TRELLIS HOPPING TURBO CODING

CASTIÑEIRA MOREIRA, J.; PETRUZZI, D. M.

Rio Cuarto, Córdoba

Congreso; XI Reunión del Procesamiento de la Información y Control (RPIC); 2005

UNRC, Cordoba

This paper presents a turbo coding scheme where the constituent codes are designed using convolutional encoders with time varying coefficients. The constituent encoders are finite statesequence machines operating over the Galois Field GF(q), whose coefficients are changed periodically in time, during transmission. This provides the scheme with an encryption procedure in which these coefficients are varying trough a key word generated by other process. In this paper this time varying rule is generated randomly.The BER performance of these schemes is very close to that of the best known classic binary turbo coding schemes, with the additional advantage of providing the system with a high level of encryption. The variation of the coefficients of the constituent encoders makes the whole trellis of the system be constructed with sub-trellises corresponding to different codes. Thus, the ransmission hops from one trellis to another, following a random sequence. It is shown that these schemes perform slightly better than classic binary turbo coding schemesusing time invariant coefficients in turbo coding schemes with medium size block interleavers, andperform very close to the best known classic binary turbo coding schemes using convolutional encoders with time invariant coefficients and large random interleavers. This shows that turbo coding and encryption techniques are not in a strong trade off, providing the whole system with both very good encryption characteristics and excellent BER performance.