Getting message while converting following matlab code to c? This structure does not have a field 'numResources'; new fields cannot be added when structure has been read or used.

function p= prmsPDSCH(chanBW, contReg, modType, varargin)
% Returns parameter structures for LTE PDSCH simulation.
%
% Assumes a FDD, normal cyclic prefix, full-bandwidth, single-user
% SISO or SIMO downlink transmission.
%%PDSCH parameters
switch chanBW
case 1 % 1.4 MHz
BW = 1.4e6; N = 128; cpLen0 = 10; cpLenR = 9;
Nrb = 6; chanSRate = 1.92e6;
case 2 % 3 MHz
BW = 3e6; N = 256; cpLen0 = 20; cpLenR = 18;
Nrb = 15; chanSRate = 3.84e6;
case 3 % 5 MHz
BW = 5e6; N = 512; cpLen0 = 40; cpLenR = 36;
Nrb = 25; chanSRate = 7.68e6;
case 4 % 10 MHz
BW = 10e6; N = 1024; cpLen0 = 80; cpLenR = 72;
Nrb = 50; chanSRate = 15.36e6;
case 5 % 15 MHz
BW = 15e6; N = 1536; cpLen0 = 120; cpLenR = 108;
Nrb = 75; chanSRate = 23.04e6;
case 6 % 20 MHz
BW = 20e6; N = 2048; cpLen0 = 160; cpLenR = 144;
Nrb = 100; chanSRate = 30.72e6;
end
p.BW = BW; % Channel bandwidth
p.N = N; % NFFT
p.cpLen0 = cpLen0; % Cyclic prefix length for 1st symbol
p.cpLenR = cpLenR; % Cyclic prefix length for remaining
p.Nrb = Nrb; % Number of resource blocks
p.chanSRate = chanSRate; % Channel sampling rate
p.contReg = contReg;
if nargin > 3
    numTx=varargin{4};
else
    numTx=1;
end
if nargin > 4
    numRx=varargin{5};
else
    numRx=1;
end
p.numTx = numTx;
p.numRx = numRx;
p.numLayers = 1;
p.numCodeWords = 1;
% For Normal cyclic prefix, FDD mode
p.deltaF = 15e3; % subcarrier spacing
p.Nrb_sc = 12; % no. of subcarriers per resource block
p.Ndl_symb = 7; % no. of OFDM symbols in a slot
% Actual PDSCH bits calculation - accounting for PDCCH, PBCH, PSS, SSS
numResources = (p.Nrb*p.Nrb_sc)*(p.Ndl_symb*2);
numCSRRE = 2*2*2 * p.Nrb; % CSR, RE per OFDMsym/slot/subframe per RB
numContRE = (10 + 12*(p.contReg-1))*p.Nrb;
numBCHRE = 60+72+72+72; % removing the CSR present in 1st symbol
numSSSRE=72;
numPSSRE=72;
numDataRE=zeros(3,1);

% Account for BCH, PSS, SSS and PDCCH for subframe 0
numDataRE(1)=numResources-numCSRRE-numContRE-numSSSRE-numPSSRE-numBCHRE;
% Account for PSS, SSS and PDCCH for subframe 5
numDataRE(2)=numResources-numCSRRE-numContRE-numSSSRE - numPSSRE;
% Account for PDCCH only in all other subframes
numDataRE(3)=numResources-numCSRRE-numContRE;
% Maximum data resources - with no extra overheads (only CSR + data)
p.numResources=numResources;
p.numCSRResources = numCSRRE;
p.numContRE = numContRE;
p.numBCHRE = numBCHRE;
p.numSSSRE=numSSSRE;
p.numPSSRE=numPSSRE;
p.numDataRE=numDataRE;
p.numDataResources = p.numResources - p.numCSRResources;
% Modulation types , bits per symbol, number of layers per codeword
Qm = 2 * modType;
p.Qm = Qm;
p.numLayPerCW = p.numLayers/p.numCodeWords;
% Maximum data bits - with no extra overheads (only CSR + data)
p.numDataBits = p.numDataResources*Qm*p.numLayPerCW;
numPDSCHBits =numDataRE*Qm*p.numLayPerCW;
p.numPDSCHBits = numPDSCHBits;
p.maxG = max(numPDSCHBits);
end

Answer 1

[Fangjun Jiang]

You are creating the structure p, adding its fields on-the-go. For example, fields "numTx", "numRx" and "numLayers" etc. are created. Then, the p structure is used in line "numResources = (p.Nrb*p.Nrb_sc)*(p.Ndl_symb*2)". Then more fields such as "numResources" are added.

According to the error message, this is not allowed. The code generation needs to know all the field names at the beginning, or at least, all the field names before the structure started being used.

You should create all those field names at the beginning of the code. Assign zero first and over-write it later. That should allow you to avoid this error message.

[Bhavanithya Thiraviaraja]

I also faced the same problem when using inside a MATLAB function of a Simulink Model. My problem is I do not know the size of the value that is added to a new field of the struct and hence I cannot assign a zero.

Example,

ft_table is the new field which can be a 2-D array with varying rows and columns throughout the simulation. So if I assign initially in the beginning of the code as,

bands.ft_table = 0;

then assign 2-D array to it, Simulink throws the below error,

Size mismatch (size [1 x 1] ~= size [:? x 2]).
The size to the left is the size of the left-hand side of the assignment.

Any suggestions how to overcome this?

[Fangjun Jiang]

In that case, don't use structure. Refer to the document to implement variable-size data.

web(fullfile(docroot, 'simulink/variable-size-data.html'))

Answer 2

[Ankur Soni]

if i understand your answer correctly .

did you means my code should begin like

function p= prmsPDSCH(chanBW, contReg, modType, varargin) P.BW=0; P.N=0, P.cplen0=0; etc and create other structure array with field

m i correct?

[Fangjun Jiang]

Yes. That is the safest way to avoid this problem.

Answer 3

[Ankur Soni]

Thank you. it worked.

[Virtualkeeda]

Hi Ankur, It didnt worked for me.

The same error came for me on this line:

dbn.rbm{3, 1}=[];

"This structure does not have a field 'rbm'; new fields cannot be added when structure has been read or used."