Bit-serial window partitioning algorithm for stack filtering

The authors introduce a new bit-serial algorithm for stack filtering, designated as the bit-serial window partitioning algorithm. It is shown that the proposed algorithm can achieve very important savings over the conventional bit-serial binary-tree search algorithm, in terms of the computational speed. This improved efficiency is obtained by evaluating the Boolean function at thresholds corresponding to the sample values within the filter window, and by taking advantage of the ordering information associated with the threshold sequences     

Mixed convection boundary layer flow along vertical thin needles: Assisting and opposing flows

The problem of steady laminar mixed convection boundary layer flow of an incompressible viscous fluid along vertical thin needles for both assisting and opposing flow cases is considered in this paper. The transformed boundary layer equations are solved numerically using an implicit finite-difference scheme known as the Keller-box method. Numerical computations are carried out for various values of the dimensionless parameters of the problem, namely the mixed convection parameter λ and the parameter a representing the needle size, with Prandtl number, Pr = 0.7. It has been found that the flow and heat transfer characteristics are significantly influenced by these parameters.     

Electrical and dielectric properties of lithium manganate nanomaterials doped with rare-earth elements

Substituted LiR_xMn_2 − xO₄ (R = La³⁺, Ce³⁺_, Pr³⁺ and x = 0.00 − 0.20) nanoparticles are prepared by the sol–gel method and the consequent changes in their lattice structure, dielectric and electrical parameters are determined by XRD, ED-XRF, SEM, LCR meter bridge and dc electrical resistivity measurements. Diffraction data show that the samples are single-phase spinel materials with crystallites sizes between 21 and 38 nm. The lattice parameter, cell volume and X-ray density are found to be affected by doping the Li-manganate with the rare-earth elements. The ED-XRF analysis confirms the stoichiometric composition of the synthesized samples and SEM reveals their morphology. Calculated values of the dielectric constant (?) and the dielectric loss (tan δ) decrease with the frequency of the applied field. This is attributed to Maxwell–Wagner polarization. Replacement of manganese by the rare-earth elements results in an improvement in the structural stability of the material, which is considered to be useful for enhancement of the cycleability of the compounds when used in lithium rechargeable batteries, and increases significantly the values of ? and tan δ (except for Ce). Lithium manganate nanomaterials with high ? and low tan δ may be attractive for application in memory storage devices.     

Ground plane impact on quadrifilar helix antenna performance with respect to deployment heights

Quadrifilar helix antenna (QHA) has its applications in satellite communications. This paper presents the performance optimisation of input and radiation characteristics of QHA in the presence of infinite and finite metallic ground planes. For the infinite ground plane, it has been observed that input parameters such as impedance and voltage standing wave ratio (VSWR) are stable, and the antenna has broader half power beamwidth (HPBW). Smaller metallic platforms that act as finite ground planes produce better 3‐dB axial ratio beamwidth and boresight axial ratio. Deployment of QHA on smaller metallic platforms such as nanosatellites and CubeSats enhances the circularly polarised beamwidth of the antenna with improved boresight axial ratio. However, on large low earth orbit (LEO) satellites, stable input characteristics and broader HPBW have been achieved at the cost of narrow circularly polarised beamwidth and degraded boresight axial ratio.     

Analytical expressions for intermodulation distortion of a MESFET small-signal amplifier using the nonlinear Volterra series

Using the nonlinear Volterra series representation, analytical expressions for the third-order intermodulation distortion power and intercept point for a MESFET small-signal amplifier are derived when its equivalent circuit is bilateral and includes the gate-to-drain capacitance (C_gd) explicitly as a nonlinear element. Previously developed analytical expressions treated C_gd as a linear element or incorporated it as a part of gate-to-source and drain-to-source capacitances (C_gs and C_ds). These new analytical expressions are then compared with experimental data and good agreement is obtained. The analytical expressions are also used to study the variation of intermodulation distortion with input power and frequency, and the effect of the individual nonlinear elements in the MESFET’s equivalent circuit.     

Lowpass and bandpass transadmittance filter using operational amplifier pole

A new topology simultaneously implementing lowpass (LP) and bandpass (BP) transadmittance filtering signals using a single operational amplifier (OA), one capacitor, and two resistors is presented. The input impedance is very high which is essential for cascading without employment of buffers. The circuit uses absolute minimum number of active and passive components. The filter employs pole-model of OA and as such has acquired suitability for extended frequency operation. The circuit permits separate adjustment of natural frequency (ω₀) and quality factor (Q) in an orthogonal manner. The circuit has low sensitivity figures unlike the reported single amplifier biquads. The PSPICE simulation results are included.     

Double-pass L-band EDFA with enhanced noise figure characteristics

A new double-pass long wavelength band erbium-doped fiber amplifier with enhanced noise figure characteristics is demonstrated by adding a short length of forward pumped erbium-doped fiber (EDF) in front of a double-pass amplifier. Compared with the conventional double-pass amplifier, the new amplifier provides noise figure improvement of about 0.8 to 6.0 dB over the flat-gain region from 1568 to 1600 nm. Since the optical circulator prevents the amplified signal and backward amplified spontaneous emission from propagating into the EDF, the population inversion of the input part of the amplifier is hardly affected by the intense lights, therefore, the noise figure could be kept low. The new double-pass system has achieved a flat-gain output at about 33.5 dB, which is 13.5 dB higher than that of the single-pass system with gain variation less than 1.3 dB at the flat-gain region. The noise figure varies from 5.9 to 6.6 dB in this region.     

Broad-band SiGe MMICs for phased-array radar applications

This paper reports the performances of several broad-band monolithic SiGe monolithic microwave integrated circuits (MMICs) suitable for phased-array radar applications. The amplitude and phase control MMIC designs are based on an optimized SiGe p-i-n diode offered by the IBM 5HP SiGe foundry process. Utilizing this diode, several control circuitries including a broad-band (1-20-GHz) monolithic single-pole double-throw switch, a five-port transfer switch, a 6-bit phase shifter, and a 5-bit attenuator, all operating over 7-11 GHz, are designed. Also, the design and performance of an SiGe heterojunction bipolar transistor variable-gain cascode amplifier that combines the functionality of an amplifier and an attenuator into one MMIC is described.     

Software‐defined networking approach for enhanced evolved packet core network

The evolved packet core (EPC) network is the mobile network standardized by the 3rd Generation Partnership Project and represents the recent evolution of mobile networks providing high‐speed data rates and on‐demand connectivity services. Software‐defined networking (SDN) is recently gaining momentum in network research as a new generation networking technique. An SDN‐based EPC is expected to introduce gains to the EPC control plane architecture in terms of simplified, and perhaps even software‐based, vendor independent infrastructure nodes. In this paper, we propose a novel SDN‐based EPC architecture along with the protocol‐level detailed implementation and provide a mechanism for identifying information fields exchanged between SDN‐EPC entities that maintains correct functionality with minimal impact on the conventional design. Furthermore, we present the first comprehensive network performance evaluation for the SDN‐based EPC versus the conventional EPC and provide a comparative analysis of 2 networks performances identifying potential bottlenecks and performance issues. The evaluation focuses on 2 network control operations, namely, the S1‐handover and registration operations, taking into account several factors, and assessing performance metrics such as end‐to‐end delay (E2ED) for completion of the respective control operation, and EPC nodes utilization figures.