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Título: On distance measurement methods for turbo codes
Autores: Ould Cheikh Mouhamedou, Youssouf.
Fecha: 2005
Publicador: McGill University - MCGILL
Fuente:
Tipo: Electronic Thesis or Dissertation
Tema: Engineering, Electronics and Electrical.
Descripción: New digital communication applications, such as multimedia, require very powerful error correcting codes that deliver low error rates while operating at low to moderate ratios (SNRs). Turbo codes have reasonable complexity and can achieve very low error rates if a proper interleaver design is in place. The use of well-designed interleavers result in very low error rates, especially for medium to long interleavers where turbo codes offer the greatest potential for achieving high minimum distance (d min) values.
The reliable determination of a code's error performance at very low error rates using simulations may take months or may not be practical at all. However, the knowledge of dmin and its multiplicities can be used to estimate the error rates at high SNR. This thesis is concerned with efficient and accurate distance measurement methods for turbo codes. Since high values of dmin can be caused by high input weight values, say up to 20 or higher, if a brute force algorithm is used the accurate determination of dmin requires that all possible input sequences of input weight up to 20 be tested. Testing all possible input sequences becomes impractical as the size of the interleaver and the value of input weight increase. Thus, the accurate determination of the distance spectrum, or at least dmin and its multiplicities, is a significant problem, especially for interleavers that yield high dmin. Based on Garello's true distance measurement method, this thesis presents an efficient and accurate distance measurement method for single- and double-binary turbo codes that uses proper trellis termination such as dual-termination or tail-biting. This method is applied to determine the distance spectra for the digital video broadcasting with return channel via satellite (DVB-RCS) standard double-binary turbo codes. It is also used to design new interleavers for DVB-RCS that yield a significant improvement in error performance compared to those in the standard.
This method fits particularly well with tail-biting turbo codes that use structured interleavers. This is because the distance properties repeat and this method can use this knowledge to reduce the search space. The reduction in search space results in significant reduction in complexity (i.e., execution time), which allows the determination of high dmin values in reasonable time. This efficiency is demonstrated for both single- and double-binary turbo codes, using structured interleavers that have high dmin values for various code rates. This method reduces the execution tunes by a factor of 40 to 400.
Idioma: en