PAPR Reduction for Improved Efficiency of OFDM Modulation for Next Generation Communication Systems

Highly linear power amplifiers are required for transferring   large amount of data for future communication. Orthogonal frequency division multiplexing (OFDM) provides high data rate transmission capability with robustness to radio channel impairments. It has been widely accepted for future communication for different services. But, it suffers from high value of peak-to-average power ratio (PAPR). High value of PAPR drives high power amplifier into its saturation region and causes it to operate in the nonlinear region.  In this paper, comparative study of four different PAPR reduction techniques: clipping and filtering (CF), selective mapping  method (SLM), partial transmit sequence (PTS) and DFT- spread technique  have been done. Mathematical modeling and Matlab simulations have been performed to arrive at the results with 4 QAM modulation format and 1024 number of sub carriers. At 0.01 % of complementary cumulative distribution function (CCDF) significant reduction of 11.3, 3.5, 3.4 and 1.0 dB have been obtained with DFT- spread, SLM, PTS and CF techniques respectively

Formulae for determining heterodyne system spurious frequencies that coincide with desired output frequency

In this paper, formulae to determine the lowest order and other higher order spurious frequencies that coincide with desired output signal frequencies of mixers have been derived. The proposed formulae give general expressions that are suitable for any order of heterodyne mixing. The formulae have been verified using a suitable example and compared with the simulation results obtained through the radio frequency simulation software of Advanced Design System. The formulae directly reveal the order of the troublesome spurious frequencies that the designers would encounter in heterodyne systems. In comparison with these direct formulae, the results of existing spurious analysis software are based on the maximum order of simulation carried out. Based on these simulations, the coinciding spurious components have to be manually sorted out. Proposed formulae are quick tools used by the microwave system and circuit designers for choosing and finalizing heterodyne frequencies in their designs without the need for any simulations

Fluorometric investigation of interaction of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine with bovine serum albumin

Interaction of 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ) with a model transport protein, bovine serum albumin (BSA), has been studied using steady state fluorescence and fluorescence anisotropy experiments. Upon binding with BSA, the charge transfer (CT) fluorescence exhibits appreciable hypsochromic shift along with an enhancement in the fluorescence intensity. Gradual addition of BSA leads to the marked increase in the fluorescence anisotropy (r). From the high value of fluorescence anisotropy (r=0.30) it is argued that the probe molecule is located in motionally restricted environment of the protein. Addition of urea to the protein bound AODIQ leads to the decrease in fluorescence intensity as well as fluorescence anisotropy (r) indicating the release of AODIQ molecule to the aqueous buffer medium, thus supporting the idea that the protein, in its native form, binds with the probe. The binding constant and free energy change (ΔG0) for the interaction of AODIQ with BSA have been evaluated from relevant fluorescence data. Polarity of the microenvironment has been determined from a comparison of the variation of fluorescence property of the probe in dioxane-water mixture with varying composition

Intersystem crossing (ISC) in DMABN and DMABA: laser induced optoacoustic spectroscopy and semi-empirical (AM1) calculations

The individual contribution of the intersystem crossing (ISC) process in the total non-radiative deactivation ofthe excited fluorophores, p-N,N-dimethylaminobenzonitrile (DMABN) and p-N,N-dimethylaminobenzaldehyde(DMABA) was determined by laser-induced optoacoustic spectroscopy (LIOAS). It was noted that, for DMABN, the ISC yield is almost insensitive to the solvent polarity, while, it is highly solvent dependent for DMABA. Semi-empirical (AM1) calculations have been performed to optimize the ground state geometry of both the fluorophores. The AM1-SCI (singly excited configuration interaction) method has been adopted to get the energies and the dipole moments of their excited states. From the calculated oscillator strengths for the optical transitions and also from absorption studies in solvents of different polarity it is revealed that DMABN is excited to the S<SUB>2</SUB> state and DMABA to the S<SUB>3</SUB> state selectively with a laser beam of 320 nm. The experimental results for the large variation of the ISC yield (Φ<SUB>ISC</SUB>) in DMABA has been ascribed to the reordering of the nΠ* and ΠΠ* states with a change in the solvent polarity

Photophysical study of 3-acetyl-4-oxo-6, 7-dihydro-12H-indolo [2, 3-a] quinolizine in biomimetic reverse micellar nanocavities: a spectroscopic approach

Photophysical properties of 3-acetyl-4-oxo-6,7-dihydro-12H-indolo[2,3-a]quinolizine (AODIQ), a bioactive molecule, has been investigated in well-characterized, monodispersed biomimicking nanocavities formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane using steady-state and picosecond time resolved fluorescence and fluorescence anisotropy. The emission behavior of AODIQ is very much dependent upon the water/surfactant mole ratio (W), i.e., on the water pool size of the reverse micellar core. AODIQ exhibits a sharp decrease in fluorescence anisotropy with increasing W, implying that the overall motional restriction experienced by the molecule is decreased with increased hydration. Some of the depth-dependent relevant fluorescence parameters, namely, fluorescence maxima and fluorescence anisotropy (r), have been monitored for exploiting the distribution and microenvironment around the probe in the reverse micelles. Fluorescence spectral position and fluorescence quenching studies suggest that the probe does not penetrate into the reverse micellar core; rather it binds at the interfacial region. Quantitaive estimates of the micropolarity and microviscosity at the binding sites of the probe molecule have been determined as a function of W

Effect of cyclodextrin encapsulation on the photocyclization of diphenylamine: Cavity imposed restriction on the reaction rate

The kinetics of the photocyclization of diphenylamine (DPA) to carbazole (CAZL) has been studied fluorometrically in air-equilibrated aqueous solution as well as in constrained microheterogeneous media provided by [alpha]-, [beta]-, and [gamma]- cyclodextrins (CDs). It is observed that the fluorophore is embedded within the CD cavities without any alteration of the overall reaction quantum yield in the different environments. However, the rate of the photoreaction is modified remarkably within the CD environments. A restriction on the intramolecular rotation of the phenyl planes of DPA, imposed by the steric rigidity within the CD cavities, has been ascribed to be responsible for the suppression of the reaction rates within the CD environments. A semi-empirical (AM1) calculation gives the molecular dimension of the substrate and corroborates the proposition from a consideration of the cavity size of the different cyclodextrins.http://www.sciencedirect.com/science/article/B6TGR-44WJT2F-D/1/fbeee114a055a066bec9406d2538f43