On the effect of a type of modulation pulse shaping in FSK transmission systems with limiter-discriminator detection

In this work we study a binary or multilevel continuous-phase FSK system with limiter-discriminator detection, in which the modulation pulses are rectangular with length τ admitting of any value not higher than the symbol time T. As an application example of the general treatment, we report numerical results in the binary case which, according to expectations, show the considerable τ influence on system performance, other conditions being fixed. In particolar, in the best operation condition of the system for Pe = 10-6 that takes place for the non-critical value τ = 0.6T, the transmission canne frequency band and the transmitting power are both smaller than those corresponding to the analogous best condition with the constraint τ = T. Besides, the transmitting power advantages which derive from the opportune choice of τ increase little by little with channel frequency band reduction. With reference to multilevel systems, we have then point out some research development lines which we think interesting.