This paper presents a bandwidth efficient multilevel concatenatedcoded modulation scheme for reliable data transmission over the shadowedmobile satellite communication (MSAT) channel. In the heavy shadowedMSAT channel which is statistically close to the Rayleigh fadingchannel, a coded modulation system suffers very severe distortion due torandomly changing phase and the multipath fading. In this scheme,bandwidth efficient block modulation codes are used as the inner codesand Reed-Solomon codes of various error correcting capabilities are usedas the outer codes. The inner and outer codes are concatenated inmultiple levels. A systematic method for constructing multilevelconcatenated modulation codes is presented and a multistage closestcoset decoding for these codes is proposed. Specific multilevelconcatenated 8-PSK modulation codes have been constructed. These codesare designed to remove the error floor phenomenon or lower the bit-errorrate of the error floor caused by the large Doppler frequency shift dueto the motion of vehicles. Simulation results show that these codesperform very well and achieve large coding gains over the uncodedreference modulation systems
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