  Posterior matching uses variable-length encoding of the message controlled by
noiseless feedback of the received symbols to achieve high rates for short
average blocklengths. Traditionally, the feedback of a received symbol occurs
before the next symbol is transmitted. The transmitter optimizes the next
symbol transmission with full knowledge of every past received symbol.
  To move posterior matching closer to practical communication, this paper
seeks to constrain how often feedback can be sent back to the transmitter. We
focus on reducing the frequency of the feedback while still maintaining the
high rates that posterior matching achieves with feedback after every symbol.
As it turns out, the frequency of the feedback can be reduced significantly
with no noticeable reduction in rate.
