A New Implementation Technique to Decode the Convolutional Code in Trellis-Coded Modulation

Anh DINH  Xiao HU  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E87-A   No.3   pp.619-627
Publication Date: 2004/03/01
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Applications and Implementations of Digital Signal Processing)
Category: Communication Theory and Systems
TCM,  look-up-table,  Viterbi decoding,  IP core,  ASIC,  VLSI architecture,  

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This paper presents a new technique to implement a convolutional codec in VLSI. The code is used in the Trellis Code Modulation. The technique aims to reduce hardware complexity and increase throughput to decode the convolutional code using Viterbi algorithm. To simplify decoding algorithm and calculation, branch cost distances are pre-calculated and stored in a Distance Look Up Table (DLUT). By using the DLUT to get each branch cost in the algorithm, the hardware implementation of the algorithm does not require any calculation circuits. Furthermore, based on the trellis diagram, an Output Look-Up-Table (OLUT) is also constructed for decoding output generation. This table reduces the amount of storage in the algorithm. The use of look-up tables reduces hardware complexity and increases throughput of the decoder. Using this technique, a 16-states, radix-4 TCM codec with 2-D and 4-D was designed and implemented in both FPGA and ASIC after mathematically simulated. The tested ASIC has a core area of 1.1 mm2 in 0.18 µm CMOS technology and yields a decoding speed over 500 Mbps. Implementation results have shown that LUT can be used to decrease hardware requirement and to increase decoding speed. The designed codec can be used as an IP core to be integrated into system-on-chip applications and the technique can be explored to use to decode the turbo code.