LTE Optimization and Troubleshooting

 

LTE Optimization Optimization and troubleshooting troubleshooting

 

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Pone Po nemo moss a su se serv rvic icio io má máss de 15 añ año os de exp xper erie ienc ncia ia en la planificación, optimización telecomunicaciones móviles.

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redes

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Contenido del Curso 1.

Unidad 1: E-UT E-UTRAN RAN / EPC Signaling.

2.

Unidad 2: KPI and and Measurement Measurementss for LTE LTE Radio Netw Network ork Optimizat Optimization. ion.

3.

Unidad 3: Access Access and throu throughput ghput trou troubleshoot bleshooting. ing.

4.

Unidad 4: Mobili Mobility ty trou troubleshoo bleshooting. ting.

 

Unidad E-UTRANI / EPC Signaling

 

EPS Network Architecture EPS CS CN

GERAN/ UTRAN

E-UTRAN

PS CN

“LTE”

EPC  

“SAE”

PCRF S6a S1-C

UE

Uu X2

MME S1-C

Rx

S11 S5

SGi

S1-U UE

E-UTRAN

EPC

Control Plane

Gx

S1-U

UE

User Plane

HSS

Operator’s

IP Service SGW

PDN-GW

 

EPS Network Architecture

Gb

SGSN

HSS

PCRF SWx

GERAN Iu S3

S4 S6a

S12

Rx Gxc Gxb

MME S11

UTRAN

Gxa Gx

S5

S1-C

SGi

S1-U E-UTRAN

SGW S2a SWn

Trusted non 3GPP IP Access

Un-trusted non STa a 3GPP IP Access ST

PDN-GW S2b

S6b

SWa ePDG

3GPP-AAA

Operator’s IP Service

 

Functions of EPC Main Elements

MME • Mobility Management • Session Management •  Authentication and key management • NAS encryption • TA LIST Managem Management ent • P-GW/S-GW Selection

Serving Gateway • Packet forwarding and routing • IP head compress • DL buffering • Legal interception

PDN Gateway • Packet forwarding and routing • Non-3GPP access anchor  • UE IP allocation

 

LTE/EPC Network Elements Main references to architecture archi tecture in 3GPP specs.: TS23.401,TS23.402,TS36.300

Evolved UTRAN (E-UTRAN)

Evolved Packet Core (EPC) HSS

eNB Mobility Management Entity Policy Rule & Charging Function

S6a

MME

X2

S10

S7

Rx+ PCRF

S11 S1-U LTE-Uu

LTE-UE

Evolved Node B (eNB)

HSS: Home subscriber server ( part of IMS)

S5/S8

Serving Gateway

SGi

PDN Gateway S-GW /P-GW

PDN

 

 Architecture

 

 Architecture Funciones

 

EPS Architecture The term EPS (Evolved Packet System) relates to the Evolved 3GPP Packet Switched Domain. In contrast to the 2G and 3G networks defined by the 3GPP, LTE can be simply divided into a flat IP basedinto bearer a service enabling network. The former can be further subdivided thenetwork E-UTRANand (Evol (Evolved ved - Universal Univer sal T Terres errestrial trial Radio Access Network) and the EPC (Evolved Packet Core) where as support for service delivery lies in the IMS (IP Multimedia Subsystem).

Whilst UMTS is based upon WCDMA technology, the 3GPP developed new specifications for the LTE air interface based upon OFDMA (Orthogonal Frequency Division Multiple Access) in the downlink and SC-FDMA SC-FDMA (Single Carrier - Frequency Frequency Division Multiple Access) Access) in the uplink. This new air interface is termed the E-UTRA (Evolved - Universal Terrestrial Terrestrial Radio

Access).  

Mobility Management Entity NAS Signaling and Security - this incorporates both EMM (EPS Mobility Management) and ESM (EPS (EPS Session Management) and thus includes procedures such as Tracking Area Updates and EPS Bearer Management. The MME is also responsible for NAS security. S-GW and PDN-GW Selection Selection - upon receipt of a request from the UE to allocate a bearer rresource, esource, the MME will select the most appropriate S-GW and PDN-GW. PDN-GW. This selection criterion is based on the location of the UE in addition to current load conditions within the network. Tracking Area List Management and Paging - whilst in the LTE Idle state, the UE is tracked by the MME to the granularity of a Tracking Area. Whilst UEs remain within the Tracking Areas provided to them in the form of a Tracking Area List, there is no requirement for them to notify the MME. The MME is also responsible for initiating the pa paging ging procedure. Inter MME Mobility - if a handover involves changing the point of attach attachment ment within the EPC, it may be necessary to involve an inter MME handover. handover. In this situation, the serving MME will select s elect a target MME with which to conduct tthis his process. Authentication - this involves interworking with the t he subscriber’s HSS (Home Subscriber Server) in order to obtain AAA (Access Authorization and Accounting) information with which to authenticate the subscriber subscriber.. Like that of other ot her 3GPP system, authentication is based on AKA (Authentication and Key Agreement).

 

Serving Gateway Gateway S-GW - Mobil Mobility ity Anch Anchor or - for in inter ter eNB hando handover vers, s, the S-GW acts as an anch anchor or point ffor or the User Plan Plane. e. Furthermore,, it also ac Furthermore acts ts as an anchor for inter 3GPP hando handovers vers to legacy networks networks - GPRS and UMTS. - Downlink Pack Packet et Buffer Buffering ing - when traffic arriv arrives es for a UE at the S-GW S-GW,, it may need to be buffer buffered ed in order to allow time for the MME to page the UE and for it to enter the LTE Active state. - Pack Packet et Rout Routing ing and F Forwarding orwarding - traffic must be rrouted outed to the correct eNB on the dow downlink nlink and the specified PDN-GW on the uplink. - GTP GTP/PMIP /PMIP Support - if PMIP (Pro (Proxy xy Mobile IP) is used on the S5/S8 Int Interfaces, erfaces, the S-GW must support MAG (Mobile Access Gateway) Gateway) functionality. Furthermore Furthermore,, support for GTP/PMIP chaining may also be required.

 

Packket Data Pac Data Network Network - Gatewa Gatewayy - The PDN-GW is the ne network twork element which tterminates erminates the SGi Interface ttowards owards the PD PDN N (Pack (Packet et Data Network). If a UE is accessing multiple PDNs, there may be a requirement for multiple PDN-GWs to be involved. Functions associated with the PDN-GW include: - Pack Packet et Filtering - this incorpor incorporates ates the deep pack packet et inspection of IP da datagrams tagrams arriving from the PDN in order to determine which TFT (Traffic Flow Template) they are to be associated with. - IP Address Allocation - IP addresses may be allocated to tthe he UE by the PDN-GW PDN-GW.. This is included as pa part rt of the initial bearer establishment phase or when UEs roam between differ different ent access technologies. - Transport Level Level Packe Packett Marking - this involves the markin marking g of uplink and dow downlink nlink packets with the appropriate appropriat e tag e.g. DSCP (Differen (Differentiated tiated Services Code Point) based on the QCI QCI (QoS Class Identifier) of the associated EPS bearer. - Accounting - through in interaction teraction with a PC PCRF RF (Policy Rules and Charging Function), the PDN-GW will monitor traffic volumes and types.

 

EPS Interfaces Interfaces  – UTRAN Uu Inte Interf rface ace The Uu Interface Interface supports both a Control Control Plane and a User plane and spans the link between the UE and the eNB / HeNB. The principle Control Control Plane protoc protocol ol is RRC (Radio Resour Resource ce Control) while the User Plane is designed to carry IP datagrams.

X2 Interface The X2 interface interface inter interconnects connects two eNBs and in so doing supports both a Control Plane and User Plane. The principle Control Plane protocol is X2AP (X2 Application Protocol).

S1 Interface

The S1 interface can be subdivided into the S1-MME interface supporting Control Plane signaling between between the eNB and the MME and the S1-U Interf Interface ace supporting User Plane Plane traffic between the eNB and the S-GW S-GW.. The principle Control Plane protocol is S1AP (S1 Application Protocol).

 

EPS Signaling CONTROL PLANE

USER PLANE

 

NAS Functionality The Non Access Stratum (NAS) protocols are used for signaling exchange between the UE and the Mobility Management Entity (MME). NAS sits on top of RRC layer in the UE and S1AP of the MME. All NAS messages are carried by RRC and SIAP messages in radio interface and S1-MME interfaceasrespectively. The NAS signaling is identified EPS Mobility Management (EMM) and EPS Session Management (ESM). The EMM Protocol signaling is related to UE mobility and security procedures. procedures. The ESM protocol handles signaling related to the default and dedicated user plane bearers.

 

NAS Functionality

The EPC uses the IMSI number as the permanent user identifier (or rather, USIM USIM identifier). As in the legacy core Network a temporary identifier is also used, for subscriber identity confidentiality reasons, in place of the IMSI whenever possible. The temporary identifier in the EPS is called the Globally Unique Temporary Temporary Identity (GUTI). The use of the GUTI is very similar to the use of the legacy TMSI (CS domain) and PTIMSI (PS domain) numbers. There is a difference however: the GUTI explicitly links with the t he MME pool Area concept. - GUTI = MCC + MNC + MME MMEGI GI + MMEC + M-TMSI, where where - MMEGI: MME Group Ide Identifier ntifier (16 bit) - MMEC MMEC:: MME Code (8 (8 bit) - M-TIMSI : M- Temporary Mobile Mobile Subscriber Identity（32 bit） The GUTI is allocated when the UE performs initial registration (Attach) (Attach) with an MME. The GUTI is then typically changed whenever the UE performs some EMM procedure, such as TA update. The S-TMSI is a shortened version of the GUTI that uniquely identifies the user with an MME Group. The S-TMIS ,rather than the complete GUTI, is used within most NAS messages.

 

NAS EMM and EMS Procedur Procedures es

 

NAS States and transitions

 

Uu Int Interf erface ace

 

X2 Interface X2 Application Protocol The X2AP is responsible for the following functions: - Mobility Manageme Management nt - this enables the serving eNB to move the responsibility of of a specified UE to a targe targett eNB. This includes includes Forwarding the User Plane, Status Transfer Transfer and UE Context Release functions. - Load Managemen Managementt - this function enables eNBs eNBs to communica communicate te with each other in order to report resour resource ce status, overload overload indications and current traffic loading. - Error Reporting - this allows for the reporting of gener general al error situations for which spec specific ific error reporting mechanism have have not been defined. - Setting / Rese Resetting tting X2 - this provides a means by which the X2 interface can be setup / reset by exchanging exchanging the necess necessary ary information between the eNBs. - Configuration Update - this allows the updating of application level data which is needed for for two eNBs to interoper interoperate ate over the X2 interface. Stream Control Tr Transmission ansmission Protocol

 

S1-MME & S1-U Interfaces Interfaces S1 interface is divided into two parts:

S1-MME (Control Plane)

S1-MME interface

NAS Protocols

• Contro Controll interfa interface ce betwe between en eNB and MME

• S1AP:S1 Application Protocol • MME and UE will exchange non-

TS 36.413

S1-AP

TS 36.412

SCTP

MME

IP

eNB

L1/L2

access signaling through stratum this interface ( i.e. via eNB authentication, tracking area updates)

TS 36.411 S1-U (User Plane) User PDUs

GTP-U TS 36.414

S1-U interface

Serving Gateway

UDP IP

plane interface between eNB and • User serving gateway

TS 36.411

L1/L2

• Pure user data interface (U=User plane) TS 36.410 [currently in TS 36.300

19]

 

S1 Interface

S1 Application Protocol The S1AP spans the S1-MME Interface and in so doing, supports the following functions: - E-RAB (E-UTRAN - Radio Access Bearer) Manag Management ement - this incorporates the setting up, modifying and rreleasing eleasing of the E-RABs by the MME. - Initial Context T Transfer ransfer - this is used to establish an S1UE contex contextt in the eNB, setup the default IP connectivity and transfer transfer NAS related signaling. - UE Capability Information Indication - this is used to inf inform orm the MME of the UE Capability Information. - Mobility - this incorporate incorporatess mobility feature featuress to support a change in eNB or change in RAT RAT. - Pag Paging ing.. - S1 Interface Managem Management ent - this incorporates a number number of sub functions dealing with resets, resets, load balancing and system system setup etc. - NAS Signaling T Transport ransport - this is used for the transport of NAS related signaling over the S1-MME Interface Interface.. - UE Context Modifica Modification tion and Releas Release e - this allows for the modific modification ation and release o off the established UE Context in the eNB and MME respectively. - Location Reporting - this enables the MME to be made aw aware are of the UEs current location within the network. network. SCTP and GTP-U The S1-MME and S1-U lower layer protocols are similar to the X2 interface. As such, they also utilize the services of SCTP (discussed in Section 2.2.13 ) and GTP-U (discussed in Section 2.2.14 ).

 

EPS Bearer Services and E-UTRA Radio Bearers

The main functions associated associated with QoS in a packet switch (router) are the the:: - Packe Packett Classifier - this function analyses analyses packets and based on a set of filters classifies the packet. packet. As such, it receives the correct packet forwarding treatment and scheduling. - Packe Packett Scheduler - this schedules packe packets ts based on priority. In so doing v various arious methods are used to ensu ensure re low latency data, e.g. voice, is optimally scheduled.

 

LTE Bearers

The main functions associated associated with QoS in a packet switch (router) are the the:: - Packe Packett Classifier - this function analyses analyses packets and based on a set of filters classifies the packet. packet. As such, it receives the correct packet forwarding treatment and scheduling. - Packe Packett Scheduler - this schedules packe packets ts based on priority. In so doing v various arious methods are used to ensu ensure re low latency data, e.g. voice, is optimally scheduled.

 

E-UTRAN Radio Bearers B earers Signaling

A SRB (Signaling Radio Bearer) is a RB (Radio Bearer) that is only used for the transmission of RRC and NAS messages. More specifically, the following three SRBs are defined: - SRB0 - this is for for RRC message messagess using a CCCH CCCH logical channel, e.g. RRC Connection Request, Setup and Re-establishment. - SRB1 - this is mainly mainly for RRC messages messages using using a DCCH logical channel. It can also be used for NAS messages prior to the establishment of SRB2. - SRB2 - this is for for NAS messages messages using a DCCH DCCH logical channel. Note that SRB2 has a lowerlo werpriority than SRB1 and is always configured by the E-UTRAN after security activation.

Data

In addition to Signaling Radio Bearers, at least one DRB (Data Radio Bearer) needs to be established for the Default EPS bearer. bearer. There are various identities used in LTE at different different layers to identify the EPS bearers. The main higher layer identifier is the EPS Bearer Identity, this has a value between 0 to 15. In a UMTS network this is referred referred to as a NSAPI (Network layer Service Access Point Identifier). When the EPS bearer is established an associated DRB Identity is assigned. These have values between 1 and 32. Finally, the lower layers, i.e. MAC, allocate the LCID (Logical Channel Identity). There are only 10 available for Radio Bearers, with the values 1 and 2 mapping to SRB1 and SRB2 respectively.. In so doing, the remaining eight LCID are respectively available for Data Radio Bearers (1 Default EPS Bearer

and 7 Dedicated EPS Bearers).  

E-UTRAN E-UT RAN QoS Radio Radio Bearer Bearerss

There are various parameters parameters that could be configured/modified to influence the performance of the E-UTRA and tthus hus aid the eNB QoS scheduling scheduling requireme requirements. nts. These inc include: lude: - PDCP Compre Compression. ssion. - RLC AM AM or UM. UM. - RLC AM Polling Polling Configuration. Configuration. - Uplink MAC Priority Priority.. - Uplink MAC Prioritiz Prioritized ed Bit Rate. - Uplink MAC Bucket Bucket Size Duration. - HARQ Configuration and re-transmissions. re-transmissions. - BSR (Buffer (Buffer Status Report) Report) Configuration. - SPS (Semi Persistent Persistent Scheduling) Configuration. - Physical Channel Channel and Power Configuration.

 

LTE Air interface function

 

Control Plane Protocols Stacks

Encryption Compress Reliable Scheduling OFDM MIMO

 

User Plane Protocols Protocols Stacks

IP Head compress TCP UDP Lower priority =

 

RRC States

 

RRC States interaction

 

RRC Signaling Radio Bearer

 

LTE SIBs

 

LTE Identities

 

LTE Identities

 

LTE Identities

 

LTE Identities

 

LTE Identities

 

LTE Identities

 

LTE Identities

 

LTE Identities

 

LTE Identities

 

LTE Identities

 

E-UTRAN Protocol Stack –S1 Interface User Plane

Control Plane

  Radio Network Layer

S1-AP

Radio Network Layer

GTP-U

SCTP UDP

Transport NetworkL ayer

IP Data link layer Physical layer

    

Transport Network Layer

IP Data link layer Physical layer

S1AP: The S1 Application Protocol is the application layer protocol between eNodeB and MME. SCTP: The Stream Control Transmission Protocol ensures the delivery of signaling messages on the S1 interface between the MME and the eNodeB. For details about SCTP SCTP,, see RFC2960. GTP-U: The GPRS Tunneling Protocol  – –User plane is used for user data transmission between the eNdoeB and S-GW. UDP: User Datagram Protocol is used for the user data transmission. For details about UDP UDP,, see RFC 768. The data link layer can use layer 2 technologies, such as PPP and Ethernet.

 

E-UTRAN Protocol Stack –X2 Interface Radio  Network  Layer  

Control Plane 

X2-AP  Transport  Network  Layer  

Transport Network User Plane

User Plane  User Plane PDUs  Transport Network User Plane

GTP-U SCTP IP (IPv6 and/or IPv4) Data link layer Physical layer

UDP IP (IPv6 and/or IPv4)  Data link layer Physical layer



The X2 interface is also divided into the user plane (X2-U) and control plane (X2-C). The X2-U interface is required to be the same as the S1-U, and the X2-C is required to be the same as S1-C.



The X2 interface data link layer can use layer 2 technologies, such as PPP and Ethernet.

 

 Air Interface Multiple ple Acce Access ss Metho Methods ds Multi

 

OFDMA

 

Fast Fourier Fourier Transformation

 

Resource Resour ce allocation in OFDMA

 

Resour Re source ce alloca allocation tion in in SC - FDMA

 

Air Interface  Acceso • •

Downlink: OFDMA Downlink: OFDMA (Or (Ortho thogon gonal al Fre Freque quency ncy Divi Divisio sion n Mul Multip tiple le Acce Access) ss) Uplink:: SCUplink SC-FDMA FDMA ( Simple Simple Car Carrie rierr Fre Freque quency ncy Divi Divisio sion n Mult Multiple iple Acc Access ess))

FDD Carrier 

Number Num ber of

BandWith [MHz]

Resource Block

1.4

6

3

15

5

25

10 15

50 75

20

100

 

Air Interface OFDMA Ventajas •  Alta eficiencia espectral • Resis Resistencia tencias s al Multi Multitraye trayecto cto y desvanecimeinto • Soporta Soporta mod modula ulaçio çiones nes más eficientes (64QAM, 16QAM...)

Desventajas •  Alta sensibilidad al ICI (Inter Carrier Interference) •  Alto PAPR (Pea eak k to Average Power Ratio)

 

Air Interface SC-FDMA Vari ariant ante e de OFDM OFDM para reduci reducirr PAP APR: R:

• It can reduce the PAPR between 6…9dB compared to OFDMA • Reduced PAPR means lower RF hardware requirements (power amplifier)

 

Air Interface OFDMA vs SC-FDMA Por que que no S C-FDMA en en DL?  •

•

eNodeB eNode B realiza proce procesamien samientos tos de múlt múltiple iples s usu usuari arios, os, lo lo que no se pu pued ede e co con n SC SC-F -FDMA DMA.. El proceso de mapeo de secuencias de datos para múltiples usuarios y la transmisión de estos seria solo posible a través de un amplificador resultando esto en un PAPR similar a OFDMA.

 

Air Interface OFDMA vs SC-FDMA

 

Air Interface

 

Air Interface

 

Air Interface

 

Air Interface OFDMA vs SC-FDMA Example

 

Air Interface OFDMA vs SC-FDMA

 

Air Interface Resource Block and Resource Element

 

Modulation Mapping

 

Overv Ov ervie iew w - Chan Channe nels ls Upper Layers DL

UL

RLC B   C   C  H

P   C   C  H

 C   C   C  H

D T   C  H

D  C   C  H

Logical channels

M  C   C  H

M T   C  H

 C   C   C  H

D T   C  H

D  C   C  H

MAC B   C  H

P   C  H

D L    S   C  H

Transport channels

M  C  H

 U L    S   C  H

R A   C  H

PHY P  B   C  H

P  D  S   C  H

P  H I     C  H

P   C  F  I     C  H

P  D  C   C  H

 S    y  n  c  h  

R  S 

 Air interface

P  M  C  H

      S       R       S

      S       R       D

P  R A   C  H

P   U  C   C  H

P   U  S   C  H

 

LTE Measurements Measurements

 

LTE Measurements Measurements

 

LTE Measurements Measurements

 

Reselection LTE -130 dBm RSRP – RSRP – High Prio

    )    7     (    o    i    r    P     h    g    i    H     –    &    P    R    S    R      m    B     d    6    2    1      E    T    L

WCDMA > -111dBm & EcNo > -20 dB Prio 5,4 (850MHz) 3 (1900MHz) tResUtra 2 Sec.

&

GSM > -105 dBm RSSI Prio 1 (1900MHz) tResGer 7 Sec. Sec.

 

Movilidad Intra LTE HO via X2

Intra LTE HO via S1

HO to WCDMA - (RL30) LTE LTE 56 Or Red Redire irect ct

eNACC to GSM - (RL30) LTE442 LTE442 (desactivado) (desactivado)

Redirect

 

LTE/3G interworking procedures (RL40/RU40) LTE 872: SRVCC (RL40) LTE 736: CSFB via IRAT HO

E-UTRA RRC_CONNECTED

(RL30) LTE 56: IRAT HO WCDMA

Cell_DCH

(RU50) RAN 2264: Smart LTE handover

   O    H    T    A    R    I    a    i    v    B    F    S    C    :    6    3    7    E    T    L     )    0    4    L    R     (

 .    s

   g

   B    F    S    C    :    2    6    5    E    T    L     )    0    2    L    R     (

   n    i    r    e    y    a     l    E    T    L    t    r    a    m    S   :    7    1    7    2    N    A    R

PCH/URA_PCH

E-UTRA

(RU20 OnTop) RAN2067: reselection

RRC_IDLE

(RL10) LTE 762: reselection

   t    c    e    r    i     d    e    r    :    3    2    4    E    T    L

UTRA_IDLE

   a    e    t    m    c    e  .    r    i    w     d    t    e    c    r    e    r    B    i    F     d    S    e    C    r    :    :    2    3    6    7    5    0    1    E    T    E    L    T    L

 

LTE/2G interworking procedures (RL40) LTE 873: SRVCC GSM Connected

E-UTRA RRC_CONNECTED

GPRS Packet Transfer

   t    c    e    r

   4    8    9    E    T    L    &    t    c    e    r    i     d    e    r    :    3    2    4    E    T    L

   B    F    S    C    :    2    6    5    E    T    L     )    0    2    L     (    R

(RG20) BSS21353: reselection

E-UTRA RRC_IDLE

(RL10) LTE 762: reselection

   M    I    R    o     /    w    C    C    A    N    e    :    2    4    4    E    T    L

    d    i    e    r    B    F    S    C    :    2    6    5    E    T    L

GSM Idle GPRS Packet Idle

 

Reselection

Ejemplo de configuración Techn Tec hnol olog ogyy Band Ba nd ARFC AR FCN N Pri Prior orit ityy Th Thre resh shol old d (R (RSC SCP/ P/RS RSSI SI)) EcNo EcNo Obse Ob serv rvac ació ión n LTE 2600 3300 7 Prioridad Absoluta LTE 700 6 Reservado WCDMA   F1 (850) 4358 5 -111 -20 WCDMA   F2 (850) 4383 WCDMA   F3 (1900) 612 GSM   PCS 1900 GSM   850

4 3 1 0

-111 -111 -105

-20 -20 No se Aplica

 

3GPP interfaces GGSN

MSC

SGi

IMS Core A-SBC

S16

Pre R8 2G/3G

Gb/

Abis/

IuPS

Iub

BTS/NodeB

Gxc(*)

Mw

Rx Mg/Mi

BG SGi

BSC

MGCF

Ia

Gx

Gb

Abis

BTS

PCRF

S/I-CSCF

SGSN

BSC/RNC

2G SGSN

R8 2G

P-CSCF w/SBC

Mn

MGW

S5

SGW

R8 3G

PGW Internet

Iub

Iu_c

CNR/HSS

NodeB

RNC

uSGSN S11

LTE S1-MME

eNodeB

S10

MME Direct Tunnel Control plane User plane * Needed only with S5 PMIP

Operator services

 

Functional Split between E-UTRAN and EPC eNB Inter Cell RRM RB Control Connection Mobility Cont. MME Radio Admission Control NAS Security eNB Measurement Configuration & Provision Idle State Mobility Handling

Dynamic Resource  Allocation (Scheduler)

EPS Bearer Control RRC PDCP S-GW

RLC

P-GW UE IP address allocation

Mobility  Anchoring

MAC S1 PHY

Packet Filtering internet

E-UTRAN

EPC

 

Protocol Stack

1 TBS per TTI per antenna

Ultimately TBS + 24 bit CRC + Coding is what is added and sent out by PHY (See note below).

 

QOS (1/3)

• QoS Class Identif Identifier ier ( Q QCI  CI   ) o

3G

EPS

o o

Traffic Class

QCI (QoS Class Identifier)

Delivery Order

ARP

Max SDU Size

•  Allocation and Retention Priority (  ARP  ) o

SDU Format Information

Max Bit Rate

SDU Error Ratio Residual Bit Error Ratio Delivery of Erroneous SDUs Transfer Delay

For GBR bearers

Guaranteed Bit Rate

Aggregate Max Bit Rate

Traffic Handling Priority Source Statistics Descriptor

Max Bitrate Guaranteed Bitrate

ARP is used to decide whether bearer establishment or modification request can be accepted in case of resource limitations/congestion ARP can also be used to decide which bearer(s) to drop during resource limitations It has been agreed in 3GPP that ARP has no impact on packet forwarding treatment

•  APN Aggregate Max Bit Rate (  APN-AMBR ) and UE  Aggregate Max Bit Rate ( UE-AMBR UE-AMBR ) for non-GBR EPS bearers o

Signalling Indication ARP

o

o

For non-GBR bearers

QCI is used to determine packet forwarding treatment (e.g. scheduling of packets) QCI can be used to mark packets with DSCP 3GPP has standardised 9 QCI values and mapping to resource type (GBR, non-GBR), priority, packet delay budget and packet error loss rate

•Number of QoS parameters has been decreased •AMBR has been introduced to support bandwidth management model familiar from fixed access

o

APN-AMBR shared by all non-GBR EPS bearers with the t he same APN – APN – downlink enforcement is done in PDN GW and uplink enforcement in UE UE-AMBR shared by all non-GBR EPS bearers of the UE – UE – downlink and uplink enforcement is done in Enb

GBR BR ) and Max Bit Rate ( MBR MBR ) • Guaranteed Bit Rate ( G

 for GBR EPS bearers

 

QOS (2/3) QCI

Resource type Priority

Packet delay budget

Packett error loss Packe rate

Example Application

1

GBR

2

100 ms

1e-2

Conversation voice

2

GBR

4

150 ms

1e-3

Conversational video

3 4

GBR GBR

3 5

50 ms 300 ms

1e-3 1e-6

Real-time gaming Non-conversational video Converted to GBR if used for IMS signaling

5

Non-GBR

1

100 ms

1e-6

IMS signalling

6

Non-GBR

6

300 ms

1e-6

Video, www, email, ftp

7

Non-GBR

7

100 ms

1e-3

Interactive gaming

8

Non-GBR

8

300 ms

1e-6

Video, www, email, ftp

9

Non-GBR

9

300 ms

1e-6

Video, www, email, ftp

Note: Usage of operator specific QCIs in addition to standardized QCIs is possible.

 

QOS (3/3) Application / Service layer Downlink Service Data Flows

Uplink Service Data Flows Uplink Traffic Flow Templates (packet filters)

QOS(labels) is defined and applied only between UE and PDN gateway for 3GPP and non-3GPP access

UE

Radio Bearers

GTP-U eNB

•

Traffic Flow Templates Templates are initiated i nitiated from the network

•

Only the PDN GW and UE have flow specific information.

•

o

Between these, the packets are carried in default or dedicated bearers

o

The application layer is non-QOS aware

Serving GW

GTP-U

PDN GW

= eNB and gateways monitor and police (enforce) the AMBR (UE cannot because eNB has anyways full control of UE UL)

Default Evolved Packet System (EPS) bearer’s Traffic Flow Template (TFT) matches/contains ALL packets o

•

GTP-U

GTP-U

Default bearer is Non-guaranteed Bit Rate and always on

Dedicated EPS bearer’s TFT match only certain packets (based on IP or TCP port) o o

o

Dedicated bearers are setup on network request for e.g. VoIP calls Policy and Charging Rules Function (PCRF) communicate communicatess with Policy and Charging Enforcemen Enforcementt Function (PCEF) within PDN GW to determine the bearer QOS Default QOS rules can alternatively be configured in PDN GW for situations when PCRF does not give instructions

 

Mobility Management

• Mobility Management is a part of LTE C-Plane of Flexi Multiradio BTS BTS (eNB) and handles the mobility of UE in active state Procedures es supported by Mobility Management: • Procedur

 – Handover  ongoing call or data session ses sion is transfered from one radio channel connected to the core network to another without call interruption

 – Redirection

 is a similar procedure, however it requires connection release prior to the transfer t ransfer the ongoing call

 – Cell change  procedure dedicated for call transfer from LTE LTE to GSM; connection release is also required

eNB C-Plane Mobility Management (MM)

 

LTE56 interRA interRAT T ha handover ndover to WCDMA •

InterRAT InterRA T and inter-frequency h hard ard handover

• •

•

gap assisted assisted measu measurements rements can be required by UE

•

UE-EUTRA Capability contains the information if for a given WCDMA band

•

measurement gaps are necessary (IE: interRAT-NeedForGaps) during measurement measurement of neigbour cells UE does not transmit or receive any data

network controlled and UE assisted

• •

eNB tak takes es the decision to start handover procedure based on measurements delivered by UE

backward handover

• •

UE is connected to only one cell at a present time

resources at target system are reserved in advance

for interRAT interRAT handover data are not forwarded

•

data transfer between between eNB and RNC is not possible; transfer between UE and eNB and UE and RNC only

 

Key topics to be considered •

Provisioning of neighbour relation to WCDMA cells Manual ually ly or wit with h ANR fe featu ature re sup suppor portt • Man

•

Verification of  byability eNB UEMME Radio Capability • eNB of UE and rrece eceive ive UE Cap Capabi lity dur during ing Net Networ work k Att Attach ach and TAU

•

Measurement Configuration for WCDMA cells • Events indicate radio conditions of serving and neighbour cells • A1 - Serving bec becomes omes better than thr threshold eshold • A2 - Serving bec becomes omes worse than thre threshold shold • A3 - Neighb Neighbour our becomes offset bette betterr than serving

• • • •

•

A4 - Neighb Neighbour our becomes better than thres threshold hold A5 - Serving becomes worse than threshold1 and neighbour becomes better than threshold2 B1 - Inter RAT neighbour neighbour becomes better than threshold threshold B2 - Serving becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2 Sta Start rt o off WCD WCDMA MA meas measurem urements ents and tri trigg gger er to hand handover over with A2, B2

 

Radio conditions for LTE56 interRAT HO to WCDMA LTE to WCDMA is triggered by poor LTE LTE radio coverage and sufficient WCDMA cell radio signal • Handover from LTE quality cell ll gets worse UE has to be informed informed first which neighbour • To make this possible in case signal level of serving LTE ce WCDMA cells cells should be observe observed d as potential potential target target cells during HO procedur procedure e Informati ormation on about target target WCDMA cells cells is provided to UE by eNB with the help of RRC:ConnectionReconfiguration • Inf message

• The trigger for sending this message is event A2, controlled with threshold2WCDMA ignal level of serving ser ving LTE cell becomes • If in the meantime, before the HO to WCDMA procedure is executed, the ssignal better bet ter again, again, then monitoring monitoring of WCDMA WCDMA neighbour neighbour cells can can be switched switched off 

• UE is informed about measurement deactivation again via RRC:ConnectionReconfiguration, this time triggered by with threshold2a threshold for m event A1, controlled threshold2a is a common threshold measurement easurement deactivation of all LLTE_interFreq TE_interFreq// WCDMA/ GERAN • please note: threshold2a neighbour cells (if activated earlier)

 

Radio conditions for LTE56 interRAT HO to WCDMA

 

Measurement Configuration Configuration 

LTE thresholds, offsets defined till RL30

 

Parameters  Reminder  LNHOW that holds first and foremost foremost info information rmation about WCDMA thresholds thresholds and timers for predefined set of ARFCNs  LNADJW – LNADJW – that conveys the details about each and every WCDMA neighboring neighborin g cell  new paramet parameters ers in structure structure for objects LNBTS, LNCEL

 

Parameters

 

Troubleshootin roubleshooting g Rate Faults aults - No transmi transmission ssion User equipment (UE) that has accessed a network cannot perform data services. - Low downlink rate rate on a single UE The observed rate of a downlink downlin k service, either a User Datagram Protocol (UDP) or Transmission Transmission Control Protocol (TCP) (TCP) service, on a UE is at least 10% lower than the baseline value. - Downlink rate rate fluctuation on a single UE The observed rate of a downlink service, either a UDP or TCP service, on a UE fluctuates by more than 50%. - Low uplink uplink rate on on a single UE The observed rate of an uplink service, either a UDP or TCP service, on a UE is at least 10% lower than the baseline value. - Uplink rate fluctuation on on a single UE The observed rate of an uplink service, either a UDP or TCP service, on a UE fluctuates by more than 50%. - Abnormal rates rates on multiple multiple UEs - A key performance indicator indicator (KPI) indicates an abnormal rate, or a large number of users complain about their traffic rates. This fault may be caused by a specific sing single-UE le-UE rate fault or a common rate fault on multiple UEs. - User-recognized User-recognized abnormal rate The rate of a data service on a UE is abnormal according to the t he user's definition. For example, the currently observed rate is noticeably lower than the rate of the previous day or a period; the observed rate is considerably lower than the rate achieved by equivalent equipment.

 

Symptoms of Throughput Faults •

 A throughout fault indicates that the UE throughput at the application layer layer or the MAC layer is low or greatly fluctuates. The throughput fluctuation can be directly observed by using the throughput measurement function of the Netmeter and other tools. • Low throughput  The peak throughput in an outdoor test is more than 5% smaller than the baseline value

and that in a lab test cannot reach the baseline value.  The average throughput under the same path loss in a stationary test is more than 10%

smaller than the baseline value.  Compared with other competitors, the throughput under the same path loss is lower for

more than 5%.

• Throughput fluctuation  When the UE is stationary, stationary, the Reference Signal Received Power (RSRP) fluctuates for

more than 6 dB or the throughput fluctuates for more than 30%. sharply.  The throughput drop sharply.

 The throughput intermittently drops. 

The UL and DL throughput reference curves are provided on the next page.

 

UL Throughput Reference Value The following gives the baseline value of the UL throughput



         )       s      p           b         M          (         t      u      p           T

60

30.0

50

25.0

40

         )      s      p         b         M          (        t      u      p         T

30 20

20.0 15.0 10.0

10

5.0

0

0.0 90

95

O L_ L_ CA CA T4 T4 _T _T pu pu t

100

105

11 0 115 PL(dB)

O L_ L_ CA CA T5 T5 _T _T pu pu t

120

C L_ L_ CA CA T4 T4 _T _T pu pu t

12 5

130

135

C L_ L_ C CA A T5 T5 _T _T pu pu t

Throughput at the bandwidth of 20 MHz

90

95

10 0

O L_ L_ CA CA T4 T4 _T _T p pu ut

1 05

110 115 PL(dB)

O L_ L_ CA CA T5 T5 _T _T pu pu t

120

C L_ L_ CA CA T4 T4 _T _T pu pu t

1 25

1 30

C L_ L_ CA CA T5 T5 _T _T pu pu t

Throughput at the bandwidth of 10 MHz

Note: OL: open-loop power control CL: closed-loop power control

1 35

The uplink capability and throughput of Cat 3 UE is the same as that of Cat 4 UE.

 

DL Throughput Reference Value • The following table on the left describes the DL peak throughput baseline. Peak Throughput (Mbit/s)

Bandwidth CAT3

CAT4

CAT5

1.4M

7.019

7.019

7.019

3M

21.126

21.126

21.126

5M

36.073

36.073

36.073

10M

73.104

73.104

73.104

15M

102

109.712

109.712

20M

102

149.855

149.855

Si gnal-to-Noise Ratio (SNR) • The table on the right describes the ratio of throughput to Signal-to-Noise on a fading channel for Cat 5 UE at the bandwidth of 20 MHz in a single cell in a lab test. The baseline varies between different UEs for about 5%. The number of radio blocks (RBs) increases and reduces based on the bandwidth. The comparison is based on the maximum capabilities of different category UEs.

 

Overall Process for Throughput Fault Location  Step 1: Check basis parameters and alarms. Check basic factors affecting the

throughput one by one. Note 1: This type of check features low cost and must be preferentially used. If some factors are difficult for check, leave these factors to subsequent steps. Check on each factor is deserved. Note 2: Basic parameters include the UE subscription rate, UE capability, UE factor, UL CL power control, eNodeB alarms, laptop, server performance, packet injection tool, license, and whether multi-UE is supported.

 Step 2: Determine whether that is a TCP fault. Compare the TCP service rate

with he UDP service rate. Note 1: Compared with UDP services, TCP services are sensitive to end-to-end packet loss, delay delay,, and jitter. Therefore, the TCP rate problem is closely related to the performance of the transmission equipment, evolved packet core (EPC), UE, server, and laptop. Historical data shows that this type of problem accounts for more than 70%. Note 2: After a TCP fault is confirmed, subsequent operations are greatly different from those for a non-TCP fault.

 Step 3: Determine a TCP fault. Check TCP parameters and use the eNodeB

TPE function and multi-point packet capture function to locate a fault step by step. Note: TCP parameters can be checked to determine a TCP fault; the TPE function can be used to check whether that is a fault of a node above the eNodeB (S1 interface and above) or a fault of a node below the eNodeB;

the multi-point packet capture function is performed to locate in which segment the packet loss and out-oforder packets occur.

 Step 4: Determine a non-TCP fault. Recheck basic factors and interference.  

Checking Basic Parameters and Alarms (1/5) Basic parameters

Check Method (Specific Operations to be Described in this Document)

UE subscription rate

The UE subscription rate can be viewed by performing S1 tracing or be observed on the UE side. Alternatively, the UE subscription rate can be queried on the home subscriber server (HSS).

UE capability

Query the UE capability by viewing the UE capability message. Generally, commercial UEs support category 2 and category 3. UEs of different categories support different UL and DL throughput.

Individual factor of the UE Use other UEs of the same brand; use UEs of a different brand for test Antenna of the UE

If external antennas are used, you are advised to place two antennas vertically at a proper interval. If built-in antennas are used, adjust the angle and location of the UE.

eNodeB alarm

If an alarm is generated, try to clear it. If the alarm does not have clearance conditions, analyze whether the alarm affects the throughput.

Whether multiple UEs are Use the cell performance monitoring function of the eNodeB to check whether a cell has multiple UEs. in the cell Whether the throughput is The license certificate may restrict the total cell throughput and therefore the throughput is low.

restricted by the license The LTE system provides larger throughput and therefore requires servers and laptops with better

Performance check on the performance. During UL packet injection, a laptop needs to connect to the power supply to prevent packet server and the laptop injection failures caused by insufficient power. If there is no valid judgment method, replace a server or laptop to test for comparison.

Compatibility of the

Inject 1000-byte packets in the test for comparison. Replace the FTP download tool with the recommended

packet injection tool

Filezilla.

Check whether the UL CL Check whether the corresponding switch of the eNodeB is turned on, whether the UE supports the UL CL power control is valid. power control. eNodeB eNode B parameter parameter chec check k For details about specific operations operations of eNodeB parameter ch check, eck, see doc for the vendor   

Checking Basic Parameters and  Alarms (2/5) Checking the UE subscription rate UE subscription rate includes Aggregate Maximum Bit Rate (AMBR) and guaranteed bit rate (GBR). The total tota l rate of non-GBR services cannot exceed the AMBR. The rate of GBR bearers cannot exceed the GBR. Both the AMBR and the GBR need to be larger than the user-required rate.  AMBR can be viewed viewed in the Initial Context Context Establishment Request message traced over the S1 interface. GBR can be viewed in the E-RAB Establishment Request or Initial Context Establishment Request message for GBR bearer establishment, as shown in the figure on the left. The UL and DL AMBRs AMBRs are 20 Kbit/s, which is insufficient.

GBR  AMBR

Unit: bit/s

 AMBR can also be observed observed on the UE side, as shown in the figure on the right.

 

Checking Basic Parameters and  Alarms (3/5) (3/5) Checking UE capability

The UE capability can be viewed in the RRC_UE_CAP_INFO message traced over the Uu interface. The following table shows the UL and DL throughput supported in various UE categories. On UL, the MCS order for UE Cat 5 can reach a maximum of 28,

The UE belongs to Cat 3.

and that for UE Cat 3 and Cat 4 reaches 24 only. UE Capability Maximum UL throughput (Mbit/s) Maximum DL throughput

Cat 1 5

10

Cat 2

Cat 3

Cat 4

Cat 5

25

50

50

75

50

100

150

300

(Mbit/s)

Checking eNodeB alarms  Alarms of the eNodeB, equipment, equipment, transmission, radio frequency, frequency, and interference affect the throughput. In case of an throughput fault, try to c clear lear eNodeB alarms. If the alarms do not have clearance conditions, analyze the alarms one by one to check the influence on the throughput or use a

better eNodeB for tests.

 

Checking Basic Parameters and  Alarms (4/5) Whether multiple UEs are in the cell

If other UEs in the same cell are performing services, RBs for the test UE decrease. Therefore, before testing, check whether any other UE exits in the cell and also pay attention to the access of other UEs during the test. Monitoring the number of UEs as shown s hown in the figure on the right

Whether the throughput is restricted by the license Whether the license expires. Whether the throughput is restricted by the t he license. Check whether whether the License suppor supports ts UEs of Cat 2, Cat 3, and Cat 4. In multi-operator core network (MOCN) ( MOCN) scenarios, check the traffic volume ratio

between operators.

 

Checking Basic Parameters and  Alarms (5/5) Whether the UL CL power control is valid (for an UL fault) Symptom: If CL power control is invalid, the throughput and number of RBs decrease for UEs located at a point far from the cell center or located in the middle of the cell while UEs close to the cell center reach the peak pe ak throughput. Specifically, Specifically, when the RSRP is  – 100 dBm, the number of RBs reaches up to 90 for UEs in 20 MHz cells and reaches 40 for UEs in 10 MHz cells if the CL power control switch is turned on and reaches a maximum of 10 if the OL power control switch is turned on.

eNode eNodeB B param parameter eter check Many parameters of the eNodeB affect the throughput. Compare configured parameters of the faulty eNodeB with baseline values or those of normal eNodeBs to find inconsistent parameters and then analyze these parameters one by one or modify the parameter to perform perf orm a test again.

 

Determining a TCP Fault or a Non-TCP Fault 

1. Simple method: UDP packet injection Judgment method • If the throughput for UDP transmission is evidently greater than that for TCP transmission (for example, greater than 10%), a TCP fault occurs. Check reasons of the TCP fault. • If the throughput for UDP transmission is almost the same as or lower than that for TCP transmission, a non-TCP fault occurs. Check reasons of the non-TCP fault.



2. If UDP packet injection fails, upload multiple files fil es using multiple threads or upload multiple files simultaneously simultaneously.. Operation method • Upload multiple files in multiple DOS windows or using the multi-thread software, such as the Flashget and Filezilla.

Judgment method • If the throughput in multi-thread-based upload is evidently greater than that in single-thread-based TCP packet injection, a TCP fault occurs. Check reasons of the TCP fault. • If the throughput in multi-thread-based upload is almost equal to or lower than that in single-thread-based TCP packet injection, a non-TCP fault occurs. Check reasons of the non-TCP fault.



If the preceding two methods cannot be used, check reasons of a TCP fault.

 

Non-TCP Fault Location: Process  If it is not a TCP fault after basis parameters and alarms are checked, further fur ther locate the fault based

on specific symptoms of the problem. A throughput problem has the following symptoms: the number of scheduling times is insufficient; the number of RBs is insufficient; the MCS order is low and the IBLER is not diverged. In addition to the symptoms of the UL throughput, a DL throughput fault has another symptom that the DL MIMO mode is incorrect and dual-code words cannot be used. symptoms of the problem, locate a fault by following the procedur procedure e corresponding to  After confirming symptoms the symptoms.  Abnormal throughput

The number of scheduling times is insufficient.

Limited performance

The number of RBs is insufficient.

Restricted

The MCS order is low.

Check interference .

Imbalance between the main and diversity of a UE

The IBLER is abnormally diverged.

DL correlation check

The DL MIMO mode is abnormal.

of the transmitting equipment

 

transmission

Throughput Fault: Routine Operation Checklist Routine Operation Confirm the problem. Check basic parameters.

Analysis Operation Compare the test result with the baseline throughput and describe the throughput fault.

deliverables Problem description with detailed values contained in the preliminary analysis report.

Check the subscription rate and the UE capability to meet service requirements. Basic parameter check results contained in Check whether the UL CL power control switch is turned on. the preliminary analysis report. Check whether there are multiple UEs in the cell.

Check the UE and the antenna of the UE.

Use a different UE or a UE of a different brand. If external antennas are used, adjust the angle of the antenna and the interval between two antennas. If built-in antennas are used, adjust the location and angle of the UE.

Check results contained in the preliminary analysis report.

Check the performance of the laptop and the server.

Use a laptop and a server with better performance. Try to shut down other software and ensure that the laptop connects to the power supply.

Test results after replacement contained in the preliminary analysis report, including the UE type and version as well as the type of laptop and server. server.

Change a packet injection tool (Iperf or Gperf) and revise the packet length to 1000 bytes. Change the FTP download tool to the FileZilla.

Test results after replacement contained in the preliminary analysis report.

Check the packet injection tool and FTP tool. Check alarms.

Check alarms on the eNodeB and clear an alarm if any. If an alarm cannot be cleared, change an eNodeB to perform  Alarms and preliminary preliminary alarm analysis analysis results tests or analyze the alarm. Check parameters of the faulty eNodeB by referring to the

Check parameters.

LTE Parameter Check Manual .

Parameter check result

 

Throughput Fault: Routine Operation Checklist Routine Operation Confirm a TCP fault. Check TCP parameters. Check the transmission.

Check interference.

Analysis Operation

Inject UDP packets or perform multi-thread Check results contained in the TCP transmission to check whether this is a preliminary analysis report. TCP fault. Follow the instructions to confirm TCP parameters of the laptop and the server.

Parameter check results and test results after parameter modification

Check the property and rate of ports on each transmission device over the S1 interface.

Configuration information about the property (duplex, half-duplex, or auto) and rate (fast Ethernet, Gigabit Ethernet, or auto) of each port on each transmission device.

Check whether interference occurs on UL and DL.

Check imbalance Check whether the main and diversity of a between the main and UE are imbalanced. diversity of a UE. Submit deliverables.

deliverables

Interference check results Check results of imbalance between the main and diversity

Provide other deliverables listed on the next Preliminary analysis report; problem log page.

 

Unidad III KPI and Measurements for  LTE Radio Network Optimization

 

Access Procedure – Procedure – Attach Introduction to the Access Procedure UE

Upon power-on, a UE first selects a cell to camp on and then initiates the Attach procedure. c o n

MME

RRC_Conn_Req (msg3)

n

e R c ti R

 The RRC connection setup cause

o C n s

value is Mo-Signaling.

E-NODEB

RRC_Conn_Setup (msg4) RRC_Conn_Setup_Cmp (msg5)

e

INITIAL UE MESSAGE

tu



Direct transmission (authentication and service negotiation)

The Attach Attach procedure consists of four steps: •

INITIAL UE CONTEXT SETUP REQ RRC SECURITY MODE CMD

E

RRC SECURITY MODE CMP

A

RRC_UE_Cap_Enquiry

Random access

•

RRC connection setup

•

NAS pro proced cedure ure

•

e-RA e-RAB B se setu tup p

-R B s

RRC_UE_Cap_Info

p

RRC CONN RECFG

e tu

RRC CONN RECFG CMP

During the Attach procedure, a data card terminal usually sets up only a default bearer. LT terminals supporting VoIP and some smart terminals such as HTC set up a dedicated bearer bearer..

INITIAL UE CONTEXT SETUP RSP

Direct transmission (service negotiation and notification)

SAEB SETUP REQ

b e

D r

ic

a e

RRC CONN RECFG

r d e p

tu

e

s

a

RRC CONN RECFG CMP

d

te

SAEB SETUP RSP

 

Access Procedure – Procedure – Service Introduction to the Access Request After attaching to the network, if the UE returns to the idle mode, the UE initiates the Service Request procedure to perform a service.

UE

E-NODEB

MME PAGING

RRC PAGING RRC CONN SETUP REQ

 The RRC connection setup cause values

are:

RRC CONN SETUP RRC CONN SETUP CMP

 Mo-data  Mt-Access

INITIAL UE MESSAGE

Direct transmission (authentication & service negotiation)

 The Service Request procedur procedure e consists of

three steps:  Random access  RRCAB conn connectio ection setup up  e-R e-RAB set setup up n set

The EPC has obtained the registration information informat ion and capability information of the UE. Therefore, The Service Request procedure does not contain the authentication and UE

INITIAL UE CONTEXT SETUP REQ RRC SECURITY MODE CMD RRC SECURITY MODE CMP

RRC CONN RECFG

RRC CONN RECFG CMP INITIAL UE CONTEXT SETUP RSP

Direct transmission (service negotiation & notification) SAEB SETUP REQ RRC CONN RECFG RRC CONN RECFG CMP SAEB SETUP RSP

capability query.

Uplink information transfer 

UPLINK NAS TRANSPORT

 

Access Procedure – Procedure – TAU Introduction to the Access Procedure  A tracking area (T (TA) A) is used to manage the UE location. Multiple TAs constitute a TAL. Afte Afterr the UE attaches to the network, the MME assigns ass igns TAL resource to the UE. If moving out of the local TAL, the UE performs TAU. A UE in idle state performs periodic T TAU. AU.  The RRC connection setup cause value is Mo-

Signaling.  The TAU procedure consists of three steps:  Random access  RRC conn connectio ection n set setup up  TAU

The TAU TAU procedure requires no authentication and bearer setup. After the TAU procedure is complete, the connection is released.

 

Details of the Access Access Procedure – Procedure  – Random Access Procedure • Objectives of random access • Synchronizing uplink transmission • Obtaining uplink scheduling resources

• Scenarios of random access • Initial access in idle mode • RRC reconnection upon radio link failure • Handover to new cells • Downlink data transmission in uplink unsynchronized state • Uplink data transmission in uplink unsynchronized state

• Two types of random access

• Contention-based (applicable to all scenarios) • Contention-free (applicable to handover or downlink data transmission)  

Details of the Access Procedure – Procedure – Random t he Access Access Procedure 

Differences of contention-based and contention-free random accesses Preamble selection The preamble is selected by the network for contention-free random access.  The preamble is randomly selected by the UE for contention-based random access.  Contention conflict risk  Contention-free: The network ensures no conflict for a certain time.







Contention-based: Conflict risk is generated. UE

1

eNB

UE

eNB

Random Access Preamble

0 Random Access Response

RA Preamble assignment

2

Random Access Preamble 3

Scheduled Transmission

Contention Resolution

4

2

Random Access Response

1

Contention-based random access

Contention-free random access

 

Details of the Access Procedure – Procedure – Random t he Access Access Procedure Preamble

PRACH CONFIGURATION INDEX = 6

format 0 1ms PUCCH

eNodeB supports the following following configurations: 

Preamble formats 0 to 3



PRACH periods: 10ms, 5ms



Random access procedure: contention-based and contention-free

F  r    e   q  u  e n  c    y 

PUSCH

PRACH

6 RBs

PUCCH

Tim Time

RACH Slot

RACH Slot

RACH period period (5 ms) Fram Frame e (10ms )

 

he Access Access Procedure – Procedure  – RRC Details of tthe Connection Setup Procedure UE

EUTRAN

UE

EUTRAN

 

 RRCConnectionRequest

 RRCConnectionRequest  

 RRCConnectionSetup 

 RRCConnectionReject  RRCConnectionSetupComplete

RRC connection failure procedure RRC connection success procedure

• Objectives •

To set up SRB1.

•

The UE sends the initial NAS message to the network.

• Key Information Elements •

UE-identity (RRCConnectionRequest and RRCConnectionSetup)

•

establishmentCause (RRCConnectionRequest)

•

radioResourceConfiguration radioResourceConfigu ration for Only SRB1 (RRCConnectionSetup)

•

selectedPLMN-Identity (RRCConnectionSetupComplete) (RRCConnectionSetupComplete)

•

nas-DedicatedInformation (RRCConnectionSetupComplete) (RRCConnectionSetupComplete)

 

Access Procedure – Procedure  – RRC Details of the t he Access Connection Setup Procedure Content of the RRC_Conn_Req message

Cause values of the RRC_Conn_Req message

 The ue-Identity of the RRC_Conn_Req message is S-TMSI if the S-TMSI stored in the UE is a valid

value or a random value if else.  The establishmentCause of the RRC_Conn_Req message depends depends on the type of the NAS

procedure. Different NAS procedure to different Extended Service Request of thecorresponds NAS procedure is usedestablishmentCause. for CS fallback of a voice service.  The

 

Details of the Access Procedure – Procedure – RRC t he Access Connection Setup Procedure Counters measured during the RRC connection setup procedure [Point A] When the cell receives the RRC Connection Request message [Point B] W hen the cell receives the RRC Connection Request message and delivers the RRC Connection Setup message to the UE

 

Details of the Access Access Procedure – Procedure  – NAS Procedure 





UE

The NAS procedure is an interaction betwee between n the UE and EPC, including authentication, security-mode procedure, identity procedure, and APN procedure. The authentication procedure generates generates a new set of keys; the security-mode procedure validates the security context generated from the new keys; in the identity procedure, the EPC obtains necessary information from the UE. During the NAS procedure, the eNodeB transparently transmits the uplink and downlink messages, except that the eNodeB needs to select a EPC node for S1 Flex or MOCN network. The following describes the authentication and securitymode procedures:

E-NODEB

MME

RRC CONN SETUP REQ

RRC CONN SETUP RRC CONN SETUP CMP

INITIAL UE MESSAGE S1AP_DL_NAS_TRANS

Authentication

S1AP_UL_NAS_TRANS S1AP_DL_NAS_TRANS S1AP_UL_NAS_TRANS

Encryption

Initial_Context_Setup_request

1. The MME initiates the AKA procedure and sends the AUTH REQ message that contains the RAND RAND and AUTN necessary for authentication. 2. The UE receives the AUTH REQ message message and sends the AUTH RES message containing the RES RES parameters. 3. If the MME receives receives the AUTH RES message, message, it triggers the security-mode procedure; if it fails to rec receive eive the  AUTH RES message, itit sends the AUTH REJ message.

4. Upon recepti reception on of the SMC SMC message, message, th the e UE does the the following following:: a) Calculates the KnasEnc and KnasInt according to the S Selected elected NAS security algorithms IE of the SMC message. b) Checks the validity validity of the UE security capabilities a and nd KSI IEs. IEs. If valid, the UE sends the MME SECURITY MODE COM COMPLETE PLETE message; if invalid, the UE sends the SECURITY MODE REJECT message.

 

Details of the Access Procedure – Procedure – e-RAB t he Access Setup Procedure 

Counters during e-RAB setup When the eNodeB receives the INITIAL CONTEXT SETUP [Point A]measured 



REQUEST or E-RAB SETUP REQUEST message from the MME, the t he number of e-RAB setup attempts increments by 1. If the message requires setup of multiple e-RABs, the counter is separately calculated for each QCI and the calculation results of all al l QCIs are summed up. [Point B] When the eNodeB receives the INITIAL CONTEXT SETUP RESPONSE or E-RAB SETUP RESPONSE message from the MME, the number of successful e-RAB setups increments by 1. If the message requires setup of multiple e-RABs, the counter is separately calculated for each QCI and the calculation results of all QCIs are summed up.

 Key information elements •

SAE Bearer Level QoS parameters (contained in the context request message)

•

Transport Layer Address (contained in the context request and response messages)

•

NAS-PDU (contained in the context request message)

•

Security key (contained in the context request message)

•

UE Radio Capability (contained in the context request message, optional)

 

Details of the Access Procedure – Procedure – e-RAB Setup Procedure UE

EUTRAN

MME

UECapabilityEnquiry

UECapabilityInformation UE Capability Ind

•

When the UE initiates the Attach procedure, the Initial Context Setup Request message sent by the EPC does not contain c ontain the UE capability. capability. The eNodeB queries the UE about UE capability; the UE reports UE capability c apability to the eNodeB; and the eNodeB sends the UE capability contained in the UE Capability Indication message over the S1 interface to the EPC.

•

During the Attach procedure, failure of the UE capability query procedure causes e-RAB setup failure.

•

During the Idle-to-active procedure, the EPC sends the Initial I nitial Context Setup Request message

containing the UE capability to the eNodeB. The eNodeB does not need to query the UE capability,, saving the Uu interface resources. capability

 

t he Access Details of the Access Procedure – Procedure – e-RAB Setup Procedure UE

EUTRAN

UE

EUTRAN

 

SecurityModeCommand

SecurityModeCommand

SecurityModeFailure

SecurityModeComplete

Security mode success procedure

Security mode failure procedure

• Objectives • The security mode procedure is used to activate the encryption and integrity protection at the access stratum. Note that the security mode of the access

stratum and that of the NAS are two independent procedures. • There are three algorithms: null encryption encryption,, AES, and Snow 3G. • Time to start the security mode •  After setting up SRB1 and before setting up up SRB2 • For the security protection, the protection is started by the security mode

command or security mode complete message; encryption is i s started by the message next to the security mode procedure. • Integrity protection is used by SRB and encryption is used by SRB and DRB.  

t he Access Details of the Access Procedure – Procedure – e-RAB Setup Procedure UE

EUTRAN

UE

EUTRAN

 

 RRCConnectionReconfiguration  RRCConnectionR econfiguration

 RRCConnectionReconfigurationComple  RRCConnectionRe configurationComplete te

 RRCConnectionReconfiguration  RRCConnectionReconfigurati on

RRC connection re-establishment

• Objectives •

During the access procedure, the SRB2 and DRB are set up in tthe he RRC connection reconfiguration procedure.

•

If the reconfiguration fails, the UE initiates the RRC connection reestablishment procedure.

• Key information elements •

radioResourceConfiguration radioResourceConfigura tion (for SRB2 and possibly DRBs) (contained in the default bearer setup)

•

nas-DedicatedInformation (contained in the default bearer setup)

The RRC connection reconfiguration is used to configure the following: • measurementConfigu measurementConfiguration ration (contained in the t he measurement control) •

mobilityControlInformation mobilityControlInformati on (contained in the handover command) command)

 

Overview of Access Problems   An access failure occurs if a UE initiates a service but fails to set up the the service.  Measurement of access failures

rat e and e The access failure is measured by two counters: RRC connection setup success rate RAB setup success rate. The access success rate is obtained by multiplying the two.  The random access procedure is not measured by the access setup success suc cess rate due to the

random nature.

 The NAS failure is not measured by the t he RRC connection setup success rate.  Therefore, the access success rate in the t he traffic statistics cannot fully reflect the user

experience.  Measurement of access failures during a drive test  In a drive test, the messages are traced on both the eNodeB and UE. An access success or

failure can be determined by checking the signaling messages.  The drive test software automatically determines an access failure and calculates the access

success rate.  In contrast to traffic measurement, the drive test tes t measurement identifies an access failure

caused by NAS failure or by random access failure.

 

Problems – Random Symptoms of Access Problems – Access Failure  Symptoms of a random access failure

The symptom is that the eNodeB fails to receive the RRC Connection Request message. A random access failure can be inferred by only examining the traffic statistics; no L3 message is traced by the eNodeB. Some details of a random access failure can be observed on a test UE.  Causes of a random access failure •

The UE does not support some specific band.

•

The UE is frequency-locked; the test UE uses some special bandwidth parameters.

•

The UE is at the t he cell edge and the uplink and downlink path loss is large.

•

The cell is sleeping.

 Symptoms of a sleeping cell

No user accesses the cell, no alarm. Traffic measurement shows that the number of RRC

connections is 0, which indicates either cell exception or no users in the cell. History traffic measurement shows that there were UEs accessing the cell but beginning from a certain

moment, no UE accesses the cell.

 

Problems – RRC Symptoms of Access Problems – Connection Setup Failure  The symptoms of an RRC connection setup failure on the eNodeB are as follows:

•

 After delivering the RRC_CONN_SETUP message, the eNodeB fails fa ils to receive the RRC_CONN_SETUP_CMP message.

•

The eNodeB sends the RRC_CONN_REJ message, indicating that the eNodeB is faulty.

The following figure shows the messages of these two failures over the Uu interface.

Counters of the RRC connection setup failures

 

Problems – NAS Failure Symptoms of Access Problems –  The NAS procedure consists of all interactions interactions beginning from the Ue_Initial_Message sent by the eNodeB to the

Initial_Ue_Context_Setup_Req Initial_Ue_Conte xt_Setup_Req message sent by the EPC.  The symptoms are as follows:

•

In case of an authentication failure, the EPC sends the release message that is not sensed by the eNodeB.

•

In case the direct message between the UE and EPC fails to be transmitted over the Uu Uu interface, the failure is sensed by the eNodeB eNodeB and the eNodeB sends the release release request request to the EPC.

•  Absence or slowness in in response of the EPC is sensed by the eNodeB. The eNodeB sends the release request to the EPC.

•  An NAS failure is not measured by the eNodeB traffic measurement, but by the EPC and UE. UE.

 

Problems – e-RAB Symptoms of Access Problems – Setup Failure e-RAB -RAB setup procedure beginning from reception  An e-RAB setup failure occurs if any step of the e of the Initial_Ue_Context_Setup_Req Initial_Ue_Context_Setup_Req or E-RAB SETUP REQUEST message to sending of a response message fails.  Symptoms of an e-RAB setup failure over the Uu interface are as follows: 

During the security procedure, the UE does not send the Complete message or sends a failure message.



During the DRB setup reconfiguration, the UE does not send the Complete message or initiates a reconnection.



During the UE capability query, the UE does not reply.

 Counters of the e-RAB setup failure

 

Symptoms of Access Problems – Problems  – e-RAB Setup Failure  Symptoms of an e-RAB setup failure over the S1 interface are as follows:  The GTP-U resource request fails.  The EPC is exceptional, such as delivering incorrect parameters.  The radio resource request fails.

 

Troubleshooting the Access Problem by Analyzing the Data Sources  Step 1: Determine the scope of the access problem: Analyze problem: Analyze the traffic statistics to

determine the scope of the access problem, whether it is i s a top-cell or top-site problem, entire-network problem, comprehensive problem, or top-terminal/top-UE problem. Note: 1. The analysis method varies for different scenarios. In a scenario of degraded performance after upgrade, you need to compare the differences before and after the upgrade to determine the scope of the degradation. In a scenario of inventory optimization where the access performance is below expectation or to be improved, you need to determine the region of performance degradation. 2. The access problem of a top cell, entire network, or a comprehensive problem can be analyzed by using the traffic statistics. The performance degradation of some terminal types or some UEs is analyzed by using KPI.

 Step 2: Classify the causes of an access problem: Analyze problem: Analyze the data sources sources to classify

the causes of an access problem.  Step 3: Do as required by the checklist: Do as required by the checklist to determine the

root cause and the closing action.

 Step 4: Close the problem: Close the problem and evaluate the result. If the result is is

unsatisfactory,, repeat the preceding steps. unsatisfactory

 

Determining the Scope of an Access Access Problem – Problem – Principles of Selecting Top Cells, Sites, etc The principles of selecting top cells or sites vary for different scenarios.

 Scenario 1: Performance degradation in the time dimension: After dimension: After an upgrade, the

access performance degrades, or degrades suddenly due to unknown reasons. Principles: Calculate the difference of the counters (access success rate and access failure count) before and after the upgrade of each cell. Sort the cells by the difference of the access success rate and the difference of the access failure count to obtain the top cells of degraded access success rate and top cells of access failure count. The principles of selecting top terminal types and top UEs are similar. si milar.

 Scenario 2: Performance degradation in an inventory optimization: The access

performance of the live network is below expectation and needs to be optimized to the target value.

Principles: Sort the cells by the access failure fail ure percentage and access failure count to obtain the top cells of degraded access success rate and top cells of access failure fail ure

count. The principles of selecting top terminal types and top UEs are similar.  

Determining the Scope of an Access Access Problem – Problem  – Criteria  Top-cell problem: After one-fifth of the top cells of low access success rate and high

access failure count are removed from calculation of the entire-network entire -network access performance, if the performance is significantly si gnificantly improved to the expected value, the

access problem is defined as a top-cell problem.  Entire-network problem: After one-fifth of the top cells is removed from calculation c alculation of the

entire-network access performance, if the performance is i s not significantly improved, the problem is defined as an entire-network problem.  Comprehens Comprehensive ive problem: After one-fifth of the top cells is removed, if the access

performance is improved a little to a value slightly below the expected value, the problem is defined as a comprehensive (top-cell plus entire-network) problem.  Top-terminal or top-UE problem: After one-fifth of the top terminals or top UEs are

removed from calculation of the entire-network access acc ess performance, if the performance is significantly improved to the expected value, the problem is defined as a top-terminal top -terminal

or top-UE problem.

 

Classifying the Causes of Access Problems 

 After determini determining ng the data scope of the the access analyze the following sources to infer problem, the causes of the problem:  Traffic measurement  Signaling  Drive test data

 

Traffic Statistics to Infer Causes Analyzing the Traffic  Analyzing the traffic statistics • Determine whether the RRC connection setup procedure, e-RAB setup procedure,

or both, is faulty. • In case of faulty RRC connection setup procedure, analyze the traffic statistics to

derive the causes of the failure.

• In case of e-RAB setup failure, analyze the traffic statistics to derive the causes.

 

Detecting Sleeping Cells by Analyzing Traffic Statistics  Obtain the following counters from the OSS at a period of hours for a duration of

one week. Number of received RRC Connection Request messages (excluding retransmission) Number of received contention-based contention-based preambles (Group (Group A) Number of received contention-based preambles (Group B) Number of transmitted RARs to contention-based preambles(Group preambles(G roup A) Number of transmitted RARs to contention-based preambles (Group B) Number of received contention-free preambles Number of received contention-free contention-free preambles (handover) Number of transmitted RARs to contention-free preambles Number of transmitted RARs to contention-free preambles (handover) Number of received MSG3 messages triggered by handover 

 Analyze the traffic statistics

Check the traffic statistics of the latest one week for change of user access, taking into account the differences of weekdays and weekends. If the cell used to work normally but,

beginning from a certain moment, user access is suddenly absent or gradually decreases to zero and the number of random access preambles is unchanged, this cell is very likely a sleeping cell.  

Analyzing the Signaling Trace to Derive Causes of Access Failures  The signaling trace clearly shows at which step the access procedure fails and is very

effective for diagnosing a drive test problem or reproducible problem. The two

constraints are that the trace must be started before the problem occurs and manual analysis is required.

• Standard interface trace (a major means): Analyze the traffic statistics to derive the

top cells and top time segments. Start standard interface trace for the top cells and

at the top time segments to check at which step the access procedure fails.

• Single-UE entire-network trace (a minor means): Use the TMSI of a top UE as an

input to obtain the IMSI from the EPC. Star the user trace in the entire network. This means is effective for guaranteeing services to VIP users.

• Cell trace (a minor means): Start cell trace for the top cells cell s and at the top time segments to determine the link quality and scheduling of the failed UE.

 

Analyzing Drive Test Data to Derive Causes of Access Failures  Compared with the signaling trace of the eNodeB, the benefits of drive dri ve test data are

that in addition to signaling trace, signal strength and scheduling information are available, depending on the drive test software and terminal type. The disadvantage is

that in terms of signaling trace, only Uu interface trace is available. Therefore, Therefore, signaling trace and drive test usually work together. •

Determine whether it is an NAS or AS problem: Analyze Analyze the signaling procedures to determine whether it is an NAS or AS problem. An NAS problem is indicated by a failure at the NAS, suc such h as authentication failure, and is strongly correlated to subscription.

•

In case of an AS problem, determine whether it is an L3 problem. An L3 problem is indicated by reply of a failure message or no reply. A problem below L3 is indicated by scheduling failure or poor signaling strength that leads to message transmission failure.

•

In case of an L3 problem, a common cause is failure of the security procedure. Check consistency of the security algorithm settings on the eNodeB and UE.

•

In case of a problem below L3, check the RSRP and SINR of the venue to determine whether

the problem is caused by interference or weak coverage.

 

Suggestions for Solving a Coverage Problem  The symptom is poor link quality caused by unbalanced uplink and downlink or weak

coverage. • The symptoms of poor uplink are minimum RB cou count, nt, MCS 0, PHR be below low 0 dB,

high uplink BLER, high CRC error rate, and negative SINR as shown in the CHR. • The symptoms of poor downlink are poor CQI or the HARQ receives a lot of DTX

and NACK messages from the UE. • Insufficient uplink means that the uplink is poor and the downlink is satisfactory; s atisfactory; insufficient downlink means that the uplink is satisfactory and the downlink is poor poor..

Weak coverage means that both the uplink and downlink are poor.  In case of insufficient uplink, the solutions are as follows:

•  Add eNodeBs, reduce uplink path loss, add TMAs, add uplink signal signal compensation.  In case of insufficient downlink, the solutions are as follows:

•  Add eNodeBs, reduce reduce downlink p path ath loss, increas increase e pilot power, power, increase the radius

of downlink cell coverage.

 In case of insufficient coverage, the solutions are as follows:

•  Add eNodeBs, increase coverage. coverage.

 

Troubleshooting Service Drops Service drop rate is an important key key performance indicator (KPI) for radio networks. It indicates the ratio of the number of dropped services to the total number of services. A high service drop rate cannot meet user requirements. A service drop is is counted each time the eNodeB sends an E-RAB RELEASE RELEASE INDICATION INDICA TION or UE CONTEXT RELEASE COMMAND message to the MME with a release cause other than Normal Release, Detach, User Inactivity, cs fallback triggered, and Inter-RAT redirection after an E-UTRAN radio access bearer (E-RAB) has been successfully set up for a UE.

 

Possible Causes

 

Troubleshootin roubleshooting g Flowchart

Ask As k ffor or God God Help Help

 

Network Optimization Methods Tilt Adjustment

Power Adjustment

 Antenna Height

 Azimuth Adjustment

Network Optimization

Reselection and Handover Parameter Adjustment

Feature Configuration

RF optimization involves adjustment of azimuths, tilts, antenna height, eNodeB transmit power, feature algorithms, and performance parameters. Optimization methods in different standards are similar, but each standard has its own ow n measurement definition.

 

RSRP Reference signal received power (RSRP), is determined for a considered cell as the linear average over the power

3GPP definition

contributions (in [W]) of the resource elements that carry cellspecific reference signals within the considered measurement frequency bandwidth.



Note: Different from GSM or TD-SCDMA systems, TD-LTE systems have multiple subcarriers multiplexed. Therefore, the measured pilot signal strength is the RSRP of a single subcarrier (15 kHz) not the total bandwidth power of the frequency frequency..

The RSRPs near a cell, in the middle of a cell, and at the edge of a cell are determined based on the distribution of signals on the entire network. Generally, Generally, the RSRP near a cell is -85 dBm, the RSRP in the middle of a cell is 95 dBm, and the RSRP at the edge of a cell is -105 dBm.

Currently,, the minimum RSRP for UEs to camp on a cell is 120 dBm. Currently 

Empirical RSRP at the edge of a cell: The RSRP is greater than -110 dBm in 99% areas at the TD-LTE site in Norway. Norway. The RSRP is greater than -110 dBm in 98.09% areas in the Huayang field in Chengdu.

 

SINR The SINR is not specifically defined in 3GPP specifications. specif ications. A common formula is as follows: SINR = S/(I + N)  S: indicates the power of measured usable signals. Reference signals (RS) and physical

downlink shared channels (PDSCHs) are mainly involved.  I: indicates the power of measured signals or channel interference signals from other cells in the

current system and from f rom inter-RAT inter-RAT cells. N: indicates background noise, which is related to measurement bandwidths and receiver noise  coefficients.

Empirical SINR at the edge of a cell:

The SINR is greater than -3 - 3 dB in 99% areas in Norway. Norway. The SINR is greater than -3 - 3 dB in 99.25% areas in the Huayang field in Chengdu.

 

Handover Success Rate  According to the signaling process in 3GPP TS 36.331, eNodeB deB stat statisti istics cs  eNo (1) Handover success rate = Number of handovers/Number of handover attempts x 100%

(2) Number RRCConnectionReconfiguration of handover attempts: indicates the number for of eNodeBtransmitted messages handovers. (3) Number of handovers: indicates the number of eNodeB-received RRCConnectionReconfigurationComplete RRCConnectionReconfigurationComple te messages for handovers.

 

Subcarriers share the transmit power of an eNodeB, and therefore the transmit power of each subcarrier depends on the configured system bandwidth (such as 5 MHz and 10

Definitions in 3GPP specifications

MHz). A larger bandwidth will result in lower power of each subcarrier. LTE LTE uses PA and PB parameters to adjust power. ρA: indicates the ratio of the data subcarrier power of OFDM symbols excluding pilot symbols to the pilot subcarrier power. ρB: indicates the ratio of the data subcarrier power of OFDM symbols including pilot symbols to the pilot subcarrier power.

Service power configuration (calculating PDSCH power based

on RS power) RS power PA and PB are delivered using RRC signaling. For two antennas, PA is ρA and ρB is calculated based on the right righ t table. PDSCH power is calculated based on PA and PB. Currently, it is recommended that PB be set to 1 dB and PA be set to -3 dB. That is, the pilot power for symbols including pilot symbols accounts for 1/3. This setting optimizes network

Control channels

performance and ensures that the pilot power for Type A and

Power of PDCCHs, PHICHs, PCFICHs,

Type B symbols is equivalent to the service channel power. In scenarios with special requirements, for example, in rural

PBCHs, primary synchron synchronization ization channels,

 

scenarios requiring low edge rates, PB can be set to 2 or 3 dB to

and secondary synchronization channels is

enhance coverage.

set using an offset from f rom RS power.

lassification of overage Problems (RSRP is mainly involved) Weak coverage and coverage holes Continuous coverage must be ensured.

Cross coverage

Imbalance between uplink and downlink

Lack of a dominant cell

The actual coverage must be consistent with the planned one to prevent service

Uplink and downlink losses must be balanced to resolve uplink and downlink

Each cell on a network must have a dominant coverage area to prevent frequent

drops caused by isolated islands during handovers.

coverage problems.

reselections or handovers caused by signal changes.

 

Factors Affecting Coverage Coverage 2

1 Downlink: •Equivalent isotropic radiated power (EIRP) •To Total tal transmit power  pow er  •Combining loss •Path loss (PL) •Frequency band •Distance between a receive point and an eNodeB •Scenarios (urban and suburban areas) and terrains (plains, mountains, and hills) of electric wave propagation •Antenna gain •Antenna height •Antenna parameters (antenna pattern)

Uplink: ••eNodeB Antennareceiver diversitysensitivity gain •UE transmit power  •Propagation loss of uplink radio signals •Impact of tower-mounted amplifiers (TMAs) on uplink

•Antenna tilt •Antenna azimuth

 

Weak Coverage and Coverage Holes The signal quality in cells is poorer than the optimization baseline in an area.

Weak coverage

As a result, UEs cannot be registered with the network or accessed services cannot meet QoS requirements.

If there is no network coverage or coverage levels are excessively low in an area, the area is called a weak coverage area. The receive level of a UE is less than its minimum access level (RXLEV_ACCESS_MIN) because downlink receive levels in a

Coverage holes

weak coverage area are unstable. In this situation, the UE is disconnected from the network. After entering a weak coverage area, UEs in connected mode cannot be handed over to a high-level cell, and even service drops occur because of low levels and signal quality. quality.

 

Resolving Weak Coverage Problems

Analyze

geographical

Deploy

new eNodeBs if

Use

RRUs, indoor

environments and check the

coverage hole problems

distribution systems, leaky

receive levels of adjacent

cannot be resolved by

feeders, and directional

eNodeBs.

adjusting antennas.

antennas to resolve the

Increase

problem with blind spots in

Analyze ze Analy

the EIRP of each

coverage by

sector based on parameter

adjacent eNodeBs to achieve

elevator shafts, tunnels,

configurations and ensure

large coverage overlapping

underground garages or

EIRPs can reach maximum

between two eNodeBs and

basements, and high

values if possible.

ensure a moderate handover

buildings.

Increase

pilot power. Adjust antenna azimuths and

area. Note: Increasing coverage

Analyze

tilts, increase antenna height,

may lead to co-channel and

coverage.

and use high-gain antennas.

adjacent-channel interference.

the impact of scenarios and terrains on

 

Case: Searching for a Weak Coverage Area by Using a Scanner or Performing Drive Tests on UEs Perform drive tests in zeroload environments to obtain the of find signals testdistribution routes. Then, a on weak coverage area based on the distribution, as shown in the figure. Adjust RF parameters of the eNodeB covering the area.

Weak coverage area

 

Lack of a Dominant Cell In an area without a dominant cell, the receive level of the serving cell is similar to the receive levels of its neighboring cells and the receive levels of downlink signals between different cells are close to cell reselection thresholds. Receive levels in an area without a

Lack of a dominant cell

dominant cell are also unsatisfactory. The SINR of the serving cell becomes unstable because of frequency reuse, and even receive quality becomes unsatisfactory. unsatisfactory. In this situation, a dominant cell is frequently reselected and changed in idle mode. As a result, frequent handovers or service drops occur on UEs in connected mode because of poor signal quality. quality. An area without a dominant cell can also be regarded as a w weak eak coverage area.

 

Resolving Problems with Lack of a Dominant Cell Determine

cells covering an

Adjust engineering

area without a dominant cell

parameters of a cell that can

during network planning, and

optimally cover the area as

adjust antenna tilts and

required.

azimuths to increase coverage by a cell with strong signals and decrease coverage of other cells with weak w eak signals.

…

 

Case: Searching for an Area Without a Dominant Cell Symptom 

UEs frequently perform cell reselections or handovers between identical cells.   Analysis  Analysis can be based on signaling procedures and PCI distribution.  According to to PCI distribution distribution shown shown in the figure, PCIs alternate in two or more colors if there is no dominant cell.  Solution  According to the coverage plan, cell 337 is a dominant cell covering the area and cell 49 also has strong signals. To ensure

handovers between cells 337 and 49 at crossroads, increase tilts in cell 49.

Lack of a dominant cell

 

Cross Coverage Cross coverage means that the coverage scope of an eNodeB exceeds the planned one and generates discontinuous dominant areas in the coverage scope of other eNodeBs. For example, if the height of a site is much higher than the average height of surrounding buildings, its transmit signals propagate far along hills or roads and form dominant coverage in the coverage scope of other eNodeBs. This is an “island” phenomenon. If a call

Cross coverage

is connected to an island that is far away aw ay from an eNodeB but is still served by the eNodeB, and cells around the island are not configured as neighboring cells of the current cell when cell handover parameters are configured, call drops may occur immediately once UEs leave the island. If neighboring cells are configured but the island is excessively small, call drops may also occur because UEs are not promptly handed over. In addition, cross coverage occurs on two sides of a bay because a short distance between the two sides. Therefore, eNodeBs on two sides of a bay must be specifically designed.

 

Resolving Cross Coverage Problems Adjust

antenna azimuths

Adjust

antenna tilts or

Decrease

the antenna

properly so that the direction

replace antennas with large-tilt

height for a high site.

of the main lobe slightly

antennas while ensuring

Decrease

obliques from the direction of a street. This reduces

proper antenna azimuths. Tilt adjustment is the most

carriers when cell performance is not affected.

excessively far coverage by

effective approach to control

electric waves because of reflection from buildings on

coverage. Tilts are classified … into electrical tilts and

two sides of the street.

mechanical tilts. Electrical tilts are preferentially adjusted if possible.

transmit power of

 

Case: Cross Coverage Caused by Improper Tilt Settings  Symptom

 As shown in the upper right figure, cross coverage occurs in a cell whose PCI is 288. Therefore, the cell interferes with other cells, which increases the probability of service drops.   Analysis

The most possible cause for cross coverage is excessively antenna height or improper tilt settings. According to a check on the current engineering parameter settings, the tilt is set to an excessively small value. Therefore, it is recommended that the tilt be increased.

 Solution

 Adjust the tilt of cell 288 from 3 to 6. As shown in the lower right figure, cross coverage of cell 288 is significantly reduced after the tilt is adjusted.  

Case: Inverse Connections Involved in the Antenna System  Symptom The RSRPs of cells 0 and 2 at the Expo Village site are low and high respectively in the red area shown in the figure. The signal quality of cells 0 and 2 is satisfactory in the areas covered by cells 2 and 0 respectively respectively..   Analysis  After installation and commissioning are complete, the RSRP in the direction of the main lobe in cell 0 is low. After After cell 0 is disabled and cell 2 is enabled, the RSRP in cell 2 is normal and the SINR is higher than that tested in cell 0. Therefore, this problem may occur because the antenna systems in the two cells are connected inversely. Test results are as expected after optical fibers on the baseband board are swapped.  Solution Swap optical fibers on the baseband board or adjust feeders and antennas properly properly.. It is recommended that optical fibers on the baseband board be swapped because this operation can be performed in the equipment room.  Suggestions Network planning personnel must m ust participate in installation. Alternat Alternatively ively,, customer service personnel have detailed network planning materials and strictly supervise project constructors for installation. After installation is complete, labels must be

attached and installation materials must be filed.

 

Imbalance Between Uplink and Downlink When UE transmit power is less than eNodeB transmit power, UEs in idle mode may receive eNodeB signals and successfully register in cells. However, the the eNodeB cannot receive uplink signals because of limited power when UEs perform random access or upload data.

Imbalance between uplink and downlink

In this situation, the uplink coverage distance is less than the downlink coverage distance. Imbalance between uplink and downlink involves limited uplink or downlink dow nlink coverage. In limited uplink coverage, UE transmit power reaches its maximum but still cannot meet the requirement for uplink BLERs. In limited downlink coverage, the downlink DCH transmit code power reaches its maximum but still cannot meet the requirement for the downlink dow nlink BLER. Imbalance between uplink and downlink leads to service drops. The most common cause is limited uplink coverage.

Uplink coverage areaDownlink coverage area coverage area  

Resolving Problems with Imbalance Between Uplink and Downlink If

no performance data is available for

If

uplink interference leads to imbalance

RF optimization, trace a single user in the

between uplink and downlink, monitor

OMC equipment room to obtain uplink

eNodeB alarms to check for interference.

measurement reports on the Uu interface, and then analyze the measurement

Check

reports and drive test files.

imbalance between uplink and downlink is

If

caused by other factors, for example, uplink

performance data is available, check

each carrier in each cell for imbalance

whether equipment works properly and whether alarms are generated if

between uplink and downlink based on

and downlink gains of repeaters and trunk amplifiers are…set incorrectly, incorrectly, the antenna

uplink and downlink balance measurements.

system for receive diversity is faulty when reception and transmission are separated, or power amplifiers are faulty. If equipment works properly or alarms are generated, take measures such as replacement,

isolation, and adjustment.

 

Signal Quality (SINR is mainly involved)

   

Frequency plan

Cell layout

⑤ ⑥

③

Site

④

selection Antenna height

Antenna azimuths Antenna tilts

 

Resolving Signal Quality Problems Caused by Improper Parameter Settings Optimizing frequencies Adjusting the antenna

Change and optimize frequencies based on drive test and performance measurement data.

Adjust antenna azimuths and tilts to change the distribution of signals in an interfered area by increasing the level of a dominant sector and decreasing levels of other sectors.

system Adding dominant coverage

Increase power of a cell and decrease power of other cells to form a dominant cell.

Decrease RS power to reduce coverage if the antenna pattern is distorted because

Adjusting power 

of a large antenna tilt. Power adjustment and antenna system adjustment can be used together.

 

Case: Adjusting Antenna Azimuths Azimuths and Tilts to Reduce Interference Symptom Cross coverage occurs at sites 1, 2, 3, 7, 8, 9, 10, 11, and 12, and co-channel co -channel interference occurs in many areas.  Analysis  According to the analysis analysis of engineering parameters parameters and drive test data, cel celll density is large in coverage areas. Coverage by each cell can be reduced r educed by adjusting antenna azimuths and tilts.  Solution Change the tilt in cell 28 from 2 degrees to 4 degrees so that the direction points to a demonstration route. Change the tilt in cell 33 from 3 degrees to 6 degrees so that the direction direct ion points to the Wanke Pavilion. Change the tilt in cells c ells 50 and 51 from 3 degrees to 6 degrees so that the direction points to the Communication Pavilion. Pavilion. Decrease the transmit power in c cell ell 33 by 3 dB to reduce its interference to overhead footpaths near China Pavilion. 

Poor signal

quality before optimization

SINR before optimization in Puxi

SINR after optimization in Puxi

 

Case: Changing PCIs of Intra-frequency Cells to Reduce Interference  Symptom

Near Japan Pavilion, UEs access a cell whose PCI is 3 and SINRs are low. UEs are about 200 m away from the eNodeB. This problem may be caused by co-channel interference.   Analysis

This problem is not caused by co-channel interference because no neighboring cell has the same ffrequency requency as the current cell. Cell 6 interferes with cell 3. SINRs increase after cell 6 is disabled. In theory theory,, staggered PCIs can reduce interference.  Solution

Change PCI 6 to PCI 8. Test results show that SINRs increase by about 10 dB.

SINR when cell 6 is enabled

SINR when cell 6 is disabled

SINR when PCI 6 is changed to PCI 8

 

Case: Handover Failure Caused by Severe Interference Symptom 

During a test, handovers from PCI 281 to PCI 279 fail.   Analysis

Cell 281 is a source sourc e cell and is interfered by cells 279 and 178. Delivered handover commands always fail and cannot be received correctly by UEs. Cell 279 is a target cell for handover, and its coverage is not adjusted preferentially because the signal strength in the handover area can ensure signal quality after handovers. Therefore, cell 178 must be adjusted to reduce its interference to cell 281. 

Solution  Adjust antenna tilts to decrease coverage by cell 178.

 

 Analysis of Handover Handover Succe Success ss Rate Problems

Poor handovers

Handover validity 1. Neighboring cell validity 2. Average receive level for handovers 3. Average receive quality for handovers 4. Ratio of the number of handovers to the number of calls 5. Measurements on neighboring cell handovers not defined

Interference 1. Uplink interference bands 2. Receive level and quality of carriers 3. Number of handovers because of poor uplink and downlink quality 4. Average receive level and power level for handovers

Coverage 1. Cross coverage 2. Imbalance between uplink and downlink 3. Receive level measurements 4. Receive quality measurements 5. Receive levels of neighboring cells 6. Average level and TA when service drops occur 

Neighboring cell optimization must be performed to ensure that UEs in idle or connected mode can promptly perform reselection to or be handed over to optimal serving cells. This helps achieve continuous coverage. In addition,

problems with delay, delay, ping pong, and non logical handovers can be resolved by optimizing coverage, interference, and handover parameters.

 

Handover Problem Analysis 

Checking handover validity

Obtain source and target cells using drive test software s oftware and then check whether handovers are performed between two cells that are geographically far using Mapinfo. 

Checking interference

Check interference in both source and target cells because handover failures may be caused c aused by uplink or downlink interference. 

Checking coverage

Check source and target cells for cross coverage, imbalance between uplink and downli downlink, nk, and carrier-level receive quality and level.



Check contents Check handovers based on RSRPs measured in UE drive tests.

1. Verify that RSRPs in the expected source and target cells are maximum. 2. Verify that the absolute RSRPs in the source and target t arget cells are reasonable at a handover point. In other words, handovers are not allowed if signal quality is excessively poor. Specific RSRPs RSRPs are determined based on the entire RSRPs on a network.

 

Case: Service Drops Caused by Missing Neighboring Cell Configuration  Symptom

 As shown in the upper right figure, a UE sends multiple measurement reports but is not handed over, which may be caused by missing m issing neighboring cell configuration.   Analysis

 According to measurement measurement reports, the UE sends an A3 report of cell 64. However, the RRCConnectionReconfiguration message in the lower right figure shows that the current cell is cell 278 (the first cell) and cell 64 is not included in the message. This indicates that cells 278 and 64 are not configured as neighboring cells. Neighboring cell configuration on live networks can be

checked for further confirmation.  Solution

Configure cells 278 and 64 as neighboring cells.

 

Overview of Handover  While a UEtomoves outconnection the sourcetocell, UE performs the t he handover procedure change the anetwork. The following figure shows the schematic diagram.

In the LTE system, the handover procedure is controlled by the network (eNodeB). Therefore, When UE has accessed in the cell, the eNodeB needs tomeasurement monitor the quality of the radio environment. To otodo so,ythe t he sends a control message to indi indicate cate UET replay repla theeNodeB signal qua quality lity of eNodeB. Trigger: eNodeB uses event A3 to trigger an intra-frequency handover and

uses events A2 and A4 to trigger an inter-frequency handover handover..

common procedure of handover: measure control

report   —> handover decision —>handover perform   —>new measure control —

>measure

 

Types of Handovers Handovers in the LTE system Intra-RAT handovers

Frequency relationship: • Intra-frequency handovers • Inter-frequency handovers

Signaling bearers: • Intra-eNodeB handovers • Intra-MME X2-based handovers (the X2 interface is configured) • Intra-MME S1-based handovers (the X2 interface is

not configured) •Inter-MME S1-based handovers (the eNB belongs to the different MME) Inter-RAT handovers

cell1

cell2

•Not mentioned in this document

 

Measurement Events

 

Parameter Configuration for Intra-frequency Handovers Handover-related parameter configuration is used to control the probability of handover. and the time to send measurement reports. • Event A3 that triggers an intra-frequency handover  •The formula is list as below: 





  

Source eNB

UE

1.A3 Measurement Control

Measure RSRP/RSRQ

A3 EventTriger 

2.





the parameters in this expression are explained as follows: Mn: Measured RSRP/RSRQ of the neighboring cell Ofn: Frequency offset of the neighboring cell Ocn:cell offset of the neighboring cell Ms: Measured RSRP/RSRQ of the serving cell Ofs: Frequency offset of the serving cell Ocs: cell offset of the serving cell

 A3 Measurement Reports

Handover preparation



 Mn Ofn Oc Ocn n  Hy  Hyss  Ms Ofs Oc Ocss Off  

Target eNB

RRC Conn. Reconf. incl.  3 mobilityControlinformation

Random access procedure 4

RRC Con Conn. n. Rec Reconf onf.. Co Compl mplete ete

Hys: Hysteresis. Closely related to UE mobility. To reduce the

probability of ping-pong handovers.  Off: Event A3 offset

 

Parameter Configuration for Inter-frequency Handovers • Events that trigger an inter-frequency handover  • Event A2 that triggers GAP measurement •GAP has a period of 40 ms (default) and the other has a period of 80 ms.

 Ms  Hy  Hys   s  Thresh

• Event A4 that triggers an inter-frequency inter -frequency handover 

  n  Hy  Mn  Ofn  Oc Ocn  Hyss  Thresh

 

Intra-eNodeB Handover  The intra-eNodeB handover procedure is relatively simple. the intra-eNodeB handover only exchange signaling in Uu interface. the resources application between the source cells and the target cells completed through the internal eNodeB messages. and the resources release in the source cells also completed by the internal eNodeB messages.

In this procedure, there is no data retransmit at the and no message exchange at the inter-eNodeB, EPC.  

Intr In traa-eN eNode odeB B Hando Handove ver  r   

Source Cell

UE

Target Cell

Serving Gateway

MME/MMEs

eNB

 Area Restriction Provided

1. Measurement Control  packet data

 packet data

data The UE reports packet the Measurement result message to the source cell. Legend

UL allocation 2. Measurement Reports

L3 signalling

Measurement Reports

L1/L2 signalling

  n   o    i    t   a   r   a

  p   e User Data command after The eNodeBadmission sends a handover   r completing and radio resource    P   r   e allocation in the target cell.   v

3. HO decision

  o    d   n   a    H

Handover Command DL allocation 4. Handover Command

Buffer packets from MME

 packet data

Detach from old cell and synchronize to new cell

The UE accesses the target cell. 5. Synchronization 6. UL allocation + TA for UE

  n   o    i    t   u   c   e   x    E   r   e   v   o    d   n   a    H

The handover is complete, and the cell resources are released in the source cell.

7. Handover Confirm Handover Confirm

Flush DL buffer, continue

  n   o    i    t   e    l   p

delivering in transit packets

 packet data  packet data

  m   o    C   r   e   v   o    d

packet data  packet data

  n   a    H

 

Inter-eNodeB Handover on the X2 Interface The handover on the interface by the event A3 report , the target cell and the source cellX2 must belongistotriggered the two different eNodeBs which exist the X2 links.

when the source eNodeB receives the measurement reports by the UE and decides UE to hand over to the target eNodeB . The source e eNodeB NodeB applies fo forr resources through the X2 interface from the target eNodeB and completes the resource preparation for the target eNodeB . then, the source s ource eNodeB notifies the UE to hand over to the target eNodeB by the reconfiguration r econfiguration message through the Uu interface. After the handover has completed, the target eNodeB notifies the source eNodeB to release the radio resources in the source eNodeB . In addition, the data which is not transmitted entirely from the source eNodeB will retrans retransmit mit to the target eNodeB and update node relationship r elationship between the user plane and control plane.

 

Inter-eNodeB Handover On the X2 Interface (I)

 

The source eNodeB delivers measurement control information to UE and Source eNB UE notifies the UE to start the neighbor cell measurement.

The users access the network Target eNB

Serving

MME

Gateway

0. Area Rest Restrictio riction n Provided Provided 1. Meas Measurem urement ent Control Control

After receiving the HandoverReq message from

packet data

packet data

After detecting the cell measurement result that meet the threshold, the UE replies the Measurement Reports. Legend

 UL allocation start the handover preparation procedure, the source eNodeB transmits the Handover Request message to the L3 signalling target eNodeB which carries the current service information other accessmakes information including encryption, Theand source eNodeB handover decision Measur sureme ement nt Re Repo ports rts 2. Mea integrality, and measurement. based on the handover algorithm and current

The target eNodeB returns the admission results User Data resource configuration information to the source eNodeB. In this step, the preparation 5. Admis Admission sion Control Con of handover hastrolcompleted. The source eNodeB transmits the handover message from the Handover over Req Request uest Ack 6. Hand target eNodeB through the Uu interface to the UE and notifies that the UE executes the handover command. 4.

DL allocation 7. Detach from old cell and synchronize to new cell

L1/L2 signalling

state.

3. HO de decis cision ion

H an an do do ve ve r Rand eq ue eq ue st stradio

Hand Ha ndov over er Com Comma mand nd

the source eNodeB, the target eNodeB starts admission control based on the carrying service information then configures radio resources.   n   o    i    t   a   r   a   p   e   r    P   r   e   v   o    d   n   a    H

Deliver buffered and in transit packets to target eNB 8.

SN Status Transfer 

Data Forwarding

The data starts to be forwarding

  n   o    i    t   u   c   e   x    E   r   e   v   o    d   n   a

   H

Buffer packets from Source eNB 9. 1 0. 0.

Synchronisation U L a llo lloca catt io io n

+

TA f or or U E

 

Inter-eNodeB Handover on the X2 Interface(II) After UE and the target eNodeB complete the random access, the Handover Confirm message is transmitted to the target eNodeB.

 

UE

Source eNB

Target eNB

11. Han Handov dover er Con Confir firm m

MME

Serving

Gateway

After receiving the HandoverConfirm message from the UE, the target eNodeB starts the PathSwitch procedure to the MME to complete the user plane handover.

12. Path Switch Switch Request Request

Plane e update update 13. User Plan request

After completing the user plane End Marker  handover from the S-GW, the MME Switch DL path 14. transmits the PathSwitchRsp PathSwitchRsp message to the target eNodeB to notify that the 15.User Plane update user plane handover is complete. response

After the16.Path PathSwitch is complete, the target Switchmessage Request Ack eNB notifies the source eNodeB of releasing resources, and in this step the handover procedure 17. Release Resource Flush DL buffer, continue delivering in -transit packets

has completed.

Data Forwarding End Marker 

18. Rele Release ase

  n   o    i    t   e    l   p   m   o    C   r   e   v   o    d   n   a    H

Resources packet data

packet data

 

Inter-eNodeB Handover on the S1 Interface The S1 handover procedure is similar to the X2 handover procedure. The difference between them is that the Handover Handover Request Acknowledge, andRequest, data forwarding messages require to be transmit by the S1 interface, because there is no direct link(X2 link( X2 interface interface) eNodeB.) between source eNodeB and target

 

Troubleshooting Inter RAT Handover

Faults

Inter-RAT handover faults are system faults that cause handover initiation failure or handover failure. RAT is short for radio access technology

The following are symptoms of inter-RAT handover faults: 1. User Users s fi file le ser servi vice ce d dro rop p comp compla lain ints ts.. 2. The succ success ess rate of outgoing outgoing inter-RA inter-RAT T handover handovers s is low. 3. Signa Signaliling ng messag message e tracin tracing g resul results ts indic indicate ate that that handover procedures are incomplete or fail.

 

Troubleshootin roubleshooting g Flowchart

Ask As k ffor or God God Help Help

 

 Air interface Information Acquisition Identifying a measurement control & a measurement report obtain the air interface signaling by uu-trace or UE standard trace

If the RRC Connection Reconfiguration message contains the field of measConfig, this message is a measurement control message. If measId contained in the reportConfigId field.this is the handover measurement ID.

open a measurement report. If the measID contained in this report is the same as contained in the measurement control, the report is a response to the measure control

 

 Air interface Information Acquisition Identifying a handover command Double-click the RRC Connection Reconfiguration message following the Measurement Report message

The RRC Connection Reconfiguration message that contains the field of targetPhysCellId.this is a handover comma handover command nd from eNB.

 

Inter-frequency Handover Capability of the UE The inter-frequency handover capability of the UE is indicated by the feature group field f ield from UE_CAPABIUTY_INFO UE_CAPABIUTY_INFO .

Bits 13, 14, and 25 indicate the inter-frequency handover capability of the UE. For details, see 3GPP TS 36.331.

 

Statistics of the Handover Procedure (Outgoing Handover) The following describes traffic statistics for outgoing handover, taking intra-eNodeB and S1-based handovers as example. Point A: number of outgoing handover attempts. If the eNodeB receives measurement reports and makes a successful handover decision, this counter adds by 1. Point B: Number of executed outgoing handovers. After the eNodeB delivers the handover command, this counter adds by 1. Point C: Number of successful outgoing handovers. For intra-eNodeB handover, when when the eNodeB receives the RRC Connection Reconfiguration Reconfiguration Complete message from the UE, this counter adds by 1. For S1-based S1 -based handover,, when the eNodeB receives the UE Context Release message from the MME , this counter adds by 1. handover

counters of traffic statistics for IntraeNodeB handovers counters of traffic statistics for inter-eNodeB S1-based handovers

 

Statistics of the Handover Procedure (Incoming (I ncoming Handover) The following describes traffic measurement points for incoming handover, taking S1-based handover and X2based handover as examples. Point A: number of incoming handover attempts. When W hen the target eNodeB receives the Handover Request message, this counter adds by 1. Point B: number of executed incoming handovers. When the target eNodeB sends the Handover Request  Acknowledge message, message, this counter adds by 1. Point C: number of successful incoming handovers. For X2-based handover, when the target eNodeB sends the UE Context Release message to source eNodeB, this counter adds by 1. For S1-based S1 -based handover, handover, when the target eNodeB sends the Handover Notify message to the MME, this counter adds by 1.

Points of of tr traffic st statistics ffo or X2 X2-based ha handover

Points of of tr traffic s sttatistics fo for S S1 1-based handover 

 

Symptoms of a Handover Problem Observing a handover problem The procedure of one handover is indicated by air interface signaling

beginning from measurement reports and ending at the Handover Complete message. If a handover succeeds, the UE has disconnected from the source cell and

connected to the target cell to keep on services, as shown by change of the PCI. If a handover fails, the symptom is a call drop or RRC connection

reestablishment.

 A handover failure is often caused by lack of signaling messages over the S1

or Uu interface. Therefore, a common diagnosis method is to check which standard air interface signaling was lost.

 

Symptoms of a Handover Problem The following example was the logs at the UE and eNodeB when a handover failure occurs.

Loss of measurement reports If the UE sends measurement reports that are not received by the eNodeB, the traced signaling messages at the UE and eNodeB are as follows: Signaling messages traced at the UE side

Signaling messages traced at the eNodeB side

 

Symptoms of a Handover Problem Loss of the handover command If the eNodeB receives measureme measurement nt reports and replies the handover command which is not received by the UE, the traced signaling messages at the UE and eNodeB are as follows: Signaling messages traced Signaling messages traced at the UE side

at the eNodeB side

 

Symptoms of a Handover Problem Failure to access the target cell The eNodeB receives the measurement reports; the UE receives the handover command to initiate access to the target cell. However H owever,, the target cell fails to receive the RRC Connection Reconfiguration Complete message. The traced signaling messages at the UE and eNodeB sides are as follows:

The signaling trace at the UE side shows that the UE sends the RRC Connection Reconfiguration Complete message to the eNodeB. However However,, this m message essage is lost over the Uu interface. Target cell fails to receive the RRC Connection Reconnection Complete message.

Signaling trace traced at the UE side

Source cell delivers the handover command.

 

Symptoms of a Handover Problem Summary: There are various signaling messages exchanged between the UE and eNodeB, any signaling loss may cause the handover failure. For all the causes of the handover failure, the UE has a common behavior: Shortly (in 2s) after sending the measurement reports, the UE restarts the RRC Conne Connection ction Request message or restarts the RRC Connection Reestablishment Request message.

 

Diagnosis and Solution of Handover Problems(1) The following describes typical symptoms of handover problems.

Handover failure caused by missing neighboring cell configuration The symptom is that as the UE moves, the RSRP & SINR of the serving cell worsen and the RSRP of the neighboring cell betters.

Signaling trace on the UE shows that the UE sends measurement reports but fails to receive the handover command. Signaling trace on the eNodeB shows that

the eNodeB receives measurement reports but does not start the handover (no handover request&over the X2 interface no handover command over the Uu interface).

 

Diagnosis and Solution of Handover Problems (1) Solution to the problem of missing neighboring cell configuration Manually add neighboring cell configuration. Tur Turn n on the ANR(Auto ANR(Automatic matic Neighbor Relationship) algorithm switch.

 

Diagnosis and Solution of Handover Problems (2) Handover failure caused by delayed handover  The symptom is that when the radio quality of the neighboring cell meets the handover threshold, the RSRP of the serving cell suddenly declines. This signaling trace shows that the UE fails to receive the handover command.

Signaling trace on the eNodeB shows that after delivering the handover command, the eNodeB fails to receive the handover complete message. Or another situation is that the eNodeB cannot receive the measurement reports.

 

Diagnosis and Solution of Handover Problems (2) Solution to the problem of delayed handover  1、The handover success rate can be improved by changing Cell Offset of the

Ocn). serving cell (Ocs Ocs)and neighboring cells(Ocn modifying odifying IntraFreqHoA3T IntraFreqHoA3Time ime 2、The handover success rate can be improved by m

Off )  )in in the serving cell when the time of Serving cell signal qualiity suddenly declines (Off rapidly. 3、The handover can be improved by modifying IntraFreqHoA3Hyst ( H ys).It ).It iis s Clo Closel sely y

related to service s ervice feature and UE mobility. T To o reduce the probability of ping ping-pong -pong handovers.

 Mn  Ofn  Oc Ocn n  H  Hys ys    Ms  Ofs  Oc Ocss  Off  

 

Diagnosis and Solution of Handover Problems (3) Handover failure caused by weak coverage

The symptom is that when the radio quality of the neighboring cell meets the handover threshold, the RSRP of both the serving cell & neighboring cell is low low.. Signaling trace on the UE shows that immediately after sending the handover complete

message, the RRCthe Connection UE sends Reestablishment Request message.

This signaling trace shows that the UE fails to receive the handover command.

Signaling trace on the eNodeB shows that after delivering the handover

command, the eNodeB fails to receive the handover complete message. Another symptom is that the eNodeB cannot receive the measurement reports.

 

Diagnosis and Solution of Handover Problems (3) Solution to the problem of weak coverage  Adjust the power. power.  Adjust the antenna tilt.  Add eNodeBs or Sector. Sector.

 

Diagnosis and Solution of Handover Problems (4) Handover failures caused by interference The symptom is that the throughput is below expectation even though the RSRP is enough, and the handover failure or call drop. The uplink or downlink interference is indicated by the following tracing result. When eNodeB is Sub-band CQI reported by UE is lower than CQI. other sub-band

empty load, some RB RSSI traced by eNodeB is much higher than other RB RSSI

PS In this situation, we need some frequency scan instrument to confirm the interference source.

 

Diagnosis and Solution of Handover Problems(4) Solution to the interference problem Properly plot the frequency configuration of the cells. Find out and remove the interference source. There is no good method to solve the transient and changing interference now now..

 

Checklist of Standard Actions 1.Vie 1.V iew w netwo network rk KP KPI. I. 1. Export the handover-related KPIs, including the following, from the M2000 HO.eRAN.Out.Cell Number of intra-eNodeB intra-eNodeB HO attempt attempts s Number of intra-eNodeB intra-eNodeB HO execu executions tions Number of successful successful intra intra-eNodeB -eNodeB HOs Number of inter-eNodeB inter-eNodeB HO attempt attempts s Number of inter-eNodeB inter-eNodeB HO execu executions tions Number of successful successful inter-eNo inter-eNodeB deB HOs HO failure cause

HO.eRAN.X2Out.Cell Number of inter-eNod inter-eNodeB eB X2 HO attempts Number of inter-eNodeB inter-eNodeB X2 HO execut executions ions Number of succes successful sful inter-eNo inter-eNodeB deB X2 HOs

2. For each KPI, sum the KPI values v alues of all cells to obtain the entire-network KPI value. 3. Calculate Calculate the intra intra-eNode -eNodeB B hand handover over succes success s rate, interinter-eNode eNodeB B hand handover over

success rate, X2-based handover success rate, and S1-based handover success rate. inter-eNodeB handove handovers rs = Number of S1-based handovers handovers + Number of X2-based (Number of inter-eNodeB handovers)

4. Determine whether a handover success rate meets the KPI. The default KPI is

98.5%. If the handover success rate is below the KPI, find out the causes and solve the problem. Output: KPI report and top types of handover failures

 

Checklist of Standard Actions 2. Find out the top cells The following describes how to determine top cells according to the KPI or cell information.

1. Sort the cells in descending order of the number of handover failures. 2. The top 5 cells that have the lowest handover succe success ss rate are top cells.

Those cells whose number of handover failures is more than 10 times tim es the average number of handover failures are of special concern.

3. If a top cell is confirmed c onfirmed by the front-line engineer, this cell is automatically regarded

as a top cell. Output: list of top cells

 

Checklist of Standard Actions 3.Check device status. 1. Check whether the cells involved in the handover are in activated state. 2. Query Query eNodeB and cell a alarms. larms. Che Check ck whet whether her there are un uncleare cleared d alarms su such ch as

X2 interface break or RRU alarm. 3. Check whether the test inter-RAT T  reselection and handover handover. . UE works and supports inter-frequency and inter-RA

4. Check Check eNodeB eNodeB parameter parameter config configurati uration on 1. Check Check wheth whether er eNB version was matche matched. d. 2. Check whether the handover switch is on. 3. Check neighbor configuration and parameter configuration (neighbor relationships,

X2 interface configuration, & transmission)

4. Check handover thresholds and time-to-trigger. ti me-to-trigger.

 

Checklist of Standard Actions 5. Standard interface trace 1. Collect S1, Uu, and X2 interface trace on the M2000 or Web LMT LMT.. 2. Perform drive test using usi ng test UEs and obtain data from UE Probe. 3. After obtaining enough log about handover failures, stop the drive test and save the

log. Output: standard interface trace on on the eNodeB and drive test da data ta on the UE P Probe robe

6. Determine the faulty procedure 1. Find out which signaling message is lost. 2. If a signaling message over the Uu interface is lost, the p problem roblem is due to the Uu

interface. 3. If a signaling message over the S1 or X2 interface i nterface is lost, the problem is due to the

S1 or X2 interface.

 

Checklist of Standard Actions 7. Check whether the handover failure is caused by a problem of the Uu, S1, or X2 interface. 1. In case of the the Uu interface problem, analysis wh which ich standard signaling in Uu

interface has lost. 2. In case of the X2 interface problem, collect coll ect log. 3. In case of the S1 interface problem, contact the core c ore network engineers for

technical support-

 

Checklist of Standard Actions 8. Perform closing actions. 1. If the parameters are to be modified by the closing actions, back up the

configuration. 2. Perform closing actions at off-peak hours. Output: backup configuration file and operation records

9. Confirm the execution result. 1. Repeat the drive test to check whether the handover statistics of the related region

are optimized. 2. Trace the KPI change for the succeeding one week to confirm that the related

handover statistics meet the KPI, that the faults are cleared, cl eared, and no other faults are introduced.

3. If the problem persists, restart from the beginning of the troubleshooting procedure. Output: KPI data

 

Checklist of Standard Actions 10. Summary Report and Case Studies 1. Tidy up the materials. If the customer participates in the troubleshooting, prepare

clarification documents. 2. Summarize the troubleshooting procedure and write case studies.

Output: Clarification documents (optional) and case studies