Multilevel turbo coded-continuous phase frequency shift keying (MLTC-CPFSK) over satellite channels in space communication

In this paper, in order to improve bit error performance and bandwidth efficiency, we introduce a new type of Turbo coded modulation scheme, called Multilevel Turbo Coded-Continuous Phase Frequency Shift Keying. (MLTC-CPFSK). The basic idea of multilevel coding is to partition a signal set into several levels and to encode separately each level by a proper component of the encoder. In MLTC-CPFSK, to provide phase continuity of the signals, Turbo encoder and Continuous Phase Encoder (CPE) are serially concatenated at the last level, while all other levels consist of only a turbo encoder. Therefore, the proposed system contains more than one turbo encoder/decoder blocks in its structure. The parallel input data sequences are encoded by our multilevel scheme and mapped to CPFSK signals. Then these modulated signals are passed through AWGN and fading channels. At the receiver side, input sequence of first level is estimated from the first turbo decoder. Then the other input sequences are computed by using the estimated input bit streams of previous levels. Simulation results are drawn for 4CPFSK two-level turbo codes over AWGN, Rician, and Rayleigh channels for three iterations while frame sizes are chosen as 100 and 1024. Higher error performances are obtained from various type of MLTC-CPFSK systems compared to Trellis Coded CPFSK systems.