Trellis Coded Modulation for Multi-State QAM--Which is Better, Signal Space Expansion or Bandwidth Expansion ?--

Yoichi SAITO  

IEICE TRANSACTIONS (1976-1990)   Vol.E73   No.10   pp.1666-1673
Publication Date: 1990/10/25
Online ISSN: 
Print ISSN: 0000-0000
Type of Manuscript: Special Section PAPER (Special Issue on Communication Theory and Its Applications)
Category: Modulation and Demodulation

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This paper describes the application of Trellis Coded Modulation (TCM) to multi-state QAM. The proposed strategy of increasing coding gain is based on the classical approach of error correction coding, in which redundant bits are added at the cost of bandwidth expansion. It is shown that symbol-rate-increased TCM is superior to the conventional TCM as the modulation state increases in number. Transparency to phase rotations is also considered. A pair of linear codes transparent to 180phase rotation is applied to the in-phase and the quadrature channels in a symbol-rate-increased manner. The tranparent code search has found a new encoder for 64-state convolutional code which has the same minimum squared distance but a smaller Nfree than the Ungerboeck nontransparent code. As an example, the new TCM approach to 256 QAM digital radio-relay systems is discussed from the fundamental system design poin of view. As a result, it has been shown that STM-1 (155.520 Mbit/s) signals can be transmitted within a 30 MHz bandwidth in spite of bandwidth expansion and a flat fade margin improvement of more than 5 dB is obtained.