An improved residual frequency offset estimation scheme for OFDM based WLAN systems

Coarse frequency offset estimate and tracking of residual frequency offset are two crucial stages for frequency synchronization in OFDM based WLAN systems. An improved frequency offset estimation scheme is proposed for tracking residual offset. The estimation scheme is dependent on the position of an OFDM symbol in a frame.     

Modified CAZAC Sequence Based Timing Synchronization Scheme for OFDM System

Wireless Personal Communications - Active queue management schemes are used to reduce the number of dropped packets at the routers. Random early detection uses dropping probability which is...     

Creep Life Degradation and Microstructure Degeneration in a Low-Pressure Turbine Blade of a Military Aircraft Engine

Journal of Failure Analysis and Prevention - Military aircraft engines operate under arduous environmental conditions with rapid throttle excursions as a part of its mission requirements. Life of...     

User‐Friendly [(Diglyme)NiBr2]‐Catalyzed Direct Alkylations of Heteroarenes with Unactivated Alkyl Halides through C?H Bond Cleavages

A nitrogen and phosphorus ligand‐free catalytic system derived from inexpensive [(diglyme)NiBr₂] allowed for efficient direct C H bond alkylations of heteroarenes with unactivated β‐hydrogen‐containing alkyl halides under basic reaction conditions.     

Effect of CeO<Subscript>2</Subscript> on dielectric,ferroelectric and piezoelectric properties of PMN–PT (67/33) compositions

Lead magnesium niobate–lead titanate [Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃] powders doped with different mole % of CeO₂ were prepared by a modified columbite route with compositions corresponding to morphotropic phase boundary (MPB) region. These powders were calcined at 800 °C for 4 h and circular test specimens were prepared by uniaxial pressing. The specimens were sintered at 1150 °C/2 h, poled at 2 kV/mm d.c. voltage and were characterized for dielectric, ferroelectric and piezoelectric properties. It was observed that the piezoelectric and ferroelectric properties initially increase up to 2 mol% of ceria addition and then decrease with increase in ceria concentration. The diffusivity of the dielectric curves increases with increase in ceria concentration. The decrease in Curie temperature was observed from 173 °C corresponding to pure PMN–PT to a temperature of 138 °C for 10 mol% of ceria addition.     

Dielectric, ferroelectric and piezoelectric properties of (1 − x)[Pb0.91La0.09(Zr0.60Ti0.40)O3]–x[Pb(Mg1/3Nb2/3)O3], 0 ≤ x ≤ 1

The dielectric, ferroelectric, and piezoelectric properties of ceramic materials of compositions (1 − x)[Pb_0.91La_0.09(Zr_0.60Ti_0.40)O₃]–x[Pb(Mg_1/3Nb_2/3)O₃], x = (0, 0.2, 0.4, 0.6, 0.8, and 1.0) were studied. The above compositions were prepared by mixing the individual Pb_0.91La_0.09(Zr_0.60Ti_0.40)O₃ (PLZT) and Pb(Mg_1/3Nb_2/3)O₃ (PMN) powders in order to design materials with different combination of piezo and dielectric properties. The powders were calcined at 850 °C for 4 h. The presence of various phases in the calcined powders was characterized by X-ray diffraction (XRD) technique. The compacts were prepared by uniaxial pressing and were sintered at 1250 °C for 2 h. The sintered compacts were electroded, poled at 2 kV/mm dc voltage and their dielectric, ferroelectric, and piezoelectric properties were measured. In general, it was observed that the dielectric constant, loss factor and the slimness of the ferroelectric curves increase with the PMN content while the remnant polarization, saturation polarization, and the coercive fields were decreased. It is now possible to design materials with a wide combination of d ₃₃, K, and loss factor by varying PLZT and PMN ratio.     

A New Timing Synchronization Metric for OFDM Based WLAN Systems

A new timing synchronization scheme for Orthogonal Frequency Division Multiplexing (OFDM) based Wireless Local Area Networks (WLANs) is presented. Specifically, use of one long OFDM symbol in the frame format of IEEE802.11a is suggested for coarse timing synchronization. A new timing metric has been proposed which results in significant improvement in performance compared to the results reported.     

Ferroelectric, dielectric and piezoelectric properties of Pb1?xCex(Zr0.60Ti0.40)O3, 0?≤?x?≤?0.08

The ferroelectric, dielectric and piezoelectric properties of compositions Pb_1−x Ce _x (Zr_0.60Ti_0.40)O₃, (x = 0.0, 0.01, 0.02, 0.04, 0.06 and 0.08) are studied. The above compositions are prepared from their constituent oxides, calcined at 900 °C for 4 h and various phases present are characterized by X-ray diffraction (XRD) technique. The above powders are uniaxially pressed into circular compacts, sintered at 1,250 °C for 2 h, electroded, poled at 2 kV/mm D.C. voltage and their electrical properties are measured. The XRD analysis shows the presence of rhombohedral phase up to 2 mol% ceria while tetragonal phase found at higher concentrations. It is observed that the ferroelectric, dielectric and piezoelectric properties increase with the addition of ceria with a maximum at 2 mol% and then decreases. The higher piezo properties associated with low ceria concentration are attributed to rhombohedral phase.