Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği

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

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Author: search.filters.author.Le Ruyet, DidierEnd date: 2009

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Now showing 1 - 10 of 12
  • Conference Object
    Citation - Scopus: 2
    Genetik Algoritma ile Çok Kullanıcı Dfbç Sistemleri için Toplam Veri Hızı Enbüyüklemeli Uyarlanır Alttaşıyıcı ve Bit Yerleşimi
    (Institute of Electrical and Electronics Engineers Inc., 2008) Özbek, Berna; Le Ruyet, Didier
    In this work, we perform the adaptive subcarrier and bit allocation to maximize the sum data rate for multiuser OFDM systems using genetic algorithm. Since the convergence time of the genetic algorithm could be slow, we propose to use a different initial condition to accelerate it without increasing the complexity of genetic algorithm and sacrificing the performance of the system. We obtain the simulation results and compare them with the classical methods. We show that the genetic algorithm with proposed initial condition gives better performances than the classical ones for sum data rate maximized allocation.
  • Conference Object
    Citation - Scopus: 3
    Reduced Feedback Designs for Sdma-Ofdma Systems
    (Institute of Electrical and Electronics Engineers Inc., 2009) Özbek, Berna; Le Ruyet, Didier
    In SDMA-OFDMA wireless communication systems, the feedback load increases with the number of users, subcarriers and antennas in the cell. In this paper, we propose two efficient reduced feedback algorithms by selecting the clusters at the user side. For each cluster, we select the users according to their norm and their orthogonality. We evaluate the performance of the user selection algorithms considering the quantization effect. We also design a specific codebook design to quantize CSI for the proposed criterion.
  • Conference Object
    Citation - WoS: 3
    Citation - Scopus: 3
    Adaptive Resource Allocation for Sdma-Ofdma Systems With Genetic Algorithm
    (Institute of Electrical and Electronics Engineers Inc., 2009) Özbek, Berna; Le Ruyet, Didier
    In this paper, we propose an adaptive resource allocation algorithm to maximize the sum data rate for spatial division multiplexing access (SDMA) orthogonal division multiple access (OFDMA) systems using genetic algorithm. We perform Zero forcing (ZF) beamforming at the transmitter constructing single and multiple beams for OFDMA systems with multiple transmit antennas. In order to reduce the complexity and convergence time of genetic algorithm (GA), we present an initial condition obtained by allocating the user to the subcarrier with maximum precoding gain. The proposed algorithm reduces the complexity without sacrificing the performance. We obtain the simulation results and compare them with the classical static and adaptive allocation methods. We show that the GA with the proposed initial condition increases the sum data rate compared to classical GA and reduces the convergence time significantly for SDMA-OFDMA systems.
  • 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.
  • Conference Object
    Semi-Orthogonal User Selection for Miso Systems With Quantized Feedback
    (Institute of Electrical and Electronics Engineers Inc., 2008) Khanfir, Hajer; Le Ruyet, Didier; Özbek, Berna
    For MISO multi-user downlink wireless communication system with precoding at the transmission, the channel state information at the transmitter can provide tremendous capacity gains. However, the amount of feedback data increases with the number of users in the cell and the number of transmit antennas. In this paper, we study on different algorithms and criteria in order to significantly reduce the amount of feedback data. We associate the classical norm criterion with a criterion based on the orthogonality between the user channels. Without cooperation between the users, we only allow users that are semi-orthogonal to feedback their channel information (CQI and CDI) to the base station. The feedback CDI is quantized using a local grassmanian packing. We show that the proposed combined criterion with a finite feedback rate gives better performance compared to the norm criterion. Furthermore we show that the performance is not affected by CQI quantization.
  • Conference Object
    Citation - WoS: 2
    Citation - Scopus: 3
    Performance of Semi-Orthogonal User Selection for Multiuser Miso Systems
    (Institute of Electrical and Electronics Engineers Inc., 2008) Le Ruyet, Didier; Khanfir, Hajer; Özbek, Berna
    In MISO multiuser downlink wireless communication systems with precoding at the transmission, the capacity depends on the channel state information at the transmitter. Since the feedback data rate increases with the number of users in the cell it is important to perform a selection of the users at the receiver. In this paper, we evaluate the performance of different user selection algorithms at the receiver side through the noisy uplink channel. We evaluate the effect of the noisy channel on the classical norm criterion and on a criterion based on the orthogonality between the user channels. Without cooperation between the users, we only allow users that are semi-orthogonal to feedback their channel information as analog and quantized information to the base station through the noisy uplink channel. We propose an algorithm to reduce the noise effect on the analog feedback for semi-orthogonal user selection algorithm. We show that the semi-orthogonal criterion with quantized feedback gives better performance compared to the norm criterion for perfect and noisy uplink channels.
  • 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: 5
    Partial and Analog Feedback for Miso Precoding Systems
    (Institute of Electrical and Electronics Engineers Inc., 2007) Le Ruyet, Didier; Özbek, Berna
    We consider a multiple input single output antenna system with a feedback link. While most of the previous works have considered perfect feedback channels, in this paper, we evaluate the impact of a noisy feedback channel on the quality and the performance of the transmission. We compare the finite rate feedback scheme with the analog feedback schemes where the channel parameters are transmitted without quantization over the uplink channel. Two analog feedback schemes are considered : the feedback of the channel vector and the feedback of the normalized channel vector. We provide bounds on the performance and give numerical results. We have shown that at low to medium uplink SNR the analog feedback of the normalized channel vector outperforms the analog feedback of the channel vector. Depending on the range of uplink SNR, quantized feedback can perform poorlz y compared to analog feedback.
  • 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.