Akademik Veri Yönetim Sistemi
Tezin Türü: Yüksek Lisans
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Elektrik ve Elektronik Mühendisliği Bölümü, Türkiye
Tezin Onay Tarihi: 2014
Öğrenci: KEREM ERKAN
Danışman: ALİ ÖZGÜR YILMAZ
Özet:In cooperative communication, a source communicates with a destination over indirect links through relays. Like most wireless systems, cooperative networks seriously suffer from secrecy related issues. In this thesis, cooperative jamming method is utilized to provide secrecy for cooperative networks in which there exist adversary receivers called eavesdroppers. The main idea is to broadcast noise signals from a selected relay to corrupt the signal-to-interference-plus-noise ratio (SINR) at eavesdroppers when the transmitter communicates with the receiver through another selected relay. Throughout the study, it is assumed that channel state information (CSI) of the links between the source, relays and the destination is available at the transmit and receive sides of links. Rich scattering channels are assumed and all channel gains are taken as independent. In contrast to the past studies in the literature, CSI of eavesdroppers’ channels exist at only themselves since they are accepted as passive devices in this study. The knowledge on channel gains except eavesdroppers’ ones are used to adaptively select the relays to support cooperative jamming. Cooperative jamming is investigated here from an outage probability perspective where probability of secure transmission is the parameter of interest for a fixed transmission rate. First, cooperative jamming is applied to cooperative networks with single-antenna nodes. The probability of secure communication increases to a degree for a range of the communication rate R with cooperative jamming and adaptive selection of relays. The results are generally encouraging, but may be insufficient for real-world cooperative networks. Second, cooperative jamming is implemented at cooperative networks with multiple-antenna nodes to increase the probability of secure communication benefiting from advantages of multiple antennas. Adaptive transmit precoding is applied at the source and the communicating relay to enhance the SINR at legitimate receivers. This advantage brings an edge over eavesdroppers. Moreover, adaptive noise generation is proposed at the noise emitting relays in order to minimize the effect of noise at legitimate receivers. It is shown that the probability of secure communication dramatically rises with these adaptive techniques. As a result, there is a certain transmission rate R at which the source is able to securely communicate with the destination with probability approaching one.