Browsing by Subject "Orthogonal Frequency Division Multiple Access (OFDMA)"

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    Base station cooperation in multiple input multiple output orthogonal frequency division multiple access systems
    (2009) Tokel, Turgut Barış
    Newly emerging advancements such as multiple input multiple output (MIMO) and orthogonal frequency division multiple access (OFDMA) techniques become indispensable parts of today’s wireless systems such as WiMAX (IEEE 802.16 standard) since they can increase the supportable data rates significantly. However, achieving the maximum spectral efficiency in a MIMO system requires perfect channel state information (CSI) at the transmitter side and multicarrier nature of OFDMA systems increase the necessary CSI feedback from users to base stations remarkably. To further increase the supportable data rates, using frequency reuse factor of 1 in the system is also mandatory. Unfortunately, this results in significant cochannel interference (CCI) observed especially by the users near cell edges, which can severely degrade the system spectral efficiency. To cope with this problem, base station cooperation may play an important role. In this thesis, the problem of cooperative data transmission from base stations to users in multicellular MIMO-OFDMA systems is considered. An efficient cooperative scheduling and data transmission scheme, requiring limited CSI feedback from users to base stations and also limited information exchange between the base stations, is proposed. The numerical results demonstrate that, the proposed algorithm offers considerable spectral efficiency gains compared to conventional frequency reuse and noncooperative schemes, under severe CCI conditions