LTE E-UTRAN FUNCTIONS AND ARCHITECTURE

E-UTRAN ARCHITECTURE

The E-UTRAN consists of eNBs:-

• Providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. 
• The eNBs are interconnected with each other by means of the X2 interface. 
• The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core),
• The MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (S-GW) by means of the S1-U. 
• The S1 interface supports a many-to-many relation between MMEs / Serving Gateways and eNBs. 

The eNB  functions: - 

• Radio Resource Management
• Radio Bearer Control,
• Radio Admission Control,
• Connection Mobility Control,
• Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
• Routing of User Plane data towards Serving Gateway;
• Measurement
• reporting configuration 

3GPP references- TS 36.300 version 9.6.0 Release 9

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LTE E-UTRAN FUNCTIONS AND ARCHITECTURE

E-UTRAN ARCHITECTURE

The E-UTRAN consists of eNBs:-

• Providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. 
• The eNBs are interconnected with each other by means of the X2 interface. 
• The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core),
• The MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (S-GW) by means of the S1-U. 
• The S1 interface supports a many-to-many relation between MMEs / Serving Gateways and eNBs. 

The eNB  functions: - 

• Radio Resource Management
• Radio Bearer Control,
• Radio Admission Control,
• Connection Mobility Control,
• Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
• Routing of User Plane data towards Serving Gateway;
• Measurement
• reporting configuration 

3GPP references- TS 36.300 version 9.6.0 Release 9

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LTE PBCH

LTE Physical Broadcast Channel (PBCH)

• Physical Broadcast Channel (PBCH) is used to broadcast the Master Information Block (MIB) using the BCH transport channel and BCCH logical channel
• For both FDD and TDD,
• the PBCH is allocated the central 72 subcarriers belonging to the first 4 OFDMA symbols of the second time slot of every 10 ms radio frame (time slot 1 in subframe 0, with time slot numbering starting from 0)
• Reference Signal Resource Elements (including those which would be allocated if antenna ports 0 to 3 were used, irrespective of the actual antenna ports used) are excluded from the PBCH allocation
•  The PBCH can be broadcast using only antenna port 0, or transmit diversity can be used to broadcast the PBCH using antenna ports {0, I} or {0, I, 2, 3}

Resource Element allocation for the PBCH

normal cyclic prefix:-

• The PBCH occupies 240 Resource Elements when using the normal cyclic prefix,i.e. (72 x 4)- 48, where 48 is the number of Resource Elements allocated to the Reference Signal.

extended cyclic prefix:-

• The PBCH occupies 216 Resource Elements when using the extended cyclic prefix, i.e. (72 x 4) - 72, where 72 is the number of Resource Elements allocated to the Reference Signal (in this case, the third column of Reference Signals also overlaps with the set of PBCH Resource Elements)

modulation:-

• The PBCH uses QPSK modulation so the 240 Resource Elements provide 480 bits when using the normal cyclic prefix, and the 216 Resource Elements provide 432 bits when using the extended cyclic prefix

* 3GPP References: TS 36.211

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LTE PBCH

LTE Physical Broadcast Channel (PBCH)

• Physical Broadcast Channel (PBCH) is used to broadcast the Master Information Block (MIB) using the BCH transport channel and BCCH logical channel
• For both FDD and TDD,
• the PBCH is allocated the central 72 subcarriers belonging to the first 4 OFDMA symbols of the second time slot of every 10 ms radio frame (time slot 1 in subframe 0, with time slot numbering starting from 0)
• Reference Signal Resource Elements (including those which would be allocated if antenna ports 0 to 3 were used, irrespective of the actual antenna ports used) are excluded from the PBCH allocation
•  The PBCH can be broadcast using only antenna port 0, or transmit diversity can be used to broadcast the PBCH using antenna ports {0, I} or {0, I, 2, 3}

Resource Element allocation for the PBCH

normal cyclic prefix:-

• The PBCH occupies 240 Resource Elements when using the normal cyclic prefix,i.e. (72 x 4)- 48, where 48 is the number of Resource Elements allocated to the Reference Signal.

extended cyclic prefix:-

• The PBCH occupies 216 Resource Elements when using the extended cyclic prefix, i.e. (72 x 4) - 72, where 72 is the number of Resource Elements allocated to the Reference Signal (in this case, the third column of Reference Signals also overlaps with the set of PBCH Resource Elements)

modulation:-

• The PBCH uses QPSK modulation so the 240 Resource Elements provide 480 bits when using the normal cyclic prefix, and the 216 Resource Elements provide 432 bits when using the extended cyclic prefix

* 3GPP References: TS 36.211

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5G NR RRC states

5G NR UE RRC States IDLE, INACTIVE, CONNECTED

The 5G NR UE states are RRC_IDLE, RRC_INACTIVE and RRC_CONNECTED mode.

UE states and state transitions including inter RAT

A UE is either in RRC_CONNECTED state or in RRC_INACTIVE state when an RRC connection has been established.

If this is not the case, i.e. no RRC connection is established, the UE is in RRC_IDLE state.

The RRC states can further be characterised as follows:-

UE RRC state machine and state transitions in NR. A UE has only one RRC state in NR at one time.

UE RRC state machine and state transitions in NR

 

UE RRC state machine and state transitions berween NR/5G, E-UTRAN/EPC

RRC_IDLE: -

• UE specific DRX may be configured by upper layers
• UE controlled mobility based on network configuration; -
• Paging
• PLMN selection
• Broadcast of system information
• Cell re-selection mobility

RRC_INACTIVE: -

• Broadcast of system information
• Cell re-selection mobility
• Paging is initiated by NG-RAN (RAN paging)
• DRX for RAN paging configured by NG-RAN
• 5GC to NG-RAN connection (both C/U-planes) is established for UE
• The UE AS context is stored in NG-RAN and the UE
• NG-RAN knows the RNA which the UE belongs to

RRC_CONNECTED: -

• 5GC – NG-RAN connection (both C/U-planes) is established for UE
• The UE AS context is stored in NG-RAN and the UE
• NG-RAN knows the cell which the UE belongs to
• Transfer of unicast data to/from the UE
• Network controlled mobility including measurements.

Reference: 3GPP TS 38.300.

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5G NR RRC states

5G NR UE RRC States IDLE, INACTIVE, CONNECTED

The 5G NR UE states are RRC_IDLE, RRC_INACTIVE and RRC_CONNECTED mode.

UE states and state transitions including inter RAT

A UE is either in RRC_CONNECTED state or in RRC_INACTIVE state when an RRC connection has been established.

If this is not the case, i.e. no RRC connection is established, the UE is in RRC_IDLE state.

The RRC states can further be characterised as follows:-

UE RRC state machine and state transitions in NR. A UE has only one RRC state in NR at one time.

UE RRC state machine and state transitions in NR

 

UE RRC state machine and state transitions berween NR/5G, E-UTRAN/EPC

RRC_IDLE: -

• UE specific DRX may be configured by upper layers
• UE controlled mobility based on network configuration; -
• Paging
• PLMN selection
• Broadcast of system information
• Cell re-selection mobility

RRC_INACTIVE: -

• Broadcast of system information
• Cell re-selection mobility
• Paging is initiated by NG-RAN (RAN paging)
• DRX for RAN paging configured by NG-RAN
• 5GC to NG-RAN connection (both C/U-planes) is established for UE
• The UE AS context is stored in NG-RAN and the UE
• NG-RAN knows the RNA which the UE belongs to

RRC_CONNECTED: -

• 5GC – NG-RAN connection (both C/U-planes) is established for UE
• The UE AS context is stored in NG-RAN and the UE
• NG-RAN knows the cell which the UE belongs to
• Transfer of unicast data to/from the UE
• Network controlled mobility including measurements.

Reference: 3GPP TS 38.300.

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5G Protocol Stack - User Plane/Control Plane

NR 5G Protocol Stack - User Plane/Control Plane

NR User Plane Protocol Stack  is shown in below figures,

User Plane

NR Control Plane Protocol Stack  is shown in below figures

Control Plane 

SDAP (Service Data Adaptation Protocol)

RRC(Radio Resource control)

PDCP (Packet Data Convergence Protocol)

RLC (Radio Link Control )

MAC (Media Access Control)

Functions :-

SDAP functions:-

• transfer of user plane data
• mapping between a QoS flow and a DRB for both DL and UL 
• marking QoS flow ID in both DL and UL packets
• reflective QoS flow to DRB mapping for the UL SDAP data PDUs.

PDCP  functions: -

• transfer of data (user plane or control plane)
• maintenance of PDCP SNs
• header compression and decompression using the ROHC
• ciphering and deciphering
• integrity protection and integrity verification
• timer based SDU discard
• reordering and in-order delivery
• duplicate discarding.

RLC functions:-

• transfer of upper layer PDUs
• error correction through ARQ (only for AM data transfer) segmentation and reassembly of RLC SDUs
• re-segmentation of RLC SDU segments
• duplicate detection (only for AM data transfer)
• RLC SDU discard (only for UM and AM data transfer)
• RLC re-establishment
• Protocol error detection (only for AM data transfer). 

MAC functions: -

• mapping between logical channels and transport channels.
• multiplexing/ de-multiplexing of MAC SDUs.
• scheduling information reporting.
• error correction through HARQ.
• logical channel prioritisation.

RRC functions: -

• Broadcast of system information.
• RRC connection control.
• Paging.
• Establishment/modification/suspension/resumption/release of RRC connection, establishment/modification/suspension/resumption/release of SRBs/ DRBs (except for SRB0).
• Access barring.
• Initial security activation.
• mobility control.
• Radio configuration control including e.g. assignment/modification of ARQ. configuration, HARQ configuration, DRX configuration.
• QoS management functions.
• Recovery from radio link failure.
• Establishment/modification/release of measurement configuration.
• Setup and release of measurement gaps; - Measurement reporting. 

3GPP references : 38.331 V15.3.0 (2018-10)

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5G Protocol Stack - User Plane/Control Plane

NR 5G Protocol Stack - User Plane/Control Plane

NR User Plane Protocol Stack  is shown in below figures,

User Plane

NR Control Plane Protocol Stack  is shown in below figures

Control Plane 

SDAP (Service Data Adaptation Protocol)

RRC(Radio Resource control)

PDCP (Packet Data Convergence Protocol)

RLC (Radio Link Control )

MAC (Media Access Control)

Functions :-

SDAP functions:-

• transfer of user plane data
• mapping between a QoS flow and a DRB for both DL and UL 
• marking QoS flow ID in both DL and UL packets
• reflective QoS flow to DRB mapping for the UL SDAP data PDUs.

PDCP  functions: -

• transfer of data (user plane or control plane)
• maintenance of PDCP SNs
• header compression and decompression using the ROHC
• ciphering and deciphering
• integrity protection and integrity verification
• timer based SDU discard
• reordering and in-order delivery
• duplicate discarding.

RLC functions:-

• transfer of upper layer PDUs
• error correction through ARQ (only for AM data transfer) segmentation and reassembly of RLC SDUs
• re-segmentation of RLC SDU segments
• duplicate detection (only for AM data transfer)
• RLC SDU discard (only for UM and AM data transfer)
• RLC re-establishment
• Protocol error detection (only for AM data transfer). 

MAC functions: -

• mapping between logical channels and transport channels.
• multiplexing/ de-multiplexing of MAC SDUs.
• scheduling information reporting.
• error correction through HARQ.
• logical channel prioritisation.

RRC functions: -

• Broadcast of system information.
• RRC connection control.
• Paging.
• Establishment/modification/suspension/resumption/release of RRC connection, establishment/modification/suspension/resumption/release of SRBs/ DRBs (except for SRB0).
• Access barring.
• Initial security activation.
• mobility control.
• Radio configuration control including e.g. assignment/modification of ARQ. configuration, HARQ configuration, DRX configuration.
• QoS management functions.
• Recovery from radio link failure.
• Establishment/modification/release of measurement configuration.
• Setup and release of measurement gaps; - Measurement reporting. 

3GPP references : 38.331 V15.3.0 (2018-10)

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LTE Paging Procedures

·      The paging procedure can be used to

·      initiate a mobile terminating PS data connection

·      initiate a mobile terminating SMS connection

·      initiate a mobile terminating CS fallback connection

·      trigger a UE to re-acquire system information

·      provide an Earthquake and Tsunami Warning System (ETWS) notification

·      provide a Commercial Mobile Alert Service (CMAS) notification

·      The paging procedure is applicable to UE in both:-

·      RRC Idle mode

·      RRC Connected mode.

·      For example :-

·      UE in RRC Idle mode could be paged to initiate a mobile terminating CS fallback connection.

·      while a UE in RRC Connected mode could be paged to signal a CMAS notification.

Paging procedure

·      Paging procedure can be initiated by either the MME or the eNode B.

·      MME can use the paging procedure to initiate a mobile terminating PS data connection

·       The eNode B could use the paging procedure to trigger a UE to re-acquire the system information

·      The MME initiated paging procedure also known as the Sl paging procedure

·      The MME starts the procedure by sending an Sl AP Msg.

·      Paging message to each eNode B with cells belonging to the relevant Tracking Area(s).

·       If the paging procedure is being used to establish a PS data connection and the UE is being addressed by its S-TMSI then the MME starts timer T3413 when sending the SlAP: Paging message.

·       Timer T3413 is not used when paging a UE for a CS fallback connection nor when paging an IMSI attached UE for an incoming SMS. Timer T3413 is also not used when addressing a UE by its IMSI (it is usual to address a registered UE by its S-TMSI. A UE may be paged by its IMSI during a network error recovery situation)

·      T3413 is a supervision timer for the paging procedure. Its expiry time is implementation dependent and is not specified by 3GPP.

·      The MME can re-attempt the paging procedure ifT3413 expires before a response is received

·      The content of the SlAP:

·      Infonnation Elements

·        UE Identity Index (0 to I 023)

·        UE Paging Identity (S-TMSI or IMSI)

·        Paging DRX (32, 64, 128, 256)

·        Core Network Domain (PS orCS)

·        List of Tracking Area Identities (T AI)( 1 to 256 instances)

·        List of Closed Subscriber Group (CSG) Identities

·        TAl CSGid(0 to 256 instances)

·        Paging Priority

·      The eNode B receives the SlAP:

·      Paging message from the MME and constructs an RRC: Paging message.

·      A single RRC: Paging message can include information from multipleS lAP: Paging messages, i.e. a single RRC:

·      Paging message can include multiple paging records to page multiple UE.

·      The RRC: Paging message is transferred using the PCCH logical channel, the PCH transport channel and the PDSCH physical channel. It uses transparent mode at the RLC layer.

·      Infonnation Elements

·        Paging Record

  List I Paging Record (1 to 16 instances)

  UE Identity (S-TMSI or IMSI)

  Core Network Domain (CS or PS)

·        System Infonnation Modification (True, False)

·        ETWS Indication (True, False)

·        CMAS Indication (True, False)

·      UE in RRC Idle mode check for paging messages once every Discontinuous Receive (DRX) cycle.

·      The Paging Occasion within the Paging Frame (PF) defines the specific subframe during which a UE checks for a paging message.

·      UE in RRC Connected mode do not have specific Paging Occasions during which they need to check for paging messages.

·      UE in RRC Idle mode search for the P-RNTI within the PDCCH of the subframe belonging to the Paging Occasion.

·      The P-RNTI has a single fixed value ofFFFE and serves as a flag to indicate that the UE may have a paging message on the PDSCH.

·      UE in RRC Connected mode also search for the P-RNTI within the PDCCH when checking for paging messages.

·      If a UE finds the P-RNTI within the PDCCH then it proceeds to decode the resource allocation information from within the PDCCH.

·      The UE decodes the RRC: Paging message from the PDSCH Resource Blocks and checks the UE identity within each of the paging records.

·      If the UE does not find its identity within a paging record then it returns to checking the PDCCH for the P-RNTI at each Paging Occasion

·      If the UE finds its identity within a paging record then it triggers the Random Access procedure to establish an RRCconnection.

·      The UE sends an RRC Connection Request message while the eNode B responds with an RRC Connection Setup message.

·      If the paging procedure is for a PS data connection, the UE includes a 'Service Request' Non-Access Stratum (NAS) message within the RRC Connection Setup Complete message

·      If the paging procedure is for a CS fallback connection, the UE includes an 'Extended Service Request' NAS message within the RRC Connection Setup Complete message.

·      The eNode B forwards the NAS message to the MME which then stops T3413 if it was running, and proceeds to establish a connection with the UE

·      Paging retransmission can be triggered if T3413 expires prior to the MME receiving a NAS message from the UE.

3GPP references: TS 36.304, TS 36.331, TS 24.301

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