Plug Custom Channel into Wireless Network Simulator

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This example shows you how to plug a custom channel into a wireless network simulator and compare its performance against a free-space propagation loss (FSPL) channel. Using this example, you can:

  1. Configure a 5G network with new radio (NR) base station (gNB) and user equipment (UE) nodes.

  2. Establish a connection between the gNB and UE nodes.

  3. Create a custom channel, and plug it into a wireless network simulator.

  4. Simulate a 5G network, and retrieve the statistics of the gNB and UE nodes.

  5. Compare the throughput performance for custom and FSPL channels.

Configure Wireless Network Simulator

Create a wireless network simulator.

rng("default")
networkSimulator = wirelessNetworkSimulator.init;

Create a gNB node with these specifications.

  • Position – [-100 100 0]

  • Channel bandwidth – 20 MHz

  • Subcarrier spacing – 30 kHz

  • Duplex mode – Frequency division duplex

gnb = nrGNB(Position=[-100 100 0],ChannelBandwidth=20e6,DuplexMode="FDD",SubcarrierSpacing=30e3);

Create two UE nodes, specifying their positions in Cartesian coordinates.

ue = nrUE(Position=[100 100 0; 5000 100 0]);

Connect the UE nodes to the gNB node, enabling full-buffer traffic in the downlink direction.

connectUE(gnb,ue,FullBufferTraffic="DL")

Add the nodes to the wireless network simulator.

addNodes(networkSimulator,gnb)
addNodes(networkSimulator,ue)

Set Up 5G CDL Channel Model

Create an individual downlink clustered delay line (CDL) channel for each UE node.

% Retrieve OFDM information based on the number of resource blocks and
% subcarrier spacing (kHz)
waveformInfo = nrOFDMInfo(gnb.NumResourceBlocks,gnb.SubcarrierSpacing/1e3);
channelFilteringFlag = strcmp(gnb.PHYAbstractionMethod,"none");

% Calculate the total number of nodes by adding up the number of gNBs and UEs
numNodes = max([gnb.ID, ue.ID]);

% Initialize the CDL channel cell array, maximum channel delay matrix, and the path filter cell array
channelInfo.CDLChannels = cell(numNodes,numNodes);
channelInfo.MaxChannelDelayMatrix = zeros(numNodes,numNodes);
channelInfo.PathFilter = cell(numNodes,numNodes);

% Create a CDL channel for each gNB-UE link
for i = 1:length(ue)
    % Create a CDL channel model by specifying sample rate and channel filtering option
    channelInfo.CDLChannels{gnb.ID,ue(i).ID} = nrCDLChannel(SampleRate=waveformInfo.SampleRate,ChannelFiltering=channelFilteringFlag);
    % Set the transmit antenna array size
    channelInfo.CDLChannels{gnb.ID,ue(i).ID}.TransmitAntennaArray.Size = [1 1 1 1 1];
    %  Set the receive antenna array size 
    channelInfo.CDLChannels{gnb.ID,ue(i).ID}.ReceiveAntennaArray.Size = [1 1 1 1 1];
    % Retrieve the channel information
    chInfo = info(channelInfo.CDLChannels{gnb.ID,ue(i).ID});
    % Calculate the maximum channel delay and update the delay matrix
    channelInfo.MaxChannelDelayMatrix(gnb.ID,ue(i).ID) = ceil(max(chInfo.PathDelays*waveformInfo.SampleRate)) + chInfo.ChannelFilterDelay;
    % Obtain path filters
    channelInfo.PathFilter{gnb.ID,ue(i).ID} = getPathFilters(channelInfo.CDLChannels{gnb.ID,ue(i).ID}).';
end

Compute Custom Channel Statistics

Add the custom channel to the wireless network simulator.

addChannelModel(networkSimulator,@(rxInfo,txData)addImpairment(channelInfo,rxInfo,txData))

Specify the simulation time in seconds.

simulationTime = 0.05;

Run the simulation for the specified simulation time.

run(networkSimulator,simulationTime)

Obtain the statistics for the gNB and UE nodes.

gnbStatsCustomChannel = statistics(gnb);
ueStatsCustomChannel = statistics(ue);
% Display MAC layer statistics for the UEs
ueStatsCustomChannel.MAC
ans = struct with fields:
     TransmittedPackets: 0
       TransmittedBytes: 0
        ReceivedPackets: 99
          ReceivedBytes: 313753
        Retransmissions: 0
    RetransmissionBytes: 0
       DLTransmissionRB: 2550
     DLRetransmissionRB: 0
       ULTransmissionRB: 0
     ULRetransmissionRB: 0


ans = struct with fields:
     TransmittedPackets: 0
       TransmittedBytes: 0
        ReceivedPackets: 99
          ReceivedBytes: 80180
        Retransmissions: 0
    RetransmissionBytes: 0
       DLTransmissionRB: 2550
     DLRetransmissionRB: 0
       ULTransmissionRB: 0
     ULRetransmissionRB: 0

Calculate the total downlink throughput (Mbps) across both UEs.

dlReceivedBytesTotal = ueStatsCustomChannel(1).MAC.ReceivedBytes + ueStatsCustomChannel(2).MAC.ReceivedBytes;
dlThroughputWithCustomChannel = (dlReceivedBytesTotal*8) / (simulationTime*1000*1000);

Set Up FSPL Channel for Analysis

Run the same scenario with FSPL channel only. Initialize, configure nodes, connect, run, and compute throughput.

rng("default")
networkSimulator = wirelessNetworkSimulator.init;
% Recreate the gNB and UEs nodes
gnb = nrGNB(Position=[-100 100 0],ChannelBandwidth=20e6, ...
                   DuplexMode="FDD",SubcarrierSpacing=30e3);
ue = nrUE(Position=[100 100 0; 5000 100 0]);                  % In Cartesian x, y, and z coordinates

% Connect and add nodes
connectUE(gnb,ue,FullBufferTraffic="DL")
addNodes(networkSimulator,gnb)
addNodes(networkSimulator,ue)
%  Run FSPL-only simulation
run(networkSimulator,simulationTime)

Obtain the statistics for the gNB and UE nodes.

gnbStats = statistics(gnb);
ueStats = statistics(ue);
% Display MAC layer statistics for the UEs
ueStats.MAC
ans = struct with fields:
     TransmittedPackets: 0
       TransmittedBytes: 0
        ReceivedPackets: 99
          ReceivedBytes: 313753
        Retransmissions: 0
    RetransmissionBytes: 0
       DLTransmissionRB: 2550
     DLRetransmissionRB: 0
       ULTransmissionRB: 0
     ULRetransmissionRB: 0


ans = struct with fields:
     TransmittedPackets: 0
       TransmittedBytes: 0
        ReceivedPackets: 99
          ReceivedBytes: 140180
        Retransmissions: 0
    RetransmissionBytes: 0
       DLTransmissionRB: 2550
     DLRetransmissionRB: 0
       ULTransmissionRB: 0
     ULRetransmissionRB: 0

Calculate the total downlink throughput (Mbps) across both UEs.

dlReceivedBytesTotal = ueStats(1).MAC.ReceivedBytes + ueStats(2).MAC.ReceivedBytes;
dlThroughputWithFSPL = (dlReceivedBytesTotal*8)/(simulationTime*1000*1000);

Visualize Throughput

Compare throughput for custom and FSPL channels using a bar chart.

networkSimulator = wirelessNetworkSimulator.init;
% Create a bar chart with two bars: one for the custom channel, one for the FSPL.
data = [dlThroughputWithCustomChannel dlThroughputWithFSPL]; % The heights of the two bars
labels = {"With Custom Channel","With FSPL"};                 % Labels for the bars

% Plot the bar chart
bar(data)

% Customize the x-axis labels
set(gca,"XTickLabel",labels)

% Add title and labels
title("Downlink Cell Performance of Wireless Network")
xlabel("Channel Models")
ylabel("Throughput (Mbps)")

Figure contains an axes object. The axes object with title Downlink Cell Performance of Wireless Network, xlabel Channel Models, ylabel Throughput (Mbps) contains an object of type bar.

Local Function

Follow these steps to create a custom channel model.

  • Create a custom function with this syntax: rxData = customFcnName(rxInfo,txData). The rxInfo input is a structure containing the receiver node information, and the txData input is a structure that specifies the transmitted packets. The simulator automatically passes information about the receiver node and the packets transmitted by a transmitter node as inputs to the custom function. For more information, see the addChannelModel object function.

  • When you add a custom channel to the 5G SLS, update the Power, Duration, and Data fields (for full PHY) in the wireless packet metadata. Also, update the PathGain, PathFilters, PathDelays and SampleTime fields in Metadata.Channel. You do not need to include PathDelays for 5G. For more information about the packet structure, refer to wirelessPacket.

  • Apply free space path loss between the base station and UE nodes.

  • Apply a CDL channel to the transmitted packets.

function outputData = addImpairment(channelInfo,rxInfo,txData)

outputData = txData;

% Calculate path loss
distance = norm(txData.TransmitterPosition - rxInfo.Position); % Distance between transmitter and receiver
lambda = physconst("LightSpeed")/txData.CenterFrequency;       % Calculate wavelength
pathLoss = fspl(distance,lambda);                              % FSPL
outputData.Power = outputData.Power - pathLoss;                % Adjust power of output data based on path loss

% Obtain the maximum channel delay matrix from the channel model information
maxChannelDelayMatrix = channelInfo.MaxChannelDelayMatrix;

% Obtain the path filter from the channel model information
pathFilter = channelInfo.PathFilter;

% Check if the CDL channel model exists for the given transmitter-receiver pair
if ~isempty(channelInfo.CDLChannels{txData.TransmitterID,rxInfo.ID})
   
    % A channel exists between the transmitter and receiver nodes
    channelInfo.CDLChannels{txData.TransmitterID,rxInfo.ID}.InitialTime = outputData.StartTime;
    if outputData.Abstraction == 0                                                                          % Full PHY
        rxWaveform = [txData.Data; zeros(maxChannelDelayMatrix(txData.TransmitterID,rxInfo.ID), ...
            size(txData.Data,2))];
        [outputData.Data,outputData.Metadata.Channel.PathGains,outputData.Metadata.Channel.SampleTimes] = ...
            channelInfo.CDLChannels{txData.TransmitterID,rxInfo.ID}(rxWaveform);
        outputData.Data = outputData.Data.*db2mag(-pathLoss);
        outputData.Duration = outputData.Duration + ...
            (1/outputData.SampleRate)*maxChannelDelayMatrix(txData.TransmitterID,rxInfo.ID);
    else                                                                                                    % Abstract PHY
        channelInfo.CDLChannels{txData.TransmitterID,rxInfo.ID}.NumTimeSamples =  ...
            txData.Metadata.NumSamples + maxChannelDelayMatrix(txData.TransmitterID,rxInfo.ID);
        [outputData.Metadata.Channel.PathGains,outputData.Metadata.Channel.SampleTimes] = ...
            channelInfo.CDLChannels{txData.TransmitterID,rxInfo.ID}();
    end
    outputData.Metadata.Channel.PathFilters = ...
        pathFilter{txData.TransmitterID,rxInfo.ID};
else
    % Set default values for channel parameters
    outputData.Metadata.Channel.PathGains = ...
        permute(ones(outputData.NumTransmitAntennas, ...
        rxInfo.NumReceiveAntennas), ...
        [3 4 1 2]) / sqrt(rxInfo.NumReceiveAntennas);
    outputData.Metadata.Channel.PathFilters = 1;
    outputData.Metadata.Channel.SampleTimes = 0;

    if outputData.Abstraction == 0                            % Full PHY
        outputData.Data = outputData.Data.*db2mag(-pathLoss);
        numTxAnts = outputData.NumTransmitAntennas;
        numRxAnts = rxInfo.NumReceiveAntennas;
        H = fft(eye(max([numTxAnts numRxAnts])));
        H = H(1:numTxAnts,1:numRxAnts);
        H = H/norm(H);
        outputData.Data = txData.Data*H;                      % Apply channel to the waveform
    end
end
end

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