Sharif Digital Repository

one of the main problems of radar identification in electronic warfare support system is analysis of pulse repetition interval (PRI) modulation. In this paper a robust method of recognizing the PRI modulation type of radar signals is proposed to improve robustness of previous recognition methods as well as to reduce the complexity. Simulation results show that the proposed method achieves much better error recognition rate in case of missing and spurious pulses than other methods such as autocorrelation based techniques and the Noone method  

Wireless broadband access has gained so much attention in recent years. IEEE 802.16d as a standard in this field has provided MAC layer and PHY layer specifications. It has adopted OFDM method for one of PHY specifications that uses 256 subcarriers. In this paper we verify the effects of subchannelization option in uplink, on bit error rates in 16QAM modulation. Simulation results show that considerable improvement is obtained using half of the subcarriers  

Feed-forward is one of the main methods for linearising microwave power amplifiers. The level of inter-modulation rejection (IMR) values can be predicted by appropriate modelling of the feed-forward microwave amplifier. Here, we have presented closed form expressions, which can be used for predicting the IMR for the first and second adjacent channels. Fifth- and third-order nonlinear models have been used for the main and error amplifiers, respectively. The predicted values have been verified using ADS simulator and a MATLAB program. © The Institution of Engineering and Technology 2007  

In this paper, by extending Space Vector Modulation (SVM) technique to three-phase four-wire systems, a new strategy is developed for the control of Active Power Filters (APFs). It is shown that the conventional SVM method cannot compensate for the current in the neutral wire in a three-phase four wire system. Simulations have been performed using PSCAD/EMTDC software. Simulation results are provided to prove the ability of the proposed technique in compensating the zero-sequence current. ©2006 IEEE  

The notable effeets of time delay aid time discretization on the torque and current ripple amplitude of the direct torque controlled induction motor scheme are investigated. A simply modified torque hysteresis comparator structure is proposed. It minimizes the undesirable effects of the time delay and time discretization on the torque ripple and allows a sensible reduction of torque and current ripple amplitudes and switching frequency in the whole rotor speed range. Numerical simulations and experimental tests have been carried out to validate the proposed torque comparator effect. © 2004 IEEE  

In this paper, we provide multiuser performance analysis of a multicarrier frequency-hopping (MC-FH) code-division multiple-access system as first introduced in the work of Lance and Kaleh. We propose to use a practical low-rate convolutional error-correcting code in this system, which does not require any additional bandwidth than what is needed by the frequency-hopping spread-spectrum modulation. We provide multiuser exact performance analysis of the system for both uncoded and coded schemes in additive white Gaussian noise and fading channels for a single-user correlator receiver. We also derive the performance analysis of the system based on a Gaussian distribution assumption for... 

This paper presents a new single-loop single-stage second order sigma-delta modulator. The circuit based on switched capacitor components just uses one Op-Amp to realize second order noise shaping. The modulator demonstrated 85 dB DR in 8kHz bandwidth, dissipating 135 μW from a 2.5 V supply. © 2002 IEEE  

This paper presents an effective hybrid optimal modulation technique for a cascaded H-bridge (CHB) multilevel inverter. The introduced method is generalized optimal pulsewidth modulation, which can be extended to any m-level CHB multilevel inverter operating at any switching frequency. The presented hybrid optimal modulation strategy includes the pattern exchange and optimal modulation techniques. In the optimal modulation technique, the hybrid interior-point algorithm, which is more flexible and efficient than conventional optimization techniques, is applied. The proposed hybrid optimal modulation strategy yields balanced units' output fundamental voltages, and low total harmonic distortion... 

Automatic Modulation Recognition (AMR) of communication signals has been an important theme in wireless communication systems. Recently, digital modulation recognition has been considered remarkably, due to the vast application of this kind of AMR technique in spectrum sensing and cognitive radio. In this paper, we propose a wavelet-based algorithm for recognition of binary digital modulation schemes including BASK, BFSK and BPSK in presence of Additive White Gaussian Noise (AWGN). In this algorithm, Haar Wavelet Transform (HWT) of the received signal is compared to templates and the similarity of them are measured. Experimental results show a perfect classification of binary digital... 

In the aspect of further development of investigations in the area of spacecraft modeling and analysis of the control scheme, a new hybrid finite-time robust three-axis cascade attitude control approach is proposed via pulse modulation synthesis. The full quaternion based control approach proposed here is organized in association with both the inner and the outer closed loops. It is shown that the inner closed loop, which consists of the sliding mode finite-time control approach, the pulse width pulse frequency modulator, the control allocation and finally the dynamics of the spacecraft is realized to track the three-axis referenced commands of the angular velocities. The pulse width pulse... 

A Multi-level asynchronous delta sigma modulator consist of several Schmitt-triggers and a novel time-to-digital converter is presented as a core of a delta sigma modulation based analog to digital converter (ADC). The modulator firstly modulates the amplitude of its analog input signal to a multilevel asynchronous duty-cycle modulated signal. Then a time to digital converter (TDC) must be applied to generate digital representation of the received signal from the multi-level asynchronous duty-cycle modulated signal. A multi-level structure has been developed in this work while the prior works often used a single Schmitt. One of the most important limitations in conventional asynchronous... 

A low-drift optoelectronic oscillator (OEO) is developed and experimentally shown. In the proposed OEO, a fiber Sagnac interferometer, including an optical phase modulator (PM) and a nonreciprocal bias unit, functions as an intrinsically drift-free intensity modulator. The phase noise of the proposed OEO is modeled in phase space, which is verified by experiments. Phase noise and frequency stability of the photonically generated microwave signals are measured. The single-sideband phase noise of the generated microwave signal is -106.6 dBc/Hz at 10-kHz offset from the 10.833-GHz carrier, with 120-fs rms timing jitter integrated from 1 kHz to 10 MHz. Frequency drift measurements show ±0.85-ppm... 

A terahertz modulator based on the Type-II superconductor flux flow oscillator has been proposed. Analytical calculations are presented and the effects of intrinsic and extrinsic parameters such as disorder strength of crystal, penetration depth, frequency, and amplitude of the modulated current on the radiation power spectrum have been studied. The proposed structure also exhibits a mixer-like behavior, in the sense that its output harmonics range from the washboard frequency up to the superconductor gap frequency, so the input signal is practically mixed with the washboard frequency and its harmonics. The modulation index for each harmonic of this modulator has also been investigated. This... 

Classifying the modulation type of radio signals plays an important role in current and future wireless communication systems. We present a modulation classification method based on convolutional neural networks that reaches high accuracy in face of various channel characteristics and signal conditions without requiring the network to have a very large depth. Experiment results show that the proposed method reaches accurate classification under different system impairment settings that include sampling rate offset, carrier frequency offset, multi-path fading, and additive white Gaussian noise. For instance, compared to a state-of-the-art method, accuracy is improved up to 25% in classifying... 

Multi-site photoplethysmography is an optoelectronic technique that measures changes in blood volume associated with cardiac contraction. Photoplethysmogram (PPG) recording enables researchers to study the vascular and hemodynamic properties of human subjects. Currently, there is no commercial system available in the market to perform multi-channel PPG recording. The measurements can be obtained from fingertips, ear lobes and toes due to their low absorption and high degree of vasculature. The main objective of this project is to develop a suitable data compression algorithm for two-channel simultaneous high resolution wireless PPG recording system. MATLAB software was used during the... 

Large signal behavior of the Laser Diode is analyzed with the aim of finding a qualitative relationship between modulation amplitude and the change in the shape of its transfer function. It is found that, at quasi-static conditions, increasing the amplitude of the modulating signal smoothes out the original piecewise-linear transfer function of the diode. It further shifts the now smoothed knee point to lower DC currents. As the frequency increases, however, these effects become less and less pronounced. In addition, the transfer function becomes rather wavy due to the failure of current density to reach the saturation level necessary for adequate stimulated emission. At even higher... 

Here, an in-depth study of a novel electro-optic phenomenon suggested earlier in optical waveguides, referred to as the conducting interfaces, is carried out. It is shown that it would be possible to achieve a very strong optical modulation effect in slab waveguides fabricated on the standard III-V InAlGaAs compound platform. The electro-optic effect is obtained by controlling the density and population of the electron and hole states in the well layer. The additional phase shift contributed to the reflection phase of the guided electromagnetic wave constitutes an ultrastrong source of optical modulation and phase control. It is estimated that a Mach-Zhender configuration based on this... 

In this article, we present a new iterative algorithm aimed at improving the performance of the sigma-delta analog to digital (A/D) converter. We subject the existing sigma-delta modulator, without changing the configuration, to an iterative procedure to increase the signal-to-noise ratio of the reconstructed signal. In other words, we demonstrate that sigma-delta modulated signals can be decoded using the iterative algorithm. Simulation results confirm that the proposed method works very well, even when less complex filters are used. The simple and regular structure of this new A/D converter, not only makes realization of the hardware as ASIC or on FPGA boards easy, but also allows it to... 

In this paper, the effect of the main rotor of an armed helicopter on radar return signal and its modulation condition are considered. After analyzing references and experimental data, this paper proposes a new method based on inherent modulation in main rotor echo. This method is able to enhance the probability of detection. The simulation is performed for both simulated and practical echo signal. Simulation results confirm that our proposed scheme is effective. Moreover, a new domain for distinguishing and measuring the rotation feature of a rotary target is proposed. This paper is based on practical experiments (rotation domain)