Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/11

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Subject: search.filters.subject.Orthogonal frequency division multiplexingWoS Q: search.filters.wosQuartile.N/A

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Now showing 1 - 4 of 4
  • Conference Object
    Yazılım Tabanlı Radyolarda Karşılıklı Kanal Özelliğinin İncelenmesi
    (Institute of Electrical and Electronics Engineers Inc., 2016) Uslu, Merve; Tuğrel, Halim Bahadır; Karabulut Kurt, Güneş; Özbek, Berna
    Kablosuz haberleşme sistemlerinde, kanal kestirimi çok önemli bir yer tutmaktadır. Bu çalışmada A ve B, iki haberleşme düğümü olduğu varsayıldığında, A düğümünden B düğümüne olan kanal için elde edilen kanal katsayıları ile, B düğümünden A düğümüne olan kanal için elde edilen kanal katsayılarının benzerliği incelenmiştir. Karşılıklı kanal özelliğinden dolayı bu kanalların birbirine benzer çıkmaları beklenmektedir. Bu çalışmada, laboratuvar ortamında yazılım tabanlı radyo kitleri kullanılarak karşılıklı kanal özelliği test ortamında test edilmiş, bu iki kanal katsayılarının genlik ve faz ortalama değerleri karşılaştırılmıştır.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 2
    Implementation of Pre-Fft Beamforming in Mimo-Ofdm
    (Institute of Electrical and Electronics Engineers Inc., 2016) Gökçeli, Selahattin; Uslu, Merve; Karabulut Kurt, Güneş; Özbek, Berna; Alakoca, Hakan; Durmaz, Mehmet Akif
    In this study, real-time software defined radio implementation of the point to point multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system using pre-fast Fourier transform (pre-FFT) beamforming technique in both the transmitter and the receiver is done for the first time in the literature. By taking benefit of the MIMO system's spatial multiplexing property, the performance of the implemented pre-FFT beamforming approach is demonstrated in terms of bit error rate and error vector magnitude measurements. As a result of the test results, the effect of the beamforming methods on the performance of communication systems are clearly observed.
  • Conference Object
    Citation - WoS: 6
    Citation - Scopus: 11
    Adaptive Resource Allocation for Multicast Ofdm Systems With Multiple Transmit Antennas
    (Institute of Electrical and Electronics Engineers Inc., 2006) Özbek, Berna; Le Ruyet, Didier; Khiari, Hajer
    We evaluate the impact of multiple transmit antennas on the performance of multicast OFDM systems by proposing a suboptimal low complexity algorithm. Associated with a powerful erasure code, it is possible to increase the data rate of multicast OFDM systems by selecting for each subcarrier to the users with a good channel condition. We show that the resource allocation which includes the precoding vector selection, subcarrier allocation and bit loading is a difficult optimization problem. We propose a suboptimal algorithm to solve this problem by avoiding the optimization to reduce complexity. When the users are not symmetrically distributed around the base station, we add a fair scheduler to guarantee that each user receives the same amount of data. We present simulation results where we compare the proposed multicast systems with the classical multicast OFDM systems. When the users are symmetrically distributed around the base station, the gain is rather small, whereas when the users are non-symmetrically distributed, the proposed algorithm outperforms OFDM systems with subcarrier allocation.
  • Conference Object
    Citation - Scopus: 7
    Pilot-Symbol Iterative Channel Estimation for Ofdm-Based Systems
    (Institute of Electrical and Electronics Engineers Inc., 2005) Özbek, Berna; Le Ruyet, Didier; Panazio, Cristiano
    In this paper, we propose a pilot-symbol-aided iterative channel estimation for coded OFDM-based systems. We use the symbol APP provided by the channel decoder to form groups of virtual pilots. According to their reliabilities, we combine these groups to improve the channel estimation. We also compare the proposed algorithm with the EM algorithm. Orthogonal frequency division multiplexing (OFDM) based systems are strong candidates for an air interface of future fourth-generation mobile wireless systems which provide high data rates and high mobility. In order to achieve the potential advantages of OFDM-based systems, the channel coefficients should be estimated with minimum error. The channel estimation can be improved using more pilot symbols [1]. However, it causes data rate reduction or bandwidth expansion. Therefore, spectrally efficient channel estimation techniques should be considered. In this case, the iterative techniques provide an improvement on the channel estimator performance without requiring additional pilots.