813 research outputs found
Beamspace Aware Adaptive Channel Estimation for Single-Carrier Time-varying Massive MIMO Channels
In this paper, the problem of sequential beam construction and adaptive
channel estimation based on reduced rank (RR) Kalman filtering for
frequency-selective massive multiple-input multiple-output (MIMO) systems
employing single-carrier (SC) in time division duplex (TDD) mode are
considered. In two-stage beamforming, a new algorithm for statistical
pre-beamformer design is proposed for spatially correlated time-varying
wideband MIMO channels under the assumption that the channel is a stationary
Gauss-Markov random process. The proposed algorithm yields a nearly optimal
pre-beamformer whose beam pattern is designed sequentially with low complexity
by taking the user-grouping into account, and exploiting the properties of
Kalman filtering and associated prediction error covariance matrices. The
resulting design, based on the second order statistical properties of the
channel, generates beamspace on which the RR Kalman estimator can be realized
as accurately as possible. It is observed that the adaptive channel estimation
technique together with the proposed sequential beamspace construction shows
remarkable robustness to the pilot interference. This comes with significant
reduction in both pilot overhead and dimension of the pre-beamformer lowering
both hardware complexity and power consumption.Comment: 7 pages, 3 figures, accepted by IEEE ICC 2017 Wireless Communications
Symposiu
A Generalized Framework on Beamformer Design and CSI Acquisition for Single-Carrier Massive MIMO Systems in Millimeter Wave Channels
In this paper, we establish a general framework on the reduced dimensional
channel state information (CSI) estimation and pre-beamformer design for
frequency-selective massive multiple-input multiple-output MIMO systems
employing single-carrier (SC) modulation in time division duplex (TDD) mode by
exploiting the joint angle-delay domain channel sparsity in millimeter (mm)
wave frequencies. First, based on a generic subspace projection taking the
joint angle-delay power profile and user-grouping into account, the reduced
rank minimum mean square error (RR-MMSE) instantaneous CSI estimator is derived
for spatially correlated wideband MIMO channels. Second, the statistical
pre-beamformer design is considered for frequency-selective SC massive MIMO
channels. We examine the dimension reduction problem and subspace (beamspace)
construction on which the RR-MMSE estimation can be realized as accurately as
possible. Finally, a spatio-temporal domain correlator type reduced rank
channel estimator, as an approximation of the RR-MMSE estimate, is obtained by
carrying out least square (LS) estimation in a proper reduced dimensional
beamspace. It is observed that the proposed techniques show remarkable
robustness to the pilot interference (or contamination) with a significant
reduction in pilot overhead
Accurate formation energies of charged defects in solids: a systematic approach
Defects on surfaces of semiconductors have a strong effect on their
reactivity and catalytic properties. The concentration of different charge
states of defects is determined by their formation energies. First-principles
calculations are an important tool for computing defect formation energies and
for studying the microscopic environment of the defect. The main problem
associated with the widely used supercell method in these calculations is the
error in the electrostatic energy, which is especially pronounced in
calculations that involve surface slabs and 2D materials. We present an
internally consistent approach for calculating defect formation energies in
inhomogeneous and anisotropic dielectric environments, and demonstrate its
applicability to the cases of the positively charged Cl vacancy on the NaCl
(100) surface and the negatively charged S vacancy in monolayer MoS2
Product structures for Legendrian contact homology
Legendrian contact homology (LCH) is a powerful non-classical invariant of Legendrian
knots. Linearization makes the LCH computationally tractable at the expense of discarding
nonlinear (and non-commutative) information. To recover some of the nonlinear information
while preserving computability, we introduce invariant cup and Massey products – and,
more generally, an A∞ structure – on the linearized LCH. We apply the products and A∞ structure in three ways: to find infinite families of Legendrian knots that are not isotopic to
their Legendrian mirrors, to reinterpret the duality theorem of the fourth author in terms of
the cup product, and to recover higher-order linearizations of the LCH
Historical impact of technological change on the US mass media advertising expenditure
Historically, the U.S. advertising industry has been experiencing enormous movements as a result of rapid advances in the media technology and the business cycle. In this paper, we study the historical behavior of the U.S. advertising industry, correcting for inflation. We find that the introduction of new media cause structural breaks in the mean growth rates of advertising expenditure for the incumbent media. In addition, we find that random components of media advertising spending follow a long-term equilibrium where the cross-elasticities across newer and older media can show substitution or complementarity patterns depending on the type of audience. We examine the influence of the economic conditions on the aggregated advertising expenditure, and on each media spending. We also measure the impact of the recent takeoff in mobile advertising
Capacity Region of Asynchronous Multiple Access Channels with FTN
This paper studies the capacity region of asynchronous multiple access
channel (MAC) with faster-thanNyquist (FTN) signaling. We first express the
capacity region in the frequency domain. Next, we calculate an achievable rate
region in time domain and prove that it is identical to the capacity region
calculated in the frequency domain. Our analysis confirms that asynchronous
transmission and FTN bring in significant gains
Maxillary protraction in adult cleft lip and palate by a rigid external distraction device with dentoskeletal anchorage
Objective: The objective is to evaluate the effects of maxillary distraction osteogenesis (DO) in an adult patient with unilateral cleft lip and palate (UCLP) by using a rigid external distraction (RED) device with dentoskeletal anchorage. Method: 31-year-old male patient with UCLP with severe maxillary hypoplasia, dolichofacial growth pattern, negative overjet and 1.5 mm openbite. After pre-surgical orthodontic treatment, an intra-oral appliance was modified to prevent extrusion of the molars and clockwise rotation of the mandible. Stainless steel plates were soldered bilaterally to the intra oral appliance at the level of canines. During surgery, miniplates were inserted in the maxillary segment and fixed to the plates of the intra oral appliance with screws. Results: The mean distraction length was 12 mm immediately after DO. SNA increased from 73o to 82o after distraction. A significant advancement of the maxilla and correction of the sagittal Class III skeletal relationship was achieved. The vertical position of the mandible and the face was kept stable, and the soft tissue profile became more balanced. Conclusion: This intra oral appliance design achieved desired skeletal changes during maxillary protraction with RED device in dolichofacial CLP patient. Occlusion and facial profile changes was found to be stable in 1-year follow-up.PubMe
Group Scheduling in a Cellular Manufacturing Shop to Minimise Total Tardiness and nT: a Comparative Genetic Algorithm and Mathematical Modelling Approach
In this paper, family and job scheduling in a cellular manufacturing shop is addressed where jobs have individual due dates. The objectives are to minimise total tardiness and the number of tardy jobs. Family splitting among cells is allowed but job splitting is not. Two optimisation methods are employed in order to solve this problem, namely mathematical modelling (MM) and genetic algorithm (GA). The results showed that GA found the optimal solution for most of the problems with high frequency. Furthermore, the proposed GA is efficient compared to the MM especially for larger problems in terms of execution times. Other critical aspects of the problem such as family preemption only, impact of family splitting on common due date scenarios and dual objective scenarios are also solved. In short, the proposed comparative approach provides critical insights for the group scheduling problem in a cellular manufacturing shop with distinctive cases
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