B. Chatterjee

Design of a Nearest Neighbour Classifier System for Bengali Character Recognition

A simple method has been described in this article for the design of a nearest-neighbour classifier for recognising hand-printed Bengali alphabetic characters. A set of simple features have been extracted using a string connectivity criterion. The performance of the classifier system has been presented.

Some Digitally Controlled Devices for Adaptive Control

In adaptive control systems the controller parameters are to be adjusted in real time in accordance with the information received from the measurements on system dynamics. A special purpose or general purpose digital computer is often necessary for generating the signals for controller parameter adjustments. In this paper we describe a few electronic devices whose parameters are directly under the control of digital signals. These devices will be of great use for many applications including adaptive control. The devices described in this paper are, digitally controlled variable gain amplifier, digitally controlled compensating network and digitally controlled variable frequency sampler.

Machine Recognition of Hand-printed Devnagri Numerals

A method for machine recognition of hand-printed Devnagri numerals is described. The experimental results using computer are given.

Analysis of Control Systems with Time Delay

The stability and sensitivity of a fourth-order feedback control system with time delay have been studied. The condition for the stability has been found out. The permissible loop gain and time delay for the stability of the system have been analytically evaluated. The closed-loop transfer function sensitivities w.r.t. both loop gain and time delay have been derived. The results obtained for a practical 4th-order system are discussed and a design example is presented.

Adaptive Quantization in Digital Control Systems

Adaptive quantization has been shown to be very useful in digital systems for reducing the quantization noise. A digital control system is simulated with (a) no quantizer, (b) with uniform step quantizers, and (c) with adaptive quantizers. It is observed that an appreciable improvement in the system performance may be achieved by using adaptive quantization.The upper bound on the percentage quantization error is introduced to replace the upper bound on the absolute value of the error. The process graph technique is applied to calculate the upper bound on the percentage error.

Adaptive Controllers Using Sequential Logic Circuits

Sequential logic circuits are described for adjusting the parameters of the controller in a linear control system operating in time varying environments. The adaptive loop operates to make discrete-time adjustments in the adjustable controller parameters, while the basic control system operates in continuous time. The adjustable controller parameters can have only discrete values instead of continuous range of values. The value of the parameters at a particular instant depends upon the control inputs which are the outputs of the sequential logic circuit. The sequential logic circuit described here utilizes the information/signals obtained by identifying certain characteristic of the control system. The system performance always tends towards the optimum response despite the variations in the system dynamics.

A New Performance Index for Optimal Adaptive Quantization

A new performance index is suggested for finding out the optimal adaptive quantization scheme. This performance index takes into account the utility of the system, and the cost to extract this utility. Thus this is termed the utility cost function.Using this function, computation of optimal adaptive quantization scheme is illustrated, using the decision theoretic approach. The methods of computation of the Bayes and the minimax strategies are developed. Using a numerical example, computation of these strategies is illustrated.

Minimum-Sensitivity Condition of a Time-Delay System with a Given Gain Margin

The relative stability curves, the time-delay sensitivity and loop-gain sensitivity over a wide frequency range have been evaluated for both linear and non-linear time-delay systems designed with a relative stability (6-dB gain margin) and minimum time-delay sensitivity conditions imposed on the system. The resultant system shows an improved performance.

Development Of A Low-Cost Photoelectric Scanner System

The design and development of a low-cost photo-electric scanner using discrete photodiodes has been briefly described here. A simple arrangement for storing the scanned data into memory has also been explained. Results of experimental observation using different character patterns are reported.

Adaptive Quantization with Prediction at the Receiver

Computer simulation has been made earlier on the adaptive quantizer at the transmitter with prediction at the receiver, to study the effects of different quantizer parameters on the SNR value of such a quantization scheme. To eliminate the need of a separate channel, the quantization step size was predicted earlier at the receiver. In this paper, the input source taken is a Gauss-Markov sequence and studies are made for different values of wordlength, range factors and for different input sequences. It is shown that for a resonably large wordlength, this type of quantization gives a better SNR value than most other existing quantization schemes.