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lteACKDecode

HARQ-ACK channel decoding

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Syntax

[out,blkerr] = lteACKDecode(chs,in)

Description

[out,blkerr] = lteACKDecode(chs,in) performs block decoding on soft input data in, assumed to be encoded using the procedure defined for HARQ-ACK in Section 5.2.2.6 of [1], for PUSCH channel transmission configuration chs. The decoded output, out, is a vector of length OACK, the number of uncoded HARQ-ACK bits transmitted.

Note

If NBundled is 0, TDD ACK-NACK descrambling is disabled.

Multiple codewords can be parameterized by two different forms of the chs structure. Each codeword can be defined by separate elements of a 1-by-2 structure array, or the codeword parameters can be combined together in the fields of a single scalar, or 1-by-1, structure. Any scalar field values apply to both codewords and a scalar chs.NLayers is the total number. See UL-SCH Parameterization for further details.

The block decoding is performed separately on each soft input data codeword using a maximum likelihood (ML) approach, assuming that in has been demodulated and equalized to best restore the originally transmitted values.

The HARQ-ACK decoder performs different types of block decoding depending upon the number of uncoded HARQ-ACK bits to be recovered (OACK). For OACK less than 3 bits, the decoder assumes the bits are encoded using the procedure defined in TS 36.212 [1], Section 5.2.2.6.

For decoding between 3 and 11 HARQ-ACK bits, the decoder assumes the bits are block encoded using the procedure defined in TS 36.212 [1], Section 5.2.2.6.4. For decoding between 12 and 22 bits, the decoder performs the inverse procedure described in TS 36.212 [1], Section 5.2.2.6.5. For decoding more than 22 bits, the decoder performs rate-matching, tail-biting Viterbi decoding, and 8-bits CRC decoding, which is the inverse procedure described in Section 5.2.2.6.

example

Examples

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Open Live Script

Show the block decoding of 3 coded HARQ-ACK information bits.

Create input and initialize channel structure. Encode bits and turn logical bits into soft data compatible with log-likelihood ratio check. Use pskmod with an initial phase offset of π to align mapping with LTE codebook.

Perform HARQ-ACK bit encoding and modulation.

in = [1;0;1];
chs = struct('Modulation','QPSK','QdACK',2,'OACK',length(in));

encodedBits = lteACKEncode(chs,in);
encodedBits = pskmod(double(encodedBits),2,pi());

Pass transmitted encoded bits through an AWGN channel with a 20 dB signal-to-noise ratio. Show a scatterplot of the noisy received HARQ-ACK softbits.

rxBits = awgn(encodedBits,20);
scatterplot(rxBits)

Figure Scatter Plot contains an axes object. The axes object with title Scatter plot, xlabel In-Phase, ylabel Quadrature contains a line object which displays its values using only markers. This object represents Channel 1.

Decode the received softbits. Compare the decoded bits with the input bits to show the bits have been recovered with no error.

decodedBits = lteACKDecode(chs,rxBits)
decodedBits = 3x1 logical array

   1
   0
   1


isequal(in,decodedBits)
ans = logical
   1

Input Arguments

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PUSCH-specific channel transmission configuration, specified as a structure or a structure array, which contains the following parameter fields.

Parameter FieldRequired or OptionalValuesDescription
ModulationRequired

'QPSK', '16QAM', '64QAM', or '256QAM'

Modulation type, specified as a character vector, cell array of character vectors, or string array. If blocks, each cell is associated with a transport block.

OACKOptional

nonnegative scalar integer, 0 (default)

Number of uncoded HARQ-ACK bits.

The HARQ-ACK decoder performs different types of block decoding depending on the number of uncoded HARQ-ACK bits to be recovered (OACK). For OACK less than 3 bits, the decoder assumes the bits are encoded using the procedure defined in TS 36.212 [1], Section 5.2.2.6. For decoding between 3 and 11 HARQ-ACK bits, the decoder assumes the bits are block encoded using the procedure defined in TS 36.212 [1], Section 5.2.2.6.4. For decoding between 12 and 22 bits, the decoder performs the inverse procedure described in TS 36.212 [1], Section 5.2.2.6.5. For decoding more than 22 bits, the decoder performs rate-matching, tail-biting Viterbi decoding, and 8-bits CRC decoding, which is the inverse procedure described in Section 5.2.2.6.

NLayersOptional

1 (default), 2, 3, 4

Number of transmission layers.

NBundledOptional

0 (default), 1, …, 9

TDD HARQ-ACK bundling scrambling sequence index. When set to 0, the function disables the TDD HARQ-ACK bundling scrambling. Therefore, it is off by default.

Soft input data, specified as a numeric vector. The input data is assumed to be encoded using the procedure defined for HARQ-ACK in TS 36.212 [1], Section 5.2.2.6.

Output Arguments

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Decoded HARQ-ACK channel output, returned as an OACK-by-1 column vector.

Data Types: logical

Block error, returned as a logical scalar. If the number of transmitted bits is 22 or fewer, blkerr is 0. Otherwise, blkerr is a logical value that reports if a decoding error has occurred.

Data Types: logical

References

[1] 3GPP TS 36.212. “Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.

Version History

Introduced in R2014a

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See Also

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