transmit antennas with the
strongest channel gains. Confidential messages are then transmitted to a
multi-antenna legitimate receiver while the channel is being overheard by a
multi-antenna eavesdropper. For this setup, we approximate the distribution of
the instantaneous secrecy rate in the large-system limit. The approximation
enables us to investigate the optimal number of selected antennas which
maximizes the asymptotic secrecy throughput of the system. We show that
increasing the number of selected antennas enhances the secrecy performance of
the system up to some optimal value, and that further growth in the number of
selected antennas has a destructive effect. Using the large-system
approximation, we obtain the optimal number of selected antennas analytically
for various scenarios. Our numerical investigations show an accurate match
between simulations and the analytic results even for not so large dimensions.Comment: 6 pages, 4 figures, IEEE GLOBECOM 201
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