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# ltePDCCHSpace

PDCCH search space candidates

## Syntax

``ind = ltePDCCHSpace(enb,ue)``
``ind = ltePDCCHSpace(enb,ue,opts)``

## 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 defined in `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
`NSubframe`Required

0 (default), nonnegative scalar integer

0 is default

Subframe number

`NREG`Optional

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.
`NDLRB`Optional

Numeric scalar value

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

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

`CyclicPrefix`Optional

`'Normal'` (default), `'Extended'`

Cyclic prefix length

`CFI`Optional1, 2, 3

Control format indicator value, specified as a double value.

`CellRefP`Optional

1, 2, 4

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

`Ng`Optional

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

HICH group multiplier

`DuplexMode`Optional

`'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'`.
`TDDConfig`Optional

0 (default), 1, 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
`PDCCHFormat`Required

0, 1, 2, 3

PDCCH format

`RNTI`OptionalScalar 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 or a cell array of character vectors that can contain the following values.

OptionValuesDescription
Index base

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

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

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 tocontrol channel elements (CCEs) indices.

Data Types: `char` | `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. “Physical layer procedures.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA). URL: http://www.3gpp.org.