lteSLSCFDMADemodulate

Sidelink SC-FDMA demodulation

Syntax

grid = lteSLSCFDMADemodulate(ue,waveform)

grid = lteSLSCFDMADemodulate(ue,waveform,cpfraction)

Description

grid = lteSLSCFDMADemodulate(ue,waveform) performs sidelink SC-FDMA demodulation of the input time-domain waveform for the specified UE settings structure. For more information, see Sidelink SC-FDMA Demodulation.

grid = lteSLSCFDMADemodulate(ue,waveform,cpfraction) allows the specification of the starting waveform sample for demodulation as a fraction of the cyclic prefix.

Examples

Sidelink Demodulation

Perform sidelink SC-FDMA modulation of one subframe containing the sidelink synchronization signals and add noise at an SNR of 3.0 dB. The demodulator zeros the resource elements in the last SC-FDMA symbol. This behavior is consistent with the operation of the SC-FDMA modulator which does not modulate the last SC-FDMA symbol of the subframe. Plot the received waveform and the demodulated resource grid magnitude.

Create a UE settings structure.

ue.NSLRB = 15;
ue.CyclicPrefixSL = 'Normal';
ue.NSLID = 17;

Populate the resource grid with PSSS and SSSS. Modulate the PSSS and SSSS.

txgrid = lteSLResourceGrid(ue);
txgrid(ltePSSSIndices(ue)) = ltePSSS(ue);
txgrid(lteSSSSIndices(ue)) = lteSSSS(ue);

[txwaveform,info] = lteSLSCFDMAModulate(ue,txgrid);

Add AWGN with an SNR of 3.0 dB.

rxwaveform = awgn(txwaveform,3.0,'measured');

Perform sidelink SC-FDMA demodulation.

rxgrid = lteSLSCFDMADemodulate(ue,rxwaveform);

Calculate the RMS of each SC-FDMA symbol in the received resource grid.

rms = sqrt(sum(abs((rxgrid./double(info.Nfft)).^2)));

Plot the magnitude of the resulting time-domain waveform, overlaying the RMS for each SC-FDMA symbol after demodulation. Plot the demodulated resource grid magnitude.

t = (0:size(rxwaveform,1))/info.SamplingRate;
figure

subplot(2,1,1)
plot(t(1:end-1),abs(rxwaveform),'r')
hold on
n = cumsum([1 info.CyclicPrefixLengths + info.Nfft]);
n = [n(1:end-1); n(2:end)];
rmsplot = repmat(rms,[2 1]);
plot(t(n(:)),rmsplot(:),'b')
xlabel('time (s)')
ylabel('magnitude')
title('RX Waveform vs. Time')
legend('RX waveform magnitude','RMS per demodulated SC-FDMA symbol')

subplot(2,1,2)
imagesc(abs(rxgrid))
title('Demodulated Resource Grid Magnitude')
xlabel('SC-FDMA symbol index')
ylabel('subcarrier index')

Input Arguments

ue — User equipment settings

structure

User equipment settings, specified as a parameter structure containing these fields:

NSLRB — Number of sidelink resource blocks

integer scalar from 6 to 110

Number of sidelink resource blocks, specified as an integer scalar from 6 to 110.

Example: 6, which corresponds to a channel bandwidth of 1.4 MHz.

Data Types: double

CyclicPrefixSL — Cyclic prefix length

'Normal' (default) | 'Extended' | optional

Cyclic prefix length, specified as 'Normal' or 'Extended'.

Data Types: char | string

Data Types: struct

waveform — Sidelink SC-FDMA modulated waveform

numeric matrix

Sidelink SC-FDMA modulated waveform, specified as an N_S-by-N_T numeric matrix, where N_S is the number of the time-domain samples and N_T is the number of transmission antennas. N_S = K × 30720 / 2048 × N_fft, where N_fft is the FFT size and K is the number of subframes in waveform.

For more information about the FFT size, see lteSLSCFDMAInfo.

Data Types: double
Complex Number Support: Yes

cpfraction — Fraction of cyclic prefix

0.55 (default) | numeric scalar from 0 to 1

Fraction of cyclic prefix, specified as a numeric scalar from 0 to 1. A value of 0 represents the start of the cyclic prefix and a value of 1 represents the end of the cyclic prefix. The default value is 0.55 which assumes for the default level of windowing in the lteSLSCFDMAModulate function.

Data Types: double

Output Arguments

grid — Resource element grid

numeric 3-D array

Resource element grid, returned as an N_SC-by-N_SYM-by-N_T numeric array. N_SC is 12 × NSLRB subcarriers. N_SYM is a multiple of the number of SC-FDMA symbols in a subframe (14 for normal cyclic prefix and 12 for extended cyclic prefix).  N_T is the number of antenna ports. grid defines the RE allocation across one or more subframes. Multiple subframes are defined by concatenation across the columns (second dimension).

Each antenna plane in grid is SC-FDMA modulated, resulting in the columns of waveform, as described in Represent Resource Grids.

Data Types: double
Complex Number Support: Yes

More About

Sidelink SC-FDMA Demodulation

Sidelink SC-FDMA demodulation recovers the received subcarrier values by performing one FFT operation per received sidelink SC-FDMA symbol. The recovered subcarrier values are used to construct each column of the output resource array grid. The FFT is positioned partway through the cyclic prefix, to account for some channel delay spread while avoiding the overlap between adjacent SC-FDMA symbols. The input FFT is also shifted by half of one subcarrier. The position of the FFT chosen in the function avoids the SC-FDMA symbol overlapping used in the lteSLSCFDMAModulate function. Because the FFT is performed away from the original zero-phase point on the transmitted subcarriers, lteSLSCFDMADemodulate applies a phase correction to each subcarrier after the FFT.

Note

• TS 36.211 specifies that for PSSCH (Section 9.3.6), PSCCH (9.4.6), PSDCH (9.5.6) and PSBCH (9.6.6), resource elements in the last SC-FDMA symbol within a subframe should be counted in the mapping process but not transmitted. The resource elements of the last SC-FDMA symbol in each subframe of the output resource array grid are set to zero by lteSLSCFDMADemodulate. This behavior is consistent with SC-FDMA modulation, performed by lteSLSCFDMAModulate.

• The sampling rate of the time-domain sidelink waveform must be the same as the rate used in the lteSLSCFDMAModulate function, for the specified number of resource blocks, NRB.

• The input waveform must be time aligned, such that the first sample is the first sample of the cyclic prefix of the first sidelink SC-FDMA symbol in a subframe.

References

[1] 3GPP TS 36.211. “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.

Version History

Introduced in R2016b