Analysis and code design of variable time-fraction collaborative communications

Recent results have shown that it is possible to obtain the diversity advantages promised by multiple transmit/receive antennas through the use of collaboration. Collaboration entails having a source wishing to communicate to a destination with the help of a relay. Two-phase protocols have been developed to provide collaboration in wireless networks. Previous work has assumed a fixed amount of time spent in each phase of communication. Following the results of, in this paper we have proposed and studied a variable time-fraction collaborative communication protocol. We provide guidelines for the construction of codes with better performance than the use of traditional space-time codes in the collaborative phase. We also provide an analysis of the upper bound on FER of the proposed scheme. Analytical as well as simulated results reveal the advantages of using a variable time-fraction over a fixed time-fraction. The results also show that for any relay location, the variable time-fraction protocol will perform at least as well as the fixed time-fraction protocol. Therefore, unlike with fixed time-fraction, there is no need for a relay to select an optimal time-fraction based on its relative position with respect to the source and destination.