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% cell-wide settings
% the cell-wide parameters are grouped into a single structure enb. a
% number of the functions used in this example require a subset of the
% parameters specified below. in this example we use the configuration
% according to the rmc r.14 fdd specified in ts 36.101 annex a.3.4 which
% uses 50 rb, 4 port, 'spatialmux' transmission scheme, '16qam' symbol
% modulation, 2 codewords and a code rate of 1/2.
enb.ndlrb = 50;                 % number of resource blocks
enb.cellrefp = 4;               % cell-specific reference signal ports
enb.ncellid = 0;                % cell id
enb.cyclicprefix = 'normal';    % normal cyclic prefix
enb.cfi = 2;                    % length of control region
enb.duplexmode = 'fdd';         % fdd duplex mode
enb.tddconfig = 1;              % uplink/downlink configuration (tdd only)
enb.ssc = 4;                    % special subframe configuration (tdd only)
enb.nsubframe = 0;              % subframe number
% transport/physical channel settings for ease of use the dl-sch and pdsch
% channel specific settings are specified in a parameter structure pdsch.
% for the r.14 fdd rmc, there are two codewords, so the modulation scheme
% is specified as a cell array containing the modulation schemes of both
% codewords. if configuring for one codeword, the modulation scheme can be
% a character vector or a cell array with character vectors.
% it is also important to configure the trblksizes parameter to have the
% correct number of elements as the intended number of codewords. the
% number of soft bits for the rate matching stage is decided by the ue
% category as specified in ts 36.306 table 4.1-1. in this example, the
% transport block size is looked up from tables in ts 36.101 annex a.3.4.
% this can also be done by using the ltermcdl function for r.14 rmc.
% dl-sch settings
trblksizes = [11448; 11448];    % 2 elements for 2 codeword transmission
pdsch.rv = [0 0];               % rv for the 2 codewords
pdsch.nsoftbits = 1237248;      % no of soft channel bits for ue category 2
% pdsch settings
pdsch.txscheme = 'spatialmux';  % transmission scheme used
pdsch.modulation = {'16qam','16qam'}; % symbol modulation for 2 codewords
pdsch.nlayers = 2;              % two spatial transmission layers
pdsch.ntxants = 2;              % number of transmit antennas
pdsch.rnti = 1;                 % the rnti value
pdsch.prbset = (0:enb.ndlrb-1)';% the prbs for full allocation
pdsch.pmiset = 0;               % precoding matrix index
pdsch.w = 1;                    % no ue-specific beamforming
% only required for 'port5', 'port7-8', 'port8' and 'port7-14' schemes
if any(strcmpi(pdsch.txscheme,{'port5','port7-8','port8', 'port7-14'}))
    pdsch.w = transpose(ltecsicodebook(pdsch.nlayers,pdsch.ntxants,[0 0]));
end

% random number initialization for creating random transport block(s)
rng('default');
% convert the modulation scheme char array or cell array to string array
% for uniform processing
 pdsch.modulation = string(pdsch.modulation);
% get the number of codewords from the number of transport blocks
ncodewords = numel(trblksizes);
% generate the transport block(s)
trblk = cell(1,ncodewords); % initialize the codeword(s)
for n=1:ncodewords
    trblk{n} = randi([0 1],trblksizes(n),1);
end
% get the physical channel bit capacity required for rate matching from
% ltepdschindices info output
[~,pdschinfo] = ltepdschindices(enb,pdsch,pdsch.prbset);
% define a structure array with parameters for lteratematchturbo
chs = pdsch;
chs(ncodewords) = pdsch; % for 2 codewords, the array has two elements
% initialize the codeword(s)
cw = cell(1,ncodewords);
for n=1:ncodewords
    % crc addition for the transport block
    crccoded = ltecrcencode(trblk{n},'24a');
    % code block segmentation returns a cell array of code block segments
    % with filler bits and type-24b crc appended as required
    blksegmented = ltecodeblocksegment(crccoded);
    % channel coding returns the turbo coded segments in a cell array
    chencoded = lteturboencode(blksegmented);
    % bundle the parameters in structure chs for rate matching as the
    % function requires both cell-wide and channel specific parameters
    chs(n).modulation = pdsch.modulation{n};
    chs(n).duplexmode = enb.duplexmode;
    chs(n).tddconfig = enb.tddconfig;
    % calculate number of layers for the codeword
    if n==1
        chs(n).nlayers = floor(pdsch.nlayers/ncodewords);
    else
        chs(n).nlayers = ceil(pdsch.nlayers/ncodewords);
    end
    % rate matching returns a codeword after sub-block interleaving, bit
    % collection and bit selection and pruning defined for turbo encoded
    % data and merging the cell array of code block segments
    cw{n} = lteratematchturbo(chencoded,pdschinfo.g(n),pdsch.rv(n),chs(n));
end

% initialize the modulated symbols
modulated = cell(1,ncodewords);
for n=1:ncodewords
   % generate the scrambling sequence
   scramseq = ltepdschprbs(enb,pdsch.rnti,n-1,length(cw{n}));
   % scramble the codewords
   scrambled = xor(scramseq,cw{n});
   % symbol modulate the scrambled codewords
   modulated{n} = ltesymbolmodulate(scrambled,pdsch.modulation{n});
end
% layer mapping results in a (symbols per layer)-by-nlayers matrix
layermapped = ltelayermap(pdsch,modulated);
% precoding results in a (symbols per antenna)-by-ntxants matrix
precoded = ltedlprecode(enb, pdsch, layermapped);
% apply beamforming optionally (w should be 1 or identity if no beamforming)
pdschsymbols = precoded*pdsch.w;

% deprecoding (pseudo-inverse based) returns (number of symbols)-by-nlayers matrix
if (any(strcmpi(pdsch.txscheme,{'port5' 'port7-8' 'port8' 'port7-14'})))
    rxdeprecoded=pdschsymbols*pinv(pdsch.w);
else
    rxdeprecoded = ltedldeprecode(enb,pdsch,pdschsymbols);
end
% layer demapping returns a cell array containing one or two codewords. the
% number of codewords is deduced from the number of modulation scheme
% character vectors
layerdemapped = ltelayerdemap(pdsch,rxdeprecoded);
% initialize the recovered codewords
cws = cell(1,ncodewords);
for n=1:ncodewords
    % soft demodulation of received symbols
    demodulated = ltesymboldemodulate(layerdemapped{n},pdsch.modulation{n},'soft');
    % scrambling sequence generation for descrambling
    scramseq = ltepdschprbs(enb,pdsch.rnti,n-1,length(demodulated),'signed');
    % descrambling of received bits
    cws{n} = demodulated.*scramseq;
end

% initialize the received transport block and crc
rxtrblk = cell(1,ncodewords);
crcerror = zeros(1,ncodewords);
for n=1:ncodewords
    % rate recovery stage also allows combining with soft information for
    % the harq process, using the input cbsbuffers. for the first
    % transmission of the transport block, the soft buffers are initialized
    % as empty. for retransmissions, the parameter cbsbuffers should be the
    % soft information from the previous transmission
    cbsbuffers = [];  % initial transmission of the harq process
    % rate recovery returns a cell array of turbo encoded code blocks
    raterecovered = lteraterecoverturbo(cws{n},trblksizes,pdsch.rv(n),chs(n),cbsbuffers);
    nturbodecits = 5; % number of turbo decoding iteration cycles
    % turbo decoding returns a cell array of decoded code blocks
    turbodecoded = lteturbodecode(raterecovered,nturbodecits);
    % code block desegmentation concatenates the input code block segments
    % into a single output data block, after removing any filler and
    % type-24b crc bits that may be present
    [blkdesegmented,segerr] = ltecodeblockdesegment(turbodecoded,(trblksizes 24));
    % crc decoding returns the transport block after checking for crc error
    [rxtrblk{n},crcerror(n)] = ltecrcdecode(blkdesegmented,'24a');
end