Intercell Correlations Research Articles

SINR Prediction in Presence of Correlated Shadowing in Cellular Networks

Signal-to-interference-plus-noise ratio (SINR) evaluates the quality of the link between the base station (BS) and the user equipment (UE), taking into account the interference coming from neighboring cells and the thermal noise. Predicting the SINR with good accuracy ensures proper planning and optimization of radio coverage and good estimation of end-user throughput. In this paper, SINR is predicted at any user location based on UE geo-located measurements, using the Kriging technique and assuming that the received signals from serving and interfering cells undergo shadowing fading. Unlike previous works where only the prediction of the received powers is studied, the current functionality also considers the prediction error on the received signals. We consider both spatial correlation of shadowing signals for each cell and also inter-cell correlation and we propose a new model to generate multiple links shadowing signals for the downlink of cellular networks. For validation, we perform Monte-Carlo network simulations in which the shadowing samples are generated based on the proposed model. Results show a good prediction accuracy of the SINR at a new location resulting in a good estimation of the end-user perceived average data rate.

Near-Optimal Detection for Both Data and Sneak-Path Interference in Resistive Memories With Random Cell Selector Failures

Resistive random-access memory is one of the most promising candidates for the next generation of non-volatile memory technology. However, its crossbar array structure causes severe “sneak-path” interference, which also leads to strong inter-cell correlation. Recent works have mainly focused on sub-optimal data detection schemes by ignoring inter-cell correlation and assuming sneak-path interference is independent between different array cells. In this paper, we propose a near-optimal data detection scheme that can approach the performance bound of the optimal detection scheme. Our detection scheme leverages a joint data and sneak-path interference recovery and can use all inter-cell correlations. The proposed scheme is suitable for data detection of large memory arrays with only linear operation complexity.

Overcoming 5G PRACH Capacity Shortfall: Supersets of Zadoff–Chu Sequences With Low-Correlation Zone

5G physical random access channel (PRACH) will use new preamble formats based on short Zadoff-Chu (ZC) sequences to enable new use cases. These formats result however in a PRACH capacity shortfall where the number of sequences available for network planning may just be enough to support few cells without sequence reuse. To overcome this issue, two enlarged constant-amplitude sequence constructions that include ZC sequences, and thus being backward-compatible with the current 5G PRACH design, are presented. Both constructions feature a desirable subset structure from which follows a natural cellular network sequence allocation where each cell-specific sequence subset has a controllable low-correlation zone similar to ZC sequences, and thus enables a similar detection performance inside a cell. The two extensions are meanwhile structurally different and offer different network allocations, as for one, new sequences are distributed among all cells, while for the other, they are in separated cells. With both proposed supersets and the new 5G PRACH formats, hundred-times more cells without sequence reuse can be supported compared to ZC sequences for a moderately larger inter-cell correlation than intra-cell correlation. Simulation results confirm that using the proposed supersets instead of reusing sequences in the network can significantly improve detection performance.

Perfect cellular disorder in a two-dimensional system: Si cells on the 3C-SiC(001) surface

Using scanning tunneling microscopy, we have observed a random orientation of the two possible inter-dimer buckling directions without any intercell correlation on a vacancy-free 3C-SiC(001)-(3×2) surface. The very small surface state dispersions observed by photoemission support the picture of essentially non-interacting (3×2) cells. The perfect cellular disorder, with no intercell correlation, originates from the electron localization that can be inferred from the weak surface state dispersions. Our experimental findings indicate a zero dimensionality of this system.

Precursor structures in ferroelectrics from first-principles calculations

Based on an analysis of the wavevector dependence of lattice instabilities in KNbO3, the existence of a real-space chain-like instability was deduced[1] To further study this instability, we have constructed an ab initio effective Hamiltonian for KNbO3 that reproduces the low-energy Born-Oppenheimer surface. Classical molecular dynamics (MD) simulations yield the observed sequence of ferroelectric phase transitions. The transition temperatures are lower than experiment, especially for the higher temperature transitions. Simulations of the static structure factor reveal features consistent with chain-like correlations and qualitatively reproduce diffuse X-ray scattering measurements. The calculated dynamic structure factor reveals anharmonically stabilized TO vibrational modes that soften along the entire Γ − X line in the Brillouin zone, as the phase transition is approached from above. A real-space analysis of the intercell correlations of the soft-mode coordinate, unambiguously establishes the long-lived dynamic character of these chain-like structures.

Statistical-Mechanical Theory of Systems Composed of Interacting Ellipsoidal Molecules at a Solid Surface

Abstract A statistical-mechanical theory which takes into account translational-translational, orientational-orientational and mixed correlations based upon the method of conditional distribution functions is applied to calculations of the order parameters and the rotational viscosity coefficient (RVC) of a system composed of interacting ellipsoidal molecules near an interacting wall. The calculations have been carried out for cubic close packing with the nearest-neighbor Gay-Berne intermolecular potential and with a (9–3) like orientation-dependent molecule-wall interaction. The theory shows that the number of surface layers which must be taken into account depends more on the character of intercell correlations in the system than on the direct wall-nematic interaction. The equilibrium order parameters and rotational viscosity coefficient at the solid-nematic fluid interface have been calculated.

Conditional distribution function approach to the theory of the solid-nematic-fluid interface.

A statistical-mechanical theory which takes into account translational-translational, orientational-orientational, and mixed correlations, based upon the method of conditional distribution functions, is applied to calculations of the order parameters and surface free energy of a system composed of interacting ellipsoidal molecules near an interacting wall. The calculations have been carried out for cubic close packing with the nearest-neighbor Gay-Berne intermolecular potential and with a (9-3)-like orientation-dependent molecule-wall interaction. The theory shows that the number of surface layers which must be taken into account depends more on the character of intercell correlations in the system than on the direct wall-nematic interaction. The equilibrium order parameter and surface free energy profiles at the solid--nematic-fluid interface have been calculated. It is found that the number of surface layers for the case of a strong interaction between the solid wall and nematic phase and for the case of a weak one is the same and equal approximately four.

Spectral-weight transfer in effective single-band models for the high-Tc cuprates.

The low-energy physics of the Emery model, representing the high-${\mathit{T}}_{\mathit{c}}$ cuprates, can be understood by separating intracell interference within ${\mathrm{CuO}}_{4}$ cells from intercell correlations described by an effective single-band Hubbard model. This decomposition explains the anomalous transfer of spectral intensity from the high- to the low-energy scale, the asymmetry between electron and hole doping, and the breakdown of low-energy sum rules. These features are related to the existence of an antibound charge transfer exciton band, are are very sensitive to the strength of the Coulomb repulsion ${\mathit{U}}_{\mathit{d}}$.

Inelastic neutron scattering in tetragonal KNbO3

Inelastic neutron scattering experiments in tetragonal KNb${\mathrm{O}}_{3}$ show a high anisotropy in some regions of the phonon dispersion relation and the existence of strong one-dimensional intercell correlations between atomic motions along the [100] and [010] directions, in agreement with x-ray diffuse-scattering measurements in the same phase. The transverse phonon modes propagating normally to these directions of strong correlations, that is, with polarization vectors parallel to them, are relatively soft, not only near the zone center but all the way to the zone boundary. Comparison of these results with the Raman, neutron, and x-ray data obtained in the other phases suggests a description of the ferroelectric phase transition mechanism in KNb${\mathrm{O}}_{3}$ in terms of soft modes and dynamic correlations in each phase.

Intercell Corrections for Ionic Motion in Displacement Ferroelectrics

A set of microscopic parameters determined for LiTa${\mathrm{O}}_{3}$ in an earlier paper by comparing dielectric properties with the results of a statistical calculation are analyzed in terms of a point-charge-plus-electronic-polarizability model for the system. The results indicate the existence of very strong intercell correlations for ionic motion to temperatures considerably in excess of the Curie point ${T}_{C}$. These correlations are weak functions of temperatures to the extent that they do not produce deviations from effective-field (e.g., Curie-Weiss) behavior near ${T}_{C}$. Neglect of correlation effects leads to many inconsistencies and indicates that the use of random-phase Lorentz fields in statistical theories for displacement ferroelectrics is qualitatively unsound. Spontaneous polarization for LiTa${\mathrm{O}}_{3}$ is found to be 45% ionic, 55% electronic; the tantalum-oxygen bond is very markedly covalent, with estimated ionic charges of + 0.8 and - 0.6 electronic units, respectively.