The Experts below are selected from a list of 22812 Experts worldwide ranked by ideXlab platform
Hoi-to Wai - One of the best experts on this subject based on the ideXlab platform.
-
Discrete Sum Rate Maximization for MISO Interference Broadcast Channels: Convex Approximations and Efficient Algorithms
IEEE Transactions on Signal Processing, 2016Co-Authors: Hoi-to WaiAbstract:This paper considers the Discrete Sum rate maximization (DSRM) problem for beamformer optimization in multi-input single-output interference broadcast channels. In this problem, the achievable rates of the receivers are restricted to be taken from a set of finite Discrete rate values, and such constraints arise from practical limitations with the modulation and coding schemes. Many existing studies consider Sum rate maximization without the Discrete rate constraints, and that may result in performance loss. In this paper, the DSRM problem is tackled via a convex approximation approach. Due to the Discrete rate constraints, DSRM is a mixed-integer program. The idea of the proposed approach is to reformulate DSRM as a continuous, but still nonconvex, optimization problem. Then, appropriate convex approximations are applied. The advantage of the proposed approach is that the resulting approximate problems can be easily decomposed from a first-order optimization viewpoint. Utilizing this special feature, low-complexity and decentralized algorithms based on projected gradient are derived. Numerical results are used to show the efficiencies of the proposed algorithms in a multicell coordinated beamforming scenario. Also, this paper provides a proof for the convergence guarantee of one decentralized optimization strategy, namely, inexact maximum block improvement.
-
a convex approximation method for multiuser miso Sum rate maximization under Discrete rate constraints
International Conference on Acoustics Speech and Signal Processing, 2013Co-Authors: Hoi-to WaiAbstract:This paper considers a Discrete Sum rate maximization (DSRM) problem for transmit optimization in multiuser MISO downlink. Unlike many existing Sum rate maximization designs, DSRM focuses on a scenario where each user's achievable rate can only be chosen from a given Discrete rate set. This Discrete rate-based design is motivated by the fact that practical communication systems can support only a finite number of combinations of modulation and coding schemes. We tackle the DSRM problem first by deriving a novel reformulation of DSRM, in which the Discrete rate variables are absorbed by the objective function. Then, from this reformulation, an approximation algorithm based on convex optimization and iterative solution refinement is developed. Simulations results are provided to demonstrate the performance of the proposed algorithm compared with some state-of-the-art algorithms.
-
ICASSP - A convex approximation method for multiuser MISO Sum rate maximization under Discrete rate constraints
2013 IEEE International Conference on Acoustics Speech and Signal Processing, 2013Co-Authors: Hoi-to WaiAbstract:This paper considers a Discrete Sum rate maximization (DSRM) problem for transmit optimization in multiuser MISO downlink. Unlike many existing Sum rate maximization designs, DSRM focuses on a scenario where each user's achievable rate can only be chosen from a given Discrete rate set. This Discrete rate-based design is motivated by the fact that practical communication systems can support only a finite number of combinations of modulation and coding schemes. We tackle the DSRM problem first by deriving a novel reformulation of DSRM, in which the Discrete rate variables are absorbed by the objective function. Then, from this reformulation, an approximation algorithm based on convex optimization and iterative solution refinement is developed. Simulations results are provided to demonstrate the performance of the proposed algorithm compared with some state-of-the-art algorithms.
Christof Gattringer - One of the best experts on this subject based on the ideXlab platform.
-
The lattice Schwinger model as a Discrete Sum of filled Wilson loops
Nuclear Physics, 1999Co-Authors: Christof GattringerAbstract:Abstract Using techniques from hopping expansion we identically map the lattice Schwinger model with Wilson fermions to a model of oriented loops on the lattice. This is done by first computing the explicit form of the fermion determinant in the external field. Subsequent integration of the gauge fields renders a Sum over all loop configurations with simple Gaussian weights depending on the number of plaquettes enclosed by the loops. In our new representation vacuum expectation values of local fermionic operators (scalars, vectors) can be computed by simply counting the loop flow through the sites (links) supporting the scalars (vectors). The strong coupling limit, possible applications of our methods to 4-D models and the introduction of a chemical potential are discussed.
-
The lattice Schwinger model as a Discrete Sum of filled Wilson loops
Nuclear Physics B, 1999Co-Authors: Christof GattringerAbstract:Using techniques from hopping expansion we identically map the lattice Schwinger model with Wilson fermions to a model of oriented loops on the lattice. This is done by first computing the explicit form of the fermion determinant in the external field. Subsequent integration of the gauge fields renders a Sum over all loop configurations with simple Gaussian weights depending on the number of plaquettes enclosed by the loops. In our new representation vacuum expectation values of local fermionic operators (scalars, vectors) can be computed by simply counting the loop flow through the sites (links) supporting the scalars (vectors). The strong coupling limit, possible applications of our methods to 4-D models and the introduction of a chemical potential are discussed.Comment: Revised version, to appear in Nucl. Phys. B. More technical details, Comment on chemical potential shortened, references adde
Toshiyuki Kobayashi - One of the best experts on this subject based on the ideXlab platform.
-
Discrete decomposability of the restriction of A_q(λ)with respect to reductive subgroups II-micro-local analysis and asymptotic K-support
Annals of Mathematics, 1998Co-Authors: Toshiyuki KobayashiAbstract:Let G' c G be real reductive Lie groups. This paper offers a criterion on the triplet (G, G', ir) that the irreducible unitary representation ir of G splits into a Discrete Sum of irreducible unitary representations of a subgroup G' when restricted to G', each of finite multiplicity. Furthermore, we shall give an upper estimate of the multiplicity of an irreducible unitary representation of G' occurring in WrIG'
-
Discrete decomposability of the restriction of A q (λ) with respect to reductive subgroups and its applications
Inventiones Mathematicae, 1994Co-Authors: Toshiyuki KobayashiAbstract:LetG′⊂G be real reductive Lie groups and q a θ-stable parabolic subalgebra of Lie (G) ⊗ ℂ. This paper offers a sufficient condition on (G, G′, q) that the irreducible unitary representation $$\mathop {A_q }\limits^--- $$ ofG with non-zero continuous cohomology splits into a Discrete Sum of irreducible unitary representations of a subgroupG′, each of finite multiplicity. As an application to purely analytic problems, new results on Discrete series are also obtained for some pseudo-Riemannian (non-symmetric) spherical homogeneous spaces, which fit nicely into this framework. Some explicit examples of a decomposition formula are also found in the cases whereA q is not necessarily a highest weight module.
Jingran Lin - One of the best experts on this subject based on the ideXlab platform.
-
joint uplink downlink Discrete Sum rate maximization for full duplex multicell heterogeneous networks
IEEE Transactions on Vehicular Technology, 2020Co-Authors: Silei Wang, Jingran LinAbstract:Consider multicell heterogeneous networks (HetNets), where each cell consists of a number of small (micro/pico) base stations (SBSs) and the SBSs perform coordinated multipoint (CoMP) transmission/reception to serve a number of downlink/uplink (DL/UL) users over the same frequency band. The SBSs work in full-duplex (FD) mode and the DL/UL users are half-duplex (HD). Due to co-channel transmissions, the DL and the UL are mutually interfered. This motivates us to consider a joint DL/UL beamformer design for maximizing the system Sum rate. Different from the conventional Sum rate maximization (SRM), where the user's rate is allowed to be any nonnegative real number, herein we focus on the Discrete-rate case — each user's rate is constrained to a prescribed Discrete-rate set. This Discrete-rate constraint is motivated by the fact that practical communication systems are designed for a finite number of transmission rates, owing to the finite number of modulation and coding schemes (MCS). In view of this, our SRM problem is coined as Discrete SRM (DSRM). The DSRM problem is essentially a mixed-integer nonlinear program, and NP-hard. To tackle it, two different approaches are proposed. The first approach is built upon the simplex reformulation of the Discrete rate and the mirror descent (MD) algorithm. The second approach exploits the correspondence between the rate and minimum mean-square error (MMSE), and employs the block-coordinate descent (BCD) method to find an approximate solution. Simulation results demonstrate the superior rate performance of the proposed designs as compared with the weighted MMSE (WMMSE) design with naive rate quantization.
-
Joint Uplink/Downlink Discrete Sum Rate Maximization for Full-Duplex Multicell Heterogeneous Networks
IEEE Transactions on Vehicular Technology, 2020Co-Authors: Silei Wang, Jingran LinAbstract:Consider multicell heterogeneous networks (HetNets), where each cell consists of a number of small (micro/pico) base stations (SBSs) and the SBSs perform coordinated multipoint (CoMP) transmission/reception to serve a number of downlink/uplink (DL/UL) users over the same frequency band. The SBSs work in full-duplex (FD) mode and the DL/UL users are half-duplex (HD). Due to co-channel transmissions, the DL and the UL are mutually interfered. This motivates us to consider a joint DL/UL beamformer design for maximizing the system Sum rate. Different from the conventional Sum rate maximization (SRM), where the user's rate is allowed to be any nonnegative real number, herein we focus on the Discrete-rate case — each user's rate is constrained to a prescribed Discrete-rate set. This Discrete-rate constraint is motivated by the fact that practical communication systems are designed for a finite number of transmission rates, owing to the finite number of modulation and coding schemes (MCS). In view of this, our SRM problem is coined as Discrete SRM (DSRM). The DSRM problem is essentially a mixed-integer nonlinear program, and NP-hard. To tackle it, two different approaches are proposed. The first approach is built upon the simplex reformulation of the Discrete rate and the mirror descent (MD) algorithm. The second approach exploits the correspondence between the rate and minimum mean-square error (MMSE), and employs the block-coordinate descent (BCD) method to find an approximate solution. Simulation results demonstrate the superior rate performance of the proposed designs as compared with the weighted MMSE (WMMSE) design with naive rate quantization.
H.c. Ren - One of the best experts on this subject based on the ideXlab platform.
-
Path integrals as Discrete Sums.
Physical review letters, 1991Co-Authors: Khalil M. Bitar, N. N. Khuri, H.c. RenAbstract:We present a new formulation of Feynman's path integral, based on Voronin's theorems on the universality of the Riemann zeta function. The result is a Discrete Sum over paths,'' each given by a zeta function. A new measure which leads to the correct quantum mechanics is explicitly given.
-
Path integrals and Voronin's theorem on the universality of the Riemann zeta function
Annals of Physics, 1991Co-Authors: Khalil M. Bitar, N. N. Khuri, H.c. RenAbstract:Abstract We present a new approach to the path integral in latticized quantum theories. Our method is based on Voronin's theorems on the universality of the Riemann zeta function. We obtain a formula for the partition function as a Discrete Sum over “paths” with each path labeled by an integer and given by a zeta function evaluated at a fixed set of points in the critical strip. These points are the image of the space-time lattice resulting from a simple linear mapping. A new measure appears in our Sum, and its properties are extensively discussed and a method to calculate it is given. We carried out extensive checks of the method for Euclidean quantum mechanics, and compared the results with those obtained from well-established methods as well as exact results. The comparison confirms the validity of the zeta-function method and our calculation of the measure.