Repeated-segment preamble parameters: num_repeats identical segments of
repeat_len samples each, optionally followed by a dedicated training
symbol for integer-CFO recovery (and, in a later release, channel
estimation).
Dedicated training symbol used for integer-CFO recovery: one full
n_fft-point OFDM symbol (plus cyclic prefix) with a known value on
every subcarrier bin, maximizing discriminating structure for the
integer-bin-shift search.
Generates a repeated-segment preamble: a deterministic, reproducible
pseudo-random unit-average-energy base sequence of repeat_len samples,
tiled num_repeats times, followed by the training symbol (time-domain,
CP included) if preamble.training_symbol is present.