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tbs = 144;                          % the transport block size
totnumblks = 1;                     % number of simulated transport blocks
ue = struct();                      % initialize the ue structure
ue.nbulsubcarrierspacing = '15khz'; % 3.75khz, 15khz
ue.nncellid = 0;                    % narrowband cell identity
chs = struct();
% npusch carries data or control information
chs.npuschformat = 'data'; % payload type (data or control)
% the number of subcarriers used for npusch 'nscru' depends on the npusch
% format and subcarrier spacing 'nbulsubcarrierspacing' as shown in ts
% 36.211 table 10.1.2.3-1. there are 1,3,6 or 12 contiguous subcarriers for
% npusch
chs.nbulsubcarrierset = 0;  % range is 0-11 (15khz); 0-47 (3.75khz)
chs.nrusc = length(chs.nbulsubcarrierset);
chs.cyclicshift = 0;   % cyclic shift required when nrusc = 3 or 6
chs.rnti = 0;          % rnti value
chs.nlayers = 1;       % number of layers
chs.nru = 2;           % number of resource units
chs.nrep = 4;          % number of repetitions of the npusch
chs.slotidx = 0;       % start slot index in a bundle
% the symbol modulation depends on the npusch format and nscru as
% given by ts 36.211 table 10.1.3.2-1
chs.modulation = 'qpsk';
rvdci = 0;             % rv offset signaled via dci (see 36.213 16.5.1.2)
% specify the npusch and dm-rs power scaling in db for plot visualization
chs.npuschpower = 30;
chs.npuschdrspower = 34;

chs.seqgrouphopping = 'on'; % enable/disable sequence-group hopping for ue
chs.seqgroup = 0;           % delta_ss. higher-layer parameter groupassignmentnpusch
% get number of time slots in a resource unit nulslots according to
% ts 36.211 table 10.1.2.3-1
if strcmpi(chs.npuschformat,'data')
    if chs.nrusc == 1
        nulslots = 16;
    elseif any(chs.nrusc == [3 6 12])
        nulslots = 24/chs.nrusc;
    else
        error('invalid number of subcarriers. nrusc must be one of 1,3,6,12');
    end
elseif strcmpi(chs.npuschformat,'control')
    nulslots = 4;
else
    error('invalid npusch format (%s). npuschformat must be ''data'' or ''control''',chs.npuschformat);
end
chs.nulslots = nulslots;
nslotsperbundle = chs.nru*chs.nulslots*chs.nrep; % number of slots in a codeword bundle
totnslots = totnumblks*nslotsperbundle;   % total number of simulated slots

% initialize the random generator to default state
rng('default');
% get the slot grid and number of slots per frame
emptyslotgrid = ltenbresourcegrid(ue);
slotgridsize = size(emptyslotgrid);
nslotsperframe = 20/(slotgridsize(1)/12);
state = [];    % npusch encoder and dm-rs state, auto re-initialization in the function
trblk = [];    % initialize the transport block
txgrid = [];   % full grid initialization
% display the number of slots being generated
fprintf('\ngenerating %d slots corresponding to %d transport block(s)\n',totnslots,totnumblks);
for slotidx = 0 (0:totnslots-1)
    % calculate the frame number and slot number within the frame
    ue.nframe = fix(slotidx/nslotsperframe);
    ue.nslot = mod(slotidx,nslotsperframe);
    if isempty(trblk)
       if strcmpi(chs.npuschformat,'data')
           % ul-sch encoding is done for the two rv values used for
           % transmitting the codewords. the rv sequence used is determined
           % from the rvdci value signaled in the dci and alternates
           % between 0 and 2 as given in ts 36.213 section 16.5.1.2
           % define the transport block which will be encoded to create the
           % codewords for different rv
           trblk = randi([0 1],tbs,1);
           % determine the coded transport block size
           [~, info] = ltenpuschindices(ue,chs);
           outblklen = info.g;
           % create the codewords corresponding to the two rv values used
           % in the first and second block, this will be repeated till all
           % blocks are transmitted
           chs.rv = 2*mod(rvdci 0,2); % rv for the first block
           cw = ltenulsch(chs,outblklen,trblk); % crc and turbo coding
           chs.rv = 2*mod(rvdci 1,2); % rv for the second block
           cw = [cw ltenulsch(chs,outblklen,trblk)]; %#ok % crc and turbo coding is repeated
       else
           trblk = randi([0 1],1); % 1 bit ack
           % for ack, the same codeword is transmitted every block as
           % defined in ts 36.212 section 6.3.3
           cw = ltenulsch(trblk);
       end
       blockidx = 0; % first block to be transmitted
    end
    % initialize grid
    slotgrid = emptyslotgrid;
    % npusch encoding and mapping onto the slot grid
    txsym = ltenpusch(ue,chs,cw(:,mod(blockidx,size(cw,2)) 1),state);
    % map npusch symbols in the grid of a slot
    indicesnpusch = ltenpuschindices(ue,chs);
    slotgrid(indicesnpusch) = txsym*db2mag(chs.npuschpower);
    % create dm-rs sequence and map to the slot grid
    [dmrs,state] = ltenpuschdrs(ue,chs,state);
    indicesdmrs = ltenpuschdrsindices(ue,chs);
    slotgrid(indicesdmrs) = dmrs*db2mag(chs.npuschdrspower);
    % concatenate this slot to the slot grid
    txgrid = [txgrid slotgrid]; %#ok
    % if a full block is transmitted, increment the clock counter so that
    % the correct codeword can be selected
    if state.endofblk
        blockidx = blockidx   1;
    end
    % trblk err count and re-initialization
    if state.endoftx
       % re-initialize to enable the transmission of a new transport block
       trblk = [];
    end
end
% perform sc-fdma modulation to create time domain waveform
ue.cyclicprefixul = 'normal'; % normal cyclic prefix length for nb-iot
[waveform,scfdmainfo] = ltescfdmamodulate(ue,chs,txgrid);

% create an image of overall resource grid
figure
im = image(abs(txgrid));
cmap = parula(64);
colormap(im.parent,cmap);
axis xy;
title(sprintf('nb-iot uplink re grid (nrep = %d, nrusc = %d, nru = %d)',chs.nrep,chs.nrusc,chs.nru))
xlabel('ofdm symbols')
ylabel('subcarriers')
% create the legend box to indicate the channel/signal types associated with the res
renames = {'npusch';'dm-rs'};
clevels = round(db2mag([chs.npuschpower chs.npuschdrspower]));
n = numel(renames);
l = line(ones(n),ones(n), 'linewidth',8); % generate lines
% set the colors according to cmap
set(l,{'color'},mat2cell(cmap( min(1 clevels,length(cmap) ),:),ones(1,n),3));
legend(renames{:});