Effect of Opportunistic Relay Selection on the diversity order of distributed turbo coded cooperative systems

In this work, the effect of Opportunistic Relay Selection (ORS), which selects relays providing cooperative communication, on the diversity order of Distributed Turbo Coded Cooperative (DTCC) systems is investigated. While only one relay is selected in a classical use of ORS, here two relays should be selected since DTCC utilizes two relays. Therefore, the effect of ORS (one relay selection and two relays selection cases) on diversity order of un-coded cooperative communication systems is firstly investigated. In the un-coded system, a single relay selected among M relays provides full diversity (i.e., diversity order is M), whereas two relay selected among M relays provides a diversity order between M and M-1. Then, the effects of two cooperative protocols, which are Amplify and Forward (AF) and Decode and Forward (DF), on the diversity orders of the un-coded cooperative system and the DTCC system, are investigated. When the relay selected among multi-relays (M relays) uses AF, the diversity order doesn´t increase with the increment of M value, whereas if the selected relay uses DF protocol, the diversity order increases with the rise of number of DF relays for both systems.