Security Level: INTERNA INTERNAL L
2013/1/16
LTE TDD Signaling Procedure and Analysis
www.huawei.com
HUAWEI TECHNOLOGIES CO., LTD.
Huawei Confidential
Objective Upon the completion of this course, you will be able to:
Recognize the LTE signaling
procedures.
Understand the typical signaling procedures of network access, paging, and handover.
Analyze basic problems. problems.
Objective Upon the completion of this course, you will be able to:
Recognize the LTE signaling
procedures.
Understand the typical signaling procedures of network access, paging, and handover.
Analyze basic problems. problems.
Contents
Chapter 1 Network Access Signaling Procedure Chapter 2 Handover Signaling Procedure Chapter 3 Paging Signaling Procedure
Contents
Chapter 1 Network Access Signaling Procedure 1 Cell Searching 2 PLMN and Cell Selection 3 Attach
Cell Searching Cell searching, known as downlink (DL) synchronization, is a process to
resolve primary synchronization signals (PSS) and secondary synchronization
signals (SSS) on DL. Power on
PSS monitoring
SSS monitoring
Timeslot layer-1 timer ID Frame timer, cell ID, CP monitoring, TDD/FDD Initial synchronization
Neighboring-cell monitoring RS monitoring
RSRP/RSRQ
PBCH decoding
MIB/ SIB
PLMN and cell selection
Idle state
PLMN/cell
Cell Searching In FDD mode, PSSs are on the last OFDM symbol of slot 0 and slot 10, and
SSSs on the second OFDM symbol from the end of slot 0 and slot 10. In TDD mode, PSSs are on the second OFDM symbol from the end of slot
2 and slot 12, and SSSs on the last OFDM symbol of slot 1 and slot 11. PSSs are the same for transmission from the two slots. Whereas, SSSs are different for transmission from the two slots. PSS resolution triggers a timer of 5 ms, and SSS resolution triggers a timer of 10 ms. The cell ID on the physical layer can be obtained by using PSS resolution,
the cell group ID (504 cells are divided into 168 groups) can be obtained by
using the SSS resolution, and the physical cell identifiers (PCIs) of the current cell (each cell group has three cell PCIs) can be obtained by using both PSS resolution and SSS resolution. PCIs of the current cell = Cell group ID x 3 + Cell ID.
Contents
Chapter 1 Network Access Signaling Procedure 1 Cell Searching 2 PLMN and Cell Selection 3 Attachment
PLMN and Cell Selection After cell searching is complete, the UE obtains the PCIs of the current cell to resolve
the master information blocks (MIBs) and system information blocks (SIBs) in the
current cell. By performing MIB resolution, the UE obtains key information, including DL synchronization and system bandwidth of the cell, detects physical dedicated control channel (PDCCH) in the SIB time domain, and then obtains the System Information Block Type1 (SIB1) information based on the PDCCH before resolving other SIB information. UE
E-UTRAN
MasterInformationBlock SystemInformationBlockType1
SystemInformation
PLMN and Cell Selection: MIB The transmission period for MIBs is 40 ms. In a period, the physical broadcast channel
(PBCH) is located in subframe 0 of each radio frame and occupies the first four symbols of slot 2 within each subframe 0. PSSs and SSSs are the same in the
frequency domain, occupying 1.08 MHz in the center, that is, the 6 RBs in the middle of the frequency domain.
PLMN and Cell Selection: SIB1 The transmission period for
SIB1 is 80 ms. The first transmission is performed in the radio frame numbered a multiple of 8 within a TTI, and repeated transmission is performed on other evennumbered radio frames in the TTI. Transmission is fixed on subframe 5 in the corresponding frame. The UE detects the PDCCH on these subframes. If there is a system information radio network temporary identity (SI-RNTI), the UE receives SIB1 on the physical dedicated sharing channel (PDSCH).
PLMN and Cell Selection: SIBn The transmission period for SIBn
is a multiple of 80 ms. SIB2 contains radio resource –related configuration. SIBs 3 to 5 contain the cell reselection configuration of the LTE system. SIBs 6 to 8 contain the reselection configuration of the UTRA, GERAN, and CDMA2000 systems. SIB 9 contains the HNB configuration. SIB 10 contains the primary earthquake and tsunami warning system (ETWS) notification, and SIB 11 contains the secondary ETWS notification.
PLMN and Cell Selection SIB1 contains the public land mobile network (PLMN) table. The
access stratum (AS) of the UE transmits the resolved PLMN table to the non-access stratum (NAS) of the UE. Then, the NAS selects an appropriate PLMN. After selecting a PLMN, the UE selects an appropriate cell of
the PLMN to camp on a cell with the strongest signal.
Contents
Chapter 1 Network Access Signaling Procedure 1 Cell Searching 2 PLMN and Cell Selection 3 Attach
Attach: Attach UE
eNB
MME
RRC connection Setup Request RRC connection Setup RRC connection Setup Complete
Initial UE message DL Information Transfer
DL NAS Transfer
UL Information Transfer
UL NAS Transfer
DL Information Transfer
DL NAS Transfer
NAS message: :Attach Request, PDN Connectivity Request Authentication
NAS Encryption
UL Information Transfer UL NAS Transfer
Security Mode Command Security Mode Complete
Initial Context Setup Request Radio Interface Encryption
NAS message: Attach Accept, Active Default EPS Bearer Context Request
UE Capability Enquiry UE Capability Information
UE Capability Information Indication
UE capability reporting
RRC connection Reconfiguration RRC connection Reconfiguration Complete
Initial Context Setup Response
UL Information Transfer UL NAS Transfer
NAS message: Attach Complete, Active Default EPS Bearer Context
Attach: RRC Connection Setup
Attach: RRC Connection Setup Request
Attach: RRC Connection Setup
Attach: RRC Connection Setup Complete The UL dedicated control channel (DCCH) carries the UE registration
information and NAS messages (Initial Direct Transfer messages).
Attach: Initial UE Message (I)
Attach: Initial UE Message (II)
Attach: DL/UL NAS/Information Transfer Uu tracing
S1 tracing
Attach: Initial Context Setup Request (I)
Attach: Initial Context Setup Request (II) Message resolution
Attach: Initial Context Setup Request (III) Message resolution (continued)
Attach: RRC Security Mode Command/Complete
Attach: UE Capability Enquiry/Information UE
eNB
Attach: RRC Connection Reconfiguration Used to establish signaling radio bearer (SRB) 2 and data radio bearer
(DRB) 1.
Attach: Initial UE Context Setup Response
Attach: Signaling over the Uu and S1 Interfaces Signaling over the Uu interface
Signaling over the S1 interface
Attach: IMSI-Based Entire-Network Signaling Tracing (I)
Attach: IMSI-Based Entire-Network Signaling Tracing (II)
Attach: IMSI-Based Entire-Network Signaling Tracing (III)
Contents
Chapter 2 Handover Signaling Procedure 1 Introduction to a Handover 2 Intra-eNodeB Handover Between Cells 3 Inter-eNodeB Handover Between Cells
Introduction to Handovers
Definition
A handover is implemented when a UE in the connected state moves to a different cell to perform the UE context update.
Objective
Coverage-based handover: to achieve continuity of services for
a moving UE
Load-based handover: load-triggered handover; to ensure the optimal performance of the whole system
Introduction to Handovers Three types of handovers in the LTE system
Introduction to Handovers: LTE System Handover is implemented in three phases: handover
measurement, handover decision, and handover execution. In the handover measurement phase, the UE performs measurements
according to the measurement configuration delivered by the eNodeB and reports measurement results to the eNodeB. In the handover decision phase, the eNodeB checks the measurement results reported by the UE and determines whether to initiate a handover. In the handover execution phase, the eNodeB controls the procedure of UE handover to the target cell based on the decision, to complete the handover. The whole handover procedure is performed based on UE-assisted
network control. The eNodeB delivers measurement configuration to the UE, the UE reports the measurement results, and then the eNodeB performs handover decision, resource preparation, handover execution, and release of original resources.
Introduction to Handovers: Measurement Control
Introduction to Handovers: Measurement Report
Introduction to Handovers: Handover Command
Contents
Chapter 2 Handover Signaling Procedure 1 Introduction to a Handover 2 Intra-eNodeB Handover Between Cells 3 Inter-eNodeB Handover Between Cells
Intra-eNodeB Handover Between Cells Intra-eNodeB handover between cells is divided into
intra-frequency handover and inter-frequency handover. In the handover, only resources on the Uu interface are updated.
The eNodeBs use internal messages to apply for and release resources of the source cell and the target cell. Inter-eNodeB data transfer is unnecessary, so are the random access procedure of the UE and the signaling interaction with the evolved packet core (EPC).
Intra-eNodeB Handover Between Cells UE
Source Cell
Target Cell
eNB
Serving Gateway
MME/MMEs
Area Restriction Provided
1. Measurement Control packet data
packet data
UL allocation
packet data
The UE reports the Measurement Report message in the source cell.
2. Measurement Reports
Measurement Reports
Legend L3 signalling L1/L2 signalling User Data
3. HO decision
Handover Command DL allocation 4. Handover Command
Buffer packets from MME
The eNodeB delivers a Handover Command message after completing cell admission control and radio resource allocation in the ntarget cell. packet data
Detach from old cell and synchronize to new cell
5. Synchronization
n o i t a r a p e r P r e v o d n a H
The UE accesses the target cell.
6. UL allocation + TA for UE
o i t u c e x E r e v o d n a H
7. Handover Confirm Handover Confirm
After the handover is complete, resources of the source cell are n released. o
Flush DL buffer, continue delivering in transit packets
packet data packet data
packet data packet data
i t e l p m o C r e v o d n a H
Intra-eNodeB Handover Between Cells Uu tracing on the UE side
Uu tracing on the eNodeB side
Contents
Chapter 2 Handover Signaling Procedure 1 Introduction to a Handover 2 Intra-eNodeB Handover Between Cells 3 Inter-eNodeB Handover Between Cells
Inter-eNodeB Handover over the X2 Interface If the target cell and source cell belong to two different eNodeBs
over two different X2 links, an inter-eNodeB handover needs to be triggered over the X2 interface, and event A3 or A4 is reported. The prerequisite is that the X2 relationship has been configured between the two eNodeBs. After receiving the measurement report from the UE and deciding a
UE handover to the target eNodeB, the source eNodeB applies to the target eNodeB over the X2 interface for resources for the purpose of resource preparation in the target cell, and then informs the UE to trigger a handover to the target cell through the reconfiguration message over the radio interface. After the handover is successful, the target eNodeB informs the source eNodeB to release radio resources of the source cell. In addition, the source eNodeB transfers non-transmitted data to the target eNodeB and updates the node relationship on the user plane and control plane.
Inter-eNodeB Handover over the X2 Interface (I) Handover preparation: The source eNodeB sends a Handover Request message to the target eNodeB. The Handover Request message contains the service information and other access layer information (encryption, integrity, and measurement information) Serving Gateway MME of the current UE.
The UE has accessed to the cell and performs services. The source eNodeB delivers UE measurement control information and notifies the UE of neighboring-cell measurement.
Source eNB
Target eNB
0. Area Restriction Provided 1. Measurement Control packet data
packet data
The UE returns the measurement report after detecting a cell that meets handover conditions.
UL allocation 2.
Measurement Reports
The source eNodeB decides a handover based on the handover algorithm and current state.
Legend L3 signalling L1/L2
signalling
3. HO decisio n 4.
The source eNodeB sends the container delivered by the target eNodeB to the UE through the radio message to inform the UE to trigger a handover.
User Data
H an do ve r R eq ue st 5. Admission Control
6. Handover Request Ack DL allocation 7. Detach from old cell synchronize and to new cell
Sequence number (SN) information is used to transfer the SN status and hyper frame number (HFN) information of the UE from the source eNodeB to the target eNodeB for the purpose of data retransmission and encryption integrity protection.
Handover Command Deliver buffered and in transit packets to target eNB 8.
The target eNodeB returns the admission result and radio resource configuration information to the source eNodeB, completing the handover preparation.
SN Status Transfer
Data forwarding. For details, see subsequent description in this document.
Data Forwarding
Buffer packets from Source eNB 9. 1 0.
n o i t a r a p e r P r e v o d n a H
n o i t u c e x E r e v o d n a H
Synchronisation U L a l oc at io n
+
T A f or U E
After receiving the Handover Request message from the source eNodeB, the target eNodeB performs admission control based on the contained service information and radio resource configuration.
Inter-eNodeB Handover over the X2 Interface (II) UE
Source eNB
Target eNB
Serving Gateway
MME
11. Handover Confirm 12. Path Switch Request After the UE complete the random access procedure to access the target eNodeB, the UE sends a Handover Confirm message to the target eNodeB.
13.User Plane update request
End Marker
After receiving the Handover Confirm message from the UE, the target eNodeB initiates a path switch to the MME to complete the use r data transmission.
15.User Plane update response 16. Path Switch Request Ack
17.Release Resource Flush DL buffer,Contiue delivering transmited packets
14.Switch DL path
After completing the user data transmission, the MME sends a Path Switch Reques t Ack message.
Data Forwarding End Marker
18.Release Resources packet data
n o i t e l p m o C r e v o d n a H
After the path switch procedure, the target eNodeB informs the source eNodeB to release related resources, completing the whole handover procedure.
packet data
Signaling Procedure for the Inter-eNodeB Handover over the X2 Interface (I) Uu tracing on the UE side
Uu tracing on the source eNodeB side
X2 tracing on the source eNodeB side (same as X2 tracing on the target
eNodeB side)
Signaling Procedure for the Inter-eNodeB Handover over the X2 Interface (II) Uu tracing on the target eNodeB side
S1 tracing on the target eNodeB side
Inter-eNodeB Handover over the S1 Interface Inter-eNodeB handover over the S1 interface is similar to that over
the X2 interface. The only difference lies in the fact that there is no X2 link between two eNodeBs. If no X2 link is configured, an intereNodeB handover is performed over the S1 interface. If X2 and S1 links are configured simultaneously, an inter-eNodeB handover is preferentially performed over the X2 interface. If a handover uses the S1 interface, the Handover Request and
Handover Acknowledge messages and data are transmitted over the S1 interface.
Inter-eNodeB Handover over the S1 Interface (I) UE
Source eNB
Target eNB
Serving Gateway
MME/MMEs
Area Restriction Provided
1. Measurement Control packet data UL allocation 2. Measurement Reports
packet data The MME transfers the Handover Request message to the corresponding target eNodeB for handover preparation.
The source eNodeB sends a Handover Request message to the MME. Legend L3 signalling L1/L2
signalling
3. HO decision
User Data
4. Handover Reauired
After completing admission control and radio resource configuration, the target eNodeB returns a Handover Ack message to the MME.
5. Handover Request
7. Admission Control
7. Handover Request Acknologe 8. Handover Command
Similar to the handover over the X2 interface, the source target send the SN information to the MME, which then transfers the SN information to the target eNodeB.
DL allocation 9. Handover Command
Detach from old cell and synchronize to new cell
Deliver buffered and in transit packets to target eNB
10. eNB SN Status Transfer
The MME transfers the Handover ACK message to the source eNodeB.
11. MME SN Status Transfer Data Forwarding Data Forwarding
Buffer packets from MME
12. Synchronization 13. UL allocation + TA for UE
n o i t a r a p e r P r e v o d n a H
n o i t u c e x E r e v o d n a H
Inter-eNodeB Handover over the S1 Interface (II)
UE
Source eNB
Target eNB
MME/MMEs
Serving Gateway
14. Handover Confirm
The target eNodeB notifies the MME of the handover completion. The UE accesses the target eNodeB.
15. Handover Notify
The MME notifies the source eNodeB of resource release. 16. UE Context Release Command
The source eNodeB returns a resource release completion message. 16. UE Context Release Completed
packet data
n o i t e l p m o C r e v o d n a H
Signaling Procedure for the Inter-eNodeB Handover over the S1 Interface (I) Uu tracing on the UE side
Uu tracing on the source eNodeB side
S1 tracing on the source eNodeB side
Signaling Procedure for the Inter-eNodeB Handover over the S1 Interface (II) Uu tracing on the target eNodeB side
S1 tracing on the target eNodeB side
Contents
Chapter 3 Paging Signaling Procedure 1 Introduction to Paging 2 Paging Signaling analysis
Introduction to Paging Paging is triggered in the following three situations: The UE is in the idle state and the network needs
to send data to the UE. The network notifies the UE of an SIB update. The network notifies the UE of an available ETWS
notification.
Introduction to the Paging Procedure (1) The UE is in the idle state and the network needs to send data to
the UE. UE
eNB
SAE S1_Paging
RRC_Paging RRC_CONN_REQ RRC_CONN_SETUP RRC_CONN_SETUP_CMP
RRC_SECUR_MODE_CMD
S1AP_INITIAL_UE_MSG S1AP_INITIAL_CONTEXT_SETUP_REQ
RRC_CONN_RECFG RRC_SECUR_MODE_CMP RRC_CONN_RECFG_CMP
S1AP_INITIAL_CONTEXT_SETUP_RSP
Introduction to the Paging Procedure (2) The network notifies the UE of an SIB update or an ETWS
notification. If a UE receives a paging message of SIB update, the UE must
resolve the SIB again and use the network configuration parameters contained in newly received SIBs. If the UE receives a paging message containing an ETWS notification,
the UE must resolve the SIB1 immediately. If the SIB1 contains the SIB10 or SIB11 scheduling, the UE must resolve SIB10 or SIB11.
UE
eNB
SAE S1_Paging
RRC_Paging
Summary Processes of cell searching, PLMN selection, and cell selection for a UE just powered on
UE attach procedure and different types of attach procedures
LTE handover procedure and several common handover types in the LTE system
LTE paging procedure
3 to 5 key points upon the completion of this course
