Efficient soft demodulation schemes for the DVB-S2X system

In this paper, we propose efficient soft demodulation methods for the 64, 128, and 256 amplitude and phase shift keying schemes defined in the digital video broadcasting via satellite second-generation system. We first derive hard decision threshold (HDT) lines for the constituent bits in a symbol and subsequently present compact equations to estimate the soft bit information. If the HDT line for a constituent bit is a simple continuous line, then the soft bit estimation is performed by simply calculating the distance between the detected symbol and the HDT line. High computational complexity and appreciable performance degradation may occur if HDT lines are too complex. In order to prevent this, we also propose a modified max-log demodulation method that achieves the same performance as the original max-log method but with reduced complexity. Depending on the application, a hybrid method can be utilized by combining the advantages of the HDT and modified max-log methods. The simulation results reveal that the proposed hybrid scheme produces almost the same performance as the original max-log method with greatly reduced computational complexity.