Delay-optimal power and precoder adaptation for multi-stream MIMO systems

In this paper, we consider delay-optimal MIMO precoder and power allocation design for a MIMO link in wireless fading channels. There are L data streams spatially multiplexed onto the MIMO link with heterogeneous packet arrivals and delay requirements. The transmitter is assumed to have knowledge of the channel state information (CSI) as well as the joint queue state information (QSI) of the L buffers. Using L-dimensional Markov decision problem (MDP), we obtain optimal precoding and power allocation policies for general delay regime, which consists of an online solution and an offline solution. The online solution has negligible complexity but the offline solution has worst case complexity part((N + 1)
^L
) where N is the buffer size. Using static sorting of the L eigenchannels, we decompose the MDP into L independent 1-dimensional subproblems and obtained low complexity offline solution with linear complexity order part(NL) and close-to-optimal performance.