Efficient decoding of trellis coded modulation waveforms
AssigneeNorthrop Grumman Corporation
InventorsMichael J. Holmes, Scott W. Enserink, Jeffrey P. Long
Life of this patent
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Abstract
A method and apparatus for decoding trellis-coded digital data. Digital data samples that have been convolutionally encoded by trellis-coded modulation (TCM) for purposes of forward error correction require a computationally intensive Viterbi decoder for best performance. A technique known as pragmatic trellis-code modulation (PTCM) reduces decoder complexity but at the expense of degraded performance in some situations. This disclosure provides a solution that retains the reduced complexity of PTCM, but uses a full trellis approach that yields significantly better performance in terms of bit error rate (BER).
Claims14
A method for decoding data encoded as trellis-code modulation (TCM) symbols, the method comprising the steps of:
- receiving the TCM symbols including digital data for a received signal constellation point as one or more pairs of in-phase (I) and quadrature (Q) values;
- calculating soft decision values, each of the soft decision values corresponding to each respective received pair of (I,Q) values that defines a set of n least significant bits of received data, where n is the number of bits of data that were subject to convolutional encoding in the TCM encoding process;
- calculating multiple branch metric values for use in the decoding process, from the soft decision values;
- Viterbi decoding said n least significant bits of data at a time using the multiple branch metric values, and producing n bits at a time of output data;
- re-encoding the n bits at a time of output data to determine the coset membership of the received TCM symbols;
- using the re-encoded data to process unencoded data bits in a hard decision process to recover multiple uncoded bits of received data;
- and
- assembling the recovered uncoded bits of received data with the n bits of decoded data output from the Viterbi decoding step, to provide a complete data symbol;
- and wherein the Viterbi decoding step employs a full rate trellis, without de-puncturing.
Digital decoding apparatus for decoding data encoded as trellis-code modulation (TCM) symbols, the apparatus comprising:
- means for receiving the TCM symbols including digital data for a received signal constellation point as one or more pairs of in-phase (I) and quadrature (Q) values;
- means for deriving soft decision values, each of the soft decision values corresponding to each respective received pair of(I,Q) values that defines a set of a least significant bits of received data, where n is the number of bits of data that were subject to convolutional encoding in the TCM process;
- means for calculating multiple branch metric values for use in the decoding process, from the soft decision values;
- a Viterbi decoder configured to decode said n least significant bits of data at a time using the multiple branch metric values, to produce n bits at a time of output data;
- a convolutional encoder, for re-encoding the n bits at a time of output data to reproduce pairs of values;
- means for selecting and processing unencoded data bits in a hard decision process to recover multiple uncoded bits of received data;
- and
- means for assembling the recovered uncoded bits of received data with the n bits of decoded data output from the Viterbi decoder, to provide a complete data symbol;
- and wherein the Viterbi decoder employs a full rate trellis, without de-puncturing.
Dependencies are inferred from the claim text.