Ankita Jain

A Hindi speech recognition system for connected words using HTK

A speech recognition system converts the speech-sound into the corresponding text. The uttered speech is first understood by the machine and then the corresponding text is displayed. This paper aims to build a connected-words speech recognition system for Hindi language. The system has been developed using hidden Markov model toolkit (HTK) that uses hidden Markov models (HMMs) for recognition. The system has been trained to recognise any sequence of words selected from the vocabulary of 102 words. Initially, Mel frequency cepstral coefficients (MFCCs) have been used to extract the features from the speech-files. Then, the system has been trained to estimate the HMM parameters using word level acoustic models. The training data has been collected from 12 speakers including both males and females. The test-data used for evaluating the system-performance has been collected from the five speakers. The experiments have also been performed on the system. The experimental results show that the presented system provides the overall word-accuracy of 87.01%, word-error rate of 12.99%, and word-correction rate of 90.93% respectively. The work has been evaluated by performing the comparative analysis with the existing similar works and the betterment has been reported.

Phase Noise Tracking and Compensation in Coherent Optical Systems Using Kalman Filter

The performance of phase-modulated coherent optical communication systems is often limited by laser and nonlinear phase noises (PN and NLPN). The laser PN and the NLPN at high launch powers degrade system performance severely. In this letter, we investigate the use of Kalman filter (KF) to estimate and track both the laser PN and the NLPN in 100-Gb/s single channel coherent optical phase-modulated systems. Initially, the KF is operated in the training mode with pilot symbols; the filter is switched to decision directed mode after training. Simulation results for single-polarization, 100-Gb/s QPSK transmission over 20 × 80 km fiber with in-line dispersion compensation show that KF can successfully mitigate NLPN at 8-dBm launch power with 1-MHz laser linewidth. Comparison with digital backpropagation algorithm (one step/span) shows that KF provides 6-dB improvement in Q-factor. Kalman estimates corresponding to the time evolution of PN and NLPN are also provided, which shows optimal tracking of both the noise processes, thereby validating our proposed scheme.

Broadband sectoral slot cut microstrip antenna

The broadband microstrip antenna is more commonly realized by cutting the slot at an appropriate position inside the patch. The slot is said to introduce a mode near the resonance frequency of the fundamental mode of the patch and yields broadband response. The compact microstrip antenna is realized by placing the shorting post or the plate along the zero field line at the fundamental mode of the patch. In this paper, the compact variation of equilateral triangular microstrip antenna, a shorted sectoral microstrip antenna is discussed. A broadband proximity fed rectangular slot cut shorted sectoral microstrip antenna is proposed. The analysis to study the effects of slot on the broadband response is presented. The slot reduces the higher order mode resonance frequencies of the shorted sectoral patch and along with the fundamental patch mode yields broadband response. The simulated and measured bandwidth of more than 550 MHz is realized. Since the shorted patch is used, the antenna shows radiation pattern in end-fire direction with a gain of more than 6 dBi over the bandwidth.

Tracking linear and nonlinear phase noise in 100G QPSK modulated systems using Kalman filter

We investigate the use of Kalman filter to estimate both linear and nonlinear phase noise in 100G QPSK modulated systems. Simulations show a considerable improvement in BER with Kalman filter compared to digital backpropagation algorithm.

Pump suppressed four-wave mixing in optical fibers for correlated photon generation using feedback technique

In this paper we propose and demonstrate a novel technique to suppress pump in four-wave mixing experiments. The residual pump powers at the fiber output are reflected by fiber-Bragg gratings (FBGs), amplified by an EDFA to compensate for pump losses in feedback path, and fed back to the fiber. With the increase in total input power to the fiber, the ratio of signal and idler to pump increases. Additional optical filters can then be used for further pump suppression. In our experiments, two pump waves of wavelengths 1549.70nm and 1549.85nm are combined using a 3dB coupler and fed to a highly-nonlinear fiber (HNLF) of length 1km, nonlinear coefficient of 12.4/W-km, and zero dispersion wavelength (ZDW) of 1513nm. Without feedback, we obtained the signal and idler to pump ratios of -21dB and -20.6dB respectively. After filtering by FBGs of 95% reflectivity and unity gain feedback, the ratio becomes - 14.1dB and -12.2dB respectively. When the residual pumps are amplified and fed back to the HNLF, the ratio improves to -7.5dB and -8.6dB indicating the potential of our method.

RF pulse shaping for QPSK, PM-QPSK and QAM formats

We propose and evaluate the performance of a novel RF pulse against rectangular pulse for three modulation formats: QPSK, PM-QPSK, and Star 16 QAM. The proposed pulse shows BER improvement by over an order of magnitude even for large phase and pre-amplifier noise.

Nonlinearity Mitigation in Coherent Optical Communication Systems: All-Optical and Digital Signal Processing Approaches

Information transmission through fiber-optic channel is subjected to several impairments such as chromatic and polarization mode dispersion, nonlinear phase noise due to interaction of amplifier noise with fiber Kerr nonlinearity, and nonlinear effects such as self- and cross-phase modulation. In addition, laser phase noise and frequency offset between signal and local oscillators also degrade the received signal quality. Unless these impairments are mitigated, the performance of high data rate optical communication systems is degraded. We describe two approaches to mitigate fiber impairments in high data rate coherent optical communication systems. In the first approach, nonlinearity and dispersion in either fibers or semiconductors is used to undo the effects of transmission fiber on the optical carrier. We propose the use of mid-span spectral inversion, realized using counter-propagating dual pumped four-wave mixing in fibers, to mitigate dispersion and nonlinearity in 40 Gbps QPSK systems. We describe our work on realizing optical phase conjugation in semiconductor optical amplifiers. In the second approach, the optical signal is sampled after coherent reception and processed using digital signal processing algorithms to mitigate dispersion and nonlinearity. We describe Kalman filters to estimate and track phase noise in 100 Gbps QPSK systems. We also describe radial basis function neural network equalizer to mitigate nonlinearity in 80 Gbps 16 QAM CO-OFDM systems.

RF pulse shaping for higher-order optical modulation

We propose a novel RF pulse shape and evaluate its performance for QPSK, PM-QPSK and 16 star QAM modulation formats under the effects of phase noise, preamplifier noise, dispersion and nonlinearity. Simulation of a 100 Gbps system with proposed pulse shape shows significant BER reduction compared to the system with rectangular pulse shape.

Continuously Tunable Multi-wavelength Actively Mode-locked EDFRL Using Intra-cavity Birefringence

We report on a continuously tunable multi-wavelength actively mode-locked EDFRL based on induced birefringence in cavity. A tuning range of 30nm over 1530-1560 nm and simultaneous operation of up to three wavelengths was achieved.

Proximity fed Broadband Microstrip Antennas

broadband microstrip antenna is realized by fabricating the patch on lower dielectric constant thicker substrate in conjunction with proximity feeding technique. Using thicker substrates, a formulation for an edge extension length and design guidelines for strip dimensions in proximity fed broadband antennas, are not available. In this paper, first by designing suspended rectangular and circular microstrip antennas on different substrate thickness and at various frequencies in 800 to 6000 MHz frequency band, graphs for an edge extension length are developed. Using them an edge extension length at given frequency and substrate thickness is calculated. The suspended patches were further designed using edge extension length graphs which give closer result with the desired frequency. Further by using proposed equations, proximity fed microstrip antennas were optimized at various frequencies in 800 to 6000 MHz frequency band. Using these optimized designs, a formulation for coupling strip parameters is proposed. By using proposed formulations for edge extension length and strip parameters, proximity fed antennas were re-designed at different frequencies in 800 to 6000 MHz frequency band. In all the configurations, broadband response with formation of loop inside VSWR = 2 circle is obtained. Also by using the proposed formulation, design procedure for proximity fed U-slot cut rectangular microstrip antenna is explained. The U-slot cut antenna gives bandwidth of more than 450 MHz at center frequency of around 1000 MHz. The proposed formulations can be used to design broadband antennas using thicker substrate at any given frequency. Keywordsctangular microstrip antenna, Circular Microstrip Antenna, Equilateral triangular microstrip antenna, Edge extension length, Proximity feeding, Broadband microstrip antenna coupling strip which is either placed below or in the plane of the patch. A larger BW is realized due to electromagnetic coupling between the patch mode and the strip. This method yields broader BW for thickness more than 0.060. The BW of MSA is also increased by cutting a slot inside the patch (4 - 8). Further increase in the BW of slot cut MSA is realized by using proximity feeding technique (9). In proximity feeding method, for the given patch and strip substrate thickness, design parameters are, the strip dimensions and its position below or in the plane of the patch. In the available literature on proximity feeding, the design guidelines for given substrate thickness and operating frequency are not available. In this paper, design formulations for broadband proximity fed MSAs on thicker substrates are proposed. First by designing rectangular MSA (RMSA) and circular MSA (CMSA) at a given frequency and for different substrate thickness in 800 to 6000 MHz frequency band, plots for an edge extension length against substrate thickness are developed. Using them an edge extension length at any given frequency and substrate thickness is calculated. By using the proposed graphs, patch was re-designed at different frequencies in the above frequency band. It gives patch resonance frequency at nearly the same desired value with an error less than 2%. Further broadband proximity fed RMSA, CMSA and equilateral triangular MSA (ETMSA) were designed at different frequencies in the 800 to 6000 MHz frequency band. Using their optimum designs, the formulations for strip dimensions and its position below the patch for the given patch substrate thickness is proposed. Using edge extensions graphs and the formulation for strip dimensions, proximity fed RMSA, CMSA and ETMSA were re-designed at different frequencies in 800 to 6000 MHz frequency band. A broadband response with the formation of loop inside the VSWR = 2 circle is obtained. Using proximity fed formulations, a detail design procedure for proximity fed U-slot cut RMSA is also presented. It gives broadband response with BW of more than 450 MHz (>45%). The above study was carried out using IE3D software followed by experimental verifications (10). In IE3D simulations an infinite ground plane was used. In measurements the antennas were fabricated using the copper plate having finite thickness and were supported in air using the foam spacer support placed towards the antenna corners. The antenna was fed using N-type connector of 0.32 cm inner wire diameter. At all the frequencies, measurements were carried out using R & S vector network analyzer (ZVH 8 model) using finite square ground plane of side length 100 cm. This larger ground plane simulates the effect of infinite ground plane. The radiation pattern was measured in minimum reflection surroundings with required minimum far field distance between reference antenna and antenna under test (11). The antenna gain was measured using three antenna method (11). The proposed