Browsing by Author "Ciflikli, Cebrail"

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Citation - WoS: 12
Citation - Scopus: 20
Artificial Neural Network Channel Estimation Based on Levenberg-Marquardt for Ofdm Systems
(Springer, 2009) Ciflikli, Cebrail; Ozsahin, A. Tuncay; Yapici, A. Cagri; 01. Atılım University
The many advantages responsible for the widespread application of orthogonal frequency division multiplexing (OFDM) systems are limited by the multipath fading. In OFDM systems, channel estimation is carried out by transmitting pilot symbols generally. In this paper, we propose an artificial neural network (ANN) channel estimation technique based on levenberg-marquardt training algorithm as an alternative to pilot based channel estimation technique for OFDM systems over Rayleigh fading channels. In proposed technique, there are no pilot symbols which added to OFDM. Therefore, this technique is more bandwidth efficient compared to pilot-based channel estimation techniques. Also, this technique is making full use of the learning property of neural network. By using this feature, there is no need of any matrix computation and the proposed technique is less complex than the pilot based techniques. Simulation results show that ANN based channel estimator gives better results compared to the pilot based channel estimator for OFDM systems over Rayleigh fading channel.
Reducing the Intermodulation Distortion in Ofdm Systems by Feedforward Linearization Technique
(Ieee, 2009) Yapici, Alparslan Cagri; Ciflikli, Cebrail; Airframe and Powerplant Maintenance; 13. School of Civil Aviation (4-Year); 01. Atılım University
This study presents a feedforward linearizer, in order to reduce the intermodulation distortion (IMD) caused by the nonlinear properties of the radio frequency (RF) power amplifier (PA) in orthogonal frequency-division multiplexing (OFDM) systems. The design procedure and validation of OFDM system and feedforward linearizer have been carried out by Agilent-ADS. In order to evaluate the performance of the feedforward linearizer, sweeping back-off power has been used. Adjacent channel power ratio (ACPR) levels versus back-off power results are investigated to evaluate the performance of the linearization technique. Efficiency improvement is figured out by investigating the power added efficiency (PAE) versus back-off power. Simulation results have been shown that ACPR improvements were acceptable for OFDM system when the PA is utilized together with feedforward linearizer.