# lteSLFrameOffsetPSSCH

PSSCH DM-RS sidelink subframe timing estimate

## Description

example

offset = lteSLFrameOffsetPSSCH(ue,waveform) performs synchronization using PSSCH demodulation reference signal (DM-RS) symbols for the time-domain waveform, waveform, given UE-specific settings, ue.

The returned offset indicates the number of samples from the start of the input waveform to the position in that waveform where the first subframe containing DM-RS begins.

example

[offset,corr] = lteSLFrameOffsetPSSCH(ue,waveform) also returns a complex matrix, corr, which is used to extract the timing offset.

## Examples

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Synchronize and demodulate a transmission that has been delayed by five samples. The transmission contains PSSCH demodulation reference signal (DM-RS) symbols that are used when estimating the waveform timing offset.

Create a UE configuration specifying 15 resource blocks, a sidelink identity of 1, a normal cyclic prefix, a PSSCH subframe number of 0, and a PRBSet of 1.

ue = struct('NSLRB',15,'NSAID',1,'CyclicPrefixSL','Normal', ...
'NSubframePSSCH',0,'PRBSet',1);

Create a resource grid and modulate the waveform containing PSSCH DM-RS symbols.

txgrid = lteSLResourceGrid(ue);
txgrid(ltePSSCHDRSIndices(ue)) = ltePSSCHDRS(ue);
txwaveform = lteSLSCFDMAModulate(ue,txgrid);

Add a time delay of five samples.

rxwaveform = [zeros(5,1); txwaveform];

Calculate the timing offset in samples.

offset = lteSLFrameOffsetPSSCH(ue,rxwaveform)
offset = 5

Correct the timing offset and demodulate the received waveform.

View the correlation peak for a transmission waveform that has been delayed by five samples. The transmission contains PSSCH demodulation reference signal (DM-RS) symbols available for estimating the waveform timing.

Create a UE configuration specifying 15 resource blocks, a sidelink identity of 1, a normal cyclic prefix, a PSSCH subframe number of 0, and a PRBSet of 1.

ue = struct('NSLRB',15,'NSAID',1,'CyclicPrefixSL','Normal', ...
'NSubframePSSCH',0,'PRBSet',1);

Create a resource grid and modulate the waveform containing PSSCH DM-RS symbols.

txgrid = lteSLResourceGrid(ue);
txgrid(ltePSSCHDRSIndices(ue)) = ltePSSCHDRS(ue);
txwaveform = lteSLSCFDMAModulate(ue,txgrid);

Calculate the timing offset in samples.

[offset corr] = lteSLFrameOffsetPSSCH(ue,txwaveform);

Add a time delay of five samples.

rxwaveform = [zeros(5,1); txwaveform];

Calculate the timing offset in samples.

[offset corrDelayed] = lteSLFrameOffsetPSSCH(ue,rxwaveform);

Plot the correlation data before and after delay is added. Zoom in on the x-axis to view correlation peaks.

plot(corr)
hold on
plot(corrDelayed)
hold off
xlim([0 100])

Correct the timing offset and demodulate the received waveform.

## Input Arguments

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

Sidelink mode, specified as 'D2D' or 'V2X'.

Data Types: char | string

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

Sidelink group destination identity, specified as an integer in the interval [0, 255].

This field is the lower eight bits of the full 24-bit ProSe Layer-2 group destination ID. This field and the NSubframePSSCH field control the value of the scrambling sequence at the start of each subframe. This field is required only for D2D sidelink.

Data Types: double

V2X scrambling identity, specified as an integer scalar. NXID is the 16 bit CRC associated with the PSCCH SCI grant. It is only required for V2X sidelink.

Data Types: double

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

Data Types: char | string

PSSCH subframe number in the PSSCH subframe pool, specified as an integer scalar. (${n}_{\text{ssf}}^{\text{PSSCH}}$)

NSubframePSSCH and NSAID control the values of the scrambling sequence. It is only required for D2D sidelink.

Data Types: double

Zero-based physical resource block (PRB) indices, specified as an integer column vector or a two-column integer matrix.

The PSSCH is intended to be transmitted in the same PRB in each slot of a subframe. Therefore, specifying PRBSet as a single column of PRB indices is recommended. However, for a nonstandard slot-hopping PRB allocation, PRBSet can be specified as a two-column matrix of indices corresponding to slot-wise resource allocations for PSSCH.

Data Types: double

Data Types: struct

Modulated sidelink waveform, specified as an NS-by-NR numeric matrix, where NS is the number of time-domain samples and NR is the number of receive antennas. waveform should be at least one subframe long and contain the DM-RS signals.

You can generate this matrix by performing SC-FDMA modulation on a resource matrix. To perform this modulation, use the lteSLSCFDMAModulate function or one of the channel model functions, such as lteFadingChannel or lteMovingChannel.

Data Types: double
Complex Number Support: Yes

## Output Arguments

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Offset number of samples, returned as a scalar integer. This output is the number of samples from the start of the waveform to the position in that waveform where the first subframe containing the DM-RS begins. offset is computed by extracting the timing of the peak of the correlation between waveform and internally generated reference waveforms containing DM-RS signals. The correlation is performed separately for each antenna. The antenna with the strongest correlation is used to compute offset.

Note

offset is the position of mod(max(abs(corr),LSF)), where LSF is the subframe length.

Signal used to extract the timing offset, returned as a complex numeric matrix. corr has the same dimensions as waveform.