5G(NR)-F1 Setup Procedure

 

F1 Setup

The purpose of the F1 Setup procedure is to exchange application level data needed for the gNB-DU and the gNB-CU to correctly interoperate on the F1 interface. This procedure shall be the first F1AP procedure triggered after a TNL association has become operational. The procedure uses non-UE associated signalling, it is cell related procedure.

This procedure erases any existing application level configuration data in the two nodes and replaces it by the one received. This procedure also re-initialises the F1AP UE-related contexts (if any) and erases all related signalling connections in the two nodes like a Reset procedure would do.

Successful Operation


The gNB-DU initiates the procedure by sending a F1 SETUP REQUEST message including the appropriate data to the gNB-CU. The gNB-CU responds with a F1 SETUP RESPONSE message including the appropriate data.

If the F1 SETUP REQUEST message contains the gNB-DU Name IE the gNB-CU may use this IE as a human readable name of the gNB-DU.

For NG-RAN, the gNB-DU shall include the gNB-DU System Information IE and the TAI Slice Support List IE.

The gNB-CU may include the Cells to be Activated List IE in the F1 SETUP RESPONSE message. The Cells to be Activated List IE includes a list of cells that the gNB-CU requests the gNB-DU to activate. The gNB-DU shall activate the cells included in the Cells to be Activated List IE and reconfigure the physical cell identity for cells for which the NR PCI IE is included.

For NG-RAN, the gNB-CU shall include the gNB-CU System Information IE in the F1 SETUP RESPONSE message.

The exchanged data shall be stored in respective node and used as long as there is an operational TNL association. When this procedure is finished, the F1 interface is operational and other F1 messages may be exchanged.

For NG-RAN, the gNB-DU may include the RAN Area Code IE in the F1 SETUP REQUEST message. The gNB-CU may use it according to TS 38.300 [6].


F1 SETUP REQUEST IEs.

This message is sent by the gNB-DU to transfer information for a TNL association.

Direction: gNB-DU ® gNB-CU

IE/Group Name

Presence

Range

IE type and reference

Semantics description

Criticality

Assigned Criticality

Message Type

M

 

9.3.1.1

 

YES

reject

Transaction ID

M

 

9.3.1.23

 

YES

reject

gNB-DU ID

M

 

9.3.1.9

 

YES

reject

gNB-DU Name

O

 

PrintableString(SIZE(1..150,…))

 

YES

ignore

gNB-DU Served Cells List

 

1

 

List of cells configured in the gNB-DU

YES

reject

>gNB-DU Served Cells Item

 

1.. <maxCellingNBDU>

 

 

EACH

reject

>>Served Cell Information

M

 

9.3.1.10

Information about the cells configured in the gNB-DU

-

-

>>gNB-DU System Information

O

 

9.3.1.18

RRC container with system information owned by gNB-DU

-

-

 

Range bound

Explanation

maxCellingNBDU

Maximum no. cells that can be served by a gNB-DU. Value is 512.

 

9.3.1.1    Message Type

The Message Type IE uniquely identifies the message being sent. It is mandatory for all messages.

IE/Group Name

Presence

Range

IE type and reference

Semantics description

Message Type

 

 

 

 

>Procedure Code

M

 

INTEGER (0..255)

 

>Type of Message

M

 

CHOICE (Initiating Message, Successful Outcome, Unsuccessful Outcome, …)

 

 Procedure Code: every message has its procedure code, so that, that can be identified their class and message type by other nodes. 

Type of Message: The Type can be Initiating Message, Successful Outcome, Unsuccessful Outcome. it is selected by sending node.

9.3.1.23  Transaction ID

The Transaction ID IE uniquely identifies a procedure among all ongoing parallel procedures of the same type initiated by the same protocol peer. Messages belonging to the same procedure shall use the same Transaction ID. The Transaction ID is determined by the initiating peer of a procedure.

IE/Group Name

Presence

Range

IE type and reference

Semantics description

Transaction ID

M

 

INTEGER (0..255, …)

 

 

9.3.1.9    gNB-DU ID

The gNB-DU ID uniquely identifies the gNB-DU at least within a gNB-CU.

IE/Group Name

Presence

Range

IE type and reference

Semantics description

gNB-DU ID

M

 

INTEGER (0 .. 236-1)

The gNB-DU ID is independently configured from cell identifiers, i.e. no connection between gNB-DU ID and cell identifiers.

9.3.1.10 Served Cell Information

This IE contains cell configuration information of a cell in the gNB-DU.

IE/Group Name

Presence

Range

IE type and reference

Semantics description

Criticality

Assigned Criticality

NR CGI

M

 

9.3.1.12

 

-

-

NR PCI

M

 

INTEGER (0..1007)

Physical Cell ID

 

 

5GS TAC

M

 

9.3.1.29

5GS Tracking Area Code

YES

reject

Configured EPS TAC

O

 

9.3.1.29a

 

–

 

Served PLMNs

 

1..<maxnoofBPLMNs>

 

Broadcast PLMNs

–

–

>PLMN Identity

M

 

9.3.1.14

 

-

-

>TAI Slice Support List

O

 

Slice Support List

9.3.1.37

Supported S-NSSAIs per TA.

YES

ignore

CHOICE NR-Mode-Info

M

 

 

 

–

–

>FDD

 

 

 

 

 

 

>>FDD Info

 

1

 

 

-

-

>>>UL FreqInfo

M

 

NR Frequency Info

9.3.1.17

 

–

–

>>>DL FreqInfo

M

 

NR Frequency Info

9.3.1.17

 

–

–

>>>UL Transmission Bandwidth

M

 

NR Transmission Bandwidth

9.3.1.15

 

–

–

>>>DL Transmission Bandwidth

M

 

NR Transmission Bandwidth

9.3.1.15

 

–

–

>TDD

 

 

 

 

-

-

>>TDD Info

 

1

 

 

-

-

>>> NR FreqInfo

M

 

NR Frequency Info

9.3.1.17

 

–

–

>>> Transmission Bandwidth

M

 

NR Transmission Bandwidth

9.3.1.15

 

–

–

Measurement Timing Configuration

M

 

OCTET STRING

Contains the MeasurementTimingConfiguration inter-node message defined in TS 38.331 [8].

–

–

RANAC

O

 

9.3.1.57

RAN Area Code

YES

ignore

 

Range bound

Explanation

maxnoofBPLMNs

Maximum no. of Broadcast PLMN Ids. Value is 6.


  


9.3.1.18          gNB-DU System Information

This IE contains the system information generated by the gNB-DU. here we have two mandatory parameters, you could further reach to 38.331 for details.

IE/Group Name

Presence

Range

IE type and reference

Semantics description

MIB message

M

 

OCTET STRING

MIB message, as defined in TS 38.331 [8].

 

SIB1 message

M

 

OCTET STRING

SIB1 message, as defined in TS 38.331 [8].

 

 


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5G-(NR): F1 SETUP FAILURE

 



If the gNB-CU cannot accept the setup, it should respond with a F1 SETUP FAILURE and appropriate cause value.

If the F1 SETUP FAILURE message includes the Time To Wait IE, the gNB-DU shall wait at least for the indicated time before reinitiating the F1 setup towards the same gNB-CU.

F1 SETUP RESPONSE

This message is sent by the gNB-CU to transfer information for a TNL association.

Direction: gNB-CU ® gNB-DU

IE/Group Name

Presence

Range

IE type and reference

Semantics description

Criticality

Assigned Criticality

Message Type

M

 

9.3.1.1

 

YES

reject

Transaction ID

M

 

9.3.1.23

 

YES

reject

gNB-CU Name

O

 

PrintableString(SIZE(1..150,…))

Human readable name of the gNB-CU.

YES

ignore

Cells to be Activated List

 

0.. 1

 

 

 

 

>Cells to be Activated List Item

 

1.. <maxCellingNBDU>

 

List of cells to be activated

YES

reject

>> NR CGI

M

 

9.3.1.12

 

-

-

>> NR PCI

O

 

INTEGER (0..1007)

Physical Cell ID

-

-

>>gNB-CU System Information

O

 

9.3.1.42

RRC container with system information owned by gNB-CU

-

-

 

Range bound

Explanation

maxCellingNBDU

Maximum no. cells that can be served by a gNB-DU. Value is 512.

 

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5G-NR: Synchronisation Signal Block(SSB/SS-Block)

 Synchronisation Signal Block(SSB/SS-Block)

3gpp technical specification:

  • 38.213
  • 38.211
  • 38.214
  • 38.101
  • 38.102
In this blog, we will discuss 5G-NR Synchronization signal block. here we have all the SSB related stubs on one place. 

During cell search procedure Synchronization Signal (SS)/ Physical Broadcast Channel (PBCH) Blocks are used. where UE search for the synchronization Signals for getting a cell information to get attach with that cell and access the radio network services. 

Before proceeding to decode the system information messages which are transmitted on the PDSCH channel in downlink, UE must decode the PBCH. SS Blocks (SSB) are also used for RSRP, RSRQ and SINR measurements.
 
 SS/PBCH block
 
1- In time domain, it consist of 4 OFDM symbols,  and in Freq domain it consists of 20 RBs. (20x12 = 240 sub carrier) , 1RB = 12 subcarrier

     OFDM symbol 0 = PSS (sub carrier  range from 56 to 182)
     OFDM symbol 1 = PBCH (sub carrier  range from 0 to 230)
     OFDM symbol 2 = SSS (sub carrier  range from 56 to 182)
                 symbol 2 = PBCH(0 to 47 and 192 to 239)              
     OFDM symbol 3 = PBCH (sub carrier  range from 0 to 230)
 
        In LTE, the position of Syncronization signal is  straight forward located around DC carrier (Center 6 PRBS/72 subcarriers).
 
But in 5G, position of Synchronization signals not fixed and can be located any where across the Carrier Bandwidth.
 
 
 
 
In time domain the first symbol Position is determined by combination of Carrier Bandwidth (CBW) + Sub-carrier spacing (SCS).
 
SSB time domain resourse allocation:
 
Start symbol of SS block in respect of sub-carrier spacing.



 

 

In the SA mode, the location of the SSB needs to be obtained through cell search. 


SSB Frequency Domain Resources

In NSA mode operation, The location of SSB is determined by information provided by higher layer in RRC Reconfiguration message from eNB to UE, fields are highlighted in below snap.
Under recongigure with sync, below IEs are present.

Following information can be extracted from above RRC Message.

  • Band = n78 is a TDD band known as TD3500 its frequency range is 3300MHz to 3800 MHz belongs to FR1
  • SCS = 30Khz with Carrier Bandwidth= 51 RB’s which is 20 MHz with reference to following figure.

FREF = FREF-Offs + ΔFGlobal (NREF – NREF-Offs)                   (i)

  • absoluteFrequencyPointA: It represents the common reference point A, this reference point is the 0th RB of 273 RBs, which is the center point of RB#0. From above logs absoluteFrequencyPointA= 642722 (NREF)
    • absoluteFrequencyPointA= 3000 MHz + 15* (642722 -600000) KHz= 3,640.83 MHz
  • absoluteFrequencySSB: It represent the center frequency of SSB Block. A SSB block is 20 RBs results 20 * 12 =240 Subcarriers and from above logs snippet absoluteFrequencySSB= 643008 (NREF)
    • absoluteFrequencySSB= 3000 MHz + 15* (643008 -600000) KHz= 3,645.12 MHz
  • Carrier Center Frequency: The total number of RB’s=51 and Resource Block corresponding to center frequency is 51/2=26
    • Center Frequency= absoluteFrequencyPointA + 26 RBs * 12 * Subcarrier Spacing
    • Center Frequency= 3,640.83 + 26 * 12 *30 KHz = 3,650.19 MHz

Position of SSB from Point A

  • offsetToPointA= It defines the frequency offset between point A and the lowest subcarrier of the RB overlapping with SSB. The unit for RB is expressed as 15KHz for FR1 and 60 KHz for FR2
  • Kssb= it defines the frequency of RB#0 of SSB and The unit for RB is expressed as 15KHz for FR1 and 60 KHz for FR2

Frequency offset to SSB from Point A = offsetToPointA + Kssb 

  • Difference between the SSB center frequency (absoluteFrequencySSB) and point A (absoluteFrequencyPointA)
    • 3,645.12 – 3,640.83 = 4290 KHz
  • Difference between the Point A and 0th subcarrier RB#0 of SSB
    • 4290 – 10 (bottom 10 RB of SSB)* 12 *30 = 690 KHz
  • Calculating No. of RBs= 690/180 =3.8
  • offsetToPointA = 3
  • Kssb = (690 – 3 * 12 *15) / 15 KHz = 10 Subcarriers
  • offset to SSB from Point A = offsetToPointA + Kssb = 3 RBs + 10 Subcarrier

 

 

when the network is not using beam forming, it may transmit only one SSB and hence there can only one SSB starting position.

 


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