122,239 research outputs found

    Low Complexity Hybrid Precoding and Channel Estimation Based on Hierarchical Multi-Beam Search for Millimeter-Wave MIMO Systems

    Full text link
    In millimeter-wave (mmWave) MIMO systems, while a hybrid digital/analog precoding structure offers the potential to increase the achievable rate, it also faces the challenge of the need of a low-complexity design. In specific, the hybrid precoding may require matrix operations with a scale of antenna size, which is generally large in mmWave communication. Moreover, the channel estimation is also rather time consuming due to the large number of antennas at both Tx/Rx sides. In this paper, a low-complexity hybrid precoding and channel estimation approach is proposed. In the channel estimation phase, a hierarchical multi-beam search scheme is proposed to fast acquire NSN_{\rm{S}} (the number of streams) multipath components (MPCs)/clusters with the highest powers. In the hybrid precoding phase, the analog and digital precodings are decoupled. The analog precoding is designed to steer along the NSN_{\rm{S}} acquired MPCs/clusters at both Tx/Rx sides, shaping an equivalent NSΓ—NSN_{\rm{S}}\times N_{\rm{S}} baseband channel, while the digital precoding performs operations in the baseband with the reduced-scale channel. Performance evaluations show that, compared with a state-of-the-art scheme, while achieving a close or even better performance when the number of radio-frequency (RF) chains or streams is small, both the computational complexity of the hybrid precoding and the time complexity of the channel estimation are greatly reduced.Comment: 11 pages, 9 figures. This paper reports a Low Complexity Hybrid Precoding and Channel Estimation method for mmWave communication

    Codebook Design for Millimeter-Wave Channel Estimation with Hybrid Precoding Structure

    Full text link
    In this paper, we study hierarchical codebook design for channel estimation in millimeter-wave (mmWave) communications with a hybrid precoding structure. Due to the limited saturation power of mmWave power amplifier (PA), we take the per-antenna power constraint (PAPC) into consideration. We first propose a metric, i.e., generalized detection probability (GDP), to evaluate the quality of \emph{an arbitrary codeword}. This metric not only enables an optimization approach for mmWave codebook design, but also can be used to compare the performance of two different codewords/codebooks. To the best of our knowledge, GDP is the first metric particularly for mmWave codebook design for channel estimation. We then propose an approach to design a hierarchical codebook exploiting BeaM Widening with Multi-RF-chain Sub-array technique (BMW-MS). To obtain crucial parameters of BMW-MS, we provide two solutions, namely a low-complexity search (LCS) solution to optimize the GDP metric and a closed-form (CF) solution to pursue a flat beam pattern. Performance comparisons show that BMW-MS/LCS and BMW-MS/CF achieve very close performances, and they outperform the existing alternatives under the PAPC.Comment: 14 pages, 10 figures. Hierarchical codebook design for mmWave channel estimation with a hybrid precoding structure. Submitted to TW

    Full-Duplex Millimeter-Wave Communication

    Full text link
    The potential of doubling the spectrum efficiency of full-duplex (FD) transmission motivates us to investigate FD millimeter-wave (FD-mmWave) communication. To realize FD transmission in the mmWave band, we first introduce possible antenna configurations for FD-mmWave transmission. It is shown that, different from the cases in micro-wave band FD communications, the configuration with separate Tx/Rx antenna arrays appears more flexible in self-interference (SI) suppression while it may increase some cost and area versus that with the same array. We then model the mmWave SI channel with separate Tx/Rx arrays, where a near-field propagation model is adopted for the line-of-sight (LOS) path, and it is found that the established LOS-SI channel with separate Tx/Rx arrays also shows spatial sparsity. Based on the SI channel, we further explore approaches to mitigate SI by signal processing, and we focus on a new cancellation approach in FD-mmWave communication, i.e., beamforming cancellation. Centered on the constant-amplitude (CA) constraint of the beamforming vectors, we propose several candidate solutions. Lastly, we consider an FD-mmWave multi-user scenario, and show that even if there are no FD users in an FD-mmWave cellular system, the FD benefit can still be exploited in the FD base station. Candidate solutions are also discussed to mitigate both SI and multi-user interference (MUI) simultaneously.Comment: This paper explores the combination of full duplex communication and millimeter wave communication. (To appear in IEEE Wireless Communications

    Enabling UAV Cellular with Millimeter-Wave Communication: Potentials and Approaches

    Full text link
    To support high data rate urgent or ad hoc communications, we consider mmWave UAV cellular networks and the associated challenges and solutions. To enable fast beamforming training and tracking, we first investigate a hierarchical structure of beamforming codebooks and design of hierarchical codebooks with different beam widths via the sub-array techniques. We next examine the Doppler effect as a result of UAV movement and find that the Doppler effect may not be catastrophic when high gain directional transmission is used. We further explore the use of millimeter wave spatial division multiple access and demonstrate its clear advantage in improving the cellular network capacity. We also explore different ways of dealing with signal blockage and point out that possible adaptive UAV cruising algorithms would be necessary to counteract signal blockage. Finally, we identify a close relationship between UAV positioning and directional millimeter wave user discovery, where update of the former may directly impact the latter and vice versa.Comment: This paper explores the potentials and approaches to exploit mmWave communication to establish a UAV cellular. It is to appear in IEEE Communications Magazin

    Maximum likelihood reconstruction for the Daya Bay Experiment

    Full text link
    The Daya Bay Reactor Neutrino experiment is designed to precisely determine the neutrino mixing angle theta13. In this paper, we report a maximum likelihood (ML) method to reconstruct the vertex and energy of events in the anti-neutrino detector, based on a simplified optical model that describes light propagation. We calibrate the key paramters of the optical model with Co60 source, by comparing the predicted charges of the PMTs with the observed charges. With the optimized parameters, the resolution of the vertex reconstruction is about 25cm for Co60 gamma

    Evolution of N=28N = 28 shell closure in relativistic continuum Hartree-Bogoliubov theory

    Full text link
    The N=28N = 28 shell gap in sulfur, argon, calcium and titanium isotopes is investigated in the framework of relativistic continuum Hartree-Bogoliubov (RCHB) theory. The evolutions of neutron shell gap, separation energy, single particle energy and pairing energy are analyzed, and it is found that N=28N = 28 shell gap is quenched in sulfur isotopes but persists in argon, calcium and titanium isotopes. The evolution of N=28N = 28 shell gap in N=28N = 28 isotonic chain is discussed, and the erosion of N=28N = 28 shell gap is understood with the evolution of potential with proton number.Comment: 9 pages, 7 figure

    A review on applications of two-dimensional materials in surface enhanced Raman spectroscopy

    Full text link
    Two-dimensional (2D) materials, such as graphene and MoS2, have been attracting wide interest in surface enhancement Raman spectroscopy. This perspective gives an overview of recent developments in 2D materials' application in surface enhanced Raman spectroscopy. This review focuses on the applications of using bare 2D materials and metal/2D material hybrid substrate for Raman enhancement. The Raman enhancing mechanism of 2D materials will also be discussed. The progress covered herein shows great promise for widespread adoption of 2D materials in SERS application.Comment: 14 pages, 7 Figure

    Probe CP violation in H→γZH\to \gamma Z through forward-backward asymmetry

    Full text link
    We suggest that the forward-backward asymmetry (AFB)(A_{FB}) of the charged lepton in ggβ†’Hβ†’Ξ³Zβ†’Ξ³β„“βˆ’β„“+gg\to H\to\gamma Z\to\gamma \ell^-\ell^+ process could be used to probe the CP violating HΞ³ZH\gamma Z coupling when the interference from ggβ†’Ξ³Zβ†’Ξ³β„“βˆ’β„“+gg\to\gamma Z\to\gamma \ell^-\ell^+ process is included. With CP violation in HΞ³ZH\gamma Z coupling, the interference effect leads to a non-vanishing AFBA_{FB}, which is also sensitive to the strong phase differences. The resonant and non-resonant strong phases together make AFB(s^)A_{FB}(\hat{s}) change sign around Higgs mass MHM_H. For phenomenology study, we suggest the integral over one-side mass region below MHM_H to magnify the AFBA_{FB} strength.Comment: 4pages, 3 figures, LHCP2017 proceeding

    A Note on the Nonlinear Attenuation of an Ultrasound Contrast Agent Calculated by Rayleigh-Plesset Equation

    Full text link
    The attenuation of small-amplitude acoustic waves in a suspension containing ultrasound contrast agents (UCAs, coated microbubbles) is determined by the linear oscillation of the UCAs in the medium, which can be estimated via a linear attenuation theory. Recently, several nonlinear phenomena of energy attenuation at very low-intensity of acoustic pressures have been observed experimentally, raising concerns on the validity of the linear attenuation theory. Explanations of the nonlinear phenomenon are still lacking. Particularly, the interpretation of the pressure-dependent attenuation phenomenon is still under debate. In this note, we investigated the energy dissipation of a single UCA via a nonlinear Rayleigh-Plesset equation and used a formula capable of estimating attenuation coefficient due to the nonlinear oscillation of the UCA. The simulation results show the linear oscillation of an UCA at low excitation pressures does not always guarantee the linearity in the energy attenuation. Although nonlinear oscillation of the UCA contributes to the occurrence of nonlinear attenuation phenomena, it is not the only trigger.Comment: 11 page

    Tronqu\'ee Solutions of the Third and Fourth Painlev\'e Equations

    Full text link
    Recently in a paper by Lin, Dai and Tibboel, it was shown that the third and fourth Painlev\'e equations have tronqu\'ee and tritronqu\'ee solutions. We obtain global information about these tronqu\'ee and tritronqu\'ee solutions. We find their sectors of analyticity, their Borel summed representations in these sectors as well as the asymptotic position of the singularities near the boundaries of the analyticity sectors. We also correct slight errors in the paper mentioned
    • …
    corecore