Cebrail Ciftlikli

A simple and useful approach for the determination process of the weighted despreading sequences in a DS‐CDMA system

In this letter, we propose a simple and useful approach based on artificial neural networks (ANNs) to help the determination process of the despreading sequences weighted by exponential chip weighting waveforms in a low processing gain direct sequence-code division multiple access (DS-CDMA) system. Numerical results show that the parameter values of the exponential chip weighting waveforms produced by the proposed network are nearly optimal and satisfactory in viewpoint of the achieved bit error rate (BER) performance. Copyright

Focusing for laser hole drilling

Abstract The power intensity distribution of a laser beam across the focal plane is important for producing good hole geometry. To examine the power intensity distribution in the region of the image plane of a practical lens, a diffraction integral method is employed. Lens aberration is accounted for by the intensity of the appropriate phase changes. In the analysis, a free-running pulsed multimode solid-state laser is considered and the lens is assumed to have aberrations. Since an on-axis object is examined, only spherical aberration is taken into account.

Optimization of affecting parameters in relation to pulsed CO2 laser design

In the present study, the optimal design of CO2 laser was investigated and a mathematical model developed for this purpose. The mathematical model covers energy levels, transitions of molecules between these levels and molecular collisional decay mechanism. The effect of gas mixture ratios on molecular population at excited states and on efficiency are interpreted as results.

A simple method for calculating the sinr in DS-CDMA systems with despreading sequences weighted by stepping chip waveforms

This article presents a simple method for calculating the signal toi nterference-plus-noise ratio in direct sequence code division multiple access systems with despreading sequences weighted by stepping chip waveforms. The method is based on a simple equality, which gives a relation among the number of occurrences of various chip patterns belonging to random spreading sequences. It is found that there is no need to scrutinize all the chips of a random spreading sequence to determine the number of transitions that occur between two consecutive chips. Several numerical examples and computation times are provided to demonstrate the validity and significance of this method.

Determination of most appropriate spreading sequences for a DS/CDMA system by using a modified approach

We have recently proposed an approach which mainly depends on code groups in a given code set to determine the most appropriate spreading sequences (codes) for a low processing gain direct sequence code division multiple access (DS/CDMA) system that uses despreading sequences weighted by stepping chip waveforms (see Develi, I. and Ciftlikli, C., Proc. Int. Conf. on Electrical and Electronics Eng. - ELECO 2001, pp.322-6, 2001). We now introduce a modified form of the approach to simplify the determination of the most appropriate spreading codes which achieve better bit error rate (BER) performances in a given code set when they are used as references. Numerical results reveal that the spreading codes designated by the new approach are the most appropriate codes for using as references in a given code set.

An improved formula obtained by simulated annealing for the computation of maximum SINR for DS-CDMA receiver with exponentially weighted despreading function

It is well known that direct sequence-code division multiple access (DS-CDMA) receiver using exponentially weighted despreading function outperforms significantly receiver using rectangular despreading function. The maximum value of the signal-to-interference-plus-noise ratio (SINR) for this type of receiver is an important indicator to evaluate the bit error rate (BER) performance of the system. In this paper, we propose an improved formula obtained by using simulated annealing (SA) algorithm to calculate the maximum value of the SINR. It is shown that the results computed by the proposed formula are more accurate than the results obtained by the simplified formula available in the literature. Copyright

Generalized Neural Method for Shaping the Exponential Chip Weighting Waveforms in Direct Sequence CDMA Systems

In recent past, artificial neural networks have been successfully introduced as a useful method for shaping the exponential chip weighting waveforms (ECWW). However, the results available in the literature are applicable to direct sequence-code division multiple access systems using a particular number of users considered, but cannot be directly generalized for systems include arbitrary number of users. In order to deal with this problem, a general and advanced methodology based on multilayer perceptron neural networks is presented in this paper. The proposed network has been tested with new set of data to demonstrate the performance and applicability of the methodology. Numerical results have shown this methodology to be robust and general use for the computation of the optimal value of the parameter belonging to ECWW. Index Terms – Spread spectrum communication, Multi-access systems, DS-CDMA, Exponential chip weighting waveforms, Artificial neural networks.

Bit error rate calculation for DS-CDMA systems with WDS in the presence of rayleigh fading and power-control error

This paper reports work in which modified expressions for the bit error rate (BER) calculation of DS-CDMA systems with weighted despreading sequences (WDS) in the presence of Rayleigh fading and power-control error are proposed. The focus of the modified expressions is based on a simple equality which was proposed in the open literature. The major benefit from using the proposed expressions which are obtained for both coherent and noncoherent receptions is that they require less definition about the spreading sequences for the BER calculation.

Use of a fiber-optic probe during CO2 laser drilling

The present study examines the effect of plasma on CO2 laser drilling of mild steel samples using oxygen assisting gas at different pressures. A fiber optic probe was used to detect the plasma on the surface of the workpiece. Mild steel samples at different thicknesses were used as workpieces. Oxygen was introduced coaxially with the laser beam.

Optimization of pulsed laser power supply system

The design criteria of pulsed laser power supply are examined. The components examined are the power supply, the pulse forming network, and the triggering circuit. In addition, the optimization and mathematical modeling of this system was achieved.