PDCCH search space candidates


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



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 will contain (0,2,4,6) 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 1-based indices define the PDCCH locations in the block of all multiplexed PDCCH data bits to be transmitted in that subframe. The indices can also be returned in a number of alternative formats.

The control region of a downlink subframe comprises the multiplexing of all PDCCHs bits into a single block of data which is subsequently processed and interleaved prior to PDCCH resource mapping. A UE has to blindly decode individual PDCCH directed at it and 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 will always contain 2, 4, or 6 candidates; therefore, ind has 2, 4, or 6 rows, unless the parameter combinations are not valid, in which case ind will be empty. For more information, see section 9.1.1 of [1]. The candidates in a space need not be unique, especially for smaller bandwidths.

ind = ltePDCCHSpace(enb,ue,opts) allows control of the format of the returned indices through a cell array of option strings, opts.


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Get PDCCH Search Space Candidates

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)
        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))
        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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enb — Cell-wide settingsstructure

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

Parameter FieldRequired or OptionalValuesDescription

Numeric scalar value

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

Number of downlink (DL) resource blocks (RBs)

CFIRequired1, 2, 3

Control format indicator value, specified as a double value.


1, 2, 4

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


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

HICH group multiplier


Nonnegative scalar integer

0 is default

Subframe number


Nonnegative scalar integer

Total number of resource element groups (REGs) associated with PDCCHs, specified as a nonnegative scalar integer. Optional. If the NREG field is absent, enb must contain the following fields.

  • CyclicPrefix

  • CellRefP

  • CFI

  • Ng

  • DuplexMode

  • TDDConfig, but only for 'TDD' duplex mode


'Normal' (default), 'Extended'

Cyclic prefix length


'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'.

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

Uplink or downlink configuration

Data Types: struct

ue — UE-specific cell-wide settingsstructure

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

Parameter FieldRequired or OptionalValuesDescription

0, 1, 2, 3

PDCCH format


Scalar integer

1 is default

Radio network temporary identifier (RNTI) value (16 bits)

Data Types: struct

opts — Format of the returned indicescell array of strings

Format of the returned indices, specified as a cell array of these option strings.

Index base — Index base of returned indices'1based' (default) | '0based'

Index base of returned indices, specified as a string.

Data Types: char

Indexing unit — Index unit of returned values'bits' (default) | 'cce'

Index unit of the returned values, specified as a string corresponding to bit indices or control channel elements (CCEs) indices.

Data Types: char

Data Types: cell

Output Arguments

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ind — Search space PDCCH candidate indices(0,2,4,6)-by-2 matrix

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 2-element row contains the inclusive [begin,end] indices of a single PDCCH candidate location. By default, the 1-based indices define the PDCCH locations in the block of all multiplexed PDCCH data bits to be transmitted in that subframe. The indices can also be returned in a number of alternative formats.

Data Types: double


[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:

Introduced in R2014a

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