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Interference Alignment Techniques for Heterogeneous Wireless Networks
(Izmir Institute of Technology, 2016) Aycan, Esra; Özbek, Berna
In this thesis, we study the stream selection based interference alignment (IA) algorithms, which can provide large multiplexing gain, to deal with the interference in the heterogeneous networks. Firstly, different deployment scenarios for the pico cells are investigated assuming perfect channel state information (CSI) at the transmitters. Two different stream selection IA algorithms are proposed for fully and partially connected interference networks and selecting at least one stream is guaranteed for each user. A stream sequence is selected among a predetermined set of sequences that mostly contribute to the sum-rate while performing an exhaustive search. In the proposed algorithms, the complexity of the exhaustive search is significantly decreased while keeping the performance relatively close. After selecting a stream, the interference generated between the selected and the unselected streams is aligned by orthogonal projections. Then, the influence of the imperfect CSI on the proposed algorithms is analyzed and it is observed that the intra-stream interference causes a significant degradation in the performance due to the quantization error. Therefore, we propose an algorithm for the limited feedback scheme. Finally, adaptive bit allocation schemes are presented to maximize the overall capacity for all the proposed algorithms. The performance evaluations are carried out considering different scenarios with different number and placements of pico cells. It is shown that the proposed algorithm for the limited feedback is more robust to channel imperfections compared to the existing IA algorithms. The presented bit allocation schemes improve the performances of the algorithms compared to the equal bit allocation.
Resource Management for Multiuser Systms With Multiple Antennas in Wireless Networks
(Izmir Institute of Technology, 2014) Baştürk, İlhan; Özbek, Berna
In this thesis, we explore radio resource management algorithms for OFDMA based cellular networks. Firstly, we combine the OFDMA technology with multiple antennas technology and handle the resource allocation problem for the MISO-OFDMA systems. We take care of the fairness issue among users to prevent the users, which have good channel conditions, to obtain most of the system resources. Thus, we propose a fairness aware resource allocation algorithm and compare it with the existing schemes. Next, we enhance the conventional cellular network structure with mobile relays and examine relay selection and resource allocation algorithms for the OFDMA-based mobile relay enhanced cellular networks. We propose a novel relaying frame structure with efficient resource management algorithms in order to reveal the opportunities of the mobile relays. Then, we consider the queue-lengths of the users and propose a queue and channel aware joint relay selection and resource allocation algorithm to use the system resources efficiently. Finally, we combine mobile relaying and offloading technologies in order to overcome the capacity and coverage problems of the conventional cellular networks. We focus on the radio resource management problem for the OFDMA-based mobile relay-enhanced heterogenous cellular networks that contains multiple radio access technologies. We propose a network interface selection algorithm that consider the bandwidth availability information of each network in order to prevent sending the users to overloaded networks.

Phd Degree / Doktora

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