Modulo decoder
First Claim
1. A method comprising the steps ofreceiving a sequence of signal points that represent a sequence of transmitted symbols, each symbol of said sequence of transmitted symbols being selected in accordance with a convolutional code from a constellation comprising a plurality of subsets, each subset comprising a plurality of symbols, anddecoding the received sequence of signal points to provide a sequence of received symbols which represent an estimate of the sequence of transmitted symbols,where the decoding step includes a step of calculating a transition metric for each subset of said constellation for each one of the received signal points, where at least one of this plurality of transition metrics for a respective subset is calculated as a function of an error metric of a different subset.
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Abstract
A high-speed convolutional decoder is constructed by performing the transition, or branch, metric calculations in reference to a subset of a constellation, which comprises a plurality of subsets. In addition, any subset can be chosen as the reference subset through the use of "modulo decoding." In a modulo decoder, the constellation space is folded into a modulo set area that is centered around the arbitrarily chosen reference subset. The branch, or transition, metrics are calculated within the modulo set area. As a result, the branch metric computations are only performed on a small area of the signal space, with the result that only one error is extracted, the branch metrics are easily computed, and one slicing is performed--thus reducing overall computation time.
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Citations
9 Claims
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1. A method comprising the steps of
receiving a sequence of signal points that represent a sequence of transmitted symbols, each symbol of said sequence of transmitted symbols being selected in accordance with a convolutional code from a constellation comprising a plurality of subsets, each subset comprising a plurality of symbols, and decoding the received sequence of signal points to provide a sequence of received symbols which represent an estimate of the sequence of transmitted symbols, where the decoding step includes a step of calculating a transition metric for each subset of said constellation for each one of the received signal points, where at least one of this plurality of transition metrics for a respective subset is calculated as a function of an error metric of a different subset.
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5. Apparatus for receiving a signal comprising:
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means for receiving the signal to provide a received sequence of signal points, means for calculating a reference error metric for each one of the sequence of received signal points, said reference error metric determined in reference to a predefined symbol taken from a constellation comprising a plurality of subsets, each subset comprising a plurality of symbols, and means for decoding the received sequence of signal points to provide a received data sequence, where said means for decoding calculates a plurality of transition metrics for each one of the plurality of subsets for each one of the received sequence of signal points, where each one of the plurality of transition metrics is calculated in reference to said reference error metric. - View Dependent Claims (6, 7)
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8. Apparatus for receiving a signal, comprising
means for receiving the signal to provide a received sequence of signal points, means for decoding the received sequence of signal points to select for each one of the received sequence of signal points a subset from a constellation comprising a plurality of subsets, each subset comprising a plurality of symbols, and means for performing no more than one slicing operation on each one of the received sequence of signal points in response to the respective selected subset to select a symbol from said constellation.
Specification