Serially concatenated continuous phase modulation with low density generator matrix codes: property, optimization and performance analysis

We propose a new scheme of serially concatenated continuous phase modulation (SCCPM) by using nonsystematic low density generator matrix (LDGM) codes as the outer code. A property of the LDGM code degree is investigated. We use the exit chart/function to optimize the LDGM codes. The exit function of CPM with a fixed SNR (signal-to-noise-ratio) is shown. We derive the union bound to analyze the error floor performance. Design principles are proposed from the analysis process. Numerical results show that this scheme converge earlier (lower SNR) than previous SCCPM for iterative decoding.