Nyquist DMSK for minimum BER
Robert A. Monzingo · 2002
The BER performance of classical differential minimum shift keying (DMSK) suffers by comparison with classical differential phase shift keying (DPSK) due to the inherent presence of intersymbol interference (ISI) that is manifest in the fact that the modulating pulses fail to yield an output phase trajectory that attains multiples of /spl pi//2 at the prescribed detection times. Despite this difficulty, DMSK remains an attractive alternative to DPSK because of its improved spectral containment. This paper addresses a means of overcoming the inherent ISI by developing a new DMSK modulation standard. This result is accomplished by adopting two alterations as follows: (1) modify the simple phase ramp of classical MSK into a three part function that undershoots, then overshoots, and finally returns to the final value of /spl pi//2, and, (2) substitute a matched filter in the receiver that yields a phase trajectory which attains exact multiples of /spl pi//2 at the prescribed detection times. These measures eliminate the underlying cause of communication efficiency, and yield a BER performance that essentially matches that of classical DPSK.