A three-phase a.c. controller using power MOSFETs operating in high- frequency chopping mode has been developed fabricated and tested with resistive load the microprocessor based firing scheme is used to test the four-quadrant switch realizations. The output voltage is smoothly varied using symmetrical multipulse modulation by varying the duty cycle, and relevant experimental results are furnished. The harmonic analysis of the chopped wave is made in terms of the number of pulses per cycle and pulse width. For same values of power factor and per unit output voltage, it can be concluded from the test results that the proposed scheme has much lower values of lower order harmonics as compared to conventional thyristor phase control. The computed resulted have been experimentally validated.

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Techniques. This has two important disadvantages; firstly, there are significant chances that long-term exposure to ultrasound may harm the unborn, and secondly, the ultrasound machines and its trained operators would prove to be an expensive proposition and could not be utilized for longer period of time. Because of these reasons, the existing instruments are not suitable for carrying out frequent and long-term measurement of FHR, which is highly recommended in high-risk pregnancies. In this paper an alternative method for long-term FHR monitoring is proposed. With the help of a designed acoustic cone, sound wave guide and piezoelectric sensor, acoustic energy produced by fetal heart movement is detected from subject’s (mother’s) abdomen. An additional microphone is used to detect ambient noise, which will be used for adaptive subsequently filtered, amplified and recorded in a two-channel removable memory device. All these components were assembled in a low power portable electronic instrument to allow long term fetal surveillance. Later on, the recorded data is transferred to a personal computer where it is further digitized, filtered, analyzed and displayed. The designed instrument has been examined and tested in Government Hospital on women with gestation age between 28 to 41 weeks. The results showed that the technique is suitable and effective for long- term fetal heart sound monitoring.

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Classification of material and its surface roughness by means of a plunger probe and optical mouse is presented in this appear. An experimental prototype was developed which involves bouncing or hopping of the plunger based impact probe freely on the plain surface of an object under test. The time and features of bouncing signal are related to the material type and its surface properties, and each material has a unique set of such properties. During the bouncing of the probe, a time varying signal is generated from optical mouse that is recorded in a data file on PC. Some dominant unique features are then extracted using Digital Signal Processing tools to optimize neural network based classifier used in the existing system. The classifier is developed on the basis of application of supervised structures of Neural Networks. For this, an optimum Multilayer Perceptron Neural Network (MLP NN) model is designed to maximize accuracy under the constraints of minimum network dimension. The optimal parameters of MLP NN model based on various performance measures and classification accuracy on the testing datasets even after attempting different data partitions are determined. The classification accuracy of MLP NN is found very good even after carrying out rigorous testing using different data partitions.

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The performance of modern radar systems with active phased array antennas is mainly driven by the performance of the microwave T/R modules. To reduce the size, weight, cost and power consumption, as well as to accurate beam steering, T/R modules, now-a -days, employ MMICs(Monolithic Microwave Integrated Circuits) for implementing transmit/Receive chain. The L-band SPDT switch, 6 bit digital attenuator, 6-bit digital shifter have been designed using GAETEC Hyderabad 0.7µm GaAs MESFET Switch model to handle 39dbm peak number. All the above components have been designed and simulated using Agilent ADS CAD tool interfaced with Academy Layout. The SPDT Switch with insertion loss than –1db, isolation greater than 60db and return loss better than 20db has been realized on a single 3.0mm x 2.35mm GaAs chip. A 6-bit Digital Attenuator has a 31.5dB attenuation range in o.5 dB increments. 2.50 phase error and return loss better than 15dB. The 6bits are cascaded to form a complete attenuator on a double 3.5mm x 2.35mm GaAs chip with 3 attenuator bits in each for a better yield. A 6 – bit digital phase shifter with 9dB insertion loss, return loss better than 15 dB has been realized on a two GaAs chips with size 4.0mm x 2.35mm and 3.0mm x 2.35 mm and 3 phase bits in each chip for the better yield.

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Orthogonal Frequency Division Multiplexing (OFDM) systems are highly sensitive to frequency synchronization errors, which cause inter-carrier interference, leading to degradation in the system performance. In this paper, a pragmatic timing and frequency synchronization scheme for reuse-I OFDMA systems that is compatible with IEEE 802, 16d/e wireless MAN standard is proposed. The algorithm uses cyclic prefix correlation technique for estimating and tracking the OFDMA frame boundary and fractional frequency offset. Once the preamble is captured, the integral part of the frequency offset and cell-specific preamble code can be estimated. This novel scheme is computationally efficient and robust to co-channel interference and multipath fading. Simulation results show that the proposed algorithm gives excellent performance even at very low signal to interference noise ratios.

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We address initial ranging process in OFDMA system such as IEEE 802.16e. The proposed ranging method includes two main tasks multi-user ranging code detection and timing estimation. The multi-user ranging code is detected based on a time domain channel (impulse response) detection corresponding to each ranging user through a correlation process that can be performed efficiently in the frequency domain. For initial ranging users, the timing offset also needs to be extracted, which is straightforward after channel is estimated in the process. The simplicity and the efficiency of the proposed method are demonstrated through computer simulation studies.

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This paper proposes a novel technique for securing and preventing the misuse of images by digital image watermarking. The technique is based on a hybrid approach employing the Wavelet Transform (WT), and the fractional Fourier transform (FRT) termed as the Fractional Wavelet Transform(FWT). We present experimental evidence to establish the advantages of this scheme over other watermarking schemes when subject to attacks such as noise and compression.

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This paper presents an improved loss less image compression of gray-scale images in terms of entropy (bits/pixel). The given image is re-ordered using various topologies based on uniformity measure, if required. The entropy of the given image/re-ordered image is calculated for the residues, i.e., the difference between the actual pixel intensity values and estimated of the pixel intensity value, obtained using different estimation procedures. The estimation of the pixel intensity is based on the uniformity measure, calculated using pixel intensities in the given image. In this work, the method of estimating pixel intensity is presented. Superior performance is observed in this approach over three standard techniques available in the literature.

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