On the Achievable Diversity-vs-Multiplexing Tradeoff in Cooperative Channels

In this paper, we propose new cooperation protocols for coherent flat-fading channels consisting of two (half-duplex) partners and one cell site. In our work, we differentiate between the multiple access (up-link) and broadcast (downlink) channels. For the cooperative multiple access channel, we upper-bound the achievable diversityvs-multiplexing tradeoff by that of a point-to-point system with two transmit and one receiver antenna. We then proceed to show that the proposed protocol achieves this optimal diversity-vs-multiplexing tradeoff for all multiplexing gains. For the cooperative broadcast channel, the proposed protocol is shown to achieve the extreme points of the tradeoff curve of the corresponding point-to-point system (i.e., d r and d r ). For other multiplexing gains (i.e., r ), the proposed scheme is shown to uniformally dominate all known cooperative protocols. A distinguishing feature of the proposed schemes is that they do not rely on orthogonal subspaces, allowing for a more efficient use of resources. Furthermore, our analysis reveals a fundamental difference between the cooperative multiple access channel and the relay channel model which inspires most known cooperation protocols.