Iterative Decoding of Concatenated Convolutional Codes: Implementation Issues

Abstract

This tutorial paper gives an overview of the implementation aspects related to turbo decoders, where the term turbo generally refers to iterative decoders intended for Parallel Concatenated Convolutional Codes as well as for Serial Concatenated Convolutional Codes. We start by considering the general structure of iterative decoders, and the main features of the SISO algorithm that forms the heart of iterative decoders. Then, we show that very efficient parallel architectures are available for all types of turbo decoders allowing high speed implementations. Other implementation aspects like quantization issues and stopping rules used in conjunction with buffering for increasing throughput are considered. Finally, we perform an evaluation of the complexities of the turbo decoders as a function of the main parameters of the code.

Design of Fixed-Point Processing Based LDPC Codes Using EXIT Charts

“…Our results indicate that as a rule of thumb an overall OW of y + z = 6 may offer an attractive trade-off between an LDPC code's complexity and performance. As summarized in Table I, this result agrees with the conclusions of [7]- [13], [19], where the slight differences observed may be attributed to the different algorithms and quantization schemes considered.…”

Hardware implementation issues of turbo decoders

“…As stated by Forney (Boutillon et al, 2007), concatenation is a method of building long codes out of shorter ones in order to resolve the problem of decoding complexity by breaking the required computation into manageable segments according to the divide and conquer strategy. Turbo codes, also known as parallel concatenated convolutional codes (PCCC), are based on a parallel concatenation of two recursive systematic convolutional codes separated by an interleaver.…”

“…The turbo decoding principle calls for an iterative algorithm involving two component decoders exchanging information in order to improve the error correction performance with the decoding iterations. This iterative decoding principle was soon applied to other concatenations of codes separated by interleavers, such as serial concatenated convolutional codes (SCCC), sometimes called serial turbo codes, or concatenation of block codes, also named block turbo codes (Boutillon et al, 2007). Fig.…”

“…Once the processing of half iteration is finished, all codewords are shifted in the linear processor array (Boutillon et al, 2007).…”

“…That was not the end, more recently; they were also selected for the next generation of 3GPP2/cdma2000 wireless communication systems (3GPP2, Feb. 2004) as well as for the IEEE 802.16 standard (WiMAX) (IEEE, Nov. 2004) which was intended for broadband connections over long distances. Besides the parallel codes a serial turbo code was also adopted in 2003 by the European Space Agency for the implementation of a very high speed (1 Gb/s) adaptive coded modulation modem for satellite applications (Boutillon et al, 2007). This paper discusses the various implementation methods and aspects of Turbo Decoders.…”