Journal Information:- Sindh Univ. Res. Jour. (Sci. Ser.) Vol.45 (4) 743-748 (2013)

Authors :- E Ali, G MUSTAFA, KB AMUR, N Nizamani, AR KHATRI, TR MEMON 

Abstract:- The charge-pump phase-locked loop (CP-PLL) circuit is most suitable technique used to align the two signals in different applications in communication. The CP-PLL is mostly feasible because of its low cost, integerable and precise features. The charge pump produces an error current, which is then integrated by the following loop filter. The error current is constant if the charge-pump is based on constant current sources however the pump current varies in the case of voltage switched charge-pump (VSCP). The conventional gain of the detecting unit is directly proportional to the error current. It behaves non-constantly when the voltage switched charge pump (VSCP) structure is used. Hence, the pump current applied to the loop filter (LF) is no more constant. This latent peculiarity in the form of non-constant pump current delivered from the VSCP influences the system dynamically. In this paper, it is focused on comparing the transient dynamics of the second order CP-PLL system considering the current output of both charge pump circuits. The simulation results are achieved using a discrete-time non-linear event-driven model considering the balanced and unbalanced pump current situations. 

Keywords—Phase- locked loop, Non-linear discrete-time model, voltage switched charge pump.

Journal Information:- 

Authors :- Abdul Sattar Saand, Ehsan Ali, Adnan Ahmed Arain, Abdul Rafay Khatri and Varun Jeoti

Abstract:- The purpose of this research is to achieve maximum ergodic capacity of wireless MIMO relay assisted network by designing relay linear processing. A novel linear beamforming is developed for amplify-and-forward two-hop multi-relay wireless network. In this design matched-filter beamforming is applied as receive processing for multiple relays and leakage based beamforming is designed as the relay transmit beamforming. Each terminal of the network is fitted with multiple antennas for intra node array gain. The information of both links is exploited at the relay terminals. The link (direct) from the source to user terminal is avoided. The relay terminals operate in half duplex mode. Through Matlab® simulations, it is revealed that the proposed scheme out performs the existing conventional relay beamformings for multi-relay case in the two-hop network.

Keywords—Amplify-and-forward Relay, Capacity; Leakage; Multiple relays; Perfect CSI

Journal Information:- International Journal of Computing and Network Technology, Vol 5, issue 3

Authors:- Imtiaz A. Halepoto, Nazar H. Phulpoto, Fareed A. Jokhio, Abdul R. Khatri 

Abstract:- Concurrent Multipath Transfer using the Stream Control Transmission Protocol (CMT-SCTP) enables multi-interface devices to send and receive data at the same time over more than one path. However, because of the fair Round robin scheduling, the paths with a longer delay (low quality) cause performance degradation due to gathered outstanding data at the receiver. The outstanding data are the data packets sent by the sender for which it is waiting for an acknowledgement. In networks with dissimilar paths, the blockage in the buffer space at the receiver side is also one of the side effects of large outstanding data. This paper presents an evaluation study on the multipath transmission using the SCTP, particularly the techniques that deal with the outstanding data. A simulation scenario is proposed that contains multiple paths from the source to the destination, where each path differs with the other path by the propagation delay. The results of the evaluation show that the technique that uses the outstanding data in the packet scheduling decision (CMT-OUT) increases the data transmission over multiple paths when it is compared to the CMT-SCTP. 

Keywords— CMT-SCTP, outstanding data, round robin scheduling, propagation delay.

Journal Information:- INTERNATIONAL JOURNAL OF COMPUTER SCIENCE AND NETWORK SECURITY, Vol 17, issue 11

Authors:- Ehsan Ali, Nasreen Nizamani, Abdul Sattar Saand, Abdul Rafay Khatri, Ghulam Mustafa Bhutto 

Abstract:- The Charge Pump Phase Locked Loop (CP-PLL) are widely used component in modern-day highly integrated electronic systems involved in wireless communication and smart system applications to perform several functions like frequency synthesis, clock recovery, and clock generation. The CP-PLL is a switching device because of the triggering nature of the digital phase detector. Mostly a second-order CP-PLL is utilized in consumer electronics applications. The Voltage Controlled Oscillator (VCO) generates a signal with frequency excursion due to a non-linear effect, called jump frequencies arising due to the filter impedance. These jump frequencies may lead to an overload of the VCO. This paper highlights the overload situation of the two different architectures of mixed-signal PLLs. The simulations are performed using a fast and efficient Event-Driven (ED) model. The effect of jump frequencies on both architectures of the CP-PLL is analyzed. 

Keywords— Phase locked loop, VCO, Overload, non-linear system, frequency jumps.

Journal Information:- (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 10, No. 6, 2019

Authors:- Nasreen Nizamani, Mujtaba Shaikh, Jawed Unar, Ehsan Ali, Ghulam Mustafa Bhutto, Abdul Rafay

Abstract:- The scale invariance characteristics play an essential role in pattern recognition applications, for example in computer vision, OCR (Optical Character Recognition), electronic publication, etc. In this paper, the shape based feature extraction techniques are used in terms of invariant properties and the region based FD (Fourier Descriptors) have been used for the recognition of isolated printed Sindhi characters. There are 56 isolated characters in Sindhi language than can be categorized to 20 different classes considering the shape of the base of each character. In this work, the dataset contains 4704 images of isolated printed Sindhi characters. The simulation result shows that the proposed method is a capable discriminating algorithm of Similar Sindhi characters and can easily extract the scale invariant features. 

Keywords— Features extraction; Sindhi optical character recognition; Fourier Descriptors; machine printed Sindhi characters.

Journal Information:- Indian Journal of Science and Technology, Vol. 13, No. 28, 2020

Authors:- MK Kaloi, E Ali, G Mustafa, N Nizamani, MA Memon, AR Khatri, GS Kaloi 

Abstract:- PID controllers are widely used in different industrial appliations especially in achieving stable speed control of DC motors. Hower, due to their limitations, most often other methods like Sliding Mode controller, or fuzzy based controller are used. Since the Fuzzy controlers are more adaptive to non-linearity. This study is to analyse a fuzzy-based speed control scheme for tuning/adusting the performance of PID controller for the purpose of speed control of DC motor under the load condition. Methods/Statistical Analysis: Because of low precision and slow response in different control schemes, a performance comparison is shown between three different control approaches for the DC motor speed control. MATLAB’s Simulink platform is used to realize DC Motor and to implement the PID, Fuzzy and Fuzzy-based PID controllers to run the DC motor on the desired speed. Fuzzy controller is based on very few rule & performance is analyzed considering the load. Findings: The performance of three controllers is evaluated in terms of transient domain characteristics like Percentage overshoot, settling and rise times and percentage error under load (2000 rpm). The PID controller has the highest overshoot and hence a faster rise time while FLC has significantly reduced the overshoot, therefore causing rise time to increase. For the Fuzzy-PID controller the percentage overshoot has almost vanished. The rise time also decreased as compared to the FLC. The simulated controller’s responses confirm that Fuzzy-based PID controller has better performance comparing to independent PID and FLC controllers. Novel/Applications: In this work, the design of an intelligent Fuzzy-PID controller for the speed control of the DC motor with reduced complexity and a faster response using with minimum number of Fuzzy rules producing more optimized performance is presented. The design of a control strategy that has capability to control nonlinear behaviors and to stabilize the performance of linear systems specially to provide optimized performance for speed tracking system which is an important aspect in real time system design.

Keywords— PMDC motor; PID Controller; fuzzy controller; fuzzy-based PID controller; transient response.

Journal Information:- Engineering, Technology & Applied Science Research (ETASR), Vol. 11, No. 01, 2021

Authors:- Narwani Darshna, Ehsan Ali, Bughio Ahsan Murtaza, Nizamani Nasreen, Siyal Shahid Hussain, Khatri Abdul Rafay 

Abstract:- The analysis of the behavior of the Charge Pump Phase-Locked Loop (CP-PLL) is a challenging task due to its mixed-signal architecture. Out of its two types, i.e. Current Switched CP-PLL (CSCP-PLL) and Voltage Switched CP-PLL (VSCP-PLL), the prior produces symmetrical pump currents, resulting in an appropriate transient performance to be analyzed. The loop parameters are important to set the gain, target frequency and assure the stability of the system. The more important is the bandwidth of the loop, which is dependent on the loop filter parameters to perform a stable operation and locking time. In this paper, the impact of loop parameter variations on the overall transient behavior of the system is investigated. It has been shown that loop parameters play an important role to ease the design of mixed-signal PLLs.

Keywords— charge pump PLL, voltage switched charge pump, transient analysis, loop parameter variation, behavioral model simulations

Journal Information:- Micromachines, Vol. 13, No. 02, 2022

Authors:- Abdul Aleem Jamali and Abdul Rafay Khatri Muhammad Rizwan Amirzada, Yousuf Khan, Muhammad Khurram Ehsan, Atiq Ur Rehman

Abstract:- An analytical model to predict the surface roughness for the plasma-enhanced chemical vapor deposition (PECVD) process over a large range of temperature values is still nonexistent. By using an existing prediction model, the surface roughness can directly be calculated instead of repeating the experimental processes, which can largely save time and resources. This research work focuses on the investigation and analytical modelling of surface roughness of SiO2 deposition using the PECVD process for almost the whole range of operating temperatures, i.e., 80 to 450 °C. The proposed model is based on experimental data of surface roughness against different temperature conditions in the PECVD process measured using atomic force microscopy (AFM). The quality of these SiO2 layers was studied against an isolation layer in a microelectromechanical system (MEMS) for light steering applications. The analytical model employs different mathematical approaches such as linear and cubic regressions over the measured values to develop a prediction model for the whole operating temperature range of the PECVD process. The proposed prediction model is validated by calculating the percent match of the analytical model with experimental data for different temperature ranges, counting the correlations and error bars. 

Keywords—  surface roughness; PECVD process; SiO2 thin-films; analytical prediction; MEMS; micro-mirrors.

Journal Information:- Crystals, Vol. 12, No. 03, 2022

Authors:- Umair Ahmed, Yousuf Khan, Muhammad Khurram Ehsan, Muhammad Rizwan Amirzada, Naqeeb Ullah, Abdul Rafay Khatri, Atiq Ur Rehman, Muhammad A Butt 

Abstract:- In this work, the spectral properties of distributed Bragg reflector-based photonic crystal (DBR-PhC) structures were studied for the near-infrared (NIR) range. Different structural properties were varied to study their effect on the quality of the stopband and the appearance of the resonant dips in the reflection spectra of the DBR-PhC structure. The investigated structural features included the depth of PhC holes, hole radius, and a number of PhC elements in the DBR structure. The 11-layered DBR structure was designed with a 2.4/1.4 refractive index contrast of alternating layers. The study aimed to achieve optical filtering properties in the DBR-PhC structure, to simplify the structural complexity of Fabry-Pérot filters by eliminating the FP cavity and upper-DBR mirror. The proposed DBR-PhC device can be used in different optical filtering and sensing applications.

Keywords—  DBR-PhC; photonic crystals; DBR; optical filters; dielectric PhCs.

Journal Information:- IEEE Access, Vol. 11, 2023

Authors:- Samandar Khan Afridi, Abdul Sattar Saand, Abdul Rafay Khatri, Mohsin Ali Koondhar, Wonsuk Ko, Sisam Park, Hyeong-Jin Choi, Waqas Ahmed 

Abstract:- The prototype development of an automatic and floating structured hydropower plant constitutes a pioneering initiative aimed at addressing the critical issue of energy scarcity in remote areas. This research is centered on the creation of an innovative and sustainable energy solution that capitalizes on diverse water flow conditions. It involves design and construction of a floating hydropower plant that seamlessly integrates a Pico hydro turbine, generator, and control system. The IoT technology is incorporated to enable real-time monitoring and visualization of essential electrical parameters through mobile apps. In light of the escalating global demand for renewable energy solutions, this research holds immense significance. By extending access to electricity to off-grid communities, especially those residing in remote regions where conventional energy infrastructure is impractical, the proposed floating hydropower plant offers a reliable, eco-friendly power source. Its deployment in rivers and water bodies underscores its adaptability and potential to significantly alleviate energy deficits in underserved areas. As the world grapples with the pressing need for a transition toward sustainable energy sources, this project serves as a beacon of ingenuity and progress. By broadening the scope of the original research and exploring avenues for further enhancement, this endeavor underscores the commitment to a future where accessible, clean, and efficient power generation can transform the lives of communities plagued by energy scarcity. The outcomes and implications of this research endeavor not only contribute to the field of renewable energy but also provide a foundation for future innovations in sustainable power generation systems.

Keywords—  Power generation, Hydraulic turbines, Renewable energy sources, Dams, Wheels, Rivers, Hydroelectric power generation, Internet of Things