Diversity and freedom: a fundamental tradeoff in wireless systems

Summary form only given. The amount of diversity and the total number of degrees of freedom are two important resources in a wireless system. Traditionally they have been considered in isolation. We propose the point of view of describing the performance of communication schemes as a tradeoff between the actual utilized amount of these two resources. The optimal tradeoff achievable by any scheme provides a fundamental benchmark with respect to which the actual schemes can be judged. We give several examples on which this framework can be applied: 1) point-to-point MIMO links, 2) multiple access MIMO channels, 3) frequency selective ISI channels, 4) cooperative relaying systems.