# lteSSSSIndices

SSSS resource element indices

## Description

example

ind = lteSSSSIndices(ue) returns a 124-by-1 complex column vector of resource element (RE) indices for the secondary sidelink synchronization signal (SSSS) values given the user equipment settings structure. By default, the indices are returned in one-based linear indexing form. You can use this form to directly index elements of a matrix representing the subframe resource grid for antenna port 1020. For more information, see Secondary Sidelink Synchronization Signal Indexing.

example

ind = lteSSSSIndices(ue,opts) formats the returned indices using options specified by opts.

## Examples

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Generate SSSS values and indices. Write the values into the SSSS resource elements in a synchronization subframe (extended cyclic prefix) and display an image of their locations.

Create a user equipment settings structure and a resource grid that has a 10 MHz bandwidth and extended cyclic prefix.

ue.NSLRB = 50;
ue.CyclicPrefixSL = 'Extended';
ue.NSLID = 1;
subframe = lteSLResourceGrid(ue);

Generate SSSS indices and display the first five indices. Load the SSSS symbols into the resource grid. Display an image showing the SSSS symbol locations.

ind = lteSSSSIndices(ue);
ind(1:5)
ans = 5x1 uint32 column vector

5670
5671
5672
5673
5674

subframe(ind) = lteSSSS(ue);
imagesc(100*abs(subframe))
axis xy

Generate SSSS indices using zero-based indexing style. Compare these indices to one-based indices.

Create a user equipment settings structure that has a 10 MHz bandwidth and extended cyclic prefix.

ue.NSLRB = 50;
ue.CyclicPrefixSL = 'Extended';
ue.NSLID = 1;

Generate SSSS zero-based indices and view the first five indices.

ind = lteSSSSIndices(ue,'0based');
s = size(ind)
s = 1×2

124     1

ind(1:5)
ans = 5x1 uint32 column vector

5669
5670
5671
5672
5673

Generate SSSS one-based indices and view the first five indices.

ind = lteSSSSIndices(ue,'1based');
s = size(ind)
s = 1×2

124     1

ind(1:5)
ans = 5x1 uint32 column vector

5670
5671
5672
5673
5674

For zero-based indexing, the first assigned index is one lower than the one-based indexing style.

## Input Arguments

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User equipment settings, specified as a structure. ue contains the following fields.

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

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

Data Types: char | string

Output format options for resource element indices, specified as a character vector, cell array of character vectors, or string array. For convenience, you can specify several options as a single character vector or string scalar by a space-separated list of values placed inside the quotes. Values for opts when specified as a character vector include (use double quotes for string) :

Category Options Description

Indexing style

'ind' (default)

The returned indices are in linear index style.

'sub'

The returned indices are in [subcarrier,symbol,port] subscript row style.

Index base

'1based' (default)

The returned indices are one-based.

'0based'

The returned indices are zero-based.

Example: 'ind 1based', "ind 1based", {'ind','1based'}, or ["ind","1based"] specify the same formatting options.

Data Types: char | string | cell

## Output Arguments

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SSSS resource element indices, returned as an integer column vector or a three-column integer matrix. This output is generated using the cell-wide settings structure, ue. For more information, see Secondary Sidelink Synchronization Signal Indexing.

Data Types: uint32

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### Secondary Sidelink Synchronization Signal Indexing

Use the indexing function, lteSSSSIndices, and the corresponding sequence function, lteSSSS, to populate the resource grid for the desired subframe number. The SSSS values are output by lteSSSS, ordered as they should be mapped, applying frequency-first mapping into the resource elements of the adjacent symbols using lteSSSSIndices. When indexing is zero-based, the SC-FDMA symbols used are {11,12} for normal cyclic prefix and {9, 10} for extended cyclic prefix.

Note

The indicated symbol indices are based on TS 36.211, Section 9.7. However to align with the LTE Toolbox™ subframe orientation, these indices are expanded from symbol index per slot to symbol index per subframe.

For more information on mapping symbols to the resource element grid, see Resource Grid Indexing.

The secondary sidelink synchronization signal (SSSS) is transmitted in the central 62 resource elements of two adjacent SC-FDMA symbols in a synchronization subframe. The same sequence of 62 complex values is repeated in each of the symbols, resulting in a 124-by-1 element vector returned by the lteSSSS function. The values of this sequence are ordered as they should be mapped into the resource elements of the adjacent symbols using lteSSSSIndices. If a terminal is transmitting SSSS then it should be sent every 40 ms for D2D sidelink or every 160 ms for V2X sidelink, with the exact subframe dependent on the RCC signaled subframe number offset (syncOffsetIndicator-r12). The SSSS is sent on antenna port 1020, along with the primary sidelink synchronization signal (PSSS). A synchronization subframe also contains the PSBCH, which is sent on antenna port 1010. The transmission power of the SSSS symbols should be the same as the PSBCH therefore they should be scaled by $\sqrt{72}{62}}$ in a subframe. No PSCCH or PSSCH transmission will occur in a sidelink subframe configured for synchronization purposes.

As specified in TS 36.211, Section 9.7, the SSSS identity assignment depends on the network coverage. The set of all ${N}_{\text{ID}}^{\text{SL}}$ is divided into two sets, id_net {0, ..., 167} and id_oon {168, ..., 335}, which are used by terminals that are in-network and out-of-network coverage, respectively. The sidelink physical layer cell identity number, ${N}_{\text{ID}}^{\text{SL}}$, corresponds to the lteSSSS input UE settings structure field ue.NSLID. Within each set, all identities result in the same SSSS. For an in-network terminal, the ue.NSLID value corresponds to the RRC sidelink synchronization signal identity (slssid-r12) associated with the cell.

## 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.