7,505 research outputs found
An Exposition of the Connection between Limit-Periodic Potentials and Profinite Groups
We classify the hulls of different limit-periodic potentials and show that
the hull of a limit-periodic potential is a procyclic group. We describe how
limit-periodic potentials can be generated from a procyclic group and answer
arising questions. As an expository paper, we discuss the connection between
limit-periodic potentials and profinite groups as completely as possible and
review some recent results on Schroedinger operators obtained in this context
Joint Beamforming Optimization and Power Control for Full-Duplex MIMO Two-Way Relay Channel
In this paper, we explore the use of full-duplex radio to improve the spectrum efficiency in a two-way relay channel where two sources exchange information through an multi-antenna relay, and all nodes work in the full-duplex mode. The full-duplex operation can reduce the overall communication to only one phase but suffers from the self-interference. Instead of purely suppressing the self-interference, we aim to maximize the end-to-end performance by jointly optimizing the beamforming matrix at the relay which uses the amplify-and-forward protocol as well as the power control at the sources. To be specific, we propose iterative algorithms and 1-D search to solve two problems: finding the achievable rate region and maximizing the sum rate. At each iteration, either the analytical solution or convex formulation is obtained. We compare the proposed full-duplex two-way relaying with the conventional half-duplex two-way relaying, a full-duplex one-way relaying and a performance upper bound. Numerical results show that the proposed full-duplex scheme significantly improves the achievable data rates over the conventional scheme
Robust Monotonic Optimization Framework for Multicell MISO Systems
The performance of multiuser systems is both difficult to measure fairly and
to optimize. Most resource allocation problems are non-convex and NP-hard, even
under simplifying assumptions such as perfect channel knowledge, homogeneous
channel properties among users, and simple power constraints. We establish a
general optimization framework that systematically solves these problems to
global optimality. The proposed branch-reduce-and-bound (BRB) algorithm handles
general multicell downlink systems with single-antenna users, multiantenna
transmitters, arbitrary quadratic power constraints, and robustness to channel
uncertainty. A robust fairness-profile optimization (RFO) problem is solved at
each iteration, which is a quasi-convex problem and a novel generalization of
max-min fairness. The BRB algorithm is computationally costly, but it shows
better convergence than the previously proposed outer polyblock approximation
algorithm. Our framework is suitable for computing benchmarks in general
multicell systems with or without channel uncertainty. We illustrate this by
deriving and evaluating a zero-forcing solution to the general problem.Comment: Published in IEEE Transactions on Signal Processing, 16 pages, 9
figures, 2 table
Exploiting Known Interference as Green Signal Power for Downlink Beamforming Optimization
We propose a data-aided transmit beamforming scheme for the multi-user multiple-input-single-output (MISO) downlink channel. While conventional beamforming schemes aim at the minimization of the transmit power subject to suppressing interference to guarantee quality of service (QoS) constraints, here we use the knowledge of both data and channel state information (CSI) at the transmitter to exploit, rather than suppress, constructive interference. More specifically, we design a new precoding scheme for the MISO downlink that minimizes the transmit power for generic phase shift keying (PSK) modulated signals. The proposed precoder reduces the transmit power compared to conventional schemes, by adapting the QoS constraints to accommodate constructive interference as a source of useful signal power. By exploiting the power of constructively interfering symbols, the proposed scheme achieves the required QoS at lower transmit power. We extend this concept to the signal to interference plus noise ratio (SINR) balancing problem, where higher SINR values compared to the conventional SINR balancing optimization are achieved for given transmit power budgets. In addition, we derive equivalent virtual multicast formulations for both optimizations, both of which provide insights of the optimal solution and facilitate the design of a more efficient solver. Finally, we propose a robust beamforming technique to deal with imperfect CSI, that also reduces the transmit power over conventional techniques, while guaranteeing the required QoS. Our simulation and analysis show significant power savings for small scale MISO downlink channels with the proposed data-aided optimization compared to conventional beamforming optimization
Secure Full-Duplex Two-Way Relaying for SWIPT
This letter studies bi-directional secure information exchange in a
simultaneous wireless information and power transfer (SWIPT) system enabled by
a full-duplex (FD) multiple-input multiple-output (MIMO) amplify-and-forward
(AF) relay. The AF relay injects artificial noise (AN) in order to confuse the
eavesdropper. Specifically, we assume a zeroforcing (ZF) solution constraint to
eliminate the residual self-interference (RSI). As a consequence, we address
the optimal joint design of the ZF matrix and the AN covariance matrix at the
relay node as well as the transmit power at the sources. We propose an
alternating algorithm utilizing semi-definite programming (SDP) technique and
one-dimensional searching to achieve the optimal solution. Simulation results
are provided to demonstrate the effectiveness of the proposed algorithm.Comment: Submitted to IEEE Wireless Communications Letter
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