Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Özbek, BernaSubject: search.filters.subject.Wireless networks

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Now showing 1 - 3 of 3
  • Master Thesis
    Wireless Physical Layer Network Coding for Multiple Antenna Systems
    (01. Izmir Institute of Technology, 2020) İlgüy, Mert; Özbek, Berna
    Wireless networks are prone to interference due to their broadcast nature. In the design of most of the traditional networks, this broadcast nature is perceived as a performance-degrading factor. However, physical layer network coding (PNC) exploits this broadcast nature by enabling simultaneous transmissions from different sources and facilitates an increase in the spectral efficiency of the wireless networks. Besides, the massive multiple input multiple output (MIMO) is considered as one of key technologies to improve the spectral efficiency for wireless communication systems. The combination of PNC and multi-user massive MIMO in the sixth generation (6G) networks can increase further the spectral efficiency. In this thesis, PNC based systems are examined via bit error rate (BER) and coverage probability by focusing on the BER of the network coded symbol (NCS). Hence, PNC based systems are compared with network coding (NC) and conventional schemes. The influence of the signal-to-noise ratio (SNR) differences of the users are examined on the BER performances. Thereby, an alternative method to estimate NCS is proposed for the MIMO-PNC systems without using log likelihood ratio (LLR). We derive a closed form expression for the coverage probability in PNC based multi-user massive MIMO systems by employing zero forcing (ZF) equalization. The non-orthogonal multiple access (NOMA) based PNC system is proposed. We show the applicability of the PNC in the NOMA based MIMO systems by giving the the BER performance results.
  • Master Thesis
    Offloading Strategies for Heterogeneous Wireless Networks
    (Izmir Institute of Technology, 2016) Tuna, Evren; Özbek, Berna
    There has been a tremendous increase in the usage of multimedia services with the rapid penetration of mobile devices. In parallel to the technological developments in hardware and software of communication devices, users demand to have higher quality and more reliable services. The developments in network technologies are towards forming a converged structure that mobile, fixed and internet access technologies are able to operate together. Heterogeneous wireless networks have a critical role in order to meet dramatically increasing traffic demand. As a result of better operation of the systems with the help of heterogeneous wireless networks, it is possible to serve subscribers with higher performance with the help of offloading which transfer the traffic load from a network to another one. Various strategies are used in order to offload traffic between different wireless communication technologies. The main objective of this thesis is to examine offloading strategies which provides operation of different wireless communication technologies efficiently in heterogeneous wireless networks. The performance evaluations of different offloading strategies in various scenarios are implemented. The comparisons of strategies which are user initiated and network initiated are provided by considering their overhead load.
  • Master Thesis
    Interference Management Techniques for Femtocell Networks
    (Izmir Institute of Technology, 2015) Bayrak, Uğur; Özbek, Berna
    The need for high capacity and data rate increases with the growing demand for wireless communication. In order to meet this demand, one of the most effective ways of improving capacity and data rate is deployment of femtocell networks which are considered to be a promising technique for future wireless networks. However, mass deployment of these low-power base stations brings many challenges. Interference management will be one of the major challenges for the dense deployment scenarios of femtocells in coverage of the macro base stations. To cope with interference problem, there are many interference management techniques. In this thesis, power control and beamforming techniques are implemented separately and jointly in order to deal with cross-tier downlink interference which occurs between macro base station and users of femtocell. In this two-tier network system involving femtocell and macrocell layers, power control problem, first, is investigated. Feasible transmission power region for femtocell is determined with respect to the user locations so that targeted signal-to-interference-plus-noise-ratio (SINR) values are satisfied. Secondly, beamforming technique is applied using partial zero-forcing method. In this method, beamforming vectors are designed to remove cross-tier interference. It is observed that SINR of macro base station’s user does not undergoes any degradation in the nearfield region of femtocell. Finally, we apply these two techniques jointly. Since both interference suppression and power-efficiency is provided, joint technique seems to be a viable and environment-friendly solution for femtocell networks.