On the Availability of Multilevel CPFSK Systems with Modulation Pulse Shaping During Multipath Propagation

The behavior of CPFSK systems with modulation pulse shaping and limiter-discriminator detection is tested in the prsence of multipath fading. With the aim of determining the eye-closure domain, a theoretical analysis is presented for a generic number of modulation levels. It is shown that, by suitably varying the maximum angular frequency deviation ω
d
, control of outage probability P
out
is possible. Moreover, the choice of duty-cycle in the modulation pulse
\tau/T < 1
leads to a lower value of P
out
with respect to the conventional case
\tau/T = 1
, if we fix, as happens in practice, an upper bound in the transmitted power. This promising characteristic deeply differentiates the CPFSK from the PSK, DCPSK, and QAM systems: CPFSK systems, with a fixed number of modulation levels, allow us to obtain decreasing values of P
out
at the cost of increasing transmission power by suitably varying the set of signal parameters, even in the absence of diversity techniques and/or adaptive equalization.