15,810 research outputs found
Dynamic Resource Allocation in Cognitive Radio Networks: A Convex Optimization Perspective
This article provides an overview of the state-of-art results on
communication resource allocation over space, time, and frequency for emerging
cognitive radio (CR) wireless networks. Focusing on the
interference-power/interference-temperature (IT) constraint approach for CRs to
protect primary radio transmissions, many new and challenging problems
regarding the design of CR systems are formulated, and some of the
corresponding solutions are shown to be obtainable by restructuring some
classic results known for traditional (non-CR) wireless networks. It is
demonstrated that convex optimization plays an essential role in solving these
problems, in a both rigorous and efficient way. Promising research directions
on interference management for CR and other related multiuser communication
systems are discussed.Comment: to appear in IEEE Signal Processing Magazine, special issue on convex
optimization for signal processin
The Spectrum of a Binding System for a Heavy Quark with an Anti-Sbottom or for a Sbottom and Anti-Sbottom Pair
Since long-lived light bottom squark (sbottom) and its anti-particle with a
mass close to the bottom quark have not been excluded by experiments so far, we
consider such a sbottom to combine with its anti-particle to form a color
singlet meson-like bound state or to combine with a common anti-quark to form a
fermion-like one, or accordingly their anti-particles to form an anti-particle
bound system. Namely we calculate the low-lying spectrum of the systems based
on QCD inspired potential model. To be as relativistic as possible, we start
with the framework of Bethe-Salpeter (BS) equation even for non-relativistic
binding systems. Finally, we obtain the requested spectrum by constructing
general forms of the BS wave functions and solving the BS equations under
instantaneous approximation.Comment: 13 pages, 1 figur
Optimal Beamforming for Two-Way Multi-Antenna Relay Channel with Analogue Network Coding
This paper studies the wireless two-way relay channel (TWRC), where two
source nodes, S1 and S2, exchange information through an assisting relay node,
R. It is assumed that R receives the sum signal from S1 and S2 in one
time-slot, and then amplifies and forwards the received signal to both S1 and
S2 in the next time-slot. By applying the principle of analogue network (ANC),
each of S1 and S2 cancels the so-called "self-interference" in the received
signal from R and then decodes the desired message. Assuming that S1 and S2 are
each equipped with a single antenna and R with multi-antennas, this paper
analyzes the capacity region of an ANC-based TWRC with linear processing
(beamforming) at R. The capacity region contains all the achievable
bidirectional rate-pairs of S1 and S2 under the given transmit power
constraints at S1, S2, and R. We present the optimal relay beamforming
structure as well as an efficient algorithm to compute the optimal beamforming
matrix based on convex optimization techniques. Low-complexity suboptimal relay
beamforming schemes are also presented, and their achievable rates are compared
against the capacity with the optimal scheme.Comment: to appear in JSAC, 200
New Perspectives on Axion Misalignment Mechanism
A zero initial velocity of the axion field is assumed in the conventional
misalignment mechanism. We propose an alternative scenario where the initial
velocity is nonzero, which may arise from an explicit breaking of the PQ
symmetry in the early Universe. We demonstrate that, depending on the specifics
about the initial velocity and the time order of the PQ symmetry breaking vs.
inflation, this new scenario can alter the conventional prediction for the
axion relic abundance in different, potentially significant ways. As a result,
new viable parameter regions for axion dark matter may open up.Comment: 7 pages, 7 figure
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