# ltePDCCHSpace

PDCCH search space candidates

## Description

example

ind = ltePDCCHSpace(enb,ue) returns the (0,2,4,6)-by-2 matrix ind of search space PDCCH candidate indices given the structures enb and ue. Depending on input parameters, each search space contains (0,2,4, or 6) PDCCH candidate locations defined by the rows of ind. Each two-element row contains the inclusive [begin,end] indices of a single PDCCH candidate location. By default, the one-based indices define the PDCCH locations in the block of all multiplexed PDCCH data bits to be transmitted in that subframe.

The control region of a downlink subframe comprises the multiplexing of all PDCCHs bits into a single block of data which is then processed and interleaved before PDCCH resource mapping. A UE has to blindly decode individual PDCCH directed at it. This task is simplified by subdividing the whole region into common and UE-specific search spaces which the UE should monitor. Each space comprises 2, 4, or 6 PDCCH candidates whose data length depends on its PDCCH format. Each PDCCH must be transmitted on 1, 2, 4, or 8 control channel elements (CCE) (1 CCE = 72 bits).

The returned search space is of the UE-specific type unless the RNTI field is missing from the structure ue when a common search space is returned. The search space always contains 2, 4, or 6 candidates; therefore, ind has 2, 4, or 6 rows, unless the parameter combinations are not valid, in which case the ind output returned is empty. For more information, see TS 36.213 [1], Section 9.1.1. The candidates in a space do not need to be unique, especially for smaller bandwidths.

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

## Examples

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Find and use PDCCH search space candidates.

To illustrate the search space structuring of the PDCCH, set up a cell wide parameter structure, enb, with the following field values.

enb.NDLRB = 50;
enb.CFI = 2;
enb.CellRefP = 2;
enb.Ng = 'Sixth';
enb.NSubframe = 0;

This configuration defines a control region with the following information.

resInfo = ltePDCCHInfo(enb)
resInfo = struct with fields:
NREG: 240
NRE: 960
NCCE: 26
NREGUsed: 234
NREUsed: 936
MTot: 1920
NSymbols: 2

The entire data block of padded, multiplexed PDCCHs needs to be 1920 bits, resInfo.MTot, in length. Using -1 to represent NIL padding "bits", create an "empty" multiplex.

pdcchs = -1*ones(1,resInfo.MTot);

Suppose you want to transmit all zeros in the first candidate of the UE-specific search space for PDCCH format 2 and the UE's RNTI = 1. For this format, a PDCCH spans 4 CCE or 288 bits, and the UE-specific search space contains two PDCCH candidates.

candidates = ltePDCCHSpace(enb,struct('PDCCHFormat',2,'RNTI',1))
candidates = 2x2 uint32 matrix

1441   1728
1    288

These location values arise for enb.NSubframe = 0. They change in a pseudorandom fashion as the subframe number increases. Since the default candidate indices define inclusive, 1-based bounds, we can use them to index the PDCCH data multiplex directly by using the MATLAB® colon operator.

pdcchs(candidates(1,1):candidates(1,2)) = 0;

This command sets the 288 bits of the first PDCCH candidate to all zeros. The second candidate actually falls within the common search space also.

## Input Arguments

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Cell-wide settings, specified as a structure with these fields.

Parameter FieldRequired or OptionalValuesDescription
NSubframeRequired

0 (default), nonnegative scalar integer

0 is default

Subframe number

NREGOptional

Nonnegative scalar integer

Total number of resource element groups (REGs) associated with PDCCHs, specified as a nonnegative scalar integer.

If NREG is absent, then 'enb' must contain these fields.
NDLRBOptional

Numeric scalar value

6, 15, 25, 50, 75, and 100

Number of downlink resource blocks. (${N}_{\text{RB}}^{\text{DL}}$)

CyclicPrefixOptional

'Normal' (default), 'Extended'

Cyclic prefix length

CFIOptional1, 2, 3

Control format indicator value, specified as a double value.

CellRefPOptional

1, 2, 4

Number of cell-specific reference signal (CRS) antenna ports

NgOptional

'Sixth', 'Half', 'One', 'Two'

HICH group multiplier

DuplexModeOptional

'FDD' (default), 'TDD'

Duplexing mode, specified as:

• 'FDD' for Frequency Division Duplex or

• 'TDD' for Time Division Duplex

The following field is required only when DuplexMode is set to 'TDD'.
TDDConfigOptional

0, 1 (default), 2, 3, 4, 5, 6

Data Types: struct

UE-specific cell-wide settings, specified as a structure with the following fields.

Parameter FieldRequired or OptionalValuesDescription
PDCCHFormatRequired

0, 1, 2, 3

PDCCH format

RNTIOptionalScalar integer between 0 and 65535Radio network temporary identifier (RNTI) value (16 bits). If RNTI field is missing, see Description section for specific behaviour.

Data Types: struct

Index generation options, 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):

OptionValuesDescription
Index base

'1based' (default), '0based'

Base value of the returned indices. Specify '1based' to generate indices where the first value is 1. Specify '0based' to generate indices where the first value is 0.

Indexing unit'bits' (default), 'cce'

Unit of the returned indices. Specify 'bits' to indicate that the returned values correspond to bit indices. Specify 'cce' to indicate that the returned values correspond to control channel elements (CCEs) indices.

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

Data Types: char | string | cell

## Output Arguments

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Search space PDCCH candidate indices, returned as a (0,2,4,6)-by-2 matrix given the structures enb and ue. It is a matrix of indices identifying a common or UE-specific PDCCH search space. Each two-element row contains the inclusive [begin,end] indices of a single PDCCH candidate location. By default, the one-based indices define the PDCCH locations in the block of all multiplexed PDCCH data bits to be transmitted in that subframe. opts defines alternative formats for returning the indices.

Data Types: double

## References

[1] 3GPP TS 36.213. “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.

## Version History

Introduced in R2014a