nrBCHDecode

Broadcast channel (BCH) decoding

Syntax

scrblk = nrBCHDecode(softbits,L)

[scrblk,errFlag] = nrBCHDecode(softbits,L)

[scrblk, errFlag,民国lk,lsbofsfn,hrf,msbidxoffset] = nrBCHDecode(softbits,L,lssb,ncellid)

Description

scrblk= nrBCHDecode(softbits,L)decodes the log-likelihood ratios (LLRs)softbitsin accordance with TS 38.212, Section 7.1[1]. The function returns the decoded scrambled BCH transport blockscrblk. The input argumentL是the list length used for polar decoding.

[scrblk,errFlag] = nrBCHDecode(softbits,L)返回一个错误标志,errFlag, to indicate whetherscrblkcontains an error after decoding.

[scrblk,errFlag,trblk,lsbofsfn,hrf,msbidxoffset] = nrBCHDecode(softbits,L,lssb,ncellid)also returns the decoded and unscrambled BCH transport blocktrblk. The additional input arguments are the number of candidate synchronization signal / physical broadcast channel (SS/PBCH) blocks,lssb, and the physical layer cell identity number,ncellid. The function also returns these information elements:

lsbofsfn, the four least significant bits (LSBs) of the system frame number
hrf, the half frame bit
msbidxoffset, the most significant bits (MSBs) of the index offset

Examples

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Decode Scrambled BCH Transport Block

Open Live Script

Generate a random sequence of binary values corresponding to a BCH transport block of 24 bits.

trblk = randi([0 1],24,1,'int8');

Specify the physical layer cell identity number as 321, the system frame number as 10, and the second half frame.

nid = 321; sfn = 10; hrf = 1;

Specify the number of candidate SS/PBCH blocks as 8. When you specify the number of candidate SS/PBCH blocks as4or8, you can specify the subcarrier offsetkssbas an input argument to the BCH encoder.

lssb = 8; kssb = 18;

Encode the BCH transport block using the specified arguments.

bch = nrBCH(trblk,sfn,hrf,lssb,kssb,nid);

Decode the encoded transport block and recover information by using a polar decoding list length of 8 bits.

listLen = 8; [~,errFlag,rxtrblk,rxSFN4lsb,rxHRF,rxKssb] = nrBCHDecode(...double(1-2*bch),listLen,lssb,nid);

Verify that the decoding has no errors.

errFlag

errFlag =uint320

是equal(trblk,rxtrblk)

ans =logical1

是equal(bit2int(rxSFN4lsb,4),mod(sfn,16))

ans =logical1

[isequal(hrf,rxHRF) isequal(int2bit(floor(kssb/16),1,false),rxKssb)]

ans =1x2 logical array1

Input Arguments

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`softbits`—Approximate log-likelihood ratio (LLR) soft bits
864-by-1 real-valued column vector

Approximate log-likelihood ratio (LLR) soft bits, specified as an 864-by-1 real-valued column vector.

Data Types:single|double

`L`—Polar decoding list length
power of 2

Polar decoding list length, specified as a power of 2.

Data Types:double

`lssb`—Number of candidate SS/PBCH blocks in a half frame
`4`|`8`|`64`

Number of candidate SS/PBCH blocks in a half frame, specified as4,8, or64.

Data Types:double

`ncellid`—Physical layer cell identity number
integer

Physical layer cell identity number, specified as an integer from 0 to 1007.

Data Types:double

Output Arguments

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`scrblk`——解码炒BCH transport block
32-by-1 binary column vector

Decoded scrambled BCH transport block, returned as a 32-by-1 binary column vector.

Data Types:int8

`errFlag`— Error flag
`0`|`1`

Error flag to indicate whetherscrblkcontains an error, returned as0or1. IferrFlag是1, then an error has occurred.

Data Types:uint32

`trblk`— Decoded and unscrambled BCH transport block
24-by-1 binary column vector

Decoded and unscrambled BCH transport block, returned as a 24-by-1 binary column vector. The outputtrblk是theBCCH-BCH-Message, as defined in TS 38.331 Section 6.2.1[2]. TheBCCH-BCH-Messagecontains the master information block (MIB), as defined in TS 38.331 Section 6.2.2.

Data Types:logical

`lsbofsfn`— LSBs of the system frame number
4-by-1 column vector

The four LSBs of the system frame number, returned as a 4-by-1 column vector.

Data Types:logical

`hrf`— Half frame bit in SS/PBCH block transmissions
`0`|`1`

Half frame bit in SS/PBCH block transmissions, returned as0indicating the first half of a frame or1indicating the second half of a frame. For more information, see TS 38.214 Section 4.1[3].

Data Types:logical

`msbidxoffset`— MSBs of index offset
scalar | 3-by-1 column vector

MSBs of index offset, returned as a scalar or 3-by-1 column vector.

Iflssb是4or8,msbidxoffset是the decoded MSB of the subcarrier index, returned as a scalar.
Iflssb是64, the entries ofmsbidxoffsetare the three decoded MSBs of the SSB index, returned as a 3-by-1 column vector.

Data Types:logical

References

[1]3GPP TS 38.212. “NR; Multiplexing and channel coding.”3rd Generation Partnership Project; Technical Specification Group Radio Access Network.

[2]3GPP TS 38.331. “NR; Radio Resource Control (RRC) protocol specification.”3rd Generation Partnership Project; Technical Specification Group Radio Access Network.

[3]3GPP TS 38.214. “NR; Physical layer procedures for data.”3rd Generation Partnership Project; Technical Specification Group Radio Access Network.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

The input argumentLmust be a compile-time constant. Include{coder.Constant(L)}in the-argsvalue of thecodegenfunction. For more information, seecoder.Constant(MATLAB Coder).

Version History

Introduced in R2018b

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R2020a: Polar decoding metric update

Behavior changed in R2020a

In releases R2019b and before, polar decoding uses the exact form of the expression $\log (1 + e^{x})$ for internal metric evaluation. Starting in release R2020a, because the exact form leads to numerical instability for high SNR ranges, polar decoding approximates $\log (1 + e^{x})$ as 0 for $x < 0$ and as $x$ for $x \geq 0$ . This approximation affects the results of thenrBCHDecodefunction, resulting in a marginal degradation of the BLER performance in a link-level simulation.

nrBCHDecode

Syntax

Description

Examples

Decode Scrambled BCH Transport Block

Input Arguments

`softbits`—Approximate log-likelihood ratio (LLR) soft bits
864-by-1 real-valued column vector

`L`—Polar decoding list length
power of 2

`lssb`—Number of candidate SS/PBCH blocks in a half frame
`4`|`8`|`64`

`ncellid`—Physical layer cell identity number
integer

Output Arguments

`scrblk`——解码炒BCH transport block
32-by-1 binary column vector

`errFlag`— Error flag
`0`|`1`

`trblk`— Decoded and unscrambled BCH transport block
24-by-1 binary column vector

`lsbofsfn`— LSBs of the system frame number
4-by-1 column vector

`hrf`— Half frame bit in SS/PBCH block transmissions
`0`|`1`

`msbidxoffset`— MSBs of index offset
scalar | 3-by-1 column vector

References

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

R2020a: Polar decoding metric update

See Also

Functions

nrBCHDecode

Syntax

Description

Examples

Decode Scrambled BCH Transport Block

Input Arguments

softbits—Approximate log-likelihood ratio (LLR) soft bits864-by-1 real-valued column vector

L—Polar decoding list lengthpower of 2

lssb—Number of candidate SS/PBCH blocks in a half frame4|8|64

ncellid—Physical layer cell identity numberinteger

Output Arguments

scrblk——解码炒BCH transport block32-by-1 binary column vector

errFlag— Error flag0|1

trblk— Decoded and unscrambled BCH transport block24-by-1 binary column vector

lsbofsfn— LSBs of the system frame number4-by-1 column vector

hrf— Half frame bit in SS/PBCH block transmissions0|1

msbidxoffset— MSBs of index offsetscalar | 3-by-1 column vector

References

Extended Capabilities

C/C++ Code GenerationGenerate C and C++ code using MATLAB® Coder™.

Version History

R2020a: Polar decoding metric update

See Also

Functions

`softbits`—Approximate log-likelihood ratio (LLR) soft bits
864-by-1 real-valued column vector

`L`—Polar decoding list length
power of 2

`lssb`—Number of candidate SS/PBCH blocks in a half frame
`4`|`8`|`64`

`ncellid`—Physical layer cell identity number
integer

`scrblk`——解码炒BCH transport block
32-by-1 binary column vector

`errFlag`— Error flag
`0`|`1`

`trblk`— Decoded and unscrambled BCH transport block
24-by-1 binary column vector

`lsbofsfn`— LSBs of the system frame number
4-by-1 column vector

`hrf`— Half frame bit in SS/PBCH block transmissions
`0`|`1`

`msbidxoffset`— MSBs of index offset
scalar | 3-by-1 column vector

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.