Degrees of Freedom Analysis of the Non-coherent Block Fading MAC Channel

We study a two-user multiple-input multiple-output (MIMO) fading multiple-access channel (MAC), where two terminals wish to communicate with a third one. The channels between the terminals are MIMO block fading channels with channel coefficients which are constant in a block of length T, and then change in an independent realization. The system model follows the model introduced by Hochwald and Marzetta. We consider a non-coherent channel model, where all terminals are aware of the statistics of the fading but not of its realization. Instead of using pilots for channel estimation, we assume communication where the information is communicated by the use of subspaces, following the geometric approach introduced by Zheng and Tse. We focus on the high signal-to-noise ratio (SNR) regime. In particular, we study the pre-log region, defined as the limiting ratio of the achievable-rate region to log SNR as the SNR tends to infinity