Abstract

Continuous Phase Frequency Shift Keying (CPFSK) is a type of non-linear modulation, where the phase change from one symbol to the next symbol is continuous resulting in a faster spectral roll-off and smaller bandwidth. The multi-amplitude CPFSK (MACPFSK), which is created by superposition of CPFSK signals, is a class of CPFSK signals which also preserves the phase continuity; however it looses the constant envelope property. Application of trellis coding to MACPFSK significantly improves the system performance as it increases the minimum distance by introducing restrictions on the symbols that can be in a sequence. Thus a trellis code can be efficiently designed to achieve maximum separation in signals resulting in higher minimum distance value. Moreover, another class of Trellis Coded MACPFSK (TC-MACPFSK) signals can also be generated by altering the alignment of individual CPFSK signal, which is equivalent to the introduction of timing offset. This method inherently reduces the Peak to Average Power Ratio (PAPR) and also improves the system performance in terms of minimum distance for a particular value of timing offset.