The order of the modulation used in existing adaptive demodulation schemes is no higher than 16

and the decoding of channel codes is not taken into consideration in the analysis and design.In this paper

an adaptive demodulation algorithm is studied.It includes multiple demodulation modes and can be applied to higher order quadrature amplitude modulations.A rate adaptive scheme at receiver is proposed which combines this algorithm and rateless error correcting codes.The bits whose absolute values of the log-likelihood ratio are the smallest in one symbol are deleted and the number of deleted bits varies in different demodulation modes

so the reliability and the average mutual information of demodulated bits can be boosted.From the perspective of mutual information analysis

the theoretical results of the required codeword length which meet the requirements of error performance are obtained.Moreover

the selection of the demodulation mode under a decoding complexity constraint is given.A sample scheme employing 256-QAM modulation constellations and Raptor codes is provided

and the simulation results of this sample are consistent well with those of the theoretical analysis

which confirms the effectiveness of the scheme.