Design of Distributed Randomized Orthogonal Space-Time Coding schemes for Collaborative H-ARQ

In this paper we consider a collaborative hybrid ARQ protocol where retransmissions are handled by a number of cooperating nodes employing a distributed orthogonal space time coding scheme. Outage performances are analyzed by assuming a distributed randomized orthogonal space- time coding scheme (DR-OSTC) to be employed by the relaying terminals during the retransmission session. The antenna selection version of the DR-OSTC requires that each cooperating node chooses randomly and independently to serve as one of the space-time virtual antennas. By avoiding any predefined terminal-to-codeword mapping, the random selection of the space-time codewords substantially reduces the needed control overhead with respect to other distributed space-time coding strategies and it simplifies the node coordination task. According to this scheme, we develop a novel analytic model to evaluate the outage probability and tackle the problem of designing the minimum number of cooperating nodes M so as to meet a specific outage probability requirement at the destination node. Finally, according to these results, we develop simple but effective design rules tailored for the collaborative hybrid ARQ protocol in practical environments.