Two Relay-Stage Selection Cooperation in Wireless Networks and Why More than Two Is Not Necessary

The selection cooperation is a basic and attractive scheme of cooperative diversity in the multiple relays scenario Most previous schemes of selection cooperation consist only one relay stage in which one relay is selected to retransmit and the signal from the selected relay is not utilized by other relays In this paper we Introduce a two relay stage selection cooperation scheme The performance can be improved by letting all other relays to utilize the signal from the first selected relay to make an other selection and retransmission in the second relay stage We derive the closed form expression of the outage probability of the proposed scheme in the high SNR regime Both theoretical and numerical results suggest that the proposed scheme can reduce the outage probability compared with the traditional scheme with only one relay stage Furthermore we demonstrate that more than two relay stage can not further reduce the outage probability We also study the dependence of the proposed scheme on stage lengths and topology and analyze the Increased overhead