Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği

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

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Author: search.filters.author.Khanfir, HajerPublication Index: search.filters.publicationIndex.WoS

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Now showing 1 - 4 of 4
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Reduced Feedback Load Using User Selection Algorithms for the Multiuser Multi-Input Single-Output Systems
    (John Wiley and Sons Inc., 2013) Khanfir, Hajer; Le Ruyet, Didier; Özbek, Berna
    Locate full-text(opens in a new window)|Full Text(opens in a new window)|View at Publisher| Export | Download | Add to List | More... Transactions on emerging telecommunications technologies Volume 24, Issue 7-8, November-December 2013, Pages 809-819 Reduced feedback load using user selection algorithms for the multiuser multi-input single-output systems (Article) Khanfir, H.a , Le Ruyet, D.a, Özbek, B.b a Electronics and Communications Laboratory, CNAM, 292 Rue Saint Martin, 75141, Paris, France b Electrical and Electronics Engineering Department, Izmir Institute of Technology, Urla, 35430, Izmir, Turkey View references (27) Abstract For wireless multiuser multi-input single-output communication systems with adaptive scheduling and precoding, the users have to feed back their channel state information. However, the amount of feedback data increases with the number of users and the number of transmit antennas. In this paper, we propose a criterion based on the orthogonality between the users' channels to reduce this uplink load. Without cooperation between the users, we only allow users that are semi-orthogonal to feed back their quantized channel information to the base station. We propose a lower bound on the sum rate for the proposed criterion. We show that the performance is almost independent of the number of quantized channel quality information and only channel direction information is important at the transmitter. Then, we consider a noisy feedback channel and propose an algorithm to reduce the noise effect on the analogue feedback
  • 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.