Distributed Amplify-and-Forward cooperation while maintaining transmission freedom

This paper proposes a novel Distributed Amplify-and-Forward (DAF) cooperative scheme, achieving higher diversity order and yet maintaining the same transmission freedom as the conventional Amplify-and-Forward (AF) scheme. In the DAF scheme, a user´s transmitted symbols are partitioned into several sequences in order to be relayed by different users. In the cooperative network, each user still uses half of their transmission time for relaying others´ signals. But instead of relaying one user´s entire transmitted sequence, it helps different users for the relaying. Theoretical analysis of the DAF scheme is carried out in order to justify its advantages over the existing schemes. The outage behaviour and diversity-multiplexing tradeoff (DMT) analyses of the DAF scheme are presented. Through outage behaviour analysis, it is shown the DAF scheme achieves substantial diversity gains over the AF scheme. Furthermore, the DMT analysis justifies both the scheme´s achievable diversity gains and its ability to maintain the same transmission freedom as the AF scheme. The theoretical analyses are then extended to a general cooperative network consisting of N(N ≥ 2) relays, showing the diversity order can be increased with respect to the number of relays but not at the expense of each user´s transmission freedom.