Rate-Diversity-Delay Tradeoff for ARQ Systems over MIMO Block-Fading Channels

We study the effect of power adaptation on the outage diversity of incremental-redundancy automatic-repeat-request (INR-ARQ) transmission over the multi-input multi-output (MIMO) block-fading channel. In particular, we derive the optimal outage diversity achieved by power adaptation in INR-ARQ systems, and show that power adaptation provides significant gains in outage diversity. We also prove that the optimal outage diversity is achievable with random coding schemes.