Convergence of Power Control in a Random Channel Environment

In this paper, we study the Foschini Miljanic algorithm, which was originally proposed in a static channel environment. We investigate the algorithm in a random channel environment, study its convergence properties and apply the Gerschgorin theorem to derive sufficient conditions for the convergence of the algorithm. We apply the Foschini and Miljanic algorithm to cellular networks and derive sufficient conditions for the convergence of the algorithm in distribution and validate the results with simulations. In cellular networks, the conditions which ensure convergence in distribution can be easily verified.

Performance Analysis of User Selected Subband Channel Quality Indicator Feedback Scheme of LTE

Frequency-domain scheduling and rate adaptation have helped next generation orthogonal frequency division multiple access (OFDMA) based wireless cellular systems such as Long Term Evolution (LTE) achieve significantly higher spectral efficiencies. To overcome the severe uplink feedback bandwidth constraints, LTE uses several techniques to reduce the feedback required by a frequency-domain scheduler about the channel state information of all subcarriers of all users. In this paper, we analyze the throughput achieved by the User Selected Subband feedback scheme of LTE. In it, a user feeds back only the indices of the best M subbands and a single 4-bit estimate of the average rate achievable over all selected M subbands. In addition, we compare the performance with the subband-level feedback scheme of LTE, and highlight the role of the scheduler by comparing the performances of the unfair greedy scheduler and the proportional fair (PF) scheduler. Our analysis sheds several insights into the working of the feedback reduction techniques used in LTE.

Bayesian Learning for Joint Sparse OFDM Channel Estimation and Data Detection

The impulse response of a typical wireless multipath channel can be modeled as a tapped delay line filter whose non-zero components are sparse relative to the channel delay spread. In this paper, a novel method of estimating such sparse multipath fading channels for OFDM systems is explored. In particular, Sparse Bayesian Learning (SBL) techniques are applied to jointly estimate the sparse channel and its second order statistics, and a new Bayesian Cramer-Rao bound is derived for the SBL algorithm. Further, in the context of OFDM channel estimation, an enhancement to the SBL algorithm is proposed, which uses an Expectation Maximization (EM) framework to jointly estimate the sparse channel, unknown data symbols and the second order statistics of the channel. The EM-SBL algorithm is able to recover the support as well as the channel taps more efficiently, and/or using fewer pilot symbols, than the SBL algorithm. To further improve the performance of the EM-SBL, a threshold-based pruning of the estimated second order statistics that are input to the algorithm is proposed, and its mean square error and symbol error rate performance is illustrated through Monte-Carlo simulations. Thus, the algorithms proposed in this paper are capable of obtaining efficient sparse channel estimates even in the presence of a small number of pilots.

A large conductance Ca2+-activated K+ channel in alpha T3-1 pituitary gonadotrophs

The Ca2+-activated K+ channel in endocrine cells is responsible for membrane hyperpolarization and rhythmic firing of action potentials. The probability of opening of this channel is sensitive to intracellular-free Ca2+ concentration. In this study we have identified one such large conductance Ca2+-activated K+ channel in alpha T3-1 pituitary gonadotroph cell. This channel is ohmic with a unit conductance of 170 pS in symmetrical KCl (135 mM) and its current reverses near zero millivolts. When more than one channel is present in the patch membrane they open and close independent of each other, exhibiting no cooperativity between them as expected of a binomial distribution. The regulatory mechanism of this channel in modulating hormone secretion from alpha T3-1 gonadotroph cells is indicated.

Blind separation of multiple co-channel BPSK signals arriving at an antenna array

In this letter, we propose a method for blind separation of d co-channel BPSK signals arriving at an antenna array. Our method involves two steps. In the first step, the received data vectors at the output of the array is grouped into 2d clusters. In the second step, we assign the 2d d-tuples with ±1 elements to these clusters in a consistent fashion. From the knowledge of the cluster to which a data vector belongs, we estimate the bits transmitted at that instant. Computer simulations are used to study the performance of our method

Source localization in a partially known shallow?water channel

The source localization in shallow water is beset with problems arising from the presence of a large number of correlated multipaths. Nevertheless, given a complete knowledge of the water channel it is definitely possible to localize a source. A complete knowledge of the channel, however, is rarely available under most practical conditions. A new approach is proposed wherein the bottom reflection coefficients are not required; hence the bottom conditions need not be known. Further, because of the use of signal subspace for localization, the proposed approach is robust against the background noise (-20 dB) and channel depth uncertainty (10 lambda). All these nice features of the proposed approach are possible only when the array size is large (>40 sensors). (C) 1995 Acoustical Society of America.

A molecular dynamics study and molecular level explanation of pressure dependence of ionic conductivity of potassium chloride in water

Experimental ionic conductivity of different alkali ions in water shows markedly different dependences on pressure. Existing theories such as that of Hubbard-Onsager are unable to explain these dependences on pressure of the ionic conductivity for all ions. We report molecular dynamics investigation of potassium chloride solution at low dilution in water at several pressures between 1 bar and 2 kbar. Two different potential models have been employed. One of the models successfully reproduces the experimentally observed trend in ionic conductivity of K+ ions in water over the 0.001-2 kbar range. We also propose a theoretical explanation, albeit at a qualitative level, to account for the dependence of ionic conductivity on pressure in terms of the previously studied Levitation Effect. It also provides a microscopic picture in terms of the pore network in liquid water.

Phase modification of ammonium nitrate by potassium salts

Modification of the room temperature phase (IV-III) of ammonium nitrate (AN) has been attempted using a variety of potassium salts namely, KF, KCl, KI, KNO3, K2CO3, K2SO4, KSCN and K2Cr2O7. No phase transition was observed when AN containing 1-2% by mass of these potassium salts is heated from room temperature (25 degrees C) onwards in DTA and DSC scans, but the linear expansion due to phase transition was still observable in TMA measurements. Complete arrest of the linear expansion occurs only when a higher concentration of the additive is used. Similarly, in thermal cycling experiments, complete phase modification in the temperature range -80 to 100 degrees C occurs only with a higher percentage of the potassium salt. The extent of modification, however, is found to be dependent both on the concentration, and the type of the anion. Potassium dichromate when used as an additive modifies the phase as well as the decomposition pattern of AN.

Potassium titanyl phosphate and its isomorphs: Growth, properties, and applications

Potassium titanyl phosphate (KTP) and its isomorphs have received enormous attention in the last 2 decades. In particular, KTP assumes importance due to its large nonlinear optic and electrooptic coefficients together with the broad thermal and angular acceptance for second harmonic generation. This article provides an overview of the material aspects, structural, physical, and chemical properties and device feasibility of the KTP family of crystals. Some of the current areas of research and development along with their significance in understanding the physical properties as well as device applications are addressed. Optical waveguide fabrication processes and characteristics with their relevance to the present-day technology are highlighted. Studies performed so far have enabled us to understand the fundamental aspects of these materials and what needs to be pursued vigorously is the exploitation of their device applications to the maximum extent.

Transplanting the n-terminus from Kv1.4 to Kv1.1 generates an inwardly rectifying K+ channel

A chimeric channel, 4N/1, was generated from two outwardly rectifying K+ channels by linking the N-terminal cytoplasmic domain of hKv1.4 (N terminus ball and chain of hKv1.4) with the transmembrane body of hKvl.l (Delta 78N1 construct of hKvl.l). The recombinant channel has properties similar to the six transmembrane inward rectifiers and opens on hyperpolarization with a threshold of activation at -90 mV. Outward currents are seen on depolarization provided the channel is first exposed to a hyperpolarizing pulse of -100mV or more. Hyperpolarization at and beyond -130mV provides evidence of channel deactivation. Delta 78N1 does not show inward currents on hyperpolarization but does open on depolarizing from -80mV with characteristics similar to native hKvl.l. The outward currents seen in both Delta 78N1 and 4N/1 inactivate slowly at rates consistent with C-type inactivation. The inward rectification of the 4N/1 chimera is consistent with the inactivation gating mechanism. This implies that the addition of the N-terminus from hKv1.4 to hKvl.l shifts channel activation to hyperpolarizing potentials. These results suggest a mechanism involving the N-terminal cytoplasmic domain for conversion of outward rectifiers to inward rectifiers. (C) 1999 Lippincott Williams & Wilkins.

Entrapment of a Water Wire in a Hydrophobic Peptide Channel with an Aromatic Lining

A one-dimensional water wire has been characterized by X-ray diffraction in single crystals of the tripeptide Ac-Phe-Pro-Trp-OMe. Crystals in the hexagonal space group P6(5) reveal a central hydrophobic channel lined by aromatic residues which entraps an approximately linear array of hydrogen bonded water molecules. The absence of any significant van der Waals contact with the channel walls suggests that the dominant interaction between the ``water wire'' and ``peptide nanotube'' is electrostatic in origin. An energy difference of 16 KJmol(-1) is estimated for the distinct orientations of the water wire dipole with respect to the macrodipole of the peptide nanotube. The structural model suggests that Grotthuss type proton conduction may, through constricted hydrophobic channels, be facilitated by concerted, rotational reorientation of water molecules.

An experimental study of reverse transition in two-dimensional channel flow

An experimental investigation on reverse transition from turbulent to laminar flow in a two-dimensional channel was carried out. The reverse transition occurred when Reynolds number of an initially turbulent flow was reduced below a certain value by widening the duct in the lateral direction. The experiments were conducted at Reynolds numbers of 625, 865, 980 and 1250 based on half the height of the channel and the average of the mean velocity. At all these Reynolds numbers the initially turbulent mean velocity profiles tend to become parabolic. The longitudinal and vertical velocity fluctuations ($\overline{u^{\prime 2}}$ and $\overline{v^{\prime 2}}$) averaged over the height of the channel decrease exponentially with distance downstream, but $\overline{u^{\prime}v^{\prime}} $ tends to become zero at a reasonably well-defined point. During reverse transition $\overline{u^{\prime}}\overline{v^{\prime}}/\sqrt{\overline{u^{\prime 2}}}\sqrt{\overline{v^{\prime 2}}}$ also decreases as the flow moves downstream and Lissajous figures taken with u’ and v’ signals confirm this trend. There is approximate similarly between $\overline{u^{\prime 2}} $ profiles if the value of $\overline{u^{\prime 2}_{\max}} $ and the distance from the wall at which it occurs are taken as the reference scales. The spectrum of $\overline{u^{\prime 2}} $ is almost similar at all stations and the non-dimensional spectrum is exponential in wave-number. All the turbulent quantities, when plotted in appropriate co-ordinates, indicate that there is a definite critical Reynolds number of 1400±50 for reverse transition.

Flow of a stratified fluid in a wavy channel

The flow of a stratified fluid in a channel with small and large deformations is investigated. The analogy of this flow with swirling flow in tubes with non-uniform cross-sections is studied. The flow near the wall is blocked when the Froude number takes certain critical values. The possibility of preventing the stagnation zones in the flow field is also discussed

Texture evolution in an Al-Cu alloy during equal channel angular pressing: the effect of starting microstructure

In this article, the effect of initial microstructure on the texture evolution in 2014 Al alloy during equal channel angular pressing (ECAP) through route A has been reported. Three heat treatment conditions were chosen to generate the initial microstructures, namely (i) the recrystallization anneal (as-received), (ii) solution treatment at 768 K for 1 h, and (iii) solution treatment (768 K for 1 h) plus aging at 468 K for 5 h. Texture analyses were performed using orientation distribution function (ODF) method. The texture strength after ECAP processing was different for the three samples in the order, solutionised > solutionised plus aged condition > as-received. The prominent texture components were A (E) /(A) over bar (E) and B(E)/(B) over bar (E) in addition to several weaker components for the three materials. The strong texture evolution in solutionised condition has been attributed to higher strain hardening of the matrix due to higher amount of solute. In case of the as-received as well as solutionised plus aged alloy, the weaker texture could be due to the strain scattering from extensive precipitate fragmentation and dissolution during ECAP.