lteACKDecode

HARQ-ACK channel decoding

Syntax

out = lteACKDecode(chs,in)

Description

out = 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 type 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 greater than 11 bits, the decoder performs the inverse procedure described in TS 36.212 [1], Section 5.2.2.6.5.

Examples

Decode HARQ-ACK Channel

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 $$\pi$$ 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)

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

chs — PUSCH-specific channel transmission configuration

scalar structure | structure array

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

Parameter Field	Required or Optional	Values	Description
Modulation	Required	'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.
OACK	Optional	nonnegative scalar integer, 0 (default)	Number of uncoded HARQ-ACK bits. The HARQ-ACK decoder performs different type 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 greater than 11 bits, the decoder performs the inverse procedure described in TS 36.212 [1], Section 5.2.2.6.5.
NLayers	Optional	1 (default), 2, 3, 4	Number of transmission layers.
NBundled	Optional	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.

in — Soft input data

numeric vector

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

out — Decoded HARQ-ACK channel

numeric column vector

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

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