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lteEqualizeZF

Zero-forcing equalization

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Syntax

[out,csi] = lteEqualizeZF(rxgrid,channelest)

Description

[out,csi] = lteEqualizeZF(rxgrid,channelest) returns equalized data in multidimensional array, out, by applying MIMO zero-forcing equalization to the received data resource grid in matrix rxgrid, using the channel information in the channelest input matrix.

For each resource element, the function calculates the pseudoinverse of the channel and equalizes the corresponding received signal.

Alternatively, the channelest input can be provided as a 3-D array of size NRE-by-NRxAnts-by-P and the rxgrid input can be provided as a matrix of size NRE-by-NRxAnts. In this case, the first two dimensions have been reduced to one dimension by appropriate indexing through the frequency and time locations of the resource elements of interest, typically for a single physical channel. The outputs, out and csi, are of size (N × M)-by-P.

example

Examples

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Open Live Script

Equalize the received signal for RMC R.4 after channel estimation. Use the zero forcing equalizer.

Create cell-wide configuration structure and generate transmit signal. Configure propagation channel.

enb = lteRMCDL('R.4');                 
[txSignal,~,info] = lteRMCDLTool(enb,[1;0;0;1]);

chcfg.DelayProfile = 'EPA';
chcfg.NRxAnts = 1;
chcfg.DopplerFreq = 70;
chcfg.MIMOCorrelation = 'Low';
chcfg.SamplingRate = info.SamplingRate;
chcfg.Seed = 1;
chcfg.InitPhase = 'Random';
chcfg.InitTime = 0;         

txSignal = [txSignal; zeros(15,1)];
N = length(txSignal);
noise = 1e-3*complex(randn(N,chcfg.NRxAnts),randn(N,chcfg.NRxAnts));
rxSignal = lteFadingChannel(chcfg,txSignal)+noise;

Perform synchronization and OFDM demodulation.

offset = lteDLFrameOffset(enb,rxSignal);
rxGrid = lteOFDMDemodulate(enb,rxSignal(1+offset:end,:));

Create channel estimation configuration structure and perform channel estimation.

cec.FreqWindow = 9;
cec.TimeWindow = 9;
cec.InterpType = 'Cubic';
cec.PilotAverage = 'UserDefined';
cec.InterpWinSize = 3;
cec.InterpWindow = 'Causal';
hest = lteDLChannelEstimate(enb,cec,rxGrid);

Equalize and plot received and equalized grids.

eqGrid = lteEqualizeZF(rxGrid,hest);

subplot(2,1,1);
surf(abs(rxGrid));
title('Received grid');
xlabel('OFDM symbol'); 
ylabel('Subcarrier');

subplot(2,1,2);
surf(abs(eqGrid));
title('Equalized grid');
xlabel('OFDM symbol'); 
ylabel('Subcarrier');

Figure contains 2 axes objects. Axes object 1 with title Received grid, xlabel OFDM symbol, ylabel Subcarrier contains an object of type surface. Axes object 2 with title Equalized grid, xlabel OFDM symbol, ylabel Subcarrier contains an object of type surface.

Input Arguments

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Received data resource grid, specified as a 3-D numeric array or a 2-D numeric matrix. As a 3-D numeric array, it has size N-by-M-by-NRxAnts, where N is the number of subcarriers, M is the number of OFDM symbols, and NRxAnts is the number of receive antennas.

Alternatively, as a 2-D numeric matrix, it has size NRE-by-NRxAnts. In this case, the first two dimensions have been reduced to one dimension by appropriate indexing through the frequency and time locations of the resource elements of interest, typically for a single physical channel.

Data Types: double
Complex Number Support: Yes

Channel information, specified as a 4-D numeric array or a 3-D numeric array. As a 4-D numeric array, it has size N-by-M-by-NRxAnts-by-P. N is the number of subcarriers, M is the number of OFDM symbols, NRxAnts is the number of receive antennas, and P is the number of transmit antennas. Each element is a complex number representing the narrowband channel for each resource element and for each link between transmit and receive antennas. This matrix can be obtained using a channel estimation function, such as lteDLChannelEstimate.

Alternatively, as a 3-D numeric array, it has size NRE-by-NRxAnts-by-P. In this case, the first two dimensions have been reduced to one dimension by appropriate indexing through the frequency and time locations of the resource elements of interest, typically for a single physical channel.

Data Types: double
Complex Number Support: Yes

Output Arguments

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Equalized output data, returned as a 3-D numeric array or a 2-D numeric matrix. As a 3-D numeric array, it has size N-by-M-by-P. N is the number of subcarriers, M is the number of OFDM symbols, and P is the number of transmit antennas.

Alternatively, if channelest is provided as a 3-D array, out is a 2-D numeric matrix of size (N × M)-by-P. In this case, the first two dimensions have been reduced to one dimension by appropriate indexing through the frequency and time locations of the resource elements of interest, typically for a single physical channel.

Data Types: double
Complex Number Support: Yes

Soft channel state information, returned as a 3-D numeric array or a 2-D numeric matrix of the same size as out. As a 3-D numeric array, it has size N-by-M-by-P. N is the number of subcarriers, M is the number of OFDM symbols, and P is the number of transmit antennas. csi provides an estimate of the received RE gain for each received RE.

Alternatively, if channelest is provided as a 3-D array, csi is a 2-D numeric matrix of size (N×M)-by-P. In this case, the first two dimensions have been reduced to one dimension by appropriate indexing through the frequency and time locations of the resource elements of interest, typically for a single physical channel.

Data Types: double

Version History

Introduced in R2014a

See Also

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