Decoding method and decoding device for a CDMA transmission system for demodulating a received signal available in serial code concatenation

• US 6,377,610 B1
• Filed: 03/06/1998
• Issued: 04/23/2002
• Est. Priority Date: 04/25/1997
• Status: Expired due to Term

• Current Assignee: Deutsche Telekom AG
• Original Assignee: Deutsche Telekom AG
• Inventors: Herzog, Rupert, Hagenauer, Joachim, Schmidbauer, Andreas
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): BURD, KEVIN MICHAEL
• Application Number:
  US09/036,207
• Time in Patent Office: 1,509 Days
• Field of Search: 375/130, 375/146, 375/147, 375/136
• US Class Current: 375/136
• CPC Class Codes: H03M 13/29 combining two or more codes or code structures, e.g. product codes, generalised product codes, concatenated codes, inner and outer codes
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/4146 soft-output Viterbi decoding according to Battail and Hagenauer in which the soft-output is determined using path metric differences along the maximum-likelihood path, i.e. "SOVA" decoding
• CPC Class Codes: H03M 13/45 Soft decoding, i.e. using symbol reliability information H03M13/41 takes precedence
• CPC Class Codes: H03M 13/456 wherein all the code words of the code or its dual code are tested, e.g. brute force decoding
• CPC Class Codes: H03M 13/6325 Error control coding in combination with demodulation
• CPC Class Codes: H03M 13/6502 Reduction of hardware complexity or efficient processing
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 2001/70935 using a bank of matched fileters, e.g. Fast Hadamard Transform
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0065 Serial concatenated codes

Abstract

A method and a device for decoding for use in a code-division multiple access (CDMA) transmission system for demodulating a received signal available in serial code concatenation, with a two-step coding being carried out at the transmitting end of the transmission system, including an orthogonal, multi-step inner Hadamard code and an outer, error-correcting code of a predefined rate. In the receiver, a soft-in/soft-out decoder is provided, at whose input and output soft values are processed as reliability information, i.e., L-values. The soft output of the first decoder step, or inner code is the soft input for the decoder step, or outer code, that follows in each case, the first decoder step receiving the output values of the preceding demodulation, which contain the channel'"'"'s reliability information. A soft output is used by the decoder, in particular a MAP decoder, as a-priori information for the systematic bits of the Walsh function of the inner code for decoding of the inner code.

Claims

1. 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, a first step of the two-step coding including a Hadamard orthogonal multi-step inner code, a second step of the two-step coding including an outer error-correcting code of a predefined rate, 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, a second decoder step of the soft-in/soft-out decoder including an outer decoder; 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 the first decoder step of the soft-in/soft-out decoder and the second decoder step of the soft-in/soft-out decoder are configured to decode the received signal coded in the two-step coding,

wherein the receiver includes an incoherent receiver structure including a RAKE receiver, wherein a soft input of the inner decoder includes a-priori information for systematic bits of Walsh functions of the inner code, the inner Hadamard code being decoded by entering an a-priori information vector L(u) into an instruction of the inner decoder, the instruction being such that for each bit decision, in a summing of a numerator and a denominator of a term to be expressed logarithmically of each considered element of a square-law-combining fast Hadamard transform resultant decision vector w, three terms are multiplied, a first term of the three terms being a-priori probabilities P(x_j), a second term of the three terms being an exponentiated vector element, a third term of the three terms being a modified Bessel function of the first type of power (L-1) with argument, L being a number of fingers of the RAKE receiver, x being a Walsh function.

2. The method as recited in claim 1 wherein the entering the a-priori information vector L(u) is performed with the a-priori information vector L(u) in the form of a-priori probabilities P(x_j) for Walsh functions of the Hadamard code, x being a Walsh function, u being a bit.

3. The method as recited in claim 1 wherein the decoding instruction includes the equation:

$\begin{array}{c}L<br><br>\left({\hat{u}}_k\right)=\text{\hspace{1em}<br><br>}<br><br>\ln <br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{P({\hat{u}}_k=1<br><br><br><br>w)}{P({\hat{u}}_k=-1<br><br><br><br>w)}\\ =\text{\hspace{1em}<br><br>}<br><br>\ln <br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\underset{j=0,u_k=+1}{\overset{N-1}{\sum <br><br>}}<br><br>P<br><br>\left(x_j\right)·<br><br>w^{-\text{\hspace{1em}<br><br>}<br><br>\frac{L-1}{2}}·<br><br>I_{L-1}(\sqrt{w_j<br><br>\frac{s}{{\mathrm{\sigma <br><br>}}^2}}}{\underset{j=0,u_k=-1}{\overset{N-1}{\sum <br><br>}}<br><br>P<br><br>\left(x_j\right)·<br><br>w^{-\text{\hspace{1em}<br><br>}<br><br>\frac{L-1}{2}}·<br><br>I_{L-1}(\sqrt{w_j<br><br>\frac{s}{{\mathrm{\sigma <br><br>}}^2}}}\end{array}$

û

_k being a bit of the soft output of the inner decoder, w_j being a respective element of the vector w, I<sub>L−

1</sub> being the modified Bessel function of the first type of power L−

1,

j being a respective vector element index, N being a size of the code words of the inner code,

s being a non-centrality of a distribution of maxima of the vector w over time, σ

² being a mean noise power.

4. 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, a first step of the two-step coding including a Hadamard orthogonal multi-step inner code, a second step of the two-step coding including an outer error-correcting code of a predefined rate, 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, a second decoder step of the soft-in/soft-out decoder including an outer decoder; 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 the first decoder step of the soft-in/soft-out decoder and the second decoder step of the soft-in/soft-out decoder are configured to decode the received signal coded in the two-step coding,

wherein the receiver includes a coherent receiver structure, wherein a soft input of the inner decoder includes a-priori information for systematic bits of Walsh functions of the inner code, and wherein the inner code includes a Hadamard code, the Hadamard code being decoded by;

adding an a-priori information vector L(u) for systematic bits of a Walsh function of the Hadamard code to an input vector L_c·

y from a channel;

performing a fast Hadamard transformation so as to provide a fast Hadamard transform resultant vector w;

then generating exponential functions with ½

·

w_j as an argument, w_j being a respective element of the vector w; and

adding, dividing and expressing logarithmically elements of a result vector z for each symbol û

_K to be decoded according to the equation;

$\begin{array}{c}\ln <br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\underset{j,u_k=+1}{\overset{N-1}{\sum <br><br>}}<br><br>z_j}{\underset{j,u_k=-1}{\overset{N-1}{\sum <br><br>}}<br><br>z_j}=\text{\hspace{1em}<br><br>}<br><br>\ln <br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\underset{j,u_k=+1}{\overset{N-1}{\sum <br><br>}}<br><br>\exp <br><br>\left(\frac{1}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>w_j\right)}{\underset{j,u_k=-1}{\overset{N-1}{\sum <br><br>}}<br><br>\exp <br><br>\left(\frac{1}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>w_j\right)}\\ =\text{\hspace{1em}<br><br>}<br><br>\ln <br><br>\stackrel{\mathrm{Term}<br><br>\text{\hspace{1em}<br><br>}<br><br>1}{\left(\underset{j,u_k=+1}{\overset{N-1}{\sum <br><br>}}<br><br>\exp <br><br>\left(\frac{1}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>w_j\right)\right)}-\stackrel{\mathrm{Term}<br><br>\text{\hspace{1em}<br><br>}<br><br>2}{\ln <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\underset{j,u_k=-1}{\overset{N-1}{\sum <br><br>}}<br><br>\exp <br><br>\left(\frac{1}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>w_j\right)\right)}\end{array}$

z_j being a respective element of the resultant vector z, j being a respective vector element index, N being a size of the Walsh functions of the inner code;

wherein, with respect to Term 1 and Term 2 of the equation, for each step at least one maximum is used so as to provide a simplified decoder instruction of the equation, the simplified decoder instruction expressed by the relation;

$\begin{array}{c}\text{\hspace{1em}<br><br>}<br><br>\approx <br><br>\text{\hspace{1em}<br><br>}<br><br>\ln <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\underset{j,u_k=+1}{\max }<br><br>\left[\exp <br><br>\left(\frac{1}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>w_j\right)\right]\right)-\ln <br><br>\text{\hspace{1em}<br><br>}<br><br>\left(\underset{j,u_k=-1}{\max }<br><br>\left[\exp <br><br>\left(\frac{1}{2}<br><br>\text{\hspace{1em}<br><br>}<br><br>w_j\right)\right]\right)\\ =\text{\hspace{1em}<br><br>}<br><br>\frac{1}{2}<br><br>\underset{j,u_k=+1}{\max }<br><br>\left[w_j\right]-\frac{1}{2}<br><br>\underset{j,u_k=-1}{\max }<br><br>\left[w_j\right]\end{array}$

 

so that $L^I<br><br>\left({\hat{u}}_k\right)\cong <br><br>\frac{1}{2}·<br><br>\underset{j,u_k=+1}{\max }<br><br>\left(w_j^{\mathrm{\prime <br><br>}}\right)-\frac{1}{2}·<br><br>\underset{j,u_k=-1}{\max }<br><br>\left(w_j^{\mathrm{\prime <br><br>}}\right),$

w_j being a respective element of the vector w, L^I(û

_k) being the soft output of the inner decoder, u being a bit, y being a vector.