Iterative multiuser joint decoding: unified framework andasymptotic analysis

We present a framework for iterative multiuser joint decoding of code-division multiple-access (CDMA) signals, based on the factor-graph representation and on the sum-product algorithm. In this framework, known parallel and serial, hard and soft interference cancellation algorithms are derived in a unified way. The asymptotic performance of these algorithms in the limit of large code block length can be rigorously analyzed by using density evolution. We show that, for random spreading in the large-system limit, density evolution is considerably simplified. Moreover, by making a Gaussian approximation of the decoder soft output, we show that the behavior of iterative multiuser joint decoding is approximately characterized by the stable fixed points of a simple one-dimensional nonlinear dynamical system     

Lie-group method solution for two-dimensional viscous flow between slowly expanding or contracting walls with weak permeability

The non-linear equations of motion describing the laminar, isothermal and incompressible flow in a rectangular domain bounded by two weakly permeable, moving porous walls, which enable the fluid to enter or exit during successive expansions or contractions, are considered. We apply Lie-group method for determining symmetry reductions of partial differential equations. Lie-group method starts out with a general infinitesimal group of transformations under which given partial differential equations are invariant, then, the determining equations are derived. The determining equations are a set of linear differential equations, the solution of which gives the infinitesimals of the dependent and independent variables. After the group has been determined, a solution to the given partial differential equation may be found from the invariant surface condition such that its solution leads to similarity variables that reduce the number of independent variables in the system. Effect of the permeation Reynolds number R_e and the dimensionless wall dilation rate α on self-axial velocity have been studied both analytically and numerically and the results are plotted.     

Approaching the Outage Probability of the Amplify-and-Forward Relay Fading Channel

We study coding techniques for the single-relay non-orthogonal amplify-and-forward half-duplex relay fading channel. Unlike the multiple-antenna case, we show that 2times2 rotations induce large gains in outage probability with no increase in decoding complexity under iterative probabilistic decoding. We compare rotated and unrotated turbo-coded schemes and show that they both perform close to their corresponding outage limits.     

Local electronic properties of AlGaN/GaN heterostructures probed by scanning capacitance microscopy

Local electronic properties in Al_xGa_1−xN/GaN heterostructure field-effect transistor epitaxial layer structures are probed using scanning capacitance microscopy. Acquisition of scanning capacitance images over a wide range of bias voltages combined with theoretical analysis and numerical simulation allows the presence, detailed nature, and possible structural origins of nanometer- to micronscale inhomogeneities in electronic structure to be elucidated. Substantial lateral variations in local threshold voltages for transistor channel formation are observed, at length scales ranging from submicron to >2 μm, and found to arise primarily from local variations in Al_xGa_1−xN layer thickness. Features in electronic structure are also observed that are consistent with the existence of networks of negatively charged threading edge dislocations, as might be formed at island coalescence boundaries during epitaxial growth. The negative charge associated with these structures appears to lead to local depletion of carriers from the channel in the Al_xGa_1−xN/GaN transistor epitaxial layer structure.     

Some electrical properties of wood pulp

The variation with temperature and frequency of the dielectric constant ε′ and the dielectric loss ε″ for sheet wood pulp and ground wood pulp were measured. Also, the effect of the relative humidity on the dielectric behavior was measured for the ground sample at 25°C. For the dry ground wood pulp, the dielectric constant is larger than that for the dry sheet sample. This may be a result of the increase in the surface area, of the decrease in the size of crystals and/or of the decrease in the degree of crystallinity on grinding of the sheet sample. The variation of ε″ with frequency passes through a maximum. From the shift of this maximum with temperature, it is found that the apparent activation energy ΔH for this relaxation is equal to 7.06 kcal/mole and it is attributed to the polarization of the OH groups in the cellulose molecule. From the relation between the dielectric constant and the specific resistivity R_s, the dissociation energy U₀ for the ground wood pulp was calculated. U₀ for this sample below and above 52% RH is 0.315 and 5.13 × 10^?12 erg, respectively. Also, the dissociation energy of Egyptian Ashmouny cotton was calculated. The variation of the electrical conductivity σ with humidity for different types of cellulosic materials is represented graphically.     

Décodage à sortie souple des réseaux de points

We present a universalmse algorithm for lattice decoding in dimensions up to 1024 for both Gaussian and Rayleigh fading channels. This algorithm can be applied to decode high diversity multidimensional rotations. The decoding is performed by a decision feedback equalizer and provides soft output which allows a concatenation of the lattice codes with other type of error-correcting codes. The problem of selecting a good rotation is also considered, and we show that a high dimensional random rotation exhibits very good performance on a Rayleigh fading channel.     

Lattice decoding for joint detection in direct-sequence CDMA systems

A new joint detection method based on sphere packing lattice decoding is presented in this paper. The algorithm is suitable for both synchronous and asynchronous multiple access direct-sequence code-division multiple-access (DS-CDMA) systems, and it may jointly detect up to 64 users with a reasonable complexity. The detection complexity is independent of the modulation size and large M-PAM or M-QAM constellations can be used. Furthermore, a theoretical gain analysis is performed in which the multiple-access system performance is derived from the lattice parameters.     

Lie-group method of solution for steady two-dimensional boundary-layer stagnation-point flow towards a heated stretching sheet placed in a porous medium

The boundary-layer equations for two-dimensional steady flow of an incompressible, viscous fluid near a stagnation point at a heated stretching sheet placed in a porous medium are considered. We apply Lie-group method for determining symmetry reductions of partial differential equations. Lie-group method starts out with a general infinitesimal group of transformations under which the given partial differential equations are invariant. The determining equations are a set of linear differential equations, the solution of which gives the transformation function or the infinitesimals of the dependent and independent variables. After the group has been determined, a solution to the given partial differential equations may be found from the invariant surface condition such that its solution leads to similarity variables that reduce the number of independent variables of the system. The effect of the velocity parameter λ, which is the ratio of the external free stream velocity to the stretching surface velocity, permeability parameter of the porous medium k ₁, and Prandtl number Pr on the horizontal and transverse velocities, temperature profiles, surface heat flux and the wall shear stress, has been studied.     

Biotechnological Production of Xylitol: Enhancement of Monosaccharide Production by Post-Hydrolysis of Dilute Acid Sugarcane Hydrolysate

Dilute-acid hydrolysis pretreatment of sugarcane bagasse resulted in release of 48% (18.4 g/L) of the xylan in the hemicellulose fraction into the hydrolysate as monomeric xylose. In order to enhance the recuperation of this monomer, a post-hydrolysis stage consisted of thermal treatment was carried out. This treatment resulted in an increase in xylose release of 62% (23.5 g/L) of the hemicellulose fraction. Original and post-hydrolysates were concentrated to the same levels of monomeric xylose in the fermentor feed. During the fermentation process, cellular growth was observed to be higher in the post-hydrolysate (3.5 g/L, Y _x/s?=?0.075 g cells/g xylose) than in the original hydrolysate (2.9 g/L, Y _x/s?=?0.068 g cells/g xylose). The post-treated hydrolysate required less concentration of sugars resulting in a lower concentration of fermentation inhibitors, which were formed primarily in the dilute acid hydrolysis step. Post-hydrolysis step led to a high xylose–xylitol conversion efficiency of 76% (0.7 g xylitol/g xylose) and volumetric productivity of 0.68 g xylitol/L h when compared to 71% (0.65 g xylitol/g xylose and productivity of 0.61 g xylitol/L h) for the original hemicellulosic hydrolysate.     

Space–Time Coding Techniques With Bit-Interleaved Coded Modulations for MIMO Block-Fading Channels

The space-time bit-interleaved coded modulation (ST-BICM) is an efficient technique to obtain high diversity and coding gain on a block-fading multiple-input multiple-output (MIMO) channel. Its maximum-likelihood (ML) performance is computed under ideal interleaving conditions, which enables a global optimization taking into account channel coding. Thanks to a diversity upper bound derived from the Singleton bound, an appropriate choice of the time dimension of the space-time coding is possible, which maximizes diversity while minimizing complexity. Based on the analysis, an optimized interleaver and a set of linear precoders, called dispersive nucleo algebraic (DNA) precoders are proposed. The proposed precoders have good performance with respect to the state of the art and exist for any number of transmit antennas and any time dimension. With turbo codes, they exhibit a frame error rate which does not increase with frame length.