Patent ID: 6925107

Claim:
A decoding method for demodulating a received signal available in serial code concatenation in a code-division multiple access transmission system, a two-step coding being carried out at the transmitting end of the transmission system, the method comprising: providing a soft-in/soft-out decoder in a receiver of the transmission system, a first decoder step of the soft-in/soft-out decoder including an inner decoder and a Hadamard orthogonal multi-step inner code, a second decoder step of the soft-in/soft-out decoder including an outer decoder and an outer error correcting code of a predefined rate; and processing soft values as reliability information at an output and an input of the soft-in/soft-out decoder, a soft output of the inner decoder being a soft input for the outer decoder, a channel reliability information output from a preceding demodulation being an input for the inner decoder; wherein one of the following is satisfied: (1) a modified soft-decision Viterbi algorithm is used in which reconstruction is performed for coded bits of the outer code, and is not performed for transmitted information bits; and (2) a maximum a posteriori decoder is used, in which soft information pertaining to calculations of the outer, coded bits is used partially as a priori information for systematic bits of the inner code, so that soft values are fed back to the first decoder; wherein using logarithmic likelihood algebra, a maximum a posteriori (MAP) decoder for the inner code is expressed by the following first equation: L I ⁡ ( u ^ ⁢ k ) = ⁢ ln ⁢ ⁢ ∑ x ∈ C I , uk = + 1 ⁢ P ⁡ ( x ∣ y ) ∑ x ∈ C I , uk = - 1 ⁢ P ⁡ ( ∣ y ) = ⁢ ln ⁢ ⁢ ∑ x ∈ C I , uk = + 1 ⁢ exp ⁡ ( 1 2 ⁢ ∑ i = 0 N - 1 ⁢ L ⁡ ( x i ; y i ) · x i ) ∑ x ∈ C I , uk = - 1 ⁢ exp ⁡ ( 1 2 ⁢ ∑ i = 0 N - 1 ⁢ L ⁡ ( x i ; y i ) · x i ) , where the values satisfy the following second equation: L ⁡ ( xi , yi ) = ⁢ { Le · y i + L I ⁡ ( Ui ) ; ⁢ for ⁢ ⁢ i = 1 2 k + 1 ⁢ N ; k = 0 , … ⁢ , K - 1 Le · y ; otherwise describe a probability of all elements of the resulting vector, x i and y i , being Walsh functions, x and y being a vector, C being a code, U i being a bit.