Cooperative Diversity Relaying Techniques in Wireless Communication Networks

In wireless networks, link budget can be relaxed by delivering the data using intermediate relay nodes. Although the immediate purpose of relaying is to obtain gain against path loss, it can also create spatial diversity due to the broadcast nature of the wireless medium. The objective of this work is to design and analyze relaying protocols that induce e2e cooperative diversity for ad hoc and infrastructure based networks. One of the main limitations of digital multi-hop relaying is the occurrence of detection errors at the relays. If the relaying is not done selectively, these errors cause significant performance degradation at the destination, a problem usually called error propagation. The first part of this thesis studies threshold digital relaying techniques to reduce error propagation. A set of optimal thresholds are derived and their performance for a single relay network is evaluated. It is shown that threshold digital relaying achieves full – in this case dual diversity. A good approximation to the optimal threshold is also derived. For multiple relay scenarios, a relay selection protocol based on threshold is proposed and threshold functions that achieve full diversity are provided. Most studies on cooperative diversity assume relays at favorable locations, which cannot be justified in random topologies. These studies are not necessarily good indicators of network-wide benefits of cooperative relaying. The second part of this thesis analyzes the network-wide benefits of cooperative relaying in random topologies. Assuming that the relays are distributed according to Poisson point process, the performance of cooperative relaying is derived as a function of relay density. The relays can be user terminals serving for each other, as well as dedicated fixed relays that are part of the infrastructure. Due to their less stringent space and cost constraints, infrastructure-based relays can accommodate multiple-antennas. The last part of this thesis is a preliminary study on an uplink scenario, where multiple single-antenna users communicate with a common multi-antenna destination with the help of a multi-antenna relay. It is shown that using multi-stream relaying and practical Multiple Input Multiple Output (MIMO) receivers, e2e diversity benefits can be achieved. Yol arkadaşım İlker’e, Yerlerimiz, hep, yeni yollarımızın başları; yollarımız da, hep, yeni yerlerimizin sonları ola...