Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği

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

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End date: 2009Subject: search.filters.subject.Orthogonal frequency division multiplexing

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  • Article
    Citation - WoS: 7
    Citation - Scopus: 8
    Performance Evaluation of Multicast Miso-Ofdm Systems
    (Springer Verlag, 2008) Özbek, Berna; Le Ruyet, Didier; Khanfir, Hajer
    In this paper, we analyze the performance of multicast orthogonal frequency division multiplexing (OFDM) systems with single and multiple transmit antennas. We show that the resource allocation that includes the subcarrier allocation, bit loading, and the precoding vector selection in the multiple-input single-output (MISO) case is a difficult optimization problem. Consequently, we propose suboptimal algorithms based on the maximization of the sum data rate and the maximization of the minimum user data rate criteria. For practical application, we consider a complete transmission chain by combining powerful erasure codes with the proposed algorithms. Using this scheme, we guarantee that each user receives the same amount of information to decode the same data. Simulation results show that, for both single-input single-output (SISO)-OFDM and MISO-OFDM cases, the proposed multicast OFDM systems achieve gains over the worst user case algorithm.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 3
    Low Complexity Zf Receiver for Orthogonal Sfbc-Ofdm in Broadband Wireless Channels
    (Institution of Engineering and Technology, 2006) Özbek, Berna; Le Ruyet, Didier
    Orthogonal space-frequency block coded (SFBC) orthogonal frequency division multiplexing (OFDM) systems are analysed in broadband wireless channels where adjacent subcarriers do not have the same channel coefficients and the matched filter receiver causes an error floor in bit error rate performance. To avoid this, a low complexity zero forcing (ZF) receiver for the orthogonal schemes with two and three transmit and one receive antennas are proposed.
  • 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.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 7
    The Adaptive Channel Estimation for Stbc-Ofdm Systems
    (İstanbul Üniversitesi, 2005) Özbek, Berna; Yılmaz, Reyat
    In this paper, we propose adaptive channel estimation methods based on LMS and RLS for orthogonal STBC-OFDM systems with three transmit antennas. The performance of the proposed algorithms is obtained in the frequency selective channels using Hiperlan/2 characteristics.