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The initial solution of a massive multiple-input multiple-output (M-MIMO) detector for uplink (UL) is greatly influence the balance between the bit error rate (BER) performance and the computational complexity. Although the maximum likelihood (ML) detector obtains the best BER performance, it has an extremely high computational complexity. Iterative linear minimum mean square error (MMSE) detector based on the Gauss–Seidel (GS), the successive over-relaxation (SOR), and the Jacobi (JA), obtains a good performance-complexity profile when the base station (BS)-to-user-antenna-ratio (BUAR) is large. However, when the BUAR is small, the system suffers from a considerable performance loss. In this paper, a hybrid detector based on the joint GS and SOR methods is proposed where the initial solution is determined by the first iteration of GS method. Numerical results show a considerable complexity reduction and performance enhancement using the proposed GS-SOR method over all methods when the BUAR is small. [ABSTRACT FROM AUTHOR]

The physical existence of microwave toroidal dipole in a dogbone metallic inclusion-based miniaturized cloaking structure is verified in this paper. The excitation of toroidal dipole moments on the studied composite is verified using multipole scattering formalism. The presence of the toroidal Fano resonance significantly enhances resonant forward scattering from the structure for normal incidence. Multipolar contribution from the electric, magnetic and toroidal moments significantly enhances the scattering cross-section of the composite as compared to a bare cylindrical metallic object. Applicability of the proposed scheme is tested inside an anechoic chamber using reflection measurements on the fabricated structure and is subsequently validated in computer simulations in the microwave frequency regime. [ABSTRACT FROM AUTHOR]

In this paper, a general preamble-based time domain channel estimation model for multiple-input multiple-output (MIMO)-filter bank multicarrier (FBMC) system based on offset quadrature amplitude modulation (OQAM) is derived. In contrast to the conventional frequency domain interference approximation method (IAM)-based channel estimation model, the derived time domain model does not require symbol time to be sufficiently longer than the maximum channel delay spread, viz. the derived time domain model does not require the channel to be frequency flat. Based on the time domain model, the weighted least squares (WLS) and minimum mean square error (MMSE) channel estimators for MIMO-FBMC/OQAM systems are investigated. The Cramer–Rao lower bound for the WLS, MMSE and IAM estimators are derived. It is shown numerically that all the estimators achieve their respective bounds, and the proposed WLS and MMSE estimators significantly outperform the existing IAM channel estimator. The comparison of the bit error rate performance of the aforementioned estimators also validates our work. [ABSTRACT FROM AUTHOR]

An approach for the linear prediction-based detection of serially concatenated turbo coded differential quaternary phase shift keyed signals, is presented for SIMO-OFDM systems. The proposed method exploits the high degree of correlation in the channel frequency response, when the channel impulse response is much smaller than the FFT length. A prediction filter is used to estimate the channel frequency response. At the receiver, the inner decoder operates on a supertrellis with just $$S_{\mathrm {ST}}=S_{\mathrm{E}}\times 2^{P-1}$$ states, where the complexity reduction is achieved by using the concept of isometry (here $$S_{\mathrm {E}}$$ denotes the number of states in the encoder trellis and P denotes the prediction order). A reduced complexity version based on per-survivor processing for the proposed receiver is also given. Simulation results for the proposed method is compared to the case where the channel is estimated using pilots in the frequency domain. Though the BER performance of the channel estimation approach using pilots is much better than the proposed method, its throughput is much lower, since the pilots have to be transmitted for every Orthogonal Frequency Division Multiplexing (OFDM) frame. However, in the proposed approach, the pilots are required only for the first OFDM frame for the purpose of estimating the statistical properties of the channel frequency response and noise. For the rest of the frames, pilots are not required since, the channel and noise statistics are assumed to be unchanged. Therefore, the proposed method is throughput efficient. [ABSTRACT FROM AUTHOR]

Vector-controlled induction motor drives are quite popular in the industry in applications that demand high dynamic performance. This paper describes the implementation of a complete industrial vector-controlled drive for a 30 kW induction motor. The control algorithms for the drive are implemented using a TMS320F28335 Digital Signal Controller (DSC). Various monitoring and protection functions for the drive are implemented using a Cyclone IV FPGA that communicates with the DSC, and acts as the master controller for the drive. The FPGA also communicates with a Human-Machine Interface to provide a simple graphical control interface to the operator. [ABSTRACT FROM AUTHOR]

In this work, we discuss techniques for coherently detecting turbo coded orthogonal frequency division multiplexed (OFDM) signals, transmitted through frequency selective Rayleigh (the magnitude of each channel tap is Rayleigh distributed) fading channels having a uniform power delay profile. The channel output is further distorted by a carrier frequency and phase offset, besides additive white Gaussian noise. A new frame structure for OFDM, consisting of a known preamble, cyclic prefix, data and known postamble is proposed, which has a higher throughput compared to the earlier work. A robust turbo decoder is proposed, which functions effectively over a wide range of signal-to-noise ratio (SNR). Simulation results show that it is possible to achieve a bit-error-rate (BER) of $$10^{-5}$$ at an SNR per bit as low as 8 dB and throughput of 82.84 %, using a single transmit and two receive antennas. We also demonstrate that the practical coherent receiver requires just about 1 dB more power compared to that of an ideal coherent receiver, to attain a BER of $$10^{-5}$$ . The key contribution to the good performance of the practical coherent receiver is due to the use of a long preamble (512 QPSK symbols), which is perhaps not specified in any of the current wireless communication standards. We have also shown from computer simulations that, it is possible to obtain even better BER performance, using a better code. A simple and approximate Cramér-Rao bound on the variance of the frequency offset estimation error for coherent detection, is derived. The proposed algorithms are well suited for implementation on a DSP-platform. [ABSTRACT FROM AUTHOR]

The key contribution of this paper is to develop transmitter and receiver algorithms in discrete-time for turbo-coded offset QPSK signals. The procedure for simulating a clock offset between the transmitter and receiver is described. Due to the use of up-sampling, matched filtering and a differential correlation approach at the receiver, the time required for detecting the start of frame (SoF) is just around 500 symbols, which is also the length of the preamble. The initial estimate of the SoF and the frequency offset, obtained using the differential correlation approach, is improved using an iterative process. A novel two-step maximum likelihood (ML) frequency offset estimation is proposed, which significantly reduces the complexity over the conventional ML estimation. The decision-directed carrier and timing recovery algorithms use simple first-order IIR filters to track the carrier phase and clock slip. The proposed synchronization and detection techniques perform effectively at an SNR per bit close to 1.5 dB, in the presence of a frequency offset as large as 30% of the symbol-rate and a clock offset of 25 ppm (parts per million). It is shown via simulations that the performance loss with respect to the bare turbo code is only about 0.5 dB, for a preamble length of 500 and a BER of 10. The proposed techniques are well suited for software implementation. [ABSTRACT FROM AUTHOR]

The geometries, electronic structures, polarizabilities and hyperpolarizabilities of organic dye sensitizer 4-phenoxyphthalonitrile was studied based on ab initio HF and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet-visible (UV-Vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands were assigned to $\pi \to \pi^*$ transitions. Calculated results suggest that the three excited states with the lowest excited energies in 4-phenoxyphthalonitrile was due to photo-induced electron transfer processes. The interfacial electron transfer between semiconductor TiO electrode and dye sensitizer 4-phenoxyphthalonitrile was due to an electron injection process from excited dye to the semiconductor's conduction band. The role of phenoxy group in 4-phenoxyphthalonitrile in geometries, electronic structures and spectral properties were analysed. [ABSTRACT FROM AUTHOR]

The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 4-Aminophthalonitrile were studied based on Hartee-Fock (HF) and Density Functional Theory (DFT) using the hybrid functional B3LYP. Ultraviolet-visible (UV-Vis) spectrum was investigated by Time Dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands have been assigned to n → π* transitions. Calculated results suggest that the three excited states with the lowest excited energies in 4-Aminophthalonitrile is due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO electrode and dye sensitizer is due to an electron injection process from excited dye to the semiconductor's conduction band. The role of cyanide and amine group in 4-Aminophthalonitrile geometries, electronic structures, and vibrational spectra were compared with experimental values and in view of these results, it was concluded that 4-Aminophthalonitrile used in Dye Sensitized Solar Cells (DSSC) gives a good conversion efficiency. [ABSTRACT FROM AUTHOR]

In this work, a series of nanocrystalline silicon films were studied with different microstructural tools to elucidate the film microstructure at different stages of growth. Thin Si films, with a series of multilayers, were deposited by radio frequency glow discharge using Plasma Enhanced Chemical Vapour Deposition (PECVD) in silane gas (SiH4) highly diluted by hydrogen. Different nanostructured films were prepared by systematically varying gas flow ratios ( R = 1/1, 1/5, 1/7.5, 1/10, 1/15, 1/20) for films having different thicknesses. By changing the structure of the material, going from pure amorphous to nanocrystalline silicon, it is possible to obtain a variation in optical gap using the same material. In these structures, layers with different individual optical gaps are stacked together in order to cover as much of the solar spectrum as possible. The nanostructures of the silicon thin films were studied using FTIR, RS, PL, XRD, AFM, SEM, TEM and HRTEM. The results were correlated for conglomerate surface, grain surface. Some theoretical calculations were used for designing the overall stack geometry and for interpretation of characterization. These agree well with experimental observation. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of various “turbo” receivers for serially concatenated turbo codes transmitted through intersymbol interference (ISI) channels. Both the inner and outer codes are assumed to be recursive systematic convolutional (RSC) codes. The optimum turbo receiver consists of an (inner) channel maximum a posteriori (MAP) decoder and a MAP decoder for the outer code. The channel MAP decoder operates on a “supertrellis” which incorporates the channel trellis and the trellis for the inner error-correcting code. This is referred to as the MAP receiver employing a SuperTrellis (STMAP). Since the complexity of the supertrellis in the STMAP receiver increases exponentially with the channel length, we propose a simpler but suboptimal receiver that employs the predictive decision feedback equalizer (PDFE). The key idea in this paper is to have the feedforward part of the PDFE outside the iterative loop and incorporate only the feedback part inside the loop. We refer to this receiver as the PDFE-STMAP. The complexity of the supertrellis in the PDFE-STMAP receiver depends on the inner code and the length of the feedback part. Investigations with Proakis B, Proakis C (both channels have spectral nulls with all zeros on the unit circle and hence cannot be converted to a minimum phase channel) and a minimum phase channel reveal that at most two feedback taps are sufficient to get the best performance. A reduced-state STMAP (RS-STMAP) receiver is also derived which employs a smaller supertrellis at the cost of performance. [ABSTRACT FROM AUTHOR]

Owing to the importance of the spot propagation characteristics in transition zone modeling, the effect of lateral streamline convergence alone on the spot propagation characteristics has been studied. It is found that for the extent of lateral straining introduced here, the two-dimensional spot propagation characteristics are unaffected. [ABSTRACT FROM AUTHOR]

A case of a young housewife having a huge solitary splenic cyst containing over five litres of clear fluid is presented. She gave a history of having fallen down the stairs four years ago. Following the accident she experienced mild abdominal pain for two weeks. What role the fall played in the development of the splenic cyst can only remain a speculation. This is the largest splenic cyst recorded in General Hospital, Madras and it is probably one of the biggest recorded in literature. [ABSTRACT FROM AUTHOR]

A new karyotype which is both viable and stable has been obtained in Delphinium following X-ray induced chromosomal rearrangements. It shows, on the whole, greater symmetry than the parental karyotype although one of the chromosome pairs was reduced to a minute size. The meiotic sequence in the structural heterozygote and the isolation of the homozygote having the altered karyotype in its progeny have been briefly described. The structural rearrangement has been found to be associated with a change in the growth habit of the plants, indicating a possible position effect. [ABSTRACT FROM AUTHOR]