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 presence 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 ωd, control of outage probabilty Pout is possible. Moreover, the choice of duty-cycle in the modulation pulse τ/T < 1 leads to a lower value of Pout with respect to the conventional case τ/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 Pout 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.