The Diversity-Multiplexing Tradeoff of Delay-Constrained Sequential Streaming

We study sequential encoding of a stream of messages over a block-fading MIMO channel. A new message arrives in each coherence block and the decoder is required to output each message after a delay of T coherence blocks. We establish the optimal DMT and show that it can be achieved using an interleaved coding scheme. The converse is based on a new outage amplification technique. We also discuss another coding scheme based on a sequential tree-code, which is delay-universal. This coding scheme only requires the knowledge of delay at the decoder and yet realizes the optimal DMT. We also discuss some extensions when multiple messages at fixed intervals, arrive within each coherence period.