nrExtractResources
Extract resource elements from resource array
Syntax
Description
re = nrExtractResources(ind,grid)grid using
resource element indices ind. The function can extract resource
elements even if grid has a dimensionality which is different than the
dimensionality of the indices ind. In this syntax, the specified
indices are 1-based using linear indexing form.
Typically, channel or signal specific functions generate resource element indices to map the channel or signal symbols to a resource grid. The indices address resource elements in an M-by-N-by-P array. M is the number of subcarriers, N is the number of OFDM symbols, and P is the number of antenna ports.
For example, the following diagram highlights resource elements of a 4-by-4-by-2 resource array. The resource element indices are in 1-based linear indexing form. The number of the antenna ports is two (P = 2).
[re1,...,reN,reind1,...,reindN] =
nrExtractResources(
extracts resource elements from multiple resource arrays using the resource element indices
ind,grid1,grid2,....,gridN)ind.
[___] = nrExtractResources(___,
specifies optional name-value pair arguments in addition to any of the input argument sets
in previous syntaxes. Use these name-value pair arguments to specify the format of the input
indices and the extraction method. Unspecified arguments take default values.Name,Value)
Examples
Extract physical broadcast channel (PBCH) symbols from a received grid and associated channel estimates in preparation for decoding a beamformed PBCH.
PBCH Coding and Beamforming
Create a random sequence of binary values corresponding to a BCH codeword. The length of the codeword is 864, as specified in TS 38.212 Section 7.1.5. Using the codeword, create symbols and indices for a PBCH transmission. Specify the physical layer cell identity number.
E = 864; cw = randi([0 1],E,1); ncellid = 17; v = 0; pbchTxSym = nrPBCH(cw,ncellid,v); pbchInd = nrPBCHIndices(ncellid);
Use nrExtractResources to create indices for the two transmit antennas of a beamformed PBCH. Use these indices to map the beamformed PBCH into the transmitter resource array.
carrier = nrCarrierConfig('NSizeGrid',20);
P = 2;
txGrid = nrResourceGrid(carrier,P);
F = [1 0.3i];
[~,bfInd] = nrExtractResources(pbchInd,txGrid);
txGrid(bfInd) = pbchTxSym*F;OFDM modulate the PBCH symbols mapped into the transmitter resource array.
txWaveform = nrOFDMModulate(carrier,txGrid);
PBCH Transmission and Decoding
Create and apply a channel matrix to the waveform. Receive the transmitted waveforms.
R = 3; H = dftmtx(max([P R])); H = H(1:P,1:R); H = H/norm(H); rxWaveform = txWaveform*H;
Create channel estimates including beamforming.
hEstGrid = repmat(permute(H.'*F.',[3 4 1 2]),[240 4]); nEst = 0;
Demodulate the received waveform using orthogonal frequency division multiplexing (OFDM).
rxGrid = nrOFDMDemodulate(carrier,rxWaveform);
In preparation for PBCH decoding, extract symbols from the received grid and the channel estimate grid.
[pbchRxSym,pbchHestSym] = nrExtractResources(pbchInd,rxGrid,hEstGrid); scatterplot(pbchRxSym(:),[],[],'y+'); title('Received PBCH Constellation');
Equalize the symbols by performing MMSE equalization on the extracted resources. Plot the results.
pbchEqSym = nrEqualizeMMSE(pbchRxSym,pbchHestSym,nEst); scatterplot(pbchEqSym(:),[],[],'y+'); title('Equalized PBCH Constellation');
Retrieve soft bits by performing PBCH decoding on the equalized symbols.
pbchBits = nrPBCHDecode(pbchEqSym,ncellid,v)
pbchBits = 864×1
1010 ×
-2.0000
-2.0000
2.0000
-2.0000
-2.0000
2.0000
2.0000
-2.0000
-2.0000
-2.0000
2.0000
-2.0000
-2.0000
2.0000
-2.0000
⋮
Input Arguments
Name-Value Arguments
Output Arguments
Algorithms
To use this method, set 'ExtractionMethod' to
'allplanes'. This method extracts resource elements from each
M-by-N plane within grid. The
indices address unique subcarrier and symbol locations over all the planes of the indexed
resource array. The diagram highlights the indices used to extract resource elements from a
resource grid with P = 2.
The following diagrams illustrate the resource element extraction from a 3-D received grid, where the number of receive antennas R = 3. Resource elements are extracted from the grid at the symbol and subcarrier locations.
The following diagram shows the extraction process for a 4-D channel estimate grid. The number of receive antennas R = 3 and the number of antenna ports P = 2. The 4-D resource grid consists of P M-by-N-by-R arrays, each associated with an antenna port. Resource elements are extracted from all planes within these arrays.
To use this method, set 'ExtractionMethod' to
'direct'. This method extracts resource elements from
grid assuming that the third and fourth dimensions of the
grid represent the same property as the planes of the indexed
resource array such as antenna ports, layers, transmit antennas. Therefore the function
extracts only the resource elements relevant to each plane of the indexed resource
grid.
For a 3-D
grid, the direct method extracts elements from each M-by-N plane ofgridusing indices addressing the same plane of the indexed resource array. This method is the same as the standard MATLAB® operationre=grid(ind). Therefore,reind=ind.For a 4-D
grid, the direct method extracts elements from each M-by-N-by-R array ofgridby using indices addressing the same plane of the indexed resource array. The function assumes that the property represented by the planes of the indexed resource array is the same as the fourth dimension ofgrid.
The following diagram shows the extraction process for a 4-D channel estimate grid. The number of receive antennas R = 3 and the number of antenna ports P = 2. The 4-D resource grid consists of P number of M-by-N-by-R arrays, each associated with an antenna port. The indices corresponding to each individual antenna port in the indexed resource array are used to extract resource elements from each of these arrays.
