Apparatus and method for saturating decoder values
First Claim
1. An apparatus comprising:
- a first adder to add a first branch metric value to a previous path metric value to generate a first path metric value; and
saturating logic to detect a saturating condition when a most signiflcaflt bit (lvlSBTM) of said first path metjic value is a specified valuet, the saturating logic arranged to select the first path metric value to form a first state metric when the saturating condition is not detected, and aftematively to select a predetermined maximum value to form the first state metric when the saturating condition is detected; and
a comparator to compare saId first state metric to second state metric transmitted from a second adder, and to responsively, and to responsively select a minimum one of said state metrics.
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Accused Products
Abstract
In one embodiment of the invention, during add-compare-select computations, the output of the adders is guaranteed to be a positive value because the only time normalization logic subtracts a normalization amount is when all accumulators are greater than the normalization amount. As such, the detection of overflow is greatly simplified. Overflow in the add-compare-select unit may be indicated simply by the value of the most significant bit (“MSB”) (i.e., the sign bit) of the result. If the MSB of the result of the adder is set then, in one embodiment, the output of the adder gets forced the maximum possible value given the number of bits. For example, this value will be forced to 7h7f if the value is represented by 7-bits. That is to say, if an overflow is detected, then the accumulator is saturated to the maximum value.
189 Citations
35 Claims
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1. An apparatus comprising:
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a first adder to add a first branch metric value to a previous path metric value to generate a first path metric value; and
saturating logic to detect a saturating condition when a most signiflcaflt bit (lvlSBTM) of said first path metjic value is a specified valuet, the saturating logic arranged to select the first path metric value to form a first state metric when the saturating condition is not detected, and aftematively to select a predetermined maximum value to form the first state metric when the saturating condition is detected; and
a comparator to compare saId first state metric to second state metric transmitted from a second adder, and to responsively, and to responsively select a minimum one of said state metrics. - View Dependent Claims (2, 3, 4, 6, 7, 8)
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5. The apparatus as in claim I wherein said predetermined maximum value is 7h7f.
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9. A decoding method comprising:
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adding a first branch metric value to a previous path metric value to generate a first path metric value;
detecting a saturating condition when a most significant bit (“
MSB”
) of said first path metric value is a specified value;
selecting the first path metric value as a first state metric when the saturating condition is not detected, end alternatively selecting a predetermined maximum value as the first state metric when the saturating condition is detected;
comparing said first state metric with a second state metric transmitted from a second adder; and
selecting a minimum one of said state metrics. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. An integrated circuit (IC), comprising:
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a first adder to add a first branch metric value to a previous path metric value to generate a first path metric value;
saturating logic to detect a saturating condition when a most significant bit (“
MSB”
) of said first path metric value is a specified value the saturating logic arranged to select the first path metric value, to form a first state metric when the saturating condition is riot detected, and alternatively to select a predetermined maximum value to form the first state metric when the saturating condition is detected; and
a comparator to compare said first state metric a second state metric transmitted from a second adder, and to responsively select a minimum one of said state metrics. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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25. A method for use in a digital decoder comprising the steps of:
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determining a branch metric distance value;
monitoring a path metric accumulator value;
responsive to the path metric accumulator value reaching a first predetermined value, normalizing the path metric accumulator value by;
selecting a normalization quantity;
adding the selected normalization quantity to the branch metric distance value to form a sum; and
inputting the sum to the path metric accumulator, thereby adding the selected normalization quantity to the path metric accumulator value to normalize it. - View Dependent Claims (26, 27)
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28. A method for use in a digital decoder comprising the steps of:
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monitoring bit settings in each of a plurality of path metric accumulators, each accumulator providing a respective path metric accumulator value during a decoding operation;
detecting when all of the path metric accumulator values reaches at least a first predetermined value; and
responsive to all of the path metric accumulator values reaching at least the first predetermined value, selecting a normalization value and adding the selected normalization value to each of the path metric accumulators to normalize the accumulators. - View Dependent Claims (29, 30, 31, 32, 33)
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34. An add compare-select (ACS) circuit for use in a digital decoder apparatus comprising:
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a first adder for adding a first branch metric value to a first path metric value to form a first sum;
saturation logic for detecting a saturation condition in the first adder;
a first multiplexer responsive to the saturation detecting logic for selecting either the first sum or a predetermined saturation value as a first state metric output;
a second adder for adding a second branch metric value to a second path metric value to form a second sum;
second saturation logic for detecting a saturation condition in the second adder;
a second multiplexer responsive to be second saturation detecting logic for selecting either the second sum or a predetermined saturation value as a second state metric output; and
a comparator for comparing the first and second state metric outputs. - View Dependent Claims (35)
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Specification