Improvements of the Information-Bit Error Rate of Trellis Code Modulation Systems

Jun DU  Masao KASAHARA  

IEICE TRANSACTIONS (1976-1990)   Vol.E72   No.5   pp.609-614
Publication Date: 1989/05/25
Online ISSN: 
Print ISSN: 0000-0000
Type of Manuscript: PAPER
Category: Foundations of Signal Theory and Communication Theory

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Trellis coded modulation (TCM) is a new and attractive communication technique which yields significant coding gain with no degradation of the bandwidth efficiency. So far, researches concerning the TCM have concentrated upon minimizing the error-event probability (EEP). However, for the various bitwise data transmission systems, decreasing the post-decoding information-bit error rate (IBER) is more important than only minimizing the EEP. This paper is concerned with a simple but important problem that how to improve the IBER in TCM systems. The IBER of a TCM system depends not only on the EEP but also on the mapping of a binary m-tuple to a 2m-ary channel signal. A signal mapping called Set Partitioning mapping has been well adopted in the previously known TCM systems. In this paper, another well known signal mapping, the Gray-code mapping, is investigated as a promising signal mapping in TCM, and compared with the Set Partitioning mapping. Through a computer search, a number of optimun trellis codes with Gray-code mapping are found. It is shown that these codes have the minimum Euclidean distances as large as those of the Ungerboeck codes and yet yield smaller EEP and IBER.