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Traceback-Based Optimizations for Maximum a Posteriori Decoding Algorithms

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Abstract

Maximum A Posteriori (MAP) decoding is a crucial enabler of turbo coding and other powerful feedback-based algorithms. To allow pervasive use of these techniques in resources constrained systems, it is important to limit their implementation complexity, without sacrificing the superior performance they are known for. We show that introducing traceback information into the MAP algorithm, thereby leveraging components that are also part of Soft-Output Viterbi Algorithms (SOVA), offers two unique possibilities to simplify the computational requirements. Our proposed enhancements are effective at each individual decoding iteration and therefore provide gains on top of existing techniques such as early termination and memory optimizations. Based on these enhancements, we will present three new architectural variants for the decoder. Each one of these may be preferable depending on the decoder memory hardware requirements and number of trellis states. Computational complexity is reduced significantly, without incurring significant performance penalty.

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Notes

  1. These numbers directly follow from equations (2)-(7). The branch metric calculation results in three additions, see reference [9], equations (4)-(5).

  2. A MAX can be implemented as a slightly simplified ADD followed by a multiplexer, and is roughly comparable in terms of energy consumption [9]. The number of traceback operations is small in each one of the cases and the approximation as one equivalent operation therefore does not impact the overall comparison to a large degree.

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  1. Curt Schurgers

    Present address: Electrical and Computer Engineering, University of California San Diego, 9500 Gilman Dr., La Jolla, CA, 92093-0407, USA

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  1. Microsystems Technology Laboratories, Massachusetts Institute of Technogy, Cambridge, MA, 02139, USA

    Curt Schurgers & Anantha Chandrakasan

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  1. Curt Schurgers
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  2. Anantha Chandrakasan
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Correspondence to Curt Schurgers.

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Schurgers, C., Chandrakasan, A. Traceback-Based Optimizations for Maximum a Posteriori Decoding Algorithms. J Sign Process Syst Sign Image Video Technol 53, 231–241 (2008). https://doi.org/10.1007/s11265-007-0160-8

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  • DOI: https://doi.org/10.1007/s11265-007-0160-8

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