Time and Location Aware Mobile Data Pricing

Mobile users' correlated mobility and data consumption patterns often lead to severe cellular network congestion in peak hours and hot spots. This paper presents an optimal design of time and location aware mobile data pricing, which incentivizes users to smooth traffic and reduce network congestion. We derive the optimal pricing scheme through analyzing a two-stage decision process, where the operator determines the time and location aware prices by minimizing his total cost in Stage I, and each mobile user schedules his mobile traffic by maximizing his payoff (i.e., utility minus payment) in Stage II. We formulate the two-stage decision problem as a bilevel optimization problem, and propose a derivative-free algorithm to solve the problem for any increasing concave user utility functions. We further develop low complexity algorithms for the commonly used logarithmic and linear utility functions. The optimal pricing scheme ensures a win-win situation for the operator and users. Simulations show that the operator can reduce the cost by up to 97.52% in the logarithmic utility case and 98.70% in the linear utility case, and users can increase their payoff by up to 79.69% and 106.10% for the two types of utilities, respectively, comparing with a time and location independent pricing benchmark. Our study suggests that the operator should provide price discounts at less crowded time slots and locations, and the discounts need to be significant when the operator's cost of provisioning excessive traffic is high or users' willingness to delay traffic is low.Comment: This manuscript serves as the online technical report of the article accepted by IEEE Transactions on Mobile Computin

Linear One-Bit Precoding in Massive MIMO: Asymptotic SEP Analysis and Optimization

This paper focuses on the analysis and optimization of a class of linear one-bit precoding schemes for a downlink massive MIMO system under Rayleigh fading channels. The considered class of linear one-bit precoding is fairly general, including the well-known matched filter (MF) and zero-forcing (ZF) precoding schemes as special cases. Our analysis is based on an asymptotic framework where the numbers of transmit antennas and users in the system grow to infinity with a fixed ratio. We show that, under the asymptotic assumption, the symbol error probability (SEP) of the considered linear one-bit precoding schemes converges to that of a scalar ``signal plus independent Gaussian noise'' model. This result enables us to provide accurate predictions for the SEP of linear one-bit precoding. Additionally, we also derive the optimal linear one-bit precoding scheme within the considered class based on our analytical results. Simulation results demonstrate the excellent accuracy of the SEP prediction and the optimality of the derived precoder.Comment: 5 pages, 2 figures, accepted for publication at SPAWC 202

Asymptotic SEP Analysis and Optimization of Linear-Quantized Precoding in Massive MIMO Systems

A promising approach to deal with the high hardware cost and energy consumption of massive MIMO transmitters is to use low-resolution digital-to-analog converters (DACs) at each antenna element. This leads to a transmission scheme where the transmitted signals are restricted to a finite set of voltage levels. This paper is concerned with the analysis and optimization of a low-cost quantized precoding strategy, referred to as linear-quantized precoding, for a downlink massive MIMO system under Rayleigh fading. In linear-quantized precoding, the signals are first processed by a linear precoding matrix and subsequently quantized component-wise by the DAC. In this paper, we analyze both the signal-to-interference-plus-noise ratio (SINR) and the symbol error probability (SEP) performances of such linear-quantized precoding schemes in an asymptotic framework where the number of transmit antennas and the number of users grow large with a fixed ratio. Our results provide a rigorous justification for the heuristic arguments based on the Bussgang decomposition that are commonly used in prior works. Based on the asymptotic analysis, we further derive the optimal precoder within a class of linear-quantized precoders that includes several popular precoders as special cases. Our numerical results demonstrate the excellent accuracy of the asymptotic analysis for finite systems and the optimality of the derived precoder.Comment: 58 pages, 8 figures, submitted for possible publicatio

Analysis of overburden layer thickness influence on dynamic response of concrete face rock-fill dam

In the past, when performing dynamic response analysis of dams on deep overburden, the dam body and the overburden have often been discussed separately. In this paper, the overburden and the dam body are considered as a whole, and the dynamic response analysis is carried out by using a completely nonlinear dynamic analysis method. From the acceleration of the earth’s surface, the displacement of the dam, and the stress distribution of the panel, the dynamic response of the structure is shown to increase first and then decrease with increasing cover thickness, and the overburden layer thickness corresponding to the extreme point is called the critical thickness. The results obtained in this study can provide a design basis for a face rock-fill dam built on a deep overburden layer

Tris[tris­(1,10-phenanthroline-κ2 N,N′)iron(II)] dodeca­tungstoferrate dihydrate

The title compound, [Fe(C12H8N2)3]3[FeW12O40]·2H2O, was prepared under hydro­thermal conditions. The discrete Keggin-type [FeW12O40]6− heteropolyoxoanion has threefold symmetry, with the FeII atom located on the threefold rotation axis. The central FeO4 tetra­hedron in the anion shares its O atoms with four W3O13 trinuclear units, each of which is made up of three edge-shared WO6 octa­hedral units. The FeII atom in the complex cation, viz [Fe(phen)3]2+ (phen is 1,10-phen­anthroline), shows a slightly distorted octa­hedral geometry defined by six N atoms from three phen ligands. The polyoxoanions pack together with the cations, with the disordered water mol­ecules located in voids; the site occupancy factor for each water O atom is 0.33

Quantum interference effect in electron tunneling through a quantum-dot-ring spin valve

Spin-dependent transport through a quantum-dot (QD) ring coupled to ferromagnetic leads with noncollinear magnetizations is studied theoretically. Tunneling current, current spin polarization and tunnel magnetoresistance (TMR) as functions of the bias voltage and the direct coupling strength between the two leads are analyzed by the nonequilibrium Green's function technique. It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling. We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR. For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively