Ibrahim Develi

Outage Probability Analysis of Dual-Hop Decode-and-Forward Relaying Over Mixed Rayleigh and Generalized Gamma Fading Channels

In this letter, outage probability of dual-hop decode-and-forward (DF) relaying scheme is analyzed over mixed Rayleigh and generalized Gamma fading channels. Cooperation model considered in this work consists of a source, a relay and a destination. It is assumed that source-relay and relay-destination channels experience Rayleigh fading and generalized Gamma fading, respectively. Exact outage probability expression is derived and outage performance is illustrated for both direct transmission and DF relaying scheme.

An Application of Artificial Neural Network to Compute the Resonant Frequency of E–Shaped Compact Microstrip Antennas

Abstract An application of artificial neural network (ANN) based on multilayer perceptrons (MLP) to compute the resonant frequency of E-shaped compact microstrip antennas (ECMAs) is presented in this paper. The resonant frequencies of 144 ECMAs with different dimensions and electrical parameters were firstly determined by using IE3D(tm) software based on the method of moments (MoM), then the ANN model for computing the resonant frequency was built by considering the simulation data. The parameters and respective resonant frequency values of 130 simulated ECMAs were employed for training and the remaining 14 ECMAs were used for testing the model. The computed resonant frequencies for training and testing by ANN were obtained with the average percentage errors (APE) of 0.257% and 0.523%, respectively. The validity and accuracy of the present approach was verified on the measurement results of an ECMA fabricated in this study. Furthermore, the effects of the slots loading method over the resonant frequency were investigated to explain the relationship between the slots and resonant frequency.

Approximate expression of bit error rate in uplink MC-CDMA systems with equal gain combining

Uplink multicarrier code-division multiple-access (MC-CDMA) with equal gain combining (EGC) over Nakagami fading channels is considered. An improved expression which is a feasible alternative for the bit error rate (BER) performance evaluation of MC-CDMA signals is proposed. Simulated annealing algorithm is employed to obtain the optimum value of the coefficients belonging to the proposed expression. Numerical examples show that the performance curves computed by the improved expression are in good agreement with the results obtained by the exact expression. Thus, the proposed expression can improve the accuracy of BER performance evaluation that has been realized by the approximate expression.

Measurement and analysis of electromagnetic pollution generated by GSM-900 mobile phone networks in Erciyes University, Turkey

Mobile phones are becoming increasingly important in our everyday lives. The rising number of mobile phones reflects a similar increase in the number of base stations. Because of this rapid evolution, the establishment and planning of new base stations has become mandatory. However, the rise in the number of base stations, in terms of human health, is potentially very harmful. It is important to analyze the radiation levels of base stations until we can confirm that they are definitely not harmful in the long term. Mapping of electromagnetic field (EMF) is also important from a medical point of view because it provides useful information, for example, on the detection of diseases caused by EMF. With the help of this information the distribution of diseases over different regions can be obtained. In this article, the electromagnetic radiation levels of base stations were measured at 80 different points in Erciyes University (ERU), Turkey and detailed information about the measurement tools and measurement method were given. It was observed that no area in ERU exceeded the national and international limits. It is also observed that the effects of base stations vary according to duration and degree of exposure. Therefore, if people are exposed to a very low-intensity electromagnetic field for a very long time, serious health problems can occur.

A Closed-Form Approximate BEP Expression for Cooperative IDMA Systems over Multipath Nakagami-

In this letter, a closed-form approximate bit error probability (BEP) expression is derived for cooperative interleave-division multiple access systems with decode-and forward relaying subject to multipath Nakagami-m fading channels. The BEP expression is obtained by using the exponential-type approximation of Gaussian Q-function. Then, the derived expression is used to analyze system performance for different parameters, such as number of relays and Nakagami-m fading parameter. The accuracy of theoretical derivation is extensively validated through comprehensive computer simulations. It is shown that the results obtained by the proposed expression are in well agreement with the simulation results.

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Abstract This paper considers the problem of detecting the optimal spreading codes (OSC) in a given code set for a direct sequence-code division multiple access system that employs despreading sequences weighted by adjustable chip waveforms. Due to computational complexity required to detect the OSC in a code set, a simple and efficient strategy is introduced. Analysis and numerical results show that the proposed strategy can successfully distinguish the spreading codes being most suitable references for a given code set in which the candidate spreading codes have equal crosscorrelation properties.

Fading Channels

In this work, the resonant frequency of C-shaped compact microstrip antennas (CCMAs) operating at UHF band is computed by using the adaptive neuro-fuzzy inference system (ANFIS). For this purpose, 144 CCMAs with various relative dielectric constants and different physical dimensions were simulated by the XFDTD software package based on the finite-difference time domain (FDTD) method. One hundred and twenty-nine CCMAs were employed for training, while the remaining 15 CCMAs were used for testing of the ANFIS model. Average percentage error (APE) values were obtained as 0.8413% and 1.259% for training and testing, respectively. In order to demonstrate its validity and accuracy, the proposed ANFIS model was also tested over the simulation data given in the literature, and APE was obtained as 0.916%. These results show that ANFIS can be successfully used to compute the resonant frequency of CCMAs.

Detection of optimal spreading codes for DS-CDMA wireless systems with despreading sequences weighted by adjustable chip waveforms

In an interleave-division multiple access (IDMA) system, interleavers have a crucial role for the system performance. This paper presents a new approach to random interleavers for traditional IDMA systems. The proposed interleaver uses a random variable which is defined by Rayleigh distribution for mapping. Simulation results demonstrate that the proposed interleaver approach improves the bit-error rate (BER) performance of the IDMA systems.

Computing resonant frequency of C-shaped compact microstrip antennas by using ANFIS

The generalized multicarrier direct sequence code-division multiple-access (MC DS-CDMA) is a well known model that can be extended to different MC DS-CDMA schemes by simply varying a single parameter called as normalized subcarrier spacing. In this paper, the effect of the rate of average power decay on the bit error rate (BER) performance of the generalized MC DS-CDMA system is presented. Two specific schemes known as multitone DS-CDMA and orthogonal MC DS-CDMA are considered for the BER performance analysis. Simulation results show that the rate of average power decay has an important effect on the BER performance comparisons between the multitone DS-CDMA system and the orthogonal MC DS-CDMA system.

A new approach to random interleavers for traditional IDMA systems

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