A modified version of the multilevel coded modulation scheme of Imai & Hirakawa is presented and analyzed. In the transmitter, the outputs of the component codes are bit interleaved prior to mapping into 8-PSK channel signals. A multistage receiver is considered, in which the output amplitudes of the Gaussian channel are soft limited before entering the second and third stage decoders. Upper bounds and Gaussian approximations for the bit error probability of every component code, which take into account errors in previously decoded stages, are presented. Aided by a comprehensive computer simulation, it is demonstrated in a specific example that the addition of the interleaver and soft limiter in the third stage improves its performance by 1.1 dB at a bit error probability of 10–5, and that the multilevel scheme improves on an Ungerboeck's code with the same decoding complexity. The rate selection of the component codes is also considered and a simple selection rule, based on information theoretic arguments, is provided.
Bibliographical noteFunding Information:
Paper approved by ~ t e p l ~ e(1;. n Wilson, the Editor for Coding Theory and Applications of the IEEE Coiiitiiunications Society. Ma~iuscriptr eceived: January 17, 1991; revised March 26, 1992. This work was supported by the Ministry of Coni~nunications,C hief Scientist, grant no. 050703, and it includes l”tiotis of a I)&. dissertation by Y. kofnim, submitted to the Senate of the Technioti in June 1992. This paper was presented in part at the 1990 Hilkent Inteniational Conference on New Trends in Communication, Control and Signal Processing, Ankara, Turkey, July 1990.