  We consider binary continuous phase modulation (CPM) signals used in some
recent low-cost and low-power consumption telecommunications standard. When
these signals are generated through a low-cost transmitter, the real modulation
index can end up being quite different from the nominal value employed at the
receiver and a significant performance degradation is observed, unless proper
techniques for the estimation and compensation are employed. For this reason,
we design new binary schemes with a much higher robustness. They are based on
the concatenation of a suitable precoder with binary input and a ternary CPM
format. The result is a family of CPM formats whose phase state is constrained
to follow a specific evolution. Two of these precoders are considered. We will
discuss many aspects related to these schemes, such as the power spectral
density, the spectral efficiency, simplified detection, the minimum distance,
and the uncoded performance. The adopted precoders do not change the recursive
nature of CPM schemes. So these schemes are still suited for serial
concatenation, through a pseudo-random interleaver, with an outer channel
encoder.
