The feasibility study of the Nyquist baseband filtered 4-level FM for digital mobile communications

In many digital FM schemes proposed for digital mobile radio communications, the Nyquist baseband filtered multilevel FM with frequency discriminator detection method features narrow bandwidth, good error rate performance and simple circuit implementation. This paper describes the Nyquist baseband filtered 4-level FM for 16 kbps transmission in a 25 kHz channel spacing. The sensitivity, occupied bandwidth and relative interference power into adjacent channel are almost the same as those for analogue FM radios. Adjacent channel selectivity is 62dB and 83dB against a modulated and a non-modulated signal interference. Intermodulation is the same as to the adjacent channel selectivity. A decision-directed automatic dc-offset and level control techniques shows excellent compensation effects against the drift of center frequency and of FM modulation/demodulation sensitivity. These results prove the high feasibility of the digital mobile radio communications.