US 7,023,934 B2 · Method and apparatus for min star calculations in a map decoder

Abstract

Method and apparatus for Min star calculations in a Map decoder. Min star calculations are performed by a circuit that includes a first circuit that performs an Min(A,B) operation simultaneously with a circuit that calculates a −log(1+e−|A−B|) value. The sign bit of the A−B calculation is used to select whether A or B is a minimum. The A−B calculation is also used to select either −log(1+e−|A−B|) or −log(1+e−|B−A|) as the correct calculation. In order to hasten the selection of either −log(1+e−|A−B|) or −log(1+e−|B−A|) as the correct calculation the apparatus does not wait for the A−B calculation to complete. Any bit of the A−B calculation between the third bit and final (sign bit) can be used for the selection. If an incorrect value is selected a log saturation circuit may correct the value. In addition an offset may be added −log(1+e−|A−B|) or −log(1+e−|B−A|) to assure that the calculation does not become negative, necessitating the use of an additional sign bit thereby increasing circuit complexity and slowing down the calculation. Additionally the log terms are computed based on a partial result of the A−B calculation.

Claims61

Dependent claims

A method performed by a decoder for computing Min star of a first input (A) and a second input (B) to the decoder (Min*(A, B)), the method comprising:

determining Min_β=minimum of the operands comparing the first input (A) and the second input (B) to the decoder, wherein A comprises an β metric, a priori values and a transition metric for a first previous state of the decoder and B comprises an β metric, a priori values and a transition metric for a second previous state of the decoder;
outputting Min_β, wherein Min_β comprises the Minimum of A and B, a first portion of the output of the Min* operation;
computing ln_β=−log(1+e−|A−B|) as a second portion of the Min* operation;
and
outputting ln_β from the decoder.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for min star calculations in a map decoder

Life of this patent

Method and apparatus for min star calculations in a map decoder

Life of this patent

Abstract

Claims61