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nrPerfectChannelEstimate

Perfect channel estimation

Description

h = nrPerfectChannelEstimate(carrier,pathGains,pathFilters) performs perfect channel estimation. The function first reconstructs the channel impulse response from the channel path gains pathGains and the path filter impulse response pathFilters. The function then performs orthogonal frequency division multiplexing (OFDM) demodulation. carrier specifies the parameters for the OFDM demodulation.

example

h = nrPerfectChannelEstimate(pathGains,pathFilters,nrb,scs,initialNSlot) performs the OFDM demodulation for nrb number of resource blocks with subcarrier spacing scs and initial slot number initialNSlot.

example

h = nrPerfectChannelEstimate(___,toffset) specifies the timing offset in addition to the input arguments in any of the previous syntaxes. The timing offset indicates the OFDM demodulation starting point on the reconstructed waveform.

h = nrPerfectChannelEstimate(___,toffset,sampleTimes) specifies the sample times of the channel snapshots in addition to the input arguments in the previous syntax.

h = nrPerfectChannelEstimate(___,cpl) specifies the cyclic prefix length in addition to the input arguments in any of the previous syntaxes that do not include the carrier input.

h = nrPerfectChannelEstimate(___,Name,Value) specifies options by using one or more name-value pair arguments in addition to the input arguments in any of the previous syntaxes.

Examples

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Define a channel configuration structure using an nrTDLChannel System object. Use delay profileTDL-C from TR 38.901 Section 7.7.2.

SR = 7.68e6;
tdl = nrTDLChannel;
tdl.DelayProfile = 'TDL-C';
tdl.DelaySpread = 100e-9;
tdl.MaximumDopplerShift = 300;
tdl.SampleRate = SR;

Create a random waveform with a duration of 1 subframe.

T = SR*1e-3;
tdlInfo = info(tdl);
Nt = tdlInfo.NumTransmitAntennas;
in = complex(randn(T,Nt),randn(T,Nt));

Transmit the input waveform through the channel. Obtain the path filters used in channel filtering.

[~,pathGains] = tdl(in);
pathFilters = getPathFilters(tdl);

Perform perfect channel estimation using the specified number of blocks, subcarrier spacing, and slot number.

NRB = 25;
SCS = 15;
nSlot = 0;

hest = nrPerfectChannelEstimate(pathGains,pathFilters,NRB,SCS,nSlot);
size(hest)
ans = 1×3

   300    14     2

Plot the estimated channel magnitude response for the first receive antenna.

figure;
surf(abs(hest(:,:,1)));
shading('flat');
xlabel('OFDM Symbols');
ylabel('Subcarriers');
zlabel('|H|');
title('Channel Magnitude Response');

Figure contains an axes. The axes with title Channel Magnitude Response contains an object of type surface.

Repeat the channel estimate for extended cyclic prefix.

hest = nrPerfectChannelEstimate(pathGains,pathFilters,NRB,SCS, ...
    nSlot,'extended');
size(hest)
ans = 1×3

   300    12     2

Plot the updated results.

figure;
surf(abs(hest(:,:,1)));
shading('flat');
xlabel('OFDM Symbols');
ylabel('Subcarriers');
zlabel('|H|');
title('Channel Magnitude Response with Extended Cyclic Prefix');

Figure contains an axes. The axes with title Channel Magnitude Response with Extended Cyclic Prefix contains an object of type surface.

Define a channel configuration structure using an nrCDLChannel System object. Use delay profile CDL-C from TR 38.901 Section 7.7.1.

 cdl = nrCDLChannel;
 cdl.DelayProfile = 'CDL-D';
 cdl.DelaySpread = 30e-9;
 cdl.MaximumDopplerShift = 5;

Create a random waveform with a duration of 1 subframe.

SR = 15.36e6;
T = SR*1e-3;
cdl.SampleRate = SR;
cdlInfo = info(cdl);
Nt = cdlInfo.NumTransmitAntennas;
in = complex(randn(T,Nt),randn(T,Nt));

Transmit the input waveform through the channel. Obtain the path filters used in channel filtering.

[~,pathGains,sampleTimes] = cdl(in);
pathFilters = getPathFilters(cdl);

Perform timing offset estimation using the path filter and path gains.

offset = nrPerfectTimingEstimate(pathGains,pathFilters);

Perform perfect channel estimation. Use the specified number of blocks, subcarrier spacing, slot number, timing offset, and sample times.

NRB = 25;
SCS = 15;
nSlot = 0;
hest = nrPerfectChannelEstimate(pathGains,pathFilters,...
    NRB,SCS,nSlot,offset,sampleTimes);
size(hest)
ans = 1×4

   300    14     2     8

Plot the estimated channel magnitude response for the first receive antenna.

figure;
surf(abs(hest(:,:,1)));
shading('flat');
xlabel('OFDM Symbols');
ylabel('Subcarriers');
zlabel('|H|');
title('Channel Magnitude Response');

Figure contains an axes. The axes with title Channel Magnitude Response contains an object of type surface.

Input Arguments

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Carrier configuration parameters for a specific OFDM numerology, specified as an nrCarrierConfig object. Only these object properties are relevant for this function.

Number of RBs in the carrier resource grid, specified as an integer from 1 to 275. The default value of 52 corresponds to the maximum number of RBs of a 10 MHz carrier with 15 kHz SCS.

Data Types: double

Subcarrier spacing in kHz, for all channels and reference signals of the carrier, specified as 15, 30, 60, 120, or 240.

Data Types: double

Slot number, specified as a nonnegative integer. You can set NSlot to a value larger than the number of slots per frame. For example, you can set this value using transmission loop counters in a MATLAB® simulation. In this case, you may have to ensure that the property value is modulo the number of slots per frame in a calling code.

Data Types: double

Cyclic prefix length, specified as one of these options.

  • 'normal' — Use this value to specify normal cyclic prefix. This option corresponds to 14 OFDM symbols in a slot.

  • 'extended' — Use this value to specify extended cyclic prefix. This option corresponds to 12 OFDM symbols in a slot. For the numerologies specified in TS 38.211 Section 4.2, extended cyclic prefix length applies for only 60 kHz subcarrier spacing.

Data Types: char | string

Channel path gains of the fading process, specified as an NCS-by-NP-by-NT-by-NR complex matrix, where:

  • NCS is the number of channel snapshots.

  • NP is the number of paths.

  • NT is the number of transmit antennas.

  • NR is the number of receive antennas.

Data Types: single | double
Complex Number Support: Yes

Path filter impulse response, specified as an NH-by-NP real matrix, where:

  • NH is the number of impulse response samples.

  • NP is the number of paths.

Each column of the matrix contains the filter impulse response for each path of the delay profile.

Data Types: double

Number of resource blocks, specified as an integer from 1 to 275.

Data Types: double

Subcarrier spacing in kHz, specified as 15, 30, 60, 120, or 240.

Data Types: double

Initial slot number, 0-based, specified as a nonnegative integer. The function selects the appropriate cyclic prefix length for the OFDM demodulation based on the value of initialNSlot modulo the number of slots per subframe.

Data Types: double

Timing offset in samples, specified as a nonnegative integer. The timing offset indicates the OFDM demodulation starting point on the reconstructed waveform. The offset accounts for propagation delays, which is essential when obtaining the perfect estimate of the channel seen by a synchronized receiver. toffset defaults to the value nrPerfectTimingEstimate(pathGains,pathFilters) when not specified as an input argument.

Data Types: double

Sample times of channel snapshots, specified as an NCS-by-1 column vector of nonnegative real numbers. sampleTimes specifies the time of occurrence of each channel snapshot. The number of channel snapshots, NCS, is identical to the first dimension of pathGains. When not specified, sampleTimes defaults to an NCS-by-1 vector of times starting at zero with sampling rate used for the OFDM modulation of the number of resource blocks nrb and subcarrier spacing scs. Ensure that the channel snapshots span at least one slot. The function performs channel estimation for each complete slot.

Data Types: double

Cyclic prefix length, specified as one of these options:

  • 'normal' — Use this value to specify normal cyclic prefix. This option corresponds to 14 OFDM symbols in a slot.

  • 'extended' — Use this value to specify extended cyclic prefix. This option corresponds to 12 OFDM symbols in a slot. For the numerologies specified in TS 38.211 Section 4.2, the extended cyclic prefix length only applies to 60 kHz subcarrier spacing.

Note

  • If you specify the carrier input, use the CyclicPrefix property of the carrier input to specify the cyclic prefix length. You cannot use the cpl input together with the carrier input.

  • If you specify the cyclic prefix length with the 'CyclicPrefix' name-value pair argument, you cannot use the cpl input.

Data Types: char | string

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'CyclicPrefixFraction',0.75 specifies the start location for demodulation relative to the cyclic prefix length.

Cyclic prefix length, specified as the comma-separated pair consisting of 'CyclicPrefix' and one of these values:

  • 'normal' — Use this value to specify normal cyclic prefix. This option corresponds to 14 OFDM symbols in a slot.

  • 'extended' — Use this value to specify extended cyclic prefix. This option corresponds to 12 OFDM symbols in a slot. For the numerologies specified in TS 38.211 Section 4.2, the extended cyclic prefix length only applies to 60 kHz subcarrier spacing.

Note

  • If you specify the carrier input, use the CyclicPrefix property of the carrier input to specify the cyclic prefix length. You cannot use this name-value pair argument together with the carrier input.

  • If you specify the cyclic prefix length with the cpl input, you cannot use this name-value pair argument.

Data Types: char | string

Number of fast Fourier transform (FFT) points, specified as the comma-separated pair consisting of 'Nfft' and a nonnegative integer greater than 127 or []. The value you specify must result in integer-valued cyclic prefix lengths and a maximum occupancy of 100%. The occupancy is defined as the value of (12 × NRB)/Nfft, where NRB is the number of resource blocks.

If you do not specify this input, or if you specify 'Nfft',[], the function sets an integer value greater than 127 as a default value for this input. The actual default value depends on other input values.

  • If you do not specify the SampleRate input, or if you specify 'SampleRate',[], the function sets Nfft satisfying these conditions.

    • Nfft is an integer power of 2.

    • Nfft results in a maximum occupancy of 85%.

  • If you specify the SampleRate input, the function sets Nfft satisfying these conditions.

    • Nfft results in integer-valued cyclic prefix lengths.

    • Nfft maximises the value of gcd (Nfft × SCS, SampleRate), where SCS is specified by the carrier.SubcarrierSpacing property or the scs input.

Data Types: double

Waveform sample rate, specified as the comma-separated pair consisting of 'SampleRate' and either a positive scalar or [].

If you do not specify this input, or if you specify 'SampleRate',[], then the function sets this input to the value of Nfft × SCS.

  • Nfft is the value of the 'Nfft' input.

  • SCS is the subcarrier spacing. Depending on the function syntax you use, SCS is specified by the carrier.SubcarrierSpacing property or the scs input.

Data Types: double

Fast Fourier transform (FFT) window position within the cyclic prefix, specified as the comma-separated pair consisting of 'CyclicPrefixFraction' and a scalar in the interval [0, 1].

The value that you specify indicates the start location for OFDM demodulation relative to the beginning of the cyclic prefix.

Data Types: double

Output Arguments

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Perfect channel estimate, returned as an NSC-by-NSYM-by-NR-by-NT complex array, where:

  • NSC is the number of subcarriers.

  • NSYM is the number of OFDM symbols.

  • NR is the number of receive antennas.

  • NT is the number of transmit antennas.

h inherits its data type from pathGains.

Data Types: double | single

References

[1] 3GPP TS 38.211. “NR; Physical channels and modulation.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network.

Extended Capabilities

Introduced in R2018b