5G NR CSI-RS Measurements

This example shows the measurement procedure of CSI-RSRP, CSI-RSSI, and CSI-RSRQ for the test environment, as described in TS 38.133 Annex A.4.6.3.3, by using the channel state information reference signal from 5G Toolbox™.

Introduction

In NR 5G, the three types of CSI-RS based reference signal measurements, as defined in TS 38.215 Sections 5.1.2 and 5.1.4, includes:

• CSI-RSRP (CSI reference signal received power): CSI-RSRP is defined as the linear average over the power contributions of the resource elements of the antenna ports, which carry CSI-RS configured for RSRP measurements. This measurement is performed across N number of resource blocks (measurement bandwidth). For this measurement, CSI-RS transmitted on antenna port(s) 3000 or 3000 and 3001 is used.

• CSI-RSSI (CSI received signal strength indicator): CSI-RSSI is defined as the linear average of the total received power observed only in the OFDM symbols, in which CSI-RS is present. This measurement is also performed across N number of resource blocks (measurement bandwidth). CSI-RSSI includes the power from sources, such as co-channel serving and non-serving cells, adjacent channel interference, and thermal noise. For this measurement, CSI-RS transmitted on antenna port 3000 is used.

• CSI-RSRQ (CSI reference signal received quality): CSI-RSRQ is defined as, $\mathit{N}*\frac{\mathrm{CSI}\_\mathrm{RSRP}}{\mathrm{CSI}\_\mathrm{RSSI}}$.

The purposes of these measurements include:

• Cell selection and reselection

• Mobility and handover management

• Beam management (beam adjustment and beam recovery)

This example configures only the CSI-RS from the test environment.

Initialize Configuration Objects

Carrier configuration

Create carrier configuration object occupying 10 MHz bandwidth with 15 kHz subcarrier spacing as per configuration 1 in TS 38.133 Table A.4.6.3.3.1-1.

carrier = nrCarrierConfig;
carrier.NSlot = 1;
carrier.NSizeGrid = 52;

CSI-RS configuration

As per the test environment TS 38.133 Table A.4.6.3.3.2-1, user equipment (UE) is configured with one CSI-RS resource set (CSI-RS 1.2 FDD), consisting of 2 CSI-RS resources.

csirs = nrCSIRSConfig;
% CSI-RS resource             #0       #1
csirs.CSIRSType           = {'nzp',   'nzp'};
csirs.CSIRSPeriod         = {[10 1],  [10 1]};
csirs.RowNumber           = [1        1]; % Single port (3000) CSI-RS resources
csirs.Density             = {'three', 'three'};
csirs.SymbolLocations     = {6,       10};
csirs.SubcarrierLocations = {0,       0};
csirs.NumRB               = [52,      52]; % Measurement bandwidth in terms of number of resource blocks

Generate CSI-RS Symbols and Indices

Generate CSI-RS symbols and indices for the specified carrier and CSI-RS configuration parameters with the output resource format as 'cell'. This output resource format provides a way to identify the outputs uniquely for each CSI-RS resource in a resource set. You can also apply different power levels to each CSI-RS resource.

ind = nrCSIRSIndices(carrier,csirs,'OutputResourceFormat','cell');
sym = nrCSIRS(carrier,csirs,'OutputResourceFormat','cell');

Signal and Noise Power Setup

Set up the signal and noise powers as described in TS 38.133 Table A.4.6.3.3.2-2. As per note 2 in TS 38.133 Table A.4.6.3.3.2-2, interference from other cells and noise from other sources is modeled as additive white Gaussian noise (AWGN) of appropriate power Noc.

SINRdB0 = 0; % For CSI-RS #0
SINRdB1 = 3; % For CSI-RS #1
NocdBm = -94.65;
NocdB = NocdBm - 30;
Noc = 10^(NocdB/10);

Calculate the power scaling of CSI-RS resources by using SINR values.

% Power scaling of CSI-RS resource #0
SINR0 = 10^(SINRdB0/10);     % linear Es/Noc
Es0 = SINR0*Noc;

% Power scaling of CSI-RS resource #1
SINR1 = 10^(SINRdB1/10);     % linear Es/Noc
Es1 = SINR1*Noc;

Initialize the Carrier Resource Grid and Map CSI-RS Symbols to the Grid

Initialize the carrier resource grid for one slot.

ports = max(csirs.NumCSIRSPorts); % Number of antenna ports
txGrid = nrResourceGrid(carrier,ports);

Apply the power scaling values to the CSI-RS resources and map them onto the grid.

txGrid(ind{1}) = sqrt(Es0)*sym{1};
txGrid(ind{2}) = sqrt(Es1)*sym{2};

% Plot the carrier grid for two CSI-RS resources
plotGrid(size(txGrid),ind)

Perform OFDM modulation

Perform OFDM modulation to generate the time-domain waveform.

[txWaveform,ofdmInfo] = nrOFDMModulate(carrier,txGrid);

Add AWGN to the Transmitted Waveform and Perform OFDM Demodulation

Consider the propagation condition as AWGN, as specified in TS 38.133 Table A.4.6.3.3.2-1.

% Generate the noise
rng('default');  % Set RNG state for repeatability
N0 = sqrt(Noc/(2*double(ofdmInfo.Nfft)));
noise = N0*complex(randn(size(txWaveform)),randn(size(txWaveform)));

% Add AWGN to the transmitted waveform
rxWaveform = txWaveform + noise;

Perform OFDM demodulation on the received time-domain waveform to get the received resource element array.

rxGrid = nrOFDMDemodulate(carrier,rxWaveform);

Perform CSI-RSRP, CSI-RSSI, and CSI-RSRQ Measurements

Finally, perform the CSI-RSRP, CSI-RSSI, and CSI-RSRQ measurements on the CSI-RS resources present in the received grid, by using the helper file hCSIRSMeasurements.

meas = hCSIRSMeasurements(carrier,csirs,rxGrid)

meas = struct with fields:
    RSRPPerAntennaPerResource: [3.8372e-13 7.3692e-13]
    RSSIPerAntennaPerResource: [2.7403e-10 3.1752e-10]
    RSRQPerAntennaPerResource: [0.0728 0.1207]
                         RSRP: [3.8372e-13 7.3692e-13]
                         RSSI: [2.7403e-10 3.1752e-10]
                         RSRQ: [0.0728 0.1207]
                      RSRPdBm: [-94.1599 -91.3258]
                      RSSIdBm: [-65.6220 -64.9823]
                       RSRQdB: [-11.3779 -9.1834]

% Plot RSRPdBm, RSSIdBm and RSRQdB measurements for all CSI-RS resources
hPlotCSIRSMeasurements(meas)

You can compare the measured CSI-RSRP values of two CSI-RS resources represented by the output field RSRPdBm to the standard specified values given in TS 38.133 Table A.4.6.3.3.2-2.

Local Functions

function plotGrid(gridSize,csirsInd)
%    plotGrid(GRIDSIZE,CSIRSIND) plots the carrier grid of size GRIDSIZE
%    by populating the grid with CSI-RS symbols of multiple resources
%    indicated by a cell array of CSI-RS indices CSIRSIND.

    figure()
    cmap = colormap(gcf);

    % Considering the following values for two CSI-RS resources and they need
    % to be updated based on the number of CSI-RS resources
    names = {'CSI-RS resource #0','CSI-RS resource #1'};
    chpval = {20,2};
    chpscale = 0.25*length(cmap); % Scaling factor
    tempGrid = zeros(gridSize);
    tempGrid(csirsInd{1}) = chpval{1};
    tempGrid(csirsInd{2}) = chpval{2};

    image(chpscale*tempGrid(:,:,1)); % Multiplied with scaling factor for better visualization
    axis xy;
    clevels = chpscale*[chpval{:}];
    N = length(clevels);
    L = line(ones(N),ones(N),'LineWidth',8); % Generate lines
    % Index the color map and associate the selected colors with the lines
    set(L,{'color'},mat2cell(cmap( min(1+clevels,length(cmap) ),:),ones(1,N),3)); % Set the colors according to cmap
    % Create legend
    legend(names{:});

    title('Carrier Grid Containing CSI-RS')
    xlabel('OFDM Symbols');
    ylabel('Subcarriers');
end

References

[1] 3GPP TS 38.133. “NR; Requirements for support of radio resource management.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network.

[2] 3GPP TS 38.215. “NR; Physical layer measurements.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network.