Rate Optimization for Digital Frequency Modulation

The data rate of a multilevel digital FM system is optimized subject to fixed RF bandwidth, signal-to-noise ratio, and output error rate. The possibility of optimizing such a system was first considered by J. R. Pierce at Bell Telephone Laboratories. He made the observation that it is possible to send many levels slowly or fewer levels rapidly for an FM wave of fixed RF bandwidth and error rate, and that there must be a choice of signaling rate and number of levels that optimize the data rate. The rigorous treatment of this problem is the subject of this paper. The mathematical model we analyze uses frequency-shift keying at the transmitter and ideal discrimination detection with an integrate-and-dump circuit as the post-detection filter. Our results are exhibited graphically showing the various dependencies among the pertinent system parameters.