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# lteDCIDecode

Downlink control information decoding

## Syntax

``````[dcibits,crc_rnti] = lteDCIDecode(dcilen,softbits)``````
``````[dcibits,crc_rnti] = lteDCIDecode(enb,softbits)``````
``````[dcibits,crc_rnti] = lteDCIDecode(enb,chs,softbits)``````

## Description

example

``````[dcibits,crc_rnti] = lteDCIDecode(dcilen,softbits)``` recovers a downlink control information (DCI) message, given the DCI vector length, `dcilen`, and a `softbits` input vector. For more information, see DCI Message Decoding.```

example

``````[dcibits,crc_rnti] = lteDCIDecode(enb,softbits)``` uses the cell-wide configuration structure, `enb`. With this syntax, the DCI message length is deduced from `enb``.``DCIFormat` and cell-wide settings in `enb`.```

example

``````[dcibits,crc_rnti] = lteDCIDecode(enb,chs,softbits)``` uses the UE-specific channel configuration structure, `chs`. With this syntax, the DCI message length is deduced from `chs``.``DCIFormat`, the cell-wide configuration in `enb`, and the UE-specific channel configuration in `chs`.```

## Examples

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Perform DCI decoding of a sample codeword and return the decoded vector, `decodedDCIbits`, of the length defined for the DCI Format 1 message.

```enb.NDLRB = 50; enb.CellRefP = 1; enb.DuplexMode = 'FDD'; dciInfo = lteDCIInfo(enb); dcilen = dciInfo.Format1 ue.PDCCHFormat = 1; ue.RNTI = 10; ue.NDLRB = 50; dciBits = zeros(dcilen,1); cw = lteDCIEncode(ue,dciBits); [decodedDCIbits,crcRNTI] = lteDCIDecode(dcilen,cw); decodedDCIbitslen = size(decodedDCIbits) crcRNTI ```
```dcilen = uint64 31 decodedDCIbitslen = 31 1 crcRNTI = uint32 10 ```

The `decodedDCIbits` length matches the value of `dcilen`. The `crcRNTI` output has a value of 10, corresponding to the RNTI values used in CRC masking.

Perform DCI decoding of a sample codeword and return the decoded vector, `decodedDCIbits`, of the length defined for the DCI Format 1 message. The `lteDCIDecode` function uses fields in `enb` to determine DCI length.

```enb.NDLRB = 25; enb.CellRefP = 1; enb.DuplexMode = 'FDD'; dciInfo = lteDCIInfo(enb); dcilen = dciInfo.Format1 ue.PDCCHFormat = 1; ue.RNTI = 7; ue.NDLRB = 25; dciBits = zeros(dcilen,1); cw = lteDCIEncode(ue,dciBits); ```
```dcilen = uint64 27 ```

Define the `enb` configuration structure for recovery of the DCI message and RNTI. Perform DCI decoding using `enb`.

```enb.DCIFormat = 'Format1'; [decodedDCIbits,crcRNTI] = lteDCIDecode(enb,cw); decodedDCIbitslen = size(decodedDCIbits) crcRNTI ```
```decodedDCIbitslen = 27 1 crcRNTI = uint32 7 ```

The `decodedDCIbits` length matches the value of `dcilen`. The `crcRNTI` value recovered corresponds to and matches `ue.RNTI`, which is the RNTI value used in the CRC masking.

Perform DCI decoding of a sample codeword and return the decoded vector, `decodedDCIbits`, of the length defined for the DCI Format 2A message.

```enb.NDLRB = 25; enb.CellRefP = 1; enb.DuplexMode = 'FDD'; dciInfo = lteDCIInfo(enb); dcilen = dciInfo.Format2A ue.PDCCHFormat = 2; ue.RNTI = 5; ue.NDLRB = 25; dciBits = zeros(dcilen,1); cw = lteDCIEncode(ue,dciBits); ```
```dcilen = uint64 36 ```

Define the ue-specific configuration structure, `chs`, for recovery of the DCI message and RNTI. Perform DCI decoding using `enb` and `chs`.

```chs.DCIFormat = 'Format2A'; chs.ControlChannelType = 'PDCCH'; chs.EnableCarrierIndication = 'Off'; [decodedDCIbits,crcRNTI] = lteDCIDecode(enb,chs,cw); decodedDCIbitslen = size(decodedDCIbits) crcRNTI ```
```decodedDCIbitslen = 36 1 crcRNTI = uint32 5 ```

The `decodedDCIbits` length matches the value of `dcilen`. The `crcRNTI` value recovered corresponds to and matches `ue.RNTI`, which is the RNTI value used in the CRC masking.

## Input Arguments

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Length of recovered DCI message vector, specified as a positive integer.

Data Types: `double`

Floating-point soft bits, specified as a column vector.

Data Types: `double` | `int8`

eNodeB cell-wide settings, specified as a structure that can contain these parameter fields.

Parameter FieldRequired or OptionalValuesDescription
`NDLRB`Required

Scalar integer from 6 to 110

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

`NULRB`Required

Scalar integer from 6 to 110

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

`DCIFormat`Required (see syntax descriptions for applicability)

`'Format0'`, `'Format1'`, `'Format1A'`, `'Format1B'`, `'Format1C'`, `'Format1D'`, `'Format2'`, `'Format2A'`, `'Format2B'`, `'Format2C'`, `'Format2D'`, `'Format3'`, `'Format3A'`, `'Format4'`, `'Format5'`

Downlink control information (DCI) format

`CellRefP`Optional

1 (default), 2, 4

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

`DuplexMode`Optional

`'FDD'` (default), `'TDD'`

Duplexing mode, specified as:

• `'FDD'` for Frequency Division Duplex or

• `'TDD'` for Time Division Duplex

User-equipment-related (UE-related) channel configuration, specified as a structure containing these UE-specific fields.

 Note:   All fields in `chs` are optional. The presence of these optional fields depends on:Whether the transmission of DCI message is in a PDCCH using common search space mapping or in an EPDCCH.The release-specific features configured at the destination UE.These additional UE-specific bit fields are off by default.

DCI format name, specified as a character vector. See syntax descriptions for applicability.

Data Types: `char`

Physical control channel type used to carry DCI formats, specified as `'PDCCH'` or `'EPDCCH'`. The setting for `ChannelControlType` affects the presence of the HARQ-ACK resource offset field and message padding.

Data Types: `char`

Search space mapping for DCI formats 0/1A/1C, specified as `'UESpecific'` or `'Common'`. This field is only applicable for PDCCH. None of the additional fields can be present when formats 0 or 1A are mapped into the PDCCH common search space.

Data Types: `char`

Option to enable carrier indication field (CIF) in the UE configuration, specified as `'Off'` or `'On'`. By default, `EnableCarrierIndication` is disabled. When `EnableCarrierIndication` is enabled (`'On'`), the CIF is present in the UE-specific configuration.

Data Types: `char`

Option to enable SRS request in the UE configuration, specified as `'Off'` or `'On'`. By default, `EnableSRSRequest` is disabled. When `EnableSRSRequest` is enabled (`'On'`), the SRS request field is present in UE-specific formats 0/1A for FDD or TDD and formats 2B/2C/2D for TDD.

Data Types: `char`

Option to enable multiple CSI requests in the UE configuration, specified as `'Off'` or `'On'`. By default, `EnableMultipleCSIRequest` is disabled. When `EnableMultipleCSIRequest` is enabled (`'On'`), the UE is configured to process multiple channel state information (CSI) requests from cells. Enabling multiple CSI requests affects the length of the CSI request field in UE-specific formats 0 and 4.

Data Types: `char`

Number of UE transmission antennas, specified as 1, 2, or 4. The number of UE transmission antennas affects the length of the precoding information field in DCI format 4.

Data Types: `double`

Data Types: `struct`

## Output Arguments

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Recovered DCI message bit vector, returned as a column vector. The length of `dcibits` is defined though structure `enb` in terms of the DCI message format and the bandwidth.

Data Types: `int8`

16-bit integer result of the CRC decoder, returned as a column vector. `crc_rnti` is equivalent to the RNTI value that would need to mask (XOR) the CRC for no CRC error.

Data Types: `uint32`

## More About

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### DCI Message Decoding

Downlink control information (DCI) message decoding performs the inverse DCI processing operation as specified in TS 36.212 [1], Section 5.3.3. Specifically, `lteDCIDecode` performs rate recovery, and Viterbi and CRC decoding to recover the DCI message bit vector (`dcibits`) from an input vector of received soft bits previously coded by the DCI processing. `lteDCIDecode` also returns the 16-bit integer result of the CRC decoder, `crc_rnti`, which is equivalent to the RNTI value that would need to mask (XOR) the CRC for no CRC error. Using the RNTI, recovered with no CRC errors, enables the system to match the recovered DCI message with a specific `ue`.

The length of the DCI information payload to be recovered can be specified

• Directly by `dcilen`

• Determined using the fields in `enb` that specify the DCI message format (`DCIFormat`) and bandwidth (either `NDLRB` or `NULRB`).

For information on link bandwidth assignment, see Specifying Number of Resource Blocks.

### Specifying Number of Resource Blocks

The number of resource blocks specifies the uplink and downlink bandwidth. The LTE System Toolbox™ implementation assumes symmetric link bandwidth unless you specifically assign different values to `NULRB` and `NDLRB`. If the number of resource blocks is initialized in only one link direction, then the initialized number of resource blocks (`NULRB` or `NDLRB`) is used for both uplink and downlink. When this mapping is used, no warning is displayed. An error occurs if `NULRB` and `NDLRB` are both undefined.

## References

[1] 3GPP TS 36.212. "Multiplexing and channel coding." 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA). URL: http://www.3gpp.org.

## See Also

#### Introduced in R2014a

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#### LTE System Toolbox for Link-Level Simulation

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