Spatially Coupled Turbo-Like Codes
Journal article, 2017

In this paper, we introduce the concept of spatially coupled turbo-like codes (SC-TCs) as the spatial coupling of a number of turbo-like code ensembles. In particular, we consider the spatial coupling of parallel concatenated codes, introduced by Berrou et al., and that of serially concatenated codes (SCCs), introduced by Benedetto et al. Furthermore, we propose two extensions of braided convolutional codes (BCCs), and a class of turbo-like codes which have an inherent spatially coupled structure, to higher coupling memories, and show that these yield improved belief propagation (BP) thresholds as compared with the original BCC ensemble. We derive the exact density evolution (DE) equations for SC-TCs and analyze their asymptotic behavior on the binary erasure channel. We also consider the construction of families of rate-compatible SC-TC ensembles. Our numerical results show that the threshold saturation of the BP decoding threshold to the maximum a posteriori threshold of the underlying uncoupled ensembles occurs for large enough coupling memory. The improvement of the BP threshold is especially significant for SCCs and BCCs, whose uncoupled ensembles suffer from a poor BP threshold. For a wide range of code rates, SC-TCs show close-to-capacity performance as the coupling memory increases. We further give a proof of threshold saturation for SC-TC ensembles with identical component encoders. In particular, we show that the DE of SC-TC ensembles with identical component encoders can be properly rewritten as a scalar recursion. This allows us to define potential functions and prove threshold saturation using the proof technique recently introduced by Yedla et al.

Braided codes

density evolution

potential function

threshold saturation

turbo codes

spatially coupled codes

serially concatenated codes


Saeedeh Moloudi

Lund University

Michael Lentmaier

Lund University

Alexandre Graell i Amat

Chalmers, Signals and Systems, Communication and Antenna Systems, Communication Systems

IEEE Transactions on Information Theory

0018-9448 (ISSN)

Vol. 63 10 6199-6215

Spatially Coupled Turbo-Like Codes

Swedish Research Council (VR), 2014-01-01 -- 2017-12-31.

Areas of Advance

Information and Communication Technology

Subject Categories


Communication Systems



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