Rational pulse-shaping filters for almost MSK-like modulation

MSK-like data-formulation formats are those for which: (1) the instantaneous phase of the transmitted signal changes by exactly 90 deg in each bit interval; (2) the envelope of the transmitted signal is constant; and (3) the power spectrum of the transmitted signal rolls off asymptotically faster than the spectrum of ordinary (rectangular or unfiltered) QPSK. Well-known members of this family include MSK (minimum-shift keying), SFSK (sinusoidal frequency-shift keying), and DSFSK (doubly sinusiodal frequency-shift keying). These modulation types are well suited both to data communication and to radar pulse compression using binary code sequences. Unfortunately, most MSK-like formats have complex implementations. In this report, new modulation formats are described which come close to being in the MSK-like class, yet are inherently simple to implement using baseband pulse-shaping filters with low-order rational transfer functions.