| There has been a great deal of research done on modulation schemes that are spectral efficient, such as M-ary PSK, MSK and Duobinary FM, to name a few.;In this research, another spectrally efficient method utilizing CPFSK as the modulation scheme, is presented. Here the data bits, d(t), are encoded such that the ratio of the maximum to minimum phase that the modulated FM signal can attain is bounded. The power spectra as well as the error probability of the system utilizing a non-coherent detector has been investigated. It has been shown that the system has a power spectral efficiency of 1 b/s/Hz. Due to encoding of d(t), the modulation waveform exhibits a trellis structure. A coding gain of about 2 dB has been realized in decoding the received signal by utilizing this structure in decoding process. In addition, it has been shown that, other trellis coded modulation systems adhering to CNFM principles result in an improved probability of error at a cost of increasing the bandwidth necessary to transmit the coded signal. |
