11,539 research outputs found
Compressed Secret Key Agreement: Maximizing Multivariate Mutual Information Per Bit
The multiterminal secret key agreement problem by public discussion is
formulated with an additional source compression step where, prior to the
public discussion phase, users independently compress their private sources to
filter out strongly correlated components for generating a common secret key.
The objective is to maximize the achievable key rate as a function of the joint
entropy of the compressed sources. Since the maximum achievable key rate
captures the total amount of information mutual to the compressed sources, an
optimal compression scheme essentially maximizes the multivariate mutual
information per bit of randomness of the private sources, and can therefore be
viewed more generally as a dimension reduction technique. Single-letter lower
and upper bounds on the maximum achievable key rate are derived for the general
source model, and an explicit polynomial-time computable formula is obtained
for the pairwise independent network model. In particular, the converse results
and the upper bounds are obtained from those of the related secret key
agreement problem with rate-limited discussion. A precise duality is shown for
the two-user case with one-way discussion, and such duality is extended to
obtain the desired converse results in the multi-user case. In addition to
posing new challenges in information processing and dimension reduction, the
compressed secret key agreement problem helps shed new light on resolving the
difficult problem of secret key agreement with rate-limited discussion, by
offering a more structured achieving scheme and some simpler conjectures to
prove
Wireless transmission protocols using relays for broadcast and information exchange channels
Relays have been used to overcome existing network performance bottlenecks in meeting the growing
demand for large bandwidth and high quality of service (QoS) in wireless networks. This thesis
proposes several wireless transmission protocols using relays in practical multi-user broadcast and
information exchange channels. The main theme is to demonstrate that efficient use of relays provides
an additional dimension to improve reliability, throughput, power efficiency and secrecy. First,
a spectrally efficient cooperative transmission protocol is proposed for the multiple-input and singleoutput
(MISO) broadcast channel to improve the reliability of wireless transmission. The proposed
protocol mitigates co-channel interference and provides another dimension to improve the diversity
gain. Analytical and simulation results show that outage probability and the diversity and multiplexing
tradeoff of the proposed cooperative protocol outperforms the non-cooperative scheme. Second,
a two-way relaying protocol is proposed for the multi-pair, two-way relaying channel to improve the
throughput and reliability. The proposed protocol enables both the users and the relay to participate
in interference cancellation. Several beamforming schemes are proposed for the multi-antenna
relay. Analytical and simulation results reveal that the proposed protocol delivers significant improvements
in ergodic capacity, outage probability and the diversity and multiplexing tradeoff if compared
to existing schemes. Third, a joint beamforming and power management scheme is proposed for
multiple-input and multiple-output (MIMO) two-way relaying channel to improve the sum-rate. Network
power allocation and power control optimisation problems are formulated and solved using
convex optimisation techniques. Simulation results verify that the proposed scheme delivers better
sum-rate or consumes lower power when compared to existing schemes. Fourth, two-way secrecy
schemes which combine one-time pad and wiretap coding are proposed for the scalar broadcast channel
to improve secrecy rate. The proposed schemes utilise the channel reciprocity and employ relays
to forward secret messages. Analytical and simulation results reveal that the proposed schemes are
able to achieve positive secrecy rates even when the number of users is large. All of these new wireless
transmission protocols help to realise better throughput, reliability, power efficiency and secrecy
for wireless broadcast and information exchange channels through the efficient use of relays
Physical-Layer Security with Multiuser Scheduling in Cognitive Radio Networks
In this paper, we consider a cognitive radio network that consists of one
cognitive base station (CBS) and multiple cognitive users (CUs) in the presence
of multiple eavesdroppers, where CUs transmit their data packets to CBS under a
primary user's quality of service (QoS) constraint while the eavesdroppers
attempt to intercept the cognitive transmissions from CUs to CBS. We
investigate the physical-layer security against eavesdropping attacks in the
cognitive radio network and propose the user scheduling scheme to achieve
multiuser diversity for improving the security level of cognitive transmissions
with a primary QoS constraint. Specifically, a cognitive user (CU) that
satisfies the primary QoS requirement and maximizes the achievable secrecy rate
of cognitive transmissions is scheduled to transmit its data packet. For the
comparison purpose, we also examine the traditional multiuser scheduling and
the artificial noise schemes. We analyze the achievable secrecy rate and
intercept probability of the traditional and proposed multiuser scheduling
schemes as well as the artificial noise scheme in Rayleigh fading environments.
Numerical results show that given a primary QoS constraint, the proposed
multiuser scheduling scheme generally outperforms the traditional multiuser
scheduling and the artificial noise schemes in terms of the achievable secrecy
rate and intercept probability. In addition, we derive the diversity order of
the proposed multiuser scheduling scheme through an asymptotic intercept
probability analysis and prove that the full diversity is obtained by using the
proposed multiuser scheduling.Comment: 12 pages. IEEE Transactions on Communications, 201
A novel semi-fragile forensic watermarking scheme for remote sensing images
Peer-reviewedA semi-fragile watermarking scheme for multiple band images is presented. We propose to embed a mark into remote sensing images applying a tree structured vector quantization approach to the pixel signatures, instead of processing each band separately. The signature of themmultispectral or hyperspectral image is used to embed the mark in it order to detect any significant modification of the original image. The image is segmented into threedimensional blocks and a tree structured vector quantizer is built for each block. These trees are manipulated using an iterative algorithm until the resulting block satisfies a required criterion which establishes the embedded mark. The method is shown to be able to preserve the mark under lossy compression (above a given threshold) but, at the same time, it detects possibly forged blocks and their position in the whole image.Se presenta un esquema de marcas de agua semi-frágiles para múltiples imágenes de banda. Proponemos incorporar una marca en imágenes de detección remota, aplicando un enfoque de cuantización del vector de árbol estructurado con las definiciones de píxel, en lugar de procesar cada banda por separado. La firma de la imagen hiperespectral se utiliza para insertar la marca en el mismo orden para detectar cualquier modificación significativa de la imagen original. La imagen es segmentada en bloques tridimensionales y un cuantificador de vector de estructura de árbol se construye para cada bloque. Estos árboles son manipulados utilizando un algoritmo iteractivo hasta que el bloque resultante satisface un criterio necesario que establece la marca incrustada. El método se muestra para poder preservar la marca bajo compresión con pérdida (por encima de un umbral establecido) pero, al mismo tiempo, detecta posiblemente bloques forjados y su posición en la imagen entera.Es presenta un esquema de marques d'aigua semi-fràgils per a múltiples imatges de banda. Proposem incorporar una marca en imatges de detecció remota, aplicant un enfocament de quantització del vector d'arbre estructurat amb les definicions de píxel, en lloc de processar cada banda per separat. La signatura de la imatge hiperespectral s'utilitza per inserir la marca en el mateix ordre per detectar qualsevol modificació significativa de la imatge original. La imatge és segmentada en blocs tridimensionals i un quantificador de vector d'estructura d'arbre es construeix per a cada bloc. Aquests arbres són manipulats utilitzant un algoritme iteractiu fins que el bloc resultant satisfà un criteri necessari que estableix la marca incrustada. El mètode es mostra per poder preservar la marca sota compressió amb pèrdua (per sobre d'un llindar establert) però, al mateix temps, detecta possiblement blocs forjats i la seva posició en la imatge sencera
Experimental demonstration of Gaussian protocols for one-sided device-independent quantum key distribution
Nonlocal correlations, a longstanding foundational topic in quantum
information, have recently found application as a resource for cryptographic
tasks where not all devices are trusted, for example in settings with a highly
secure central hub, such as a bank or government department, and less secure
satellite stations which are inherently more vulnerable to hardware "hacking"
attacks. The asymmetric phenomena of Einstein-Podolsky-Rosen steering plays a
key role in one-sided device-independent quantum key distribution (1sDI-QKD)
protocols. In the context of continuous-variable (CV) QKD schemes utilizing
Gaussian states and measurements, we identify all protocols that can be 1sDI
and their maximum loss tolerance. Surprisingly, this includes a protocol that
uses only coherent states. We also establish a direct link between the relevant
EPR steering inequality and the secret key rate, further strengthening the
relationship between these asymmetric notions of nonlocality and device
independence. We experimentally implement both entanglement-based and
coherent-state protocols, and measure the correlations necessary for 1sDI key
distribution up to an applied loss equivalent to 7.5 km and 3.5 km of optical
fiber transmission respectively. We also engage in detailed modelling to
understand the limits of our current experiment and the potential for further
improvements. The new protocols we uncover apply the cheap and efficient
hardware of CVQKD systems in a significantly more secure setting.Comment: Addition of experimental results and (several) new author
Quantum Cryptography
Quantum cryptography could well be the first application of quantum mechanics
at the individual quanta level. The very fast progress in both theory and
experiments over the recent years are reviewed, with emphasis on open questions
and technological issues.Comment: 55 pages, 32 figures; to appear in Reviews of Modern Physic
Cooperative communication in wireless networks: algorithms, protocols and systems
Current wireless network solutions are based on a link abstraction where a
single co-channel transmitter transmits in any time duration. This model severely
limits the performance that can be obtained from the network. Being inherently an
extension of a wired network model, this model is also incapable of handling the
unique challenges that arise in a wireless medium. The prevailing theme of this
research is to explore wireless link abstractions that incorporate the broadcast and
space-time varying nature of the wireless channel. Recently, a new paradigm for
wireless networks which uses the idea of 'cooperative transmissions' (CT) has garnered
significant attention. Unlike current approaches where a single transmitter transmits
at a time in any channel, with CT, multiple transmitters transmit concurrently after
appropriately encoding their transmissions. While the physical layer mechanisms for
CT have been well studied, the higher layer applicability of CT has been relatively
unexplored. In this work, we show that when wireless links use CT, several network
performance metrics such as aggregate throughput, security and spatial reuse can
be improved significantly compared to the current state of the art. In this context,
our first contribution is Aegis, a framework for securing wireless networks against
eavesdropping which uses CT with intelligent scheduling and coding in Wireless Local
Area networks. The second contribution is Symbiotic Coding, an approach to encode
information such that successful reception is possible even upon collisions. The third
contribution is Proteus, a routing protocol that improves aggregate throughput in
multi-hop networks by leveraging CT to adapt the rate and range of links in a flow.
Finally, we also explore the practical aspects of realizing CT using real systems.PhDCommittee Chair: Sivakumar, Raghupathy; Committee Member: Ammar, Mostafa; Committee Member: Ingram, Mary Ann; Committee Member: Jayant, Nikil; Committee Member: Riley, Georg
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