  This paper re-examines the well-known fundamental tradeoffs between rate and
reliability for the multi-antenna, block Rayleigh fading channel in the high
signal to noise ratio (SNR) regime when (i) the transmitter has access to
(noiseless) one bit per coherence-interval of causal channel state information
(CSI) and (ii) soft decoding delays together with worst-case delay guarantees
are acceptable. A key finding of this work is that substantial improvements in
reliability can be realized with a very short expected delay and a slightly
longer (but bounded) worst-case decoding delay guarantee in communication
systems where the transmitter has access to even one bit per coherence interval
of causal CSI. While similar in spirit to the recent work on communication
systems based on automatic repeat requests (ARQ) where decoding failure is
known at the transmitter and leads to re-transmission, here transmit
side-information is purely based on CSI. The findings reported here also lend
further support to an emerging understanding that decoding delay (related to
throughput) and codeword blocklength (related to coding complexity and delays)
are distinctly different design parameters which can be tuned to control
reliability.
