2002 Asilomar Conf. on
Signals, Systems, and Computers, Nov. 3-6, Pacific Grove, CA
A Real-Time Embedded Software Implementation of a Turbo
Encoder and Soft Output Viterbi Algorithm based Turbo Decoder
M. Farooq Sabir,
Rashmi Tripathi,
Brian L. Evans, and
Alan C. Bovik
Department of Electrical and Computer Engineering,
Engineering Science Building,
The University of Texas at Austin,
Austin, TX 78712-1084
mfsabir@ece.utexas.edu -
bevans@ece.utexas.edu -
bovik@ece.utexas.edu
Paper
Turbo codes are used for error protection, esp. in wireless systems.
A turbo encoder consists of two recursive systematic convolutional
component encoders connected in parallel and separated by a random
interleaver.
A turbo decoder, which is iterative, is typically based on either a
Soft Output Viterbi Algorithm (SOVA) or a maximum a posteri (MAP)
algorithm.
MAP is roughly three times more computationally complex than SOVA,
but provides 0.5 dB of coding gain.
In this paper, we implement a turbo encoder and SOVA-based turbo decoder
in real-time software on a TMS320C6700 digital signal processor (DSP).
The contributions of this paper are:
- first publicly available implementation of a SOVA-based turbo decoder
on a C6000 DSP,
- speedup of 162x for the encoder on a C6200 DSP and 11.7x for the
decoder on a C6700 DSP over level three C compiler optimization, and
- dataflow modeling for a turbo channel coding subsystem.
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