  This paper presents a general approach for optimizing the number of symbols
in increments (packets of incremental redundancy) in a feedback communication
system with a limited number of increments. This approach is based on a tight
normal approximation on the rate for successful decoding. Applying this
approach to a variety of feedback systems using non-binary (NB) low-density
parity-check (LDPC) codes shows that greater than 90% of capacity can be
achieved with average blocklengths fewer than 500 transmitted bits. One result
is that the performance with ten increments closely approaches the performance
with an infinite number of increments. The paper focuses on binary- input
additive-white Gaussian noise (BI-AWGN) channels but also demonstrates that the
normal approximation works well on examples of fading channels as well as
high-SNR AWGN channels that require larger QAM constellations. The paper
explores both variable-length feedback codes with termination (VLFT) and the
more practical variable length feedback (VLF) codes without termination that
require no assumption of noiseless transmitter confirmation. For VLF we
consider both a two-phase scheme and CRC-based scheme.
