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LTE SIB1 Transmission over Two Antennas

This example uses both channels of USRP® B210, X300 or X310 to transmit an LTE downlink signal that requires two antennas. The signal is generated by the LTE System Toolbox™ and random bits are inserted into the SIB1 field, the first of the System Information Blocks. The accompanying example sdruLTE2x2SIB1Rx.m receives this signal with two antennas, recovers the SIB1 data, and checks the CRC.

This example uses the SDRu Transmitter System object™. The ChannelMapping property of the object is set to [1 2] to enable use of both channels. The step method takes a two-column matrix in which the first column is the signal for 'RF A' of the radio and the second column is the signal for 'RF B' of the radio.

After starting this example, please run sdruLTE2x2SIB1Rx.m in a new MATLAB session. In Windows, if two B210 radios are used for these examples, each radio must be connected to a separate computer.

Please refer to the Setup and Configuration section of Documentation for USRP® Radio for details on configuring your host computer to work with the SDRu Transmitter System object.

Generate LTE Signal

% Check for presence of LTE System Toolbox
if isempty(ver('lte'))

% Generate LTE signal
rmc = lteRMCDL('R.12');     % Base RMC configuration
rmc.CellRefP = 2;           % 2 transmit antennas
rmc.PDSCH.NLayers = 2;      % 2 layers
rmc.NCellID = 64;           % Cell identity
rmc.NFrame = 100;           % Initial frame number
rmc.TotSubframes = 8*10;    % Generate 8 frames. 10 subframes per frame
rmc.OCNGPDSCHEnable = 'On'; % Add noise to unallocated PDSCH resource elements
rmc.PDSCH.RNTI = 61;
rmc.SIB.Enable = 'On';
rmc.SIB.DCIFormat = 'Format1A';
rmc.SIB.AllocationType = 0;
rmc.SIB.VRBStart = 0;
rmc.SIB.VRBLength = 6;
rmc.SIB.Gap = 0;
rmc.SIB.Data = randi([0 1],144,1); % Use random bits in SIB data field. This is not a valid SIB message
trData = [1;0;0;1];
[eNodeBOutput,txGrid,rmc] = lteRMCDLTool(rmc,trData);

Plot Power Spectrum of Two-Channel LTE Signal

spectrumAnalyzer = dsp.SpectrumAnalyzer;
spectrumAnalyzer.SampleRate = rmc.SamplingRate;  % 1.92e6 MHz for 'R.12'
spectrumAnalyzer.Title = 'Power Spectrum of Two-Channel LTE Signal';
spectrumAnalyzer.ShowLegend = true;
spectrumAnalyzer.ChannelNames = {'Antenna 1', 'Antenna 2'};
step(spectrumAnalyzer, eNodeBOutput);

Connect to Radio

radioFound = false;
radiolist = findsdru;
for i = 1:length(radiolist)
  if strcmp(radiolist(i).Status, 'Success')
    if strcmp(radiolist(i).Platform, 'B210')
        radio = comm.SDRuTransmitter('Platform','B210', ...
                 'SerialNum', radiolist(i).SerialNum);
        radio.MasterClockRate = 1.92e6 * 4; % Need to exceed 5 MHz minimum
        radio.InterpolationFactor = 4;      % Sampling rate is 1.92 MHz
        radioFound = true;
    if (strcmp(radiolist(i).Platform, 'X300') || ...
        strcmp(radiolist(i).Platform, 'X310'))
        radio = comm.SDRuTransmitter('Platform',radiolist(i).Platform, ...
                 'IPAddress', radiolist(i).IPAddress);
        radio.MasterClockRate = 184.32e6;
        radio.InterpolationFactor = 96;     % Sampling rate is 1.92 MHz
        radioFound = true;

if ~radioFound

radio.ChannelMapping = [1 2];     % Use both TX channels
radio.CenterFrequency = 900e6;
radio.Gain = 25;
radio.UnderrunOutputPort = true;

Checking radio connections...

radio = 

  System: comm.SDRuTransmitter 

                       Platform: 'B210'          
                      SerialNum: 'ECR04ZDBT'     
                 ChannelMapping: [1 2]           
                CenterFrequency: 900000000       
          LocalOscillatorOffset: 0               
                           Gain: 25              
                      PPSSource: 'Internal'
                    ClockSource: 'Internal'
                MasterClockRate: 7680000         
            InterpolationFactor: 4               
              TransportDataType: 'int16'
                EnableBurstMode: false           

Send Signal over Two Antennas

% Scale signal to make maximum magnitude equal to 1
eNodeBOutput = eNodeBOutput/max(abs(eNodeBOutput(:)));

% Reshape signal as a 3D array to simplify the for loop below
% Each call to step method of the object will use a two-column matrix
samplesPerFrame = 10e-3*rmc.SamplingRate;      % LTE frames are 10 ms long
numFrames = length(eNodeBOutput)/samplesPerFrame;
txFrame = permute(reshape(permute(eNodeBOutput,[1 3 2]), ...
                  samplesPerFrame,numFrames,rmc.CellRefP),[1 3 2]);

disp('Starting transmission');
disp('Please run sdruLTE2x2SIB1Rx.m in a new MATLAB session');

currentTime = 0;
while currentTime < 300                        % Run for 5 minutes
    for n = 1:numFrames
        % Call step method to send a two-column matrix
        % First column for TX channel 1. Second column for TX channel 2
        bufferUnderflow = step(radio,txFrame(:,:,n));
        if bufferUnderflow~=0
            warning('sdru:examples:DroppedSamples','Dropped samples')
    currentTime = currentTime+numFrames*10e-3; % One frame is 10 ms
disp('Transmission finished')
Starting transmission
Please run sdruLTE2x2SIB1Rx.m in a new MATLAB session
Transmission finished

Tips for Maximizing Performance

  • Run this example and sdruLTE2x2SIB1Rx.m on two computers

  • Double InterpolationFactor in this example and DecimationFactor in sdruLTE2x2SIB1Rx.m

  • Start MATLAB in -nodesktop mode before running this example

  • If you are using one computer with two B210 radios, do not connect them to adjacent USB ports

Copyright Notice

Universal Software Radio Peripheral® and USRP® are trademarks of National Instruments Corp.