Correlative Encoded Digital FM

Abstract

This paper gives a straightforward method of obtaining an explicit expression for the spectrum of a correlative encoded digital FM signal. An investigation of the band occupancy for various encoding schemes with rectangular, as well as raised-cosine pulse shaping, is carried out. Correlative encodings that are spectrally more efficient than minimum shift keying (MSK) and that promise an improved error performance are shown. In addition, if a small degradation in error performance is tolerated, substantial increases in band efficiency are possible. For example, with the polynomial (1 + 2D + D^{2})/4 the signal is spectrally 47 percent more efficient than MSK and with an SNR performance degradation of only 1.1 dB.