Distance spectrum of coded multi-amplitude CPM

Multiamplitude continuous phase modulation (MACPM) is a bandwidth efficient modulation technique that can be represented as a sum of two constant amplitude continuous phase modulation (CPM) components that have the same modulation index but different amplitudes. Considering only the case when the modulation index is rational, the number of possible encoder states defined by the current amplitude and phase becomes finite, and MACPM can be described as a trellis code. If such MACPM modulator is preceded by a convolutional encoder, a more powerful trellis code is obtained. The Euclidean distance spectrum of coded MACPM, needed for analytic error probability evaluation, is obtained using an efficient bidirectional trellis search (BIFAST)