Iterative Joint Channel Estimation and Multi-User Detection for Multiple-Antenna Aided OFDM Systems

Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems have recently attracted substantial research interest. However, compared to Single-Input-Single-Output (SISO) systems, channel estimation in the MIMO scenario becomes more challenging, owing to the increased number of independent transmitter-receiver links to be estimated. In the context of the Bell LAyered Space-Time architecture (BLAST) or Space Division Multiple Access (SDMA) multi-user MIMO OFDM systems, none of the known channel estimation techniques allows the number of users to be higher than the number of receiver antennas, which is often referred to as a “rank-deficient” scenario, owing to the constraint imposed by the rank of the MIMO channel matrix. Against this background, in this paper we propose a new Genetic Algorithm (GA) assisted iterative Joint Channel Estimation and Multi-User Detection (GA-JCEMUD) approach for multi-user MIMO SDMA-OFDM systems, which provides an effective solution to the multi-user MIMO channel estimation problem in the above-mentioned rank-deficient scenario. Furthermore, the GAs invoked in the data detection literature can only provide a hard-decision output for the Forward Error Correction (FEC) or channel decoder, which inevitably limits the system’s achievable performance. By contrast, our proposed GA is capable of providing “soft” outputs and hence it becomes capable of achieving an improved performance with the aid of FEC decoders. A range of simulation results are provided to demonstrate the superiority of the proposed scheme. Index Terms—Channel estimation, genetic algorithm, multiple-input-multiple-output, multi-user detection, orthogonal frequency division multiplexing, space division multiple access

Investigation of a universal behavior between N\'eel temperature and staggered magnetization density for a three-dimensional quantum antiferromagnet

We simulate the three-dimensional quantum Heisenberg model with a spatially anisotropic ladder pattern using the first principles Monte Carlo method. Our motivation is to investigate quantitatively the newly established universal relation $T_N/\sqrt{c^3}$ $\propto$ ${\cal M}_s$ near the quantum critical point (QCP) associated with dimerization. Here $T_N$, $c$, and ${\cal M}_s$ are the N\'eel temperature, the spinwave velocity, and the staggered magnetization density, respectively. For all the physical quantities considered here, such as $T_N$ and ${\cal M}_s$, our Monte Carlo results agree nicely with the corresponding results determined by the series expansion method. In addition, we find it is likely that the effect of a logarithmic correction, which should be present in (3+1)-dimensions, to the relation $T_N/\sqrt{c^3}$ $\propto$ ${\cal M}_s$ near the investigated QCP only sets in significantly in the region with strong spatial anisotropy.Comment: 5 pages, 7 figures, 2 table

Intense terahertz laser fields on a quantum dot with Rashba spin-orbit coupling

We investigate the effects of the intense terahertz laser field and the spin-orbit coupling on single electron spin in a quantum dot. The laser field and the spin-orbit coupling can strongly affect the electron density of states and can excite a magnetic moment. The direction of the magnetic moment depends on the symmetries of the system, and its amplitude can be tuned by the strength and frequency of the laser field as well as the spin-orbit coupling.Comment: 5 pages, 4 figures, to be published in J. Appl. Phy

An assessment of the quality of the I-DSD and the I-CAH registries - international registries for rare conditions affecting sex development

With the proliferation of rare disease registries, there is a need for registries to undergo an assessment of their quality against agreed standards to ensure their long-term sustainability and acceptability.This study was performed to evaluate the I-DSD and I-CAH Registries and identify their strengths and weaknesses. The design and operational aspects of the registries were evaluated against published quality indicators. Additional criteria included the level of activity, international acceptability of the registries and their use for research. The design of the I-DSD and I-CAH Registries provides them with the ability to perform multiple studies and meet the standards for data elements, data sources and eligibility criteria. The registries follow the standards for data security, governance, ethical and legal issues, sustainability and communication of activities. The data have a high degree of validity, consistency and accuracy and the completeness is maximal for specific conditions such as androgen insensitivity syndrome and congenital adrenal hyperplasia. In terms of research output, the external validity is strong but the wide variety of cases needs further review. The internal validity of data was condition specific and highest for conditions such as congenital adrenal hyperplasia. The shift of the registry from a European registry to an international registry and the creation of a discrete but linked CAH registry increased the number of users and stakeholders as well as the international acceptability of both registries. The I-DSD and I-CAH registries comply with the standards set by expert organisations. Recent modifications in their operation have allowed the registries to increase their user acceptability

Rotor Spectra, Berry Phases, and Monopole Fields: from Antiferromagnets to QCD

The order parameter of a finite system with a spontaneously broken continuous global symmetry acts as a quantum mechanical rotor. Both antiferromagnets with a spontaneously broken $SU(2)_s$ spin symmetry and massless QCD with a broken $SU(2)_L \times SU(2)_R$ chiral symmetry have rotor spectra when considered in a finite volume. When an electron or hole is doped into an antiferromagnet or when a nucleon is propagating through the QCD vacuum, a Berry phase arises from a monopole field and the angular momentum of the rotor is quantized in half-integer units.Comment: 4 page

The Architecture of a Novel Weighted Network: Knowledge Network

Networked structure emerged from a wide range of fields such as biological systems, World Wide Web and technological infrastructure. A deeply insight into the topological complexity of these networks has been gained. Some works start to pay attention to the weighted network, like the world-wide airport network and the collaboration network, where links are not binary, but have intensities. Here, we construct a novel knowledge network, through which we take the first step to uncover the topological structure of the knowledge system. Furthermore, the network is extended to the weighted one by assigning weights to the edges. Thus, we also investigate the relationship between the intensity of edges and the topological structure. These results provide a novel description to understand the hierarchies and organizational principles in knowledge system, and the interaction between the intensity of edges and topological structure. This system also provides a good paradigm to study weighted networks.Comment: 5 figures 11 page

Effective oscillator strength distributions of spherically symmetric atoms for calculating polarizabilities and long-range atom-atom interactions

Effective oscillator strength distributions are systematically generated and tabulated for the alkali atoms, the alkaline-earth atoms, the alkaline-earth ions, the rare gases and some miscellaneous atoms. These effective distributions are used to compute the dipole, quadrupole and octupole static polarizabilities, and are then applied to the calculation of the dynamic polarizabilities at imaginary frequencies. These polarizabilities can be used to determine the long-range $C_6$, $C_8$ and $C_{10}$ atom-atom interactions for the dimers formed from any of these atoms and ions, and we present tables covering all of these combinations