Asymptotic performance analysis of distributed space-time codes

We study the asymptotic behavior of a cooperative scheme operating in amplify-and-forward (AF) mode for a large number of relays. An optimal code design rule is derived through the investigation of pairwise error probability (PEP) expression. The design rule turns out to be an Euclidean-distance-type metric including some scaling terms due to path loss and shadowing effects associated with underlying relay links and AF operation mode. Since the design criterion is channel dependent, it does not allow itself for a practical code design. However, we demonstrate that classical Euclidean distance can be used as a sub-optimal solution for realizing cooperative diversity advantages which we further verify through our simulation study.