The performance of a CPFSK trellis code in non-Gaussian noise

Recently R. Padovani and J.K. Wolf (IEEE Trans. Commun., vol.COM-34, no.5 p.446-53, May 1986) extended the Ungerboeck class of trellis codes to signal sets based on combined PSK (phase-shift-keying) and FSK (frequency-shift-keying) modulation (CPFSK). This class of codes has important advantages in the LF and VLF bands, where bandwidth is very scarce and the available transmitter hardware is intolerant to signals that do not exhibit a constant envelope. In the present work the authors report the results of a simulation study to measure the performance of CPFSK signaling using two different LF and VLF atmospheric noise models. It is concluded that CPFSK codes should be considered for use in designs for LF and VLF broadcast systems. Although no comparisons have been made of their performance against the performance of the Wagner codes currently used in the VERDIN submarine broadcast system, the advantages of greater than 1-b/T signaling is very enticing in frequency bands where the data rate can be painfully low