Farruk Ahmed

Analytical Evaluation of Timing Offset Error in OFDM System

This paper proposes an idea of developing a model of estimating timing offset error of OFDM (Orthogonal Frequency Division Multiplexing) system without the use of additional pilots relying on inherent characteristics of the OFDM signal. An analytical expression has been derived and formulated to analyze the effect of bit error rate (BER) due to timing offset introduced by the transmission channel. This will help in determining the exact length of cyclic prefix to be added to each OFDM symbol to avoid misinterpretation by the receiver. The performances have also been evaluated under coded (convolution) and uncoded systems. The introduction of channel coding decreases this basic impairment of OFDM systems significantly. Simulated results show that the symbol error rate (SER) linearly depends on timing offset. It is expected that further works on the proposed estimated method will lead to a standard model so that at the receiving end the effect of timing offset can be eliminated totally.

Analysis and synthesis of Bangla Dental consonants

This paper describes in detail the analysis results of the Bangla dental consonants [t], [th], [d] and [dh] analyzed through the spectral estimation techniques in four long vowel contexts [a], [i], [o], and [u] for an accurate description of their acoustic characteristics and features and the differences between the corresponding cognate sounds. Various parameters like duration of closure/voice bar, duration of burst, voice onset time, duration of aspiration, rate of second formant transition and burst frequencies and amplitudes have been studied in details. For the synthesis of dental sounds, the source and vocal tract parameters of the synthesizer configuration were selected very carefully along with formant frequencies and their relative amplitudes besides the burst amplitude. The quality of synthetic speech was evaluated through subjective listening along with matching the spectra of synthetic speech with original speech.

Control of the speed of a DC motor by employeeing pulse width modulation (PWM) technique

This paper is mainly focused on the technique of pulse width modulation for controlling the speed of a 12 volt DC motor more efficiently. A potentiometer was used to generate a wide variety of pulses. The output of the controlling circuit (Pulse Width) was connected to the second circuit as input for direction control. Here a single push switch was used to change the state (stopforward-stop-reverse) of the DC motor. These two circuits were combined into one for ease of use. Third circuit was designed to measure the speed of the motor by employing an opto-electronic sensor, an amplifier and a two blade fan to interrupt the signal transmission of the sensor. Finally, the output of the sensor was connected with an oscilloscope through an amplifier and a train of square was found. By measuring the time period of the square waves, the duty cycle and Rotation per Minute (RPM) was calculated. After calculating the result from the observation proves that pulse width modulation is an efficient technique for controlling DC motor rather than other conventional technique.

Tape Transport Mechanism Control For a Magnetic Tape Recorder/Player Used for High-Speed Data Transfer

In this paper an attempt is made to develop an efficient tape transport mechanism required for high-speed data transfer. The mechanism is controlled by a microcomputer, which is a party in the data transfer operation. A commercially available transport system has been adopted for this purpose, with simple modification. During data search operation the tape speed is faster than the speed in normal Read/Write operation. At the same time, the Read/Write head position is adjusted in accordance with the tape speed. The system includes facilities for detecting the beginning and the end of the tape, and switching off the amplifier for read and write operation. Taking into account the delay for signal transfer and the time for motor torque, a tape motion velocity profile has been generated. This is used to obtain start, stop and interblock gap length.