1,912 research outputs found
Relays for Interference Mitigation in Wireless Networks
Wireless links play an important role in the last mile network connectivity. In contrast to the strictly centralized approach of today's wireless systems, the future promises decentralization of network management. Nodes potentially engage in localized grouping and organization based on their neighborhood to carry out complex goals such as end-to-end communication. The quadratic energy dissipation of the wireless medium necessitates the presence of certain relay nodes in the network. Conventionally, the role of such relays is limited to passing messages in a chain in a point-point hopping architecture. With the decentralization, multiple nodes could potentially interfere with each other. This work proposes a technique to exploit the presence of relays in a way that mitigates interference between the network nodes. Optimal spatial locations and transmission schemes which enhance this gain are identified
Adversarial Wiretap Channel with Public Discussion
Wyner's elegant model of wiretap channel exploits noise in the communication
channel to provide perfect secrecy against a computationally unlimited
eavesdropper without requiring a shared key. We consider an adversarial model
of wiretap channel proposed in [18,19] where the adversary is active: it
selects a fraction of the transmitted codeword to eavesdrop and a
fraction of the codeword to corrupt by "adding" adversarial error. It
was shown that this model also captures network adversaries in the setting of
1-round Secure Message Transmission [8]. It was proved that secure
communication (1-round) is possible if and only if .
In this paper we show that by allowing communicants to have access to a
public discussion channel (authentic communication without secrecy) secure
communication becomes possible even if . We formalize the
model of \awtppd protocol and for two efficiency measures, {\em information
rate } and {\em message round complexity} derive tight bounds. We also
construct a rate optimal protocol family with minimum number of message rounds.
We show application of these results to Secure Message Transmission with Public
Discussion (SMT-PD), and in particular show a new lower bound on transmission
rate of these protocols together with a new construction of an optimal SMT-PD
protocol
Equilibrium phases of dipolar lattice bosons in the presence of random diagonal disorder
Ultracold gases offer an unprecedented opportunity to engineer disorder and
interactions in a controlled manner. In an effort to understand the interplay
between disorder, dipolar interaction and quantum degeneracy, we study
two-dimensional hard-core dipolar lattice bosons in the presence of on-site
bound disorder. Our results are based on large-scale path-integral quantum
Monte Carlo simulations by the Worm algorithm. We study the ground state phase
diagram at fixed half-integer filling factor for which the clean system is
either a superfluid at lower dipolar interaction strength or a checkerboard
solid at larger dipolar interaction strength. We find that, even for weak
dipolar interaction, superfluidity is destroyed in favor of a Bose glass at
relatively low disorder strength. Interestingly, in the presence of disorder,
superfluidity persists for values of dipolar interaction strength for which the
clean system is a checkerboard solid. At fixed disorder strength, as the
dipolar interaction is increased, superfluidity is destroyed in favor of a Bose
glass. As the interaction is further increased, the system eventually develops
extended checkerboard patterns in the density distribution. Due to the presence
of disorder, though, grain boundaries and defects, responsible for a finite
residual compressibility, are present in the density distribution. Finally, we
study the robustness of the superfluid phase against thermal fluctuations
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