umts rno subject-2g3g interoperation analysis guide_r2.0

2G-3G Interoperation Analysis Guide

R2.0

2G-3G Interoperation Analysis Guide Internal Use Only▲

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Revision History

Product Version Document Version Serial Number Reason for Revision

RNC V3.07 R1.0 First published

RNC V3.09 R2.0

1. Add the analysis of key 2G-3G networking parameters and configuration suggestions.

2. Delete some old parts.

3. Optimize the document structure.

4. Replace some unclear figures.

Author

Date Document Version Prepared

by Reviewed by Approved by

2009-12-20 R1.0 Song Jianjun

Expert group Expert group

2012-05-16 R2.0 Ma Wei Wang Zhenhai Wang Zhenhai


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Intended audience: Radio network optimization engineers

Proposal: Before reading this document, you had better have the following knowledge and skills.

SEQ Knowledge and skills Reference material

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Follow-up document: After reading this document, you may need the following information.

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About This Document

Summary

Chapter Description

1 Preface Gives a brief introduction to this guide.

2 Introduction to 2G/3G Interoperability

Describes the PLMN selection and reselection, cell selection and reselection, and inter-RAT handover.

3 2G/3G Interoperability Parameters

Describes the key parameters of 2G-3G interoperation.

4 Interoperability Problems Analysis and Optimization

Describes the analysis of common 2G-3G interoperation problems and optimization suggestions.

5 Cases Study Gives some typical cases of 2G-3G interoperation.


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TABLE OF CONTENTS

1 Preface ............................................................................................................ 1

2 Introduction to 2G/3G Interoperability .......................................................... 2 2.1 Network Elements Structure for 2G/3G Interoperability ..................................... 2 2.2 PLMN Selection and Reselection ...................................................................... 3 2.2.1 Process Description .......................................................................................... 3 2.2.2 Application Analysis for PLMN Selection and Reselection ................................ 5 2.3 Cell Selection and Reselection ......................................................................... 6 2.3.1 Process Description for Cell Selection .............................................................. 6 2.3.2 Scenario of Inter-RAT Cell Reselection ............................................................. 7 2.3.3 Policy of Inter-RAT Cell Reselection ................................................................. 8 2.3.4 Reselection from 3G to 2G ............................................................................... 8 2.3.5 Reselection from 2G to 3G ............................................................................. 12 2.4 Inter-RAT Handover ........................................................................................ 12 2.4.1 Inter-RAT Handover Scenario ......................................................................... 12 2.4.2 Inter-RAT Handover Strategies ....................................................................... 12 2.4.3 Measurements and Decisions before Inter-RAT Handover ............................. 13 2.4.4 Inter-RAT Handover Processes ...................................................................... 17

3 2G/3G Interoperability Parameters .............................................................. 33 3.1 2G/3G Interconnection Parameters ................................................................ 33 3.2 Typical Selection and Reselection Parameters ............................................... 33 3.2.1 Key 2G->3G Reselection Parameters ............................................................. 34 3.2.2 Key 3G->2G Reselection Parameters ............................................................. 36 3.2.3 Recommended Values of Key Reselection Parameters .................................. 46 3.3 Typical Inter-RAT Handover Parameters ........................................................ 48 3.3.1 2D/2F Event Threshold ................................................................................... 48 3.3.2 3A/3C Event Threshold ................................................................................... 49 3.3.3 Hysteresis(Rat) ............................................................................................... 51 3.3.4 Recommended Values of Key Inter-RAT Handover Parameters ..................... 53 3.4 Setting for 2G/3G Inter-RAT Neighbor Cells ................................................... 53

4 Interoperability Problems Analysis and Optimization................................ 55 4.1 Reselection Problems Analysis and Optimization ........................................... 56 4.2 Handover Problems Analysis and Optimization .............................................. 57 4.2.1 Physical Channel Failure ................................................................................ 58 4.2.2 Wrong Configuration ....................................................................................... 59 4.2.3 Protocol Error ................................................................................................. 59 4.2.4 Parameter Configuration ................................................................................. 59 4.2.5 Neighbor Cell Configuration ............................................................................ 60 4.2.6 Resource Refusing ......................................................................................... 60

5 Cases Study .................................................................................................. 61 5.1 PLMN Selection and Reselection .................................................................... 61 5.1.1 Case 1 ............................................................................................................ 61


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5.2 Cell Selection and Reselection ....................................................................... 62 5.2.1 Case 1 ............................................................................................................ 62 5.2.2 Case 2 ............................................................................................................ 62 5.3 Inter-RAT Handover ........................................................................................ 63 5.3.1 Case 1 ............................................................................................................ 63 5.3.2 Case 2 ............................................................................................................ 66 5.3.3 Case 3 ............................................................................................................ 67 5.3.4 Case 4 ............................................................................................................ 67 5.3.5 Case 5 ............................................................................................................ 69 5.3.6 Case 6 ............................................................................................................ 71


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FIGURES

Figure 2-1 Network Elements Structure for 2G/3G Interoperability ....................................... 2

Figure 2-2 Idle Mode Process Description ............................................................................ 3

Figure 2-3 Scenario of 2G/3G Inter-RAT Cell Reselection for UE ......................................... 8

Figure 2-4 General Process of Reselection from 3G to 2G ................................................. 11

Figure 2-5 Reselection Process for the Case that WCDMA Signal Strength is too Weak to Maintain Normal Network Service ......................................................................................... 12

Figure 2-6 Handover from WCDMA to GSM in CS Domain ................................................ 14

Figure 2-7 Handover from GSM to WCDMA in CS Domain ................................................ 15

Figure 2-8 Signaling Process of Inter-RAT Handover in MSC: WCDMA->GSM ................. 17

Figure 2-9 Signaling Process of Handover from WCDMA to GSM ..................................... 20

Figure 2-10 Inter-RAT Handover in SGSN From UTUE To GSM (Group Domain) ............. 22

Figure 2-11 Handover between SGSNs From UMTS To GSM (group domain) .................. 24

Figure 2-12 nter-RAT Handover From GSM To UMTS in SGSN (Group Domain) .............. 27

Figure 2-13 Inter-RAT Handover From GSM To UMTS in SGSN (Group Domain) ............. 29

Figure 4-1 RR Cause Information Element ......................................................................... 57

Figure 5-1 Sites Locations of 3A Event Trigger and 3C Event Trigger ................................ 65

Figure 5-2 TRI358 Site Location ......................................................................................... 66

Figure 5-3 Relative Location of TRI119W and TRI191 ....................................................... 68

Figure 5-4 Success Rate of Handover after Deleting 2G Neighbor Cells ............................ 68

Figure 5-5 Relocation Failure ............................................................................................. 70

Figure 5-6 Signaling Flowchart of Inter-RAT Handover ...................................................... 70

Figure 5-7 Inter-RAT Handover .......................................................................................... 71

Figure 5-8 Failure Signaling of Security Mode .................................................................... 72

Figure 5-9 Value of Failure Reason .................................................................................... 72

Figure 5-10 Encryption Algorithm for PS Service ............................................................... 72

Figure 5-11 Encryption Algorithm for CS Service ............................................................... 72

Figure 5-12 Encryption Algorithm ....................................................................................... 73

TABLES

Table 2-1 WCDMA Cell Selection Parameters ..................................................................... 6

Table 2-2 WCDMA Cell Reselection Parameters ................................................................. 9


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Table 2-3 GSM Important Control Parameters of Handover Measurement......................... 16

Table 3-1 Parameters Provided to 3G by 2G ...................................................................... 33

Table 3-2 Parameters Provided to 2G by 3G ...................................................................... 33

Table 3-3 Key 2G->3G Cell Reselection Parameters ......................................................... 34

Table 3-4 Key 3G->2G Cell Reselection Parameters ......................................................... 34

Table 3-5 Qqualmin Description ......................................................................................... 36

Table 3-6 SsearchRAT Description .................................................................................... 37

Table 3-7 QRxLevMin Description ...................................................................................... 38

Table 3-8 QHyst1S Description .......................................................................................... 39

Table 3-9 Qoffset1s,n in SIB11(dB) Description ................................................................. 40

Table 3-10 Qoffset1s,nin SIB12(dB) Description ................................................................ 42

Table 3-11 Treselection Description ................................................................................... 43

Table 3-12 Qhyst2s(dB) Description .................................................................................. 44

Table 3-13 Qoffset2s,n in SIB11(dB) Description ............................................................... 45

Table 3-14 Qoffset2s,n in SIB12(dB) Description ............................................................... 46

Table 3-15 Recommended Values of Key 3G ->2G Reselection Parameters ..................... 47

Table 3-16 Key 2G ->3G Reselection Parameters ............................................................. 47

Table 3-17 2D/2F Event Configured Threshold .................................................................. 48

Table 3-18 3A/3C Threshold Parameter ............................................................................. 50

Table 3-19 Hysteresis(Rat) Parameter Description ............................................................ 51

Table 3-20 3G->2G Parameters List .................................................................................. 53

Table 4-1 Optimization Methods of Typical Scenarios ........................................................ 55

Table 4-2 Inter-RAT Handover Failure ............................................................................... 57

Table 5-1 3C Handover Trigger Parameters for the Whole Network and Sites Distribution of 3A Handover Trigger Parameters ......................................................................................... 64


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1 Preface

The low-speed data services of 2G voice, short message and circuit field have been

widely used in every corner of the world, in order to meet the new requirements for the

human communications better. Symbolized by high-speed data services, video telephone,

and a variety of online services, 3G communications have been pushed to the front. In

the current 3G and 2G development, 3G WCDMA and 2G GSM/GPRS are most widely

used; therefore, in the evolution from GSM/GPRS to WCDMA, the coexistence and

complementarity between the two parties are considered as a very important factor for

the seamless connection between 3G and 2G.

Generally speaking, 3G networks are not easy to be constructed, and it takes some time

to achieve better coverage and capacity. In the early stage of 3G network construction,

they cannot reach the scale as big as 2G due to the limited coverage. How 3G can

provide seamless services by using 2G, and how 2G can provide the newest services by

using 2G are urgent and actual problems. The better coexistence between 3G and 2G

depends on the seamless connection between 3G and 2G, which makes users

experience continuous and omnipresent services. The seamless connection here means

the interoperability between 3G and 2G, including reselection and handover between 3G

and 2G.

This article first describes the principles and policies of 2G/3G interoperability, and then it

makes an analysis on the key parameters involved in the interoperability. According to

the baseline of the ZXWR RNC radio parameters in the WCDMA network of China

Unicom, it also provides the recommended values of the main related parameters for the

2G/3G interoperability, which is a reference for commercial configuration in each field.

Finally it makes a detailed analysis on the various solutions to the problems of the 2G/3G

interoperability, and provides some cases for analysis.

Note:

Taking into account the complexity of the actual radio environment, the final values of the

parameters in different fields should be adjusted reasonably based on the actual radio

environment. It should not ignore the flexibility of network optimization and only comply

with the recommendations in this article completely.



2 Introduction to 2G/3G Interoperability

2.1 Network Elements Structure for 2G/3G Interoperability

Figure 2-1 Network Elements Structure for 2G/3G Interoperability



2.2 PLMN Selection and Reselection

2.2.1 Process Description

When a UE powers up or roams, its primary task is to find the network and contact with it,

in order to obtain the network service. The UE behaviors in the idle mode can be divided

into PLMN selection and reselection, cell selection and reselection, and location

registration. The relationship among the three processes is as follows.

Figure 2-2 Idle Mode Process Description

After the UE powers up, firstly it should select one PLMN. After one PLMN is selected, it

starts to select one cell which belongs to the PLMN. After the cell is founded, it can get

the information of the neighbor cells from system information broadcast, thus the UE can

choose one cell with the best signal to reside from all the cells. Then the UE initiates the

process of location registration, after success, the UE resides in the cell successfully.

There are four functions for cell residence:

UE can receive the system information broadcasted by PLMN.

It can initiate random access process within the cell.

It can receive network paging.

It can receive the broadcast service from the cell.

PLMN Selection and Reselection

Location Registration

PLMNs available

PLMN selected

Location Registration

response

Registration area

changes

Indication to user

User selection of PLMN

Automatic/ Manual selection

CM requests

NAS Control

Radio measurements

Cell Selection and Reselection



After the UE resides in the cell and registers successfully, as it moves, the signal strength

of the current cell and the neighbor cell is changing constantly. The UE needs to choose

the most suitable cell, which is just the cell reselection process. There are some rules for

the cell reselection, and it will be described later.

After the UE reselects the cell and another cell is selected, it finds that this cell belongs to

another LA or RA, the UE needs to initiate the location update process, so that the

network can get the latest MS location information. The system information SIB1 includes

CN common GSM-MAP NAS system information and PS domain system information, in

which LAC and RAC information exists, so the UE can know whether LA or RA changes.

If location registration or update is not successful (for example, when the network refuses

the MS), or the UE leaves the current PLMN coverage area, the UE can reselect the

PLMN and select another available PLMN.

The purpose of PLMN selection/reselection is to select an available PLMN. To achieve

this purpose, the UE will maintain a PLMN list, in which PLMN is ordered by priority, and

then is searched from the high priority to find one PLMN with the highest priority.

Additionally, there are two modes for the PLMN selection and reselection: auto and

manual. The auto selection is that UE selects one PLMN automatically according to the

PLMN priority, the manual selection is to show all the available networks for the user, and

ask the user to choose one PLMN.

In the list, RPLMN (Registered PLMN) has the highest priority. The RPLMN is the PLMN

which registered successfully last time. There are two files in the USIM card, EFLOCI and

EFLOCI, which record the RPLMN information. In these two files, LAI (=MCC+MNC+LAC)

and RAI (=LAI+RAC) include MCC and MNC, which are just RPLMN.

No matter auto or manual selection, after the UE powers up, firstly it will try to select

RPLMN; if it is successful, there will be no subsequent operation. If not, the UE will

generate a PLMN list (ordered by priority):

HPLMN

The PLMN in the USIM file ―User Controlled PLMN Selector with Access

Technology‖.

The PLMN in the USIM file ―Operator Controlled PLMN Selector with Access

Technology‖.

PLMN with better signal quality (random order).

Other PLMN (order from high to low signal quality).

In the USIM card, the file EFIMSI records IMSI (MCC + MNC + MSIN), from which the UE

can get HPLMN. 2) and 3) are the files EFPLMNwAcT and EFOPLMNwACT in the USIM.

4) and 5) are obtained through searching the frequency one by one by the UE. The UE

searches the PLMN one by one according to the PLMN list ordered by the priority above,

and attempts the location registration.



UMTS is evaluated from GSM and both access technologies are different completely

(GERAN vs. UTRAN), so it needs to specify the preferred access technology for each

PLMN. The priority of the access technologies is specified in the file ―...with Access

Technology‖. If it is not specified, generally, GERAN is preferred.

In addition, PLMN needs to be reselected for the following two cases:

In any case, the user can request to initiate PLMN reselection manually.

VPLMN (visited PLMN) reselection:

After the user registers to VPLMN for the reason of handover/roaming, as the MCC is the

same between VPLMN and HPLMN (home PLMN), only MNC is different from each other,

and this case can be judged by the UE. For this case, the UE will return to the home

network as much as possible. The method is to search the home network periodically.

This period is specified by USIM and defined in the file EFHPLMN, from 6 minutes to 8

hours. The operator can also forbid this function, in this way the value is set to 0 in the file

EFHPLMN.

Note: HPLMN is the registration handover and HLR information, and it is defined as

follows in the protocol:

The HPLMN is the GSM network that a GSM user is a subscriber of. That implies that

GSM user‘s subscription data resides in the HLR in that PLMN. The HLR may transfer

the subscription data to a VLR (during registration in a PLMN) or a GMSC (during mobile

terminating call handling). The HPLMN may also contain various service nodes, such as

a short message service centre (SMSC), service control point (SCP), etc.

VPLMN is the roaming handover information, and it is defined as follows in the protocol:

The VPLMN is the GSM network where a subscriber is currently registered. The

subscriber may be registered in her HPLMN or in another PLMN.

In the latter case, the subscriber is outbound roaming (from HPLMN‘s perspective) and

inbounds roaming (from VPLMN‘s perspective). When the subscriber is currently

registered in her HPLMN, then the HPLMN is at the same time VPLMN.

2.2.2 Application Analysis for PLMN Selection and Reselection

By using the functions of PLMN selection and reselection, the inter-RAT selection and

roaming functions can be implemented without any upgrading for the GSM and WCDMA

networks. The user can return to the WCDMA network from the GSM network by PLMN

reselection. For the WCDMA user can handover to the WCDMA network from the GSM

network when entering the coverage area of WCDMA, you can set different PLMNs for

the WCDMA and GSM networks and set HPLMN for the WCDMA network in the USIM.

And the selection time can be controlled by the operator.



2.3 Cell Selection and Reselection

2.3.1 Process Description for Cell Selection

Cell selection process includes cell searching and reading broadcast channel.

Cell searching

Firstly, if a UE has stored some relevant information of this PLMN, such as frequency,

scrambling code, etc, the UE will use this information to search the cell (stored

information cell selection) and find the network quickly. The information is stored in the

USIM card or in the non-volatile memory of the cell phone. The purpose of cell searching

is to find a cell, and the steps are as follows:

Time slot synchronization by the synchronization code of PSCH.

Frame synchronization, implemented by the synchronization code of SSCH,

and the scrambling code group of the cell is confirmed.

Obtaining the main scrambling code of the cell through CPICH, and then the

UE can read the broadcast channel.

Obviously, if the UE has already known some information of this cell, such as frequency

and main scrambling code, the steps mentioned above can be speeded up.

Reading broadcast channel

Main information block MIB‘s dispatching information is already known, that is SIB_POS

= 0, SIB_REP = 8. The UE can read out the MIB in the radio frame of SFN = 0, 8, 16 ...

After reading out the MIB, the UE can judge whether the founded PLMN is the one

expected by the field PLMN identity in the MIB. If yes, according to the other SIB‘s

dispatching information in the MIB, the UE can the find the other SIB and obtain its

content. If not, the UE needs to find the next frequency and start the process again from

the cell searching. If the current PLMN is the one that the UE is looking for, the UE reads

SIB3 and obtains ―Cell selection and re-selection info‖, in this IE, it reads out Qqualmin,

Qrxlevmin, and Maximum allowed UL TX power (UE_TXPWR_MAX_RACH), it

calculates according to the formula below:

Table 2-1 WCDMA Cell Selection Parameters

Parameter Description




Squal Cell Selection quality value, (dB)

Not applicable for TDD cells or GSM cells.

Srxlev Cell Selection RX level value (dB)

Qqualmeas Measured cell quality value. The quality of the received signal expressed in CPICH Ec/No (dB) for FDD cells. Not applicable for TDD cells or GSM cells.

Qrxlevmeas Measured cell RX level value. This is received signal, CPICH RSCP for FDD cells (dBm), P-CCPCH RSCP for TDD cells (dBm) and RXLEV for GSM cells (dBm).

Qqualmin Minimum required quality level in the cell (dB). Not applicable for TDD cells or GSM cells. (read in system information)

Qrxlevmin Minimum required RX level in the cell (dBm). (read in system information)

Pcompensation Max(UE_TXPWR_MAX_RACH - P_MAX, 0) (dB)

UE_TXPWR_MAX_RACH Maximum TX power level a UE may use when accessing the cell on RACH (read in system information), (dBm)

P_MAX Maximum RF output power of the UE, (dBm)

If

Then the UE considers this cell as a suitable cell, it resides and reads the other system

information as needed, then the UE initiates the location registration process. If the

criteria above is not satisfied, the UE reads the SIB11 to obtain the main scrambling code

and the frequency of the neighbor cell, it can measure the Qqualmeas and Qrxlevmeas

of the neighbor cell, in the IE ―Cell Selection and Re-selection info for SIB11/12‖, the UE

can know the neighbor cell‘s Maximum allowed UL TX power, Qqualmin and Qrxlevmin,

thus the UE can calculate the neighbor cell‘s Squal and Srxlev, and judge whether the

neighbor cell satisfies the criteria above. If the UE can find any neighbor cell that satisfy

the selection criteria, it will reside in the cell and read the other system information as

needed, then initiate the process of location registration. If the UE cannot find a cell that

satisfies the selection criteria, the UE will consider that it is not covered and continue to

select and reselect PLMN.

2.3.2 Scenario of Inter-RAT Cell Reselection

The 2G/3G inter-RAT cell reselection mainly occurs in the following two modes.

Idle Mode



A UE performs the inter-RAT cell reselection in the idle states of WCDMA, GSM and

GPRS. The UE measures the serving cell according to the parameters of network

broadcast and determines whether to reselect another cell.

Connected Mode

A UE performs the inter-RAT cell reselection in the group connected states of Cell_FACH

and Cell_PCH/URA_PCH.

Figure 2-3 Scenario of 2G/3G Inter-RAT Cell Reselection for UE

2.3.3 Policy of Inter-RAT Cell Reselection

The current policy of inter-RAT cell reselection for the 2G/3G interoperability is a

bidirectional reselection between 2G and 3G. However, it performs the cell reselection

from 3G to 2G only when a UE moves out the scale of 3G coverage. And once it returns

to the scale of 3G coverage, the UE will initiate the cell reselection from 2G to 3G.

2.3.4 Reselection from 3G to 2G

1. Planning for the cell reselection measurement

When a UE is in the idle mode, it needs to monitor the signal quality of the current

and neighbor cells at any moment for selecting the best cell to provide service, this

is called cell reselection.

In the following rules, the UE uses Squal for FDD cells and Srxlev for TDD for Sx.

i. If Sx > Sintrasearch, the UE does not perform co-frequency measurement; if

Sx < Sintrasearch, the UE performs co-frequency measurement. If the current

cell does not send Sintrasearch to the UE, the UE performs co-frequency

measurement.



ii. If Sx > Sintersearch, the UE does not perform inter-frequency measurement;

if Sx < Sintersearch, the UE performs inter-frequency measurement. If the

current cell does not send Sintersearch to the UE, the UE performs

inter-frequency measurement.

iii. If Sx > SsearchRATn, the UE does not perform system measurement; if Sx <

SsearchRATn, the UE performs inter-RAT measurement. If the current cell

does not send SsearchRATn to the UE, the UE performs inter-RAT system

measurement.

Sintrasearch, Sintersearch and SsearchRATn are specified in the SIB3‘s ―Cell

selection and re-selection info‖.

The UE measures the neighbor cells which satisfy the conditions mentioned above,

firstly it calculates the S values for all the cells (including the current and neighbor

cells) according to the cell selection method, for the all the cells which meet the

condition S>0, calculate the R according to the formulas below.

Rs = Qmeas,s + Qhysts

Rn = Qmeas,n - Qoffsets,n

Rs: the R value of the serving cell

Rn: the R value of the neighbor cell

Qmeas: the signal measurement value of a cell, it adopts CPICH Ec/No or

CPICH RSCP for the FDD cell

Qoffset1s,n: the offset between two cells, it is used for the FDD cell when the

measurements of the cell selection and reselection are set to be CPICH RSCP.

Qoffset2s,n: the offset between two cells, it is used for the FDD cell when the

measurements of the cell selection and reselection are set to be CPICH Ec/No.

Qhyst1s: the hysteresis value, it is used for the FDD cell when the

measurements of the cell selection and reselection are set to be CPICH RSCP.

Qhyst2s: it is used for the FDD cell when the measurements of the cell

selection and reselection are set to be CPICH Ec/No.

Treselection: the timer value for the cell reselection

Table 2-2 WCDMA Cell Reselection Parameters


Cell_selection_and_reselection_quality_measure (FDD only)

Choice of measurement (CPICH Ec/N0 or CPICH RSCP) that is used to derive




quality measures Qmap,n and Qmap,s, (read in system information).

Qmeas,s

Quality of the serving cell, derived from CPICH Ec/N0 or CPICH RSCP for FDD cells, from RXLEV for GSM cells. For FDD cells, the measurement that is used to derive the quality value is set by the Cell_selection_and_reselection_quality_measure information element.

Qmeas,n

Quality of the neighboring cell, derived from CPICH Ec/N0 or CPICH RSCP for FDD cells, from RXLEV for GSM cells. For FDD cells, the measurement that is used to derive the quality value is set by the Cell_selection_and_reselection_quality_measure information element.

Qoffset1s,n Offset value 1between the two cells considered in the evaluation (read in system information).

Qoffset2s,n, Offset value 2 between the two cells considered in the evaluation (read in system information).

Qhyst1s Hysteresis value of the serving cell.

Qhyst2s Hysteresis value of the serving cell.

Treselections Time-to-trigger for cell reselection, (s)

2. General process of reselection

A: When ―the pilot Ec/No of the WCDMA serving cell‖ is smaller than

―Qqualmin+SsearchRAT‖, the UE starts to measure the signal strength of the

neighbor GSM/GPRS cells. The SsearchRAT parameter is broadcasted in SIB3/4.

A -> B: The UE starts to rank the signal strength of WCDMA serving cells and

GSM/GPRS neighbor cells.

Rank of serving WCDMA = RSCP_WCDMA + QHyst1s

Rank of neighbor GSM/GPRSn = RSSIGSMn - Qoffset1s,n

B: When a GSM cell ranks the top, the Treselection timer is started.

C: When a GSM cell ranks the top and it keeps for Treselection seconds, the UE

reselects to the corresponding GSM cell as shown in the following figure.



Figure 2-4 General Process of Reselection from 3G to 2G

3. Reselection process for special cell

When the signal strength of WCDMA is too weak to maintain a normal network

service, the process of cell reselection is as follows.

A: The WCDMA serving cell cannot maintain a normal network service (pilot

Ec/No > Qqualmin, but pilot RSCP < Qrxlevmin)

A -> B: The WCDMA serving cell cannot maintain a normal network service, and it

lasts for a period of ―Nserv DRX Cycles‖.

B: UE measures and ranks all the neighbor cells in the neighbor cell list. It starts a

timer when a GSM cell ranks the top.

Rank of WCDMA = RSCP_WCDMA + QHyst1s

Rank of neighbor GSM/GPRSn = RSSIGSMn - Qoffset1s,n

C: When a GSM cell ranks the top and it lasts for Treselection seconds, the UE

reselects to the corresponding GSM cell as shown in the following figure.



Figure 2-5 Reselection Process for the Case that WCDMA Signal Strength is too Weak to Maintain Normal Network Service

2.3.5 Reselection from 2G to 3G

In the idle state, inter-RAT selection can be implemented by cell selection and reselection.

Additionally, the standards for the signal quality in the two GU systems are different, so

the parameters setting for the selection and reselection needs to be very cautious, or it

may occur inappropriate cell selection or ping-pong selection.

2.4 Inter-RAT Handover

2.4.1 Inter-RAT Handover Scenario

The handover between WCDMA and GSM/GPRS occurs in the Cell_DCH state of the

connected mode, and an effective handover between WCDMA and GSM/GPRS can

ensure that the users can use the current service continuously.

The typical process of inter-RAT handover: once UE is in the connection state (the

CELL_DCH state in WCDMA), it performs the ―measurement‖ instruction from network,

and reports the result to the network by period or event, the network judges the UE signal

quality based on the reported result, and determines whether the cell phone to handover.

2.4.2 Inter-RAT Handover Strategies

2.4.2.1 Inter-RAT Handover Strategies for Different Stages

1. Coverage Handover



In the initial stage of 3G construction, given the network condition of continuous

GSM coverage and limited 3G coverage, it adopts the handover based on coverage

for the places with poor coverage.

2. Load Handover

In the middle and late stages of 3G construction, 3G network extends very fast, 3G

and 2G networks overlap basically, 2G network needs to share load for 3G network,

it adopts load handover that is based on the load of 3G network.

3. Service Handover

In the middle and late stages of 3G construction, the RNC of 3G network receives

RAB assignment message, the services should be handed over to 2G according to

the requirement from core network, thus 3G users are handed over to 2G network,

and it is called service handover.

2.4.2.2 Current Inter-RAT Handover Strategy

At present, given the network condition of continuous GSM coverage and limited 3G

coverage, it adopts the handover based on coverage for the places with poor coverage.

The specific handover strategy is as follows: it is a one-way handover from 3G to 2G for

CS, and it is a two-way handover from 3G to 2G for PS. So the handover process from

2G to 3G for CS will not be described in this article.

2.4.3 Measurements and Decisions before Inter-RAT Handover

The typical process of inter-RAT handover: once UE is in the connection state (the

CELL_DCH state in WCDMA), it performs the ―measurement‖ instruction from network,

and reports the result to the network by period or event, the network judges the UE signal

quality based on the reported result, and determines whether the cell phone to handover.

The inter-RAT measurement processes in WCDMA and GSM are introduced below.

2.4.3.1 Start Measurement to GSM in WCDMA

The process of starting measurement to GSM: When a UE finds that the value of carrier

evaluation quality in the current system is lower than the assigned threshold in the

measurement control, it reports a 2D event to the network. The WCDMA system requests

the UE to start the compact mode, and the UE starts to measure the inter-RAT signal

quality (if the UE finds that the value of carrier evaluation quality in the current system is

higher than the assigned threshold in the measurement control, it stops the compact

mode and inter-RAT measurement). When it satisfies the condition of 3A (or 3C) event

trigger threshold, the UE reports the 3A (or 3C) event to the network. And the network

triggers the inter-RAT handover command according to the information of measurement

report and GSM neighbor cell in order to that the UE can switches to the destination cell.



Note: The UE also can report the signal quality periodically and the network determines

whether the trigger condition of 3A (or 3C) is satisfied.

The related process is as follows.

Figure 2-6 Handover from WCDMA to GSM in CS Domain

2.4.3.2 Start Measurement to WCDMA in GSM

The process of starting measurement to WCDMA: When a UE enters a GSM cell with 3G

neighbor cells, the information of 3G neighbor cells and 3G measurement parameters are

included in the ―measurement information‖ instruction from the network, which requires

the UE to measure the assigned 3G neighbor cells and report the result. Thus whether to

perform an inter-RAT handover is determined by the 2G network.

The related process is as follows.



Figure 2-7 Handover from GSM to WCDMA in CS Domain

2.4.3.3 Handover Measurement Parameter Setting – Preferred 3G

1. GSM Parameter Setting

The main 3G parameters in ―Measurement Information‖ include ―3G Neighbour Cell

Description‖ and ―3G MEASUREMENT PARAMETERS Description‖. The

information of 3G neighbor cells is defined in the first parameter, and the informaiton

of 3G measurement parameters setting is defined in the second parameter. In some

foreign PLMNs, there is no information of 3G measurement parameters, which

means that it will read the Qsearch_C_Initial parameter broadcasted on BCCH,

and the handover measurement is carried out through the definition of the

parameter. Other main parameters are in the

SYSTEM_INFORMATION_2QUATER.

Qsearch_C is set to 7, which shows an unconditional inter-RAT measurement.

It is same to the Qsearch_I in the inter-RAT reselection parameters.

REPORT_TYPE shows the type of measurement report, generally it is the

enhanced ―Extended Measurement Report‖, but the default value is Common

Measurement Report.

3G_SEARCH_PRIO shows that it can scan on the frame that is generally used

for BSIC decoding, because the 3G neighbor cells do not need BSIC decoding

(If indicated by the parameter 3G_SEARCH_PRIO, the UE may use up to 25

search frames per 13 seconds without considering the need for BSIC decoding

in these frames). The default value is TRUE.



FDD_REP_QUANT shows the reported type, RSCP or Ec/No.

Table 2-3 GSM Important Control Parameters of Handover Measurement

Parameter name Description Range Bits Message

Qsearch_C_Initial

Indicates the Qsearch value to be used in connected mode before Qsearch_C is received,

0 = use Qsearch_I, 1 = (always). Default value = use Qsearch_I.

0/1 1 BCCH D/L

Qsearch_C Same to Qsearch_I 0-15 4 SACCH D/L

REPORT_TYPE

Indicates which report type the UE shall use, 0 = enhanced, 1 = normal

Default value = normal

0/1 1

BCCH D/L

SACCH D/L

3G_SEARCH_PRIO

Indicates if 3G cells may be searched when BSIC decoding is required, 0 = no, 1 = yes

Default value = yes

0/1 1 SACCH D/L

FDD_REP_QUANT Indicates the reporting quantity for UTRAN FDD cells, 0 = RSCP, 1 = Ec/No

0/1 1

PBCCH D/L PCCCH D/L PACCH D/L (**)

2. GSM Signal Measurement

The measurement to a GSM cell can be divided into two modes: ―BSIC check‖ and

―no BSIC check‖. It only needs to measure ―GSM carrier RSSI‖ for the ―no BSIC

check‖ mode. For the ―BSIC check‖ mode, the two processes of ―Initial BSIC

identification‖ and ―BSIC re-confirmation‖ are also needed.

Initial BSIC identification: the process of BSIC searching and decoding

BSIC re-confirmation: the tracing and decoding processes to the BSIC of a

GSM cell after the ―Initial BSIC identification‖

If the measurement to a GSM cell is ―BSIC check‖, the UE behaviors are as follows:

The UE performs the ―GSM carrier RSSI‖ measurement according to the

TGPS setting with a target of ―GSM carrier RSSI measurements‖.

The UE performs the initial BSIC identification according to the TGPS setting

with a target of ―GSM Initial BSIC identification‖. If there are multiple GSM cells,



it will perform the process according to the order of signal strength in the recent

GSM carrier RSSI measurement.

The UE performs the BSIC reconfirmation according to the TGPS setting with a

target of ―GSM BSIC re-confirmation‖.

Judging the ―BSIC check‖:

The UE decodes the SCH on BCCH and identifies the BSIC for at least one

time, after that, the BSIC is confirmed again for each Tre-confirm_abort seconds,

then the BSIC of GSM cell is considered to be ―checked‖. Otherwise it is

considered to be ―unchecked‖.

Accepting or discarding the ―BSIC check‖:

There may be multiple cells with the same ARFCN but different BSICs among

the GSM cells in WCDMA. For the measurements without the ―BSIC check‖,

which means that the BSIC is not judged, the network cannot distinguish which

GSM cell each measurement belongs to, and the handover may fail as the

destination is not clear. Therefore it must adopt the ―BSIC check‖.

2.4.4 Inter-RAT Handover Processes

2.4.4.1 Handover From 3G to 2G in CS Domain

In the initial stage of 3G construction, in order to keep the continuity of service in the edge

of 3G coverage, it is necessary to support the handover from WCDMA to GSM.

1. Intra-MSC

Figure 2-8 Signaling Process of Inter-RAT Handover in MSC: WCDMA->GSM

UE/MS UE/MS

RNS-A 3G_MSC-A BSS-B

Relocation-Required[1]

HO-Request[2]

HO-Request-Ack[3]

Relocation-Command[4]

RRC-HO-Command RI-HO-Access

HO-Detect[5] RI-HO-Complete

HO-Complete[6]

Iu-Release-Command[7]

Iu-Release-Complete[8]



RNS-A is the RNS where the cell phone locates before handover; BSS-B is the BSS

where the cell phone locates after handover. All the messages above can be

tracked in the user interface, Iu interface, and A interface. RI is Radio Interface.

RRC is Radio Resource Control. 3G_MSC-A is the MSC where the cell phone

locates before handover.

i. RNS-A sends the RELOCATION_REQUIRED message to 3G_MSC-A. The

available cell list and handover reason are included in this message.

3G_MSC-A choose one cell in the list as the destination cell. 3G_MSC-A

queries the location of the destination cell according to the destination cell

number, and determines the handover is intra-office or interoffice.

ii. 3G_MSC-A sends the HO_REQUEST message to BSS-B. After receiving the

handover request, 3G_MSC-A queries in the corresponding tables and finds

that the destination cell is the cell controlled by its subordinated BSS. Then

3G_MSC-A constructs the corresponding GSM handover request message

according to the handover request, and sends the message to BSS-B. When

constructing the request message, 3G_MSC-A needs to complete the

interworking between UMTS and GSM handover request messages. Then

3G_MSC-A can send the HO_REQUEST message to BSC-B.

iii. BSS-B sends the HO_REQUEST_ACK message to 3G_MSC-A. After BSS-B

applies the radio resource and gets the circuit ready, it sends this message to

3G_MSC-A, the HANDOVER_COMMAND message is included in this

message and will be transmitted transparently by RNS-A to the handover

request side, which is called RNS-A.

iv. 3G_MSC-A sends the RELOCATION_COMMAND message to RNS-A. After

MSC-A receives the HO_REQUEST_ACK message from BSS-B, it means that

the radio resource of new interface A is ready and the cell phone can hand

over to BSS-B from RNS-A, at this time it sends handover command message

to notify the cell phone to hand over.

v. BSS-B sends the HO_DETECT message to 3G_MSC-A. At this time the cell

phone has already detected the new channel and has the condition to access

the new radio channel, but actually has not accessed yet. As it is voice

handover, the voice channel must be built up, so 3G_MSC-A connects the time

slot of the opposite end to time slot of new interface, and continues to call by

using the resource applied in the process of handover.

vi. BSS-B sends the HO_COMPLETE message to 3G_MSC-A. The new channel

has been built up, the user continues to call or be in the process of other

services. BSS-B reports the handover completion message to 3G_MSC-A.

vii. 3G_MSC-A sends the LU RELEASE_COMMAND message to RNS-A. After

the handover is completed, 3G_MSC-A sends RRC HO Command message to

the source RNS-A, and releases the original radio resource.



viii. RNS-A sends the LU RELEASE COMPLETE message to 3G_MSC-A. RNS-A

releases the radio resource.

2. Inter-MSC

For the inter-RAT handover, if a UE only has the circuit domain service, it follows the

handover process of the circuit domain from WCDMA to GSM. The typical handover

process includes: measurement control -> measurement report -> handover

judge->handover execute.

In the stage of measurement control, the network tells UE the measurement

parameters by sending measurement control message. In the stage of

measurement report, the UE sends measurement report to the network. In the stage

of handover judge, the network determines to handover according to the

measurement report. In the stage of handover execute, the UE and the network

follow the signaling process, and take actions according to the signaling.

For the handover from WCDMA to GSM, when the user is in the edge of WCDMA

system and needs to handover between systems, WCDMA RNC notices the UE to

start an inter-RAT measurement. The UE carries out the inter-RAT measurement

and reports the result, RNC determines whether to execute the signaling process for

inter-RAT handover according to the result. As the access mode of WCDMA is code

division multiple access, all the connected UEs work under the specified frequency

for all time, in order to continue to call in the process of inter-RAT measurement,

WCDMA system and the UE may need to start the compression mode (if the UE

only has one transceiver, it must start the compression mode; if the UE has two

transceivers, the UE can test GSM cell without starting the compression mode).

The signaling process of handover from WCDMA to GSM is as follows.



Figure 2-9 Signaling Process of Handover from WCDMA to GSM

MAP/E MAP/E

2. Prepare

Handover

BSSMAP BSSMAP

4. Handover

Request Ack

RANAP RANAP

13. Iu Release

Complete

BSSMAP BSSMAP

3. Handover

Request

MAP/E MAP/E

5. Prepare

Handover

Response

RANAP RANAP

6. Relocation

Command

BSSMAP BSSMAP

8. Handover

Detect

BSSMAP BSSMAP

10. Handover

Complete

MAP/E MAP/E

11. Send End

Signal

Request

MAP/E MAP/E

14. Send End

Signal Response

RANAP RANAP

1. Relocation

Required

UE Node B RNC

Serving

CN MSC BSC BTS

RRC

7. DCCH : Inter-System Handover

CommandRRC

[Hard Handover]

RR

9. Handover Complete

RR

RANAP RANAP

12. Iu Release

Command

i. When URRAN determines to handover between systems based on the

measurement, SRNC sends RANAP message RELOCATION REQUIRED to

CN, and requests the other system to prepare for the handover.

ii. WCDMA CN forwards this request to GSM UEC (through MAP/E message

PREPARE HANDOVER).

iii. GSM UEC sends the HANDOVER REQUEST message to BSC.

iv. After GSM BSS gets the resource ready for the handover between systems,

BSC replies the HANDOVER REQUEST ACK message to GSM UEC.

v. GSM UEC sends MAP/E message PREPARE HANDOVER RESPONSE to

WCDMA CN.



vi. WCDMA CN answers the initial request from SRNC through sending RANAP

message RELOCATION COMMAND.

vii. SRNC sends the message HANDOVER FROM UTRAN COMMAND to UE

through the existing RRC connection, and requests UE to handover from

WCDMA to GSM.

viii. UE hands over from WCDMA to GSM (hard handover), UE sends the message

HANDOVER COMPLETE to BSC, notices BSC that the handover is

completed, BSC sends the message HANDOVER COMPLETE to GSM UEC.

ix. Combined with Step viii.

x. Combined with Step viii.

xi. When detecting that UE is in the area covered by GSM, GSM UEC sends the

message SEND END SIGNAL REQUEST to WCDMA CN and notices

WCDMA CN that the handover is completed, and the WCDMA resource

occupied by this UE can be freed.

xii. CN sends LU RELEASE COMMAND to RNC and notifies the original SRNC to

free the resource. When the relevant resource in WCDMA is completed to free,

WCDMA responses to GSM UEC and then the handover process is finished.

xiii. Combined with Step xii.

xiv. Combined with Step xii.

2.4.4.2 Handover From 3G to 2G in PS Domain

Group domain handover from 3G to 2.5G is supported, and GSM BSS does not need to

change.

The version of GTP is negotiated between GSM SGSN and WCDMA SGSN by using the

standard program. The backward compatibility of GTP protocol can assure the

compatibility of GSM/WCDMA. The destination GSM SGSN will contact with the source

WCDMA SGSN. If both the source and destination SGSNs support 3GPP R99, it adopts

GTP v1; if GSM SGSN does not support 3GPP R99, it adopts GTP v0. In this case, some

services may be degraded. The destination GSM SGSN will degrade the PDP contexts

(such as Real time PDP contexts) which cannot be processed.

If HLR does not support the version of 3GPP R99 MAP either, the version of MAP

infoRetrievalContext will be rollback to v2. If it is WCDMA user, the HLR where it locates

must support MAP v3.

1. Intra-SGSN



It occurs when a UE radio interface hands over from UTRAN interface to GSM

interface, UTRAN interface and GSM interface are connected to one SGSN.

Figure 2-10 Inter-RAT Handover in SGSN From UTUE To GSM (Group Domain)

5. Security Functions

UE/MS SRNS 2G+3G-SGSN BSS

8. Iu Release Command

8. Iu Release Complete

6. SRNS Data Forward Command

7. Forward Packets

1. Intersystem change

decision

3. SRNS Context Request

4. SRNS Context Response

2. Routeing Area Update Request

12. Routeing Area Update Accept

13. Routeing Area Update Complete

15. BSS Packet Flow Context Procedure

C1

new

MSC/VLR

old

MSC/VLR

HLR

9. Location Update Request

10a. Update Location

10b. Cancel Location

10d. Insert Subscriber Data

10e. Insert Subscriber Data Ack

11. Location Update Accept

10f. Update Location

14. TMSI Reallocation Complete

10c. Cancel Location Ack

i. The UE hands over from UTRAN to the cell which supports GSM interface.

ii. The UE initiates routing area update request.

iii. 2G+3G-SGSN sends the SRNS CONTEXT REQthe UEST (IMSI) message to

SRNS, after SRNS receives the request, it begins to stop sending the downlink

data and caches, at the same time it notices SGSN the serial number of

datagram (GTP-SNDs, GTP-SNUs, PDCP-SNDs, PDCP-SNUs) through the

SRNS CONTEXT RESPONSE message.

iv. Combined with Step iii.



v. Execute security function (optional).

vi. 2G+3G-SGSN sends the SRNS DATA FORWARD COMMAND message to

SRNS, and notices SRNS to start to send the cached data back to SGSN,

SRNS forwards the cached data.

vii. Combined with Step vi.

viii. The cached data is completed to forward, 2G+3G-SGSN releases the lu link.

ix. If it is joint routing update and attached by IMSI or the location area changes,

2G+3G-SGSN sends the location update message to VLR.

x. If the user data in VLR is not confirmed by HLR, the new VLR notices HLR to

delete the user data in the old VLR, and inserts users in the new VLR.

xi. The new VLR assigns new VLR TMSI and notices SGSN.

xii. 2G+3G-SGSN checks whether the user is forbidden to roam, if it is allowed,

2G+3G-SGSN can assign new P-TMSI, and send the ROUTING AREA

UPDATE ACCEPT message to notice the UE.

xiii. the UE can send the ROUTING AREA UPDATE COMPLETE (Receive N-PDU

Number) message to SGSN, and notice SGSN that the serial number of

datagram has been received. SGSN continues to forward the datagram that is

after this serial number to the UE.

xiv. If the UE has accepted VLR Tthe UEI, 2G+3G-SGSN sends the Tthe UEI

REALLOCATION COMPLETE message to the new VLR.

xv. 2G+3G-SGSN and BSS‗s optional BSS Packet Flow Context flow, build up

BSS Packet Flow.

If UE is CAMEL user, the following processes will be triggered:

i. CAMEL_GPRS_Routeing_Area_Update_Session

ii. CAMEL_GPRS_Routeing_Area_Update_Context

2. Inter-SGSN

The process of group domain handover between SGSNs from UMTS to GSM is as

shown in figure below.



Figure 2-11 Handover between SGSNs From UMTS To GSM (group domain)

i. The UE (UE is in the non-Cell-DCH state) or UTRAN (the UE is in the state of

Cell-DCH or Cell_FACH) determines to initiate the group domain inter-RAT

handover, in this way the UE is handed over to another new cell which

supports GSM, at the same time the data transmission between the UE and

network is stopped.

ii. The UE initiates routing area update request to 2G-SGSN, routing area update

or joint RA/LA update or joint RA/LA update with IMSI attached will be

specified for the update type, before the message is sent to SGSN, BSS will

add the CGI with RAC and LAC where it locates to the message received.

UE/MS new 2G -SGSN

HLR GGSN old 3G -SGSN

2. Routing Area Update Request

10. Update PDP Context Request

10. Update PDP Context Response

11. Update GPRS Location

15. Update GPRS Location Ack

5. SGSN Context Response 6. Security Functions

19. Routing Area Update Accept

12. Cancel Location

12. Cancel Location Ack

14. Insert Subscriber Data Ack

14. Insert Subscriber Data

7. SGSN Context Acknowledge

BSS SRNS

3. SGSN Context Request

13. Iu Release Command

13. Iu Release Complete

8a. Forward Packets

9. Forward Packets

4. SRNS Context Request

4. SRNS Context Response

8. SRNS Data Forward Command

22. BSS Packet Flow Context Procedure

1. Inter-RAT change decision

C3

C1

20. Routing Area Update Complete

new MSC/VLR

old MSC/VLR

16. Location Update Request 17a. Update Location

17b. Cancel Location

17c. Cancel Location Ack 17d. Insert Subscriber Data

17e. Insert Subscriber Data Ack

17f. Update Location Ack 18. Location Update Accept


C2



iii. The new 2G-SGSN sends the SGSN Context Request message to the old

3G-SGSN for obtaining MM and PDP contexts, the old 3G-SGSN verifies the

PTMSI signature of the UE. If it is successful, the old SGSN will start a timer; if

the old SGSN does not recognize the UE, it will reply an appropriate error

reason.

iv. If the UE is in the state of PMM-CONNECTED before handover, the old

3G-SGSN sends SGSN Context Request message to SRNS, after receiving

this message, SRNS starts to cache and stops to send data to PDU, and

replies SRNS CONTEXT RESPONSE message to the old 3G-SGSN.

v. The old 3G-SGSN sends the SGSN CONTEXT RESPONSE message to

2G-SGSN, in which MM and PDP contexts are included.

vi. Execute security function.

vii. The new 2G-SGSN sends the SGSN CONTEXT ACKNOWLEDGE message

to 3G-SGSN, and notices 3G SGSN that the current 2G SGSN can accept the

relevant data PPDU of activated PDP context.

viii. If the cell phone is in the state of PMM-CONNECTED, the old 3G-SGSN sends

data forward command to SRNS. After receiving the command, SRNS starts

the data forward timer, SNNS sends the cached data PDU to the old SGSN.

ix. The old 3G-SGSN sends GTP PDUs to 2G-SGSN by tunnel mode, the serial

number in the head of GTP (obtained from the number of PDCP) does not

change.

x. The new 2G-SGSN sends the Update PDP CONTEXT REQUEST message to

each relevant GGSN. GGSN updates PDP context and returns Update PDP

Context Response.

xi. The new 2G-SGSN sends the UPDATE GPRS LOCATION message to notice

HLR to change SGSN number.

xii. HLR sends the CANCEL LOCATION message to notice the old 3G-SGSN to

cancel the location. The old 3G SGSN responses by the CANCEL LOCATION

ACK message. After the clocking of operation timeout is completed, the old

3G-SGSN deletes MM and PDP Context.

xiii. If the UE is in the state of PMM-CONNECTED, 3G-SGSN sends the LU

RELEASE COMMAND message to SRNS, after the clocking of data

forwarding is completed, SRNS responses by the LU RELEASE COMPLETE

message.

xiv. HLR sends the INSERT SUBSCRIBER DATA message to the new 2G-SGSN,

2G SGSN inserts subscription data to MM context and PDP context, and

responses by the INSERT SUBSCRIBER DATA ACK message.



xv. HLR confirms the modification is completed, and sends the UPDATE GPRS

LOCATION message to 2G-SGSN.

xvi. If the association is to be built up, the new 2G SGSN sends the LOCATION

UPDATE REQUEST message to VLR, and notices the new the UEC/VLR to

initiate location update; VLR can create or update association by saving SGSN

number.

xvii. If the user data mark in the VLR is not confirmed by HLR, VLR will notice HLR.

HLR cancels the old VLR and inserts the user data to the new VLR:

a) The new VLR sends the UPDATE LOCATION message to HLR.

b) HLR cancels the data in the old VLR by sending the CANCEL

LOCATION message to the old VLR.

c) The old VLR responses by the CANCEL LOCATION message.

d) HLR sends the INSERT SUBSCRIBER DATA ACK message to the new

VLR.

e) The new VLR responses by the INSERT SUBSCRIBER DATA ACK

message.

f) HLR responses to the new VLR by the UPDATE LOCATION ACK

message.

xviii. The new VLR assigns TMSI for the UE, and sends the LOCATION UPDATE

ACCEPT message to notice 2G-SGSN.

xix. The new 2G-SGSN verifies the validity of the UE in the new routing area, if all

the checks are successful, 2G SGSN builds up MM context and PDP context,

and establishes a logical link between the UE and 2G SGSN through 2G

SGSN, 2G SGSN responses the ROUTING AREA UPDATE ACCEPT

message to the UE.

xx. The UE confirms the new assigned PTMSI by sending the ROUTING AREA

UPDATE COMPLETE message, including confirming the data PDU sent to the

UE successfully before the routing area update is initiated.

xxi. After confirmed by the UE, 2G-SGSN sends the TMSI REALLOCATION

COMPLETE message to notice VLR TMSI that the assignment is completed

again.

xxii. 2G-SGSN and BSS execute BSS Packet Flow Context procedure.



2.4.4.3 Handover From 2G to 3G in PS Domain

1. Intra-SGSN

When a UE radio interface hands over from GSM interface to UTRAN interface,

UTRAN interface and GSM interface are connected to one SGSN.

Figure 2-12 Inter-RAT Handover From GSM To UMTS in SGSN (Group Domain)

3. Security Functions

UE/MS BSS 2G+3G-SGSN SRNS

2. Routing Area Update Request

11. RAB Assignment Request

11. RAB Assignment

Response

13. Packet Transfer Resume

1. Intersystem change decision

12. Packet Transfer Resume

7. Routing Area Update Accept

8. Routing Area Update Complete

Set up Radio

Resources

C1

new

MSC/VLR

HLR old

MSC/VLR

4. Location Update Request

5a. Update Location

5b. Cancel Location

5c. Cancel Location Ack

5d. Insert Subscriber Data

5e. Insert Subscriber Data

5f. Update Location


9. TMSI Reallocation Complete 10. Service Request

i. The UE hands over from UTRAN to the cell which supports UTRAN interface.

ii. The UE initiates routing update request, the 2G+3G-SGSN stops forwarding

data to the UE and caches.

iii. Execute security function (optional).

iv. If it is joint routing update and attached by IMSI or the location area changes,

the 2G+3G-SGSN sends the LOCATION UPDATE message to VLR.



v. If the user data in VLR is not confirmed by HLR, the new VLR notices HLR to

delete the user data in the old VLR, and inserts users in the new VLR.

vi. The new VLR assigns new VLR TUEI and notices the SGSN.

vii. The 2G+3G-SGSN checks whether the user is forbidden to roam, if it is

allowed, the 2G+3G-SGSN can assign new P-TUEI, and send the ROUTING

AREA UPDATE ACCEPT message to notice UE.

viii. The UE sends the ROUTING AREA UPDATE COMPLETE message to the

SGSN by using the new P-TUEI.

ix. If the UE accepts VLR TUEI, 2G+3G-SGSN sends the TUEI REALLOCATION

COMPLETE message to the new VLR.

x. If the UE needs to send signaling or uplink data, the UE can initiate the service

request process. If the 2G+3G-SGSN needs to forward signaling or downlink

data, the 2G+3G-SGSN will initiate the paging process.

xi. The 2G+3G-SGSN requests SRNS to build radio bearer by RAB assignment.

xii. Data forwarding recovers.

xiii. Combined with Step xii.

If the UE is CAMEL user, the following processes will be triggered:

i. CAMEL_GPRS_Routeing_Area_Update_Session

ii. CAMEL_GPRS_Routeing_Area_Update_Context.

2. Inter-SGSN

The process of group domain handover between SGSNs from GSM to UNTS is as

shown in figure below.



Figure 2-13 Inter-RAT Handover From GSM To UMTS in SGSN (Group Domain)

UE/MS

new 3

G -SGSN

HLR GGSN

old 2

G -SGSN

8. Update PDP Context Request 8. Update PDP Context Response 9. Update GPRS Location

12. Update GPRS Location

Ack

2.

Routing Area Update Request

4. SGSN Context Response 5. Security

Functions

16.

Routing Area Update Accept

10. Cancel Location 10. Cancel Location

Ack


Ack


17.

Routing Area Update Complete

6. SGSN Context Acknowledge

BSS

SRNS

3. SGSN Context Request

20. RAB Assignment Response

7. Forward Packets

1. Inter-RAT change decision

C3

C1

new MSC/VLR

old MSC/VLR

13. Location Update Request 14a. Update

Location 14b. Cancel Location 14b. Cancel Location

Ack

14c. Insert Subscriber Data 14d. Insert Subscriber Data

Ack

14e. Update Location

Ack



Set up Radio Resources

19. Service Request

C2

20. RAB Assignment Request



i. The UE or BSS determines to handover between systems for group domain,

which makes the UE handover to another new WCDMA cell, at the same time

the data transmission is stopped between the UE and the network.

ii. The UE sends routing area update request to the new 3G-SGSN. Routing area

update or joint RA/LA update or joint RA/LA update with IMSI attached will be

specified for the Update Type, before the message is sent to SGSN. Before

sending the user message to SGSN, SRNC will add the RAC and LAC routing

identifiers of the area where the UE locates.

iii. The 3G-SGSN obtains the address of the old 2G-SGSN through the old routing

area identifier from the UE, and then sends the SGSN CONTEXT REQUEST

message to the old 2G-SGSN, in order to obtain MM context and PDP context

of the user. The old 2G-SGSN verifies the P-TMSI signature of the UE, if the

P-TMSI signature is valid or 3G-SGSN indicates that the UE has already been

authenticated, the 2G-SGSN starts a timer.

iv. The old 2G-SGSN responds through the SGSN CONTEXT RESPONSE

message, which includes MM Context and PDP Context.

v. A security function process is initiated.

vi. The 3G-SGSN sends the SGSN CONTEXT ACKNOWLEDGE message to the

2G-SGSN, so the 2G-SGSN knows that the 3G-SGSN can accept the relevant

data packet of the activated PDP context.

vii. The 2G-SGSN copies and caches N-PDUs, and it starts to send data packet to

the 3G-SGSN. Before the timer times out, the extra N-PDUs received from

GGSN will be copied and sent to 3G-SGSN. After the timer times out, no

N-PDUs will be sent to 3G-SGSN.

viii. The 3G-SGSN sends the UPDATE PDP CONTEXT REQUEST message to

each GGSN related. Each GGSN updates its PDP context and responses the

UPDATE PDP CONTEXT RESPONSE message.

ix. The 3G-SGSN notices HLR that the SGSN has changed by sending the

UPDATE GPRS LOCATION message.

x. The HLR sends the CANCEL LOCATION message to the old 2G-SGSN. After

the 2G-SGSN timer times out, the old 2G- SGSN will delete MM context and

PDP context. The 2G-SGSN responds by sending the CANCEL LOCATION

ACK message.

xi. The HLR sends the INSERT SUBSCRIBER DATA message to the 3G-SGSN.

The 3G-SGSN builds up MM context and replies the INSERT SUBSCRIBER

DATA ACK message to the HLR.



xii. The HLR confirms that the modification is completed, and responds to the

3G-SGSN through the UPDATE GPRS LOCATION message by returning an

UPDATE GPRS LOCATION ACK.

xiii. If the association is to be built up, and the joint RA/LA update attached by IUEI

is specified for Update Type, or the LA changes in the routing area update, the

new SGSN will sends the LOCATION UPDATE REQUEST message to the

VLR, and notices the new VLR to initiate location update, the VLR creates or

updates association by saving SGSN number.

xiv. If the user data identifier in the VLR is not confirmed by the HLR, the VLR will

notice the HLR. The HLR cancels the old VLR and inserts user data to the new

VLR.

a) The new VLR sends Update Location to the HLR.

b) The HLR cancels the old data in the VLR by sending the CANCEL

LOCATION message to the old VLR.

c) The old VLR responds through the CANCEL LOCATION message.

d) The HLR sends the INSERT SUBSCRIBER DATA ACK to the new VLR.

e) The new VLR responds through the INSERT SUBSCRIBER DATA ACK

message.

f) The HLR responds to the new VLR through the UPDATE LOCATION

ACK message.

xv. The new VLR assigns a new TUEI and notices the 3G-SGSN through the

LOCATION UPDATE ACCEPT message.

xvi. The 3G-SGSN verifies the UE in the new routing area, if all the checks are

passed, the 3G-SGSN builds up the MM context and PDP context of the user.

The 3G-SGSN sends the ROUTING AREA UPDATE ACCEPT message to

the UE.

xvii. The UE confirms the new assigned PTMSI by sending the ROUTING AREA

UPDATE COMPLETE message.

xviii. If the confirmation is obtained from the UE, the 3G-SGSN sends the TMSI

REALLOCATION COMPLETE message to the new VLR.

xix. If the UE has uplink data or signaling, it will send the SERVICE REQUEST

message to the SGSN. The requested service will be specified in Service Type

(data or signaling)

xx. If the UE has sent the service request, the 3G-SGSN sends the RAB

ASSIGNMENT REQUEST message to request SRNS to build a radio access



bearer. The SRNS sends the RADIO BEARER SETUP REQUEST message

to the UE. The UE responds through the RADIO BEARER SETUP

COMPLETE message. The SRNS sends the RAB ASSIGNMENT

RESPONSE message to the SGSN. The SRNS sends N-PDUs to the UE.



3 2G/3G Interoperability Parameters

3.1 2G/3G Interconnection Parameters

1. Parameters Provided to 3G by 2G

The radio parameters provided to 3G by 2G include the country code (MCC),

network code (MNC), location area code (LAC), cell ID (CI), network color code

(NCC), base station color code (BCC), band indication (900 or 1800) and BCCH.

Error! Reference source not found. shows an example of parameters for 2G, and

all the parameters are decimal in the example.

Table 3-1 Parameters Provided to 3G by 2G

MCC MNC LAC CI NCC BCC Band

Indication BCCH

460 2 2 2 0 0 900 10

2. Parameters Provided to 2G by 3G

The radio parameters provided to 2G by 3G include country code (MCC), network

code (MNC), location area code (LAC), RNC ID (RNC ID), cell ID (C_ID), downlink

frequency point, primary scrambling code, and frequency bandwidth. Error!

Reference source not found. shows an example of parameters for 3G, and all the

parameters are decimal in the example.

Table 3-2 Parameters Provided to 2G by 3G

MCC MNC LAC RNC

ID C_ID

Downlink ARFCN

Primary Scrambling

Code

Frequency Bandwidth

460 2 20 1 1501 10687 126 5

3.2 Typical Selection and Reselection Parameters

The reselection parameters from WCDMA to GSM/GPRS are delivered in the SIB3 and

SIB11 WCDMA messages. The content of the current cell is delivered in the SIB3

message, and the content of the neighbor cells is delivered in the SIB11 message.



Table 3-3 Key 2G->3G Cell Reselection Parameters

FDD_Qoffset FDD Reselection Offset 0 (–∝)

FDD_Qmin Minimum value of Ec/No of UTRAN reselection cell 7(–12 dB)

Qsearch_I Threshold for UE to start UTRAN cell reselection measurement

7 (always)

Table 3-4 Key 3G->2G Cell Reselection Parameters

Parameter Description Baseline

Value

Qqualmin Lowest access quality of 3G cell signal –18 dB

QRxLevMin Lowest access strength of 3G cell signal –115 dBm

SSearchRat Inter-RAT measurement trigger threshold for cell reselection

6 dB

QHyst1S Reselection delay of serving cell 1 10 dB

Qoffset1SNSib11 Quality offset 1 of serving and neighbor cells in SIB11

10 dB


0 dB

Treselection Time duration of cell reselection timer 1 s

3.2.1 Key 2G->3G Reselection Parameters

3.2.1.1 FDD_Qoffset

Description

If a UTRAN neighbor cell has been switched on (a 3G cell itself should meet certain

conditions) and it satisfies the demand of starting measurement that is set in the cell,

a UE can reselect the UTRAN neighbor cell after it meets the three conditions

below:

The RSCP (received signal code power) of the neighbor cell is higher than the

RLA_C.

The RSCP of the neighbor cell is higher than the RLA_Cs of all the GSM

neighbor cells by at least FDD_Qoffset (FDD reselection offset), and it lasts at

least 5 seconds (if it reselected a GSM cell 15 seconds ago, the FDD_Qoffset

still needs 5 dB increment).

The Ec/No of the neighbor cell is higher than or equal to the FDD_Qmin set in

the cell (the minimum Ec/No of the UTRAN reselection cell).



If there are more than one UTRAN cells that can meet the conditions above, the cell

with the highest RSCP is selected.

Impact on the network performance

This parameter is set to 8, which shows that the signal offset between GSM and 3G

is 0. However, the 3G system is usually in the 2G band, and the propagation loss is

large. It is better to set to 0 according to the actual experience, which means that the

impact of the 3G signal is not taken into account in the reselection process from

GSM to 3G, in order to improve the reselection success rate from 2G to 3G.

Parameter configuration (iBSC V6.20.614C)

OMC GERAN Subnet User ID BSC Management NE User ID Configuration

Set ID BSC Global Resource ID BS Configuration BS ID Cell ID UTRAN

Cell Control Basic Attribute 1

3.2.1.2 FDD_Qmin

Description

When it reselects the UTRAN neighbor cell, it requires that the value of Ec/No is not

less than the value of the cell.


It is a key 2G->3G reselection parameter and the recommended value is 7(-12 dB)

for network optimization. The difference of the reselection judgment thresholds

between the WCDMA and GSM/GPRS systems should be at least 4 dB, such as the

SsearchRAT parameter for WCDMA and the FDD_Qmin parameter for

GSM/GPRS.

It is set to 7 in order to improve the reselection success rate from 2G to 3G.





3.2.1.3 Qsearch_I

Description

When the RLA_C of the cell is lower (0~6) or higher (8~14) than the threshold, a UE

starts the measurement of the UTRAN reselection cells. 7 refers to always and 15

refers to never.




For the Qsearch_I parameter, the UE measures the inter-RAT cells all the time after

it enters the cell that is expected for interoperability. As long as the 3G system signal

condition is satisfied for residence, it will reselect the system.

If the system is requested to support the GSM->3G reselection, it is recommended

to set to 7 for a cell with inter-RAT neighbor cells, in order to improve the reselection

success rate from 2G to 3G. It is set to 15 for closing the measurement.





3.2.2 Key 3G->2G Reselection Parameters

3.2.2.1 Qqualmin

Description

This parameter shows the minimum level of quality demand for selection and

reselection which is satisfied by a cell. When it is CPICH Ec/No for measurement, as

long as the quality value of the measured cell is bigger than the Qqualmin, it can

satisfy the condition of cell selection. The default value is -18 dB.

Table 3-5 Qqualmin Description

Wireless Parameter Name

Full Name Qqualmin(dB)

Abbreviation QQualMin

Description

This parameter shows the minimum level of quality demand for selection and reselection which is satisfied by a cell. When it is CPICH Ec/No for measurement, as long as the quality value of the measured cell is bigger than the Qqualmin, it can satisfy the condition of cell selection. The default value is -18 dB.

Value Range and Stepsize

[-24, 0] dB; Step 1 dB

Unit dB

Default Value (Remarks)

-18 dB




If the value of this parameter increases, the condition of cell selection is difficult to

be satisfied; if the value of this parameter decreases, the condition of cell selection

is easy to be satisfied. However, it is likely that a UE cannot receive the system

message borne by the PCCPCH correctly after it resides in the cell.

Parameter configuration

Log on the OMC-R and set in the path below.

Interface Path: view Configuration Management RNC NE RNC Radio

Resource Management Utran cell Utran cell xx Modify Advanced Parameter

SCCPCH

3.2.2.2 SsearchRAT

Description

This parameter shows the trigger threshold Ssearch,RAT of inter-RAT measurement for

reselection. The UE is used to determine whether to carry out the inter-RAT

measurement. When the HCS is not used, if the quality of the serving cell is higher

than the Ssearch,RAT , the inter-RAT measurement will not be performed, if the quality

of the serving cell is not higher than the Ssearch,RAT or the Ssearch,RAT is not configured,

the inter-RAT measurement will be performed. For details, refer to TS 25.304.

Table 3-6 SsearchRAT Description


Full Name Ssearch, RAT(dB)

Abbreviation SSearchRat

Description

This parameter shows the trigger threshold Ssearch, RAT of inter-RAT measurement for reselection. The UE is used to determine whether to carry out the inter-RAT measurement. When the HCS is not used, if the quality of the serving cell is higher than the Ssearch, RAT, the inter-RAT measurement will not be performed, if the quality of the serving cell is not higher than the Ssearch, RAT or the Ssearch, RAT is not configured, the inter-RAT measurement will be performed. For details, refer to TS 25.304.


[0, 20] dB; Step 2 dB

Unit dB


6 dB


This parameter works as the trigger threshold of inter-RAT measurement in the

selection and reselection processes for the HCS cell.



The factors that should be taken into account for parameter configuration include:

cell residence and UE battery consumption.

The higher the parameter is, the easier the inter-RAT measurement is triggered and

the more the UE battery consumes. The smaller the parameter is, the more difficult

the inter-RAT measurement is triggered; and it cannot reside in the cell with good

quality in time, which causes call loss easily.



Interface Path: View Configuration Management RNC NE RNC Radio

Resource Management Advanced Parameter Manage ueCnst Waiting Time

for Receiving "In Sync" from L1 in Connected Mode (T312 in Connected Mode)

3.2.2.3 QRxLevMin

Description

This parameter shows the minimum threshold of received level for selection and

reselection which is satisfied by a cell. When it is CPICH RSCP for measurement,

the quality value of the measured cell is bigger than the Qrxlevmin, which can just

satisfy the condition of cell selection.

Table 3-7 QRxLevMin Description


Full Name Qrxlevmin(dBm)

Abbreviation QRxLevMin

Description

This parameter shows the minimum threshold of received level for selection and reselection which is satisfied by a cell. When it is CPICH RSCP for measurement, the quality value of the measured cell is bigger than the Qrxlevmin, which can just satisfy the condition of cell selection.


[-115,-25] dBm step 2dBm

Unit dBm


-115 dBm


The higher this parameter is, the more difficult UE resides in the cell, which leads to

be off the network. The lower this parameter is, the easier it is to reside, but it may

lead to that a UE cannot receive the system message borne by PCCPCH correctly

after it resides in the cell.



Adjustment recommendation: it is not adjusted generally, and it is not recommended

to be adjusted.



OMC path: View Configuration Management RNC NE RNC Radio Resource

Management UltranCell UltranCellXXX Modify Advanced Parameter UTRAN

Cell Indicator of Cell Re-establishment when OCNS Codes Changed

3.2.2.4 QHyst1S

Description

This parameter shows the delay parameter of FDD cell reselection for judgment

when the measurement value is CPICH RSCP or Cpich EcNo. In the rule of value R

ordering for reselection, the R value of serving cell is equal to the measurement

value and reselection delay. When the measurement value is Cpich RSCP,

calculate and order the R values according to the Qhyst1s. When the measurement

value is Cpich EcNo, first calculate and order the R values according to the Qhyst1s,

the UTRAN cell ranks at the top, then calculate and order the R values according to

the signal quality of Cpich EcNo.

Table 3-8 QHyst1S Description


Full Name Qhyst1s(dB)

Abbreviation QHyst1S

Description

This parameter shows the delay parameter of FDD cell reselection for judgment when the measurement value is CPICH RSCP or Cpich EcNo. In the rule of value R ordering for reselection, the R value of serving cell is equal to the measurement value and reselection delay. When the measurement value is Cpich RSCP, calculate and order the R values according to the Qhyst1s. When the measurement value is Cpich EcNo, first calculate and order the R values according to the Qhyst1s, the UTRAN cell ranks at the top, then calculate and order the R values according to the signal quality of Cpich EcNo.


[0, 40] dB; Step2 dB

Unit dB


10 dB




The higher this parameter is, the more difficult the reselection is triggered, and the

less sensitive it is relatively for the signal variation. The lower this parameter is, the

easier the reselection is triggered, and the more ping-pong reselections occur,

which increase the signaling load.

Adjustment recommendation: It can be set to be higher properly for the scenario

where the signal changes fast.



Interface Path: view Configuration Management RNC NE RNC Radio

Resource Management Utran cell Utran cell xx Modify Advanced Parameter

PICH

3.2.2.5 Qoffset1s,n in SIB11(dB)

Description

This parameter shows the quality offset of serving and neighbor cells when the

measurement value is CPICH RSCP. It is used for cell ordering in the reselection

rule. This parameter is broadcast to UE in the SIB11. The R value of the neighbor

cell is equal to be the measured signal quality of the neighbor cell subtracting this

offset.

Note:

For idle or connected mode, when the SIB12 is not broadcast, it is equal to the value of

Qoffset1SNSib11 when the reselection measurement value is RSCP; for connected

mode, when the SIB12 is broadcast, it is equal to the value of Qoffset1SNSib12 when the

reselection measurement value is RSCP.

Table 3-9 Qoffset1s,n in SIB11(dB) Description


Full Name Qoffset1s,n in SIB11(dB)

Abbreviation Qoffset1SNSib11

Description

This parameter shows the quality offset of serving and neighbor cells when the measurement value is CPICH RSCP. It is used for cell ordering in the reselection rule. This parameter is broadcast to UE in the SIB11.


OMCR: [-50, 50] dB;

Unit dB





0 dB


The factors that should be taken into account for configuring this parameter include

the degree of difficulty for reselection and the tendentiousness of reselection.

The lower this parameter is, the easier it reselects this neighbor cell. The higher this

parameter is, the more difficult it reselects this neighbor cell. It can be set to be

different values for different GSM neighbor cells, in order to control the

tendentiousness of reselection for different GSM neighbor cells.

Adjustment recommendation:

For a co-frequency neighbor cell, adjust the value of this parameter in order to

reselect cell when the neighbor cell is better than the source cell.

For a different-frequency or inter-RAT neighbor cell, it is configured according to the

service planning of the multi-carrier networking.




Resource Management UltranCell UltranCellXXX Neighboring Cell

Advanced Parameter Manager Qoffset1s,n in SIB11(dB)


Description


measurement value is CPICH RSCP. It is used for cell ordering in the reselection

rule. This parameter is broadcast to UE in the SIB12.

Note:

For idle or connected mode, when the SIB12 is not broadcast, it is equal to the value of

Qoffset1SNSib11 when the reselection measurement value is RSCP; for connected

mode, when the SIB12 is broadcast, it is equal to the value of Qoffset1SNSib12 when the

reselection measurement value is RSCP.



Table 3-10 Qoffset1s,nin SIB12(dB) Description




Description

This parameter shows the quality offset of serving and neighbor cells when the measurement value is CPICH RSCP. It is used for cell ordering in the reselection rule. This parameter is broadcast to UE in the SIB12.


OMCR: [-50, 50]dB

Unit dB


0 dB





parameter is, the more difficult it reselects this neighbor cell. It can be different

values for different UMTS neighbor cells, in order to control the tendentiousness of

reselection for different UMTS neighbor cells.


Generally the SIB12 is not used, it is not recommended to adjust this parameter.



Interface Path: View -> Configuration Management -> RNC NE -> RNC Radio

Resource Management -> UltranCell -> UltranCellXXX -> Neighboring Cell ->

Advanced Parameter Manager -> Qoffset1s,n in SIB12(dB)

3.2.2.7 Treselection

Description

This parameter shows the timer duration of reselection. To be a serving cell, a new

cell must be the best cell according to the ordering R principle, and it lasts for

Treselections, which can be selected the new serving cell.



Table 3-11 Treselection Description


Full Name Treselection(s)

Abbreviation TReselection

Description

This parameter shows the timer duration of reselection. To be a serving cell, a new cell must be the best cell according to the ordering R principle, and it lasts for Treselections, which can be selected the new serving cell.


[0, 31]s; step 1s

Unit S


1s



the signal quality variation and ping-pong reselection.

This parameter is used to avoid the ping-pong reselection. If it is set to be too lower,

the ping-pong reselection is easy to occur. If it is set to be too higher, the reselection

is slower, which may lead to call loss.

Adjustment recommendation: In the scenario of high-speed railway or highway, it is

set to be lower in order to speed up the reselection speed and improve the call

success rate.




Resource Management Advanced Parameter Manage ueCnst Waiting Time

for Completion of Cell Update When Radio Link Fails and Radio Bearer(s)

Associated with T315 Exist (T315)

3.2.2.8 Qhyst2s(dB)

Description

This parameter shows the delay parameter of FDD cell reselection for judgment

when the measurement value is CPICH Ec/No. In the rule of value R ordering for

reselection, the R value of serving cell is equal to the measurement value and

reselection delay. Refer to TS 25.304 for details.



Table 3-12 Qhyst2s(dB) Description


Full Name Qhyst2s(dB)

Abbreviation QHyst2S

Description

This parameter shows the delay parameter of FDD cell reselection for judgment when the measurement value is CPICH Ec/No. In the rule of value R ordering for reselection, the R value of serving cell is equal to the measurement value and reselection delay. Refer to TS 25.304 for details.


[0, 40] dB; Step 2 dB

Unit dB


2 dB



the signal variation and ping-pong reselection.

The higher this parameter is, the more difficult the reselection is triggered, and the

less sensitive it is relatively for the signal variation. The lower this parameter is, the

easier the reselection is triggered, and the more ping-pong reselections occur,

which increase the signaling load.

Adjustment recommendation: it can be set to be higher properly for the scenario

where the signal varies very fast.




Resource Management -> RCP Scrambling Code Configuration Information ->

Ending No. of RCP Scrambling Code


Description


measurement value is CPICH Ec/No. It is used for cell ordering in the reselection

rule. This parameter is broadcast to UE in the SIB11. The R value of the neighbor

cell is equal to be the measured signal quality of the neighbor cell subtracting this

offset.







Description

This parameter shows the quality offset of serving and neighbor cells when the measurement value is CPICH Ec/No. It is used for cell ordering in the reselection rule. This parameter is broadcast to UE in the SIB11. The R value of the neighbor cell is equal to be the measured signal quality of the neighbor cell subtracting this offset.


OMCR: [-50, 50] dB;

Unit dB


0 dB






different values for different UMTS neighbor cells, in order to control the

tendentiousness of reselection for different UMTS neighbor cells.


For a co-frequency neighbor cell, adjust the value of this parameter in order to

reselect cell when the neighbor cell is better than the source cell.

For a different-frequency or inter-RAT neighbor cell, it is configured according to the

service planning of the multi-carrier networking.







Description




measurement value is CPICH Ec/No. It is used for cell ordering in the reselection

rule. This parameter is broadcast to UE in the SIB12.





Description

This parameter shows the quality offset of serving and neighbor cells when the measurement value is CPICH Ec/No. It is used for cell ordering in the reselection rule. This parameter is broadcast to UE in the SIB12.


OMCR: [-50, 50] dB;RNC: D=P+50, [0, 100]

Unit dB


0 dB






different values for different UMTS neighbor cells, in order to control the

tendentiousness of reselection for different UMTS neighbor cells.


Generally the SIB12 is not used, it is not recommended to adjust this parameter.






3.2.3 Recommended Values of Key Reselection Parameters

1. 3G->2G Reselection



Table 3-15 Recommended Values of Key 3G ->2G Reselection Parameters

Parameter Description Baseline

Value Value of Unicom

Qqualmin Lowest access quality of 3G cell signal

-18 dB -18 dB

QRxLevMin Lowest access strength of 3G cell signal

-115 dBm -115 dBm

SSearchRat inter-RAT measurement trigger threshold for cell reselection

6 dB 4dB

QHyst1S Reselection delay of serving cell 1 10 dB 10 dB


10 dB 0 dB


0 dB 0 dB

Treselection Time duration of cell reselection timer

1 s 1 s

Note:

The values of Unicom are different according to the different requirements from each city.

The values above are only for reference, the values for each project depend on the

actual.

2. 2G->3G Reselection

Table 3-16 Key 2G ->3G Reselection Parameters

FDD_Qoffset FDD Reselection Offset 0 (–∝)

FDD_Qmin Minimum value of Ec/No of UTRAN reselection cell

7(-12 dB)

Qsearch_I Threshold for UE to start UTRAN cell reselection measurement

7 (always)

Note:

It shows -∝ when the FDD_Qoffset is set to 0. The reason for setting it to be 0 is that

UE does not need to consider the strength comparison between 2G and 3G. If it

requires the UE to select 3G as far as possible in the field, this parameter can be set

to 0.

It is only reference for 2G parameters, which should be set according to the demands of

each project.



3.3 Typical Inter-RAT Handover Parameters

The key handover control parameters from WCDMA to 2G are mainly determined by the

parameters that trigger the 2D, 2F and 3A events. The lower the trigger thresholds of 2D

and 3A are, the more traffic stays in the 3G network. But the lower the two parameters

are, the worse 3G signal there is for handover and the easier the call drops occur. The 2D

and 3A parameters are set to be higher, thus the service can be switched to 2G cell

before the WCDMA signal gets worse, in order to decrease the call drop rate. Through

the test results, in order to avoid the call drop in the edge of 3G network, it should start

the inter-RAT measurement in the condition of a better 3G signal, which means that the

2D event trigger level should be too lower for the circuit domain service in the different

system. However, the thresholds of 2D and 3A cannot be too higher, or it will lead to that

a large number of 3G subscribers switch to the 2G cells and the GSM traffic increases.

These key parameters are described below.

3.3.1 2D/2F Event Threshold

Description

This parameter shows the absolute threshold configured for 2D/2F event (used for

judging the quality of the carrier frequency being used).

Table 3-17 2D/2F Event Configured Threshold


Full Name Absolute threshold configured for 2D/2F event (used for judging the quality of the carrier frequency being used).

Abbreviation ThreshUsedFreq[MAX_INTER_MEAS_EVENT]

Description

This parameter shows the absolute threshold configured for 2D/2F event (used for judging the quality of the carrier frequency being used). The MAX_INTER_MEAS_EVENT is the maximum number of inter-frequency measurement event, and the value is 6.


CPICH RSCP: [-115,-25] dBm;CPICH Ec/No: [-24,0] dB

Pathloss: [30,165] dB

Unit dBm /dB


Reported parameter of UE periodical measurement when the measurement value is CPICH Ec/No: -

Reported parameter of UE inter-frequency event when the measurement value is CPICH Ec/No: [-13, -5]dB

Reported parameter of UE periodical measurement when the measurement value is CPICH RSCP: -

Reported parameter of UE inter-frequency event when the measurement value is CPICH RSCP: [-95, -80] dBm




The 2D and 2F events are the switch of the compact model. The lower the 2D

threshold is, the more difficult the 2D is triggered. The lower the 2F threshold is, the

easier the 2F is triggered. As the requested signal quality and inter-RAT handover

policies are different according to different service types, so the inter-RAT

measurement thresholds are divided into CS and PS signaling. When a cell is in the

center of carrier frequency coverage, it will use the Ec/No measurement value as

the criterion of the 2D and 2F events. Therefore, if the compact model is expected to

start as early as possible, set the 2D event threshold to be higher, otherwise set it to

be lower. If the ping-pong handover is expected to decrease in the start and stop

processes of the compact model, it can increase the difference between the 2D and

2F thresholds. The easier the event is triggered, the more number of average

handover time there is, which increases the handover success rate, but consumes

the system resources.

Note:

It can choose Ec/Io or RSCP as the trigger threshold of each event, according to the

actual situation. At the edge of the cell coverage, the system is usually limited for the

uplink loss, which triggers the inter-RAT handover caused by coverage. The range of

Ec/Io is relatively smaller, which is not suitable for the handover caused by coverage as it

varies very fast, so it is recommended to adopt the RSCP. For the center of the cell

coverage, there is more interference and the system is usually limited for the downlink

interference, which triggers the inter-RAT handover. Therefore, the Ec/Io can better

reflect the interference degree of the system.

Currently it adopts RSCP for the trigger threshold of each event.



Interface Path: View->Configuration Management->RNC NE->RNC Radio

Resource Management->Modify Advanced Parameter->UE Inter-frequency

Measurement Configuration-> Absolute Threshold of the Quality of the Currently

Used Frequency for 2B/2D/2F

3.3.2 3A/3C Event Threshold

Description

This parameter shows the absolute threshold value for judging the quality of other

system, which is configured for 3A/3C event. The value range and unit of this

parameter are related to the measurement value of other system cell, which is only

for the GSM Carrier RSSI of GSM system now, corresponding to the CPICH RSCP



of local system. Therefore, the value range and unit of this parameter correspond to

the CPICH RSCP.

Table 3-18 3A/3C Threshold Parameter


Full Name Absolute threshold value for judging the quality of other system, which is configured for 3A/3C event

Abbreviation ThreshSys[MAX_RAT_MEAS_EVENT]

Description

This parameter shows the absolute threshold value for judging the quality of other system, which is configured for 3A/3C event. The value range and unit of this parameter are related to the measurement value of other system cell, which is only for the GSM Carrier RSSI of GSM system now, corresponding to the CPICH RSCP of local system. Therefore, the value range and unit of this parameter correspond to the CPICH RSCP. MAX_RAT_MEAS_EVENT is the maximum number of inter-RAT measurement event, and the value is 4.


CPICH RSCP: [-115,-25]dBm step 1dBm

CPICH Ec/No: [-24,0] dB step 1dB

Unit dBm /dB


Periodically-reported parameter when the measurement value is CPICH Ec/No of local system: -

Reported parameter by UE event when the measurement value is CPICH Ec/No of local system: [-6, -24]

Periodically-reported parameter when the measurement value is CPICH RSCP of local system: -

Reported parameter by UE event when the measurement value is CPICH RSCP of local system: [-95, -115]


The factors that should be taken into account for configuration include the

compression moulding start time, the average handover times, and the handover

success rate.

For the 3A/3C, the lower it is, the more difficult it is triggered, or the higher it is, the

easier it is triggered.

For the 3B, the higher it is, the more difficult it is triggered, or the lower it is, the

easier it is triggered.


i. In order to avoid the capacity loss caused by starting compression moulding,

as long as the compression moulding of inter-RAT measurement is enabled by

2D event trigger, it is expected to switch to the 2G system as soon as possible,

so the 2G system threshold should not be higher.



ii. If the quality of inter-RAT neighbor cell is also poor, the service switches

rashly. There is a high rate of call drop, and the service quality cannot be

guaranteed after handover. So this threshold cannot be set to be lower, in

order to guarantee the service to be normal.

Note:

According to the current 3G strategy, let the 3G subscribers enjoy the 3G services as far

as possible, and it adopts the 3A event trigger for the network.




Resource Management-> Modify Advanced Parameter->UE Inter-RAT

Measurement Configuration Information-> Absolute Threshold of the Quality of

Other RAT for 3A/3B/3C

3.3.3 Hysteresis(Rat)

Description

This parameter shows the delay for judging whether a event satisfies the event

trigger condition.

Table 3-19 Hysteresis(Rat) Parameter Description


Full Name Hystersis(dB)

Abbreviation Hysteresis[MAX_RAT_MEAS_EVENT]

Description

This parameter shows the delay for judging whether a event satisfies the event trigger condition. Using this parameter will generate a difference value between the state of triggering an event and the left state of triggering an event, which avoids that even a little variation can change the trigger state. It is configured for different events individually with different values.

The MAX_INTER_MEAS_EVENT is the maximum number of inter-frequency measurement event, and the value is 6.


(0, 0.5..14.5) dB step 0.5 dB

Unit dB


Periodically-Reported parameter by UE when the measurement value is CPICH Ec/No: -

Reported parameter by UE inter-frequency event when the




measurement value is CPICH Ec/No: [4,4,4,4,4,4]dB

Periodically-Reported parameter by UE when the measurement value is CPICH RSCP: -

Reported parameter by UE inter-frequency event when the measurement value is CPICH RSCP: [4,4,4,4,4,4]dB

Reported parameter by UE inter-frequency event when the measurement value is CPICH Ec/No (GSM): [4, 4]dB

Reported parameter by UE inter-frequency event when the measurement value is CPICH RSCP (GSM): [4, 4]dB


The factors that should be taken into account for configuration include the average

handover times, handover success rate, terminal movement speed and the

handover area size.

The higher this parameter is, the less probability the inter-frequency event is

triggered, and the less times of average handover there are, which increases the

risk of call drop.

The lower this parameter is, the more probability the inter-frequency event is

triggered, and the more times of average handover there are, which may lead to a

mistake handover.

Adjustment recommendation: For the scenario of small handover area or terminal

moving fast, in order to complete the handover timely, it can be set to be lower

properly. On the contrary, it needs to be set to be a little higher.

This parameter is related to the measurement value and event type. If decreasing

the delay, it can increase the probability of reporting the corresponding events. On

the contrary, it can decrease the probability of reporting the corresponding events if

increasing the delay.




Resource Management-> Modify Advanced Parameter->UE Inter-RAT

Measurement Configuration Information-> Hysteresis



3.3.4 Recommended Values of Key Inter-RAT Handover Parameters

Table 3-20 3G->2G Parameters List

Parameter Definition Class Unit Baseline

Value Value of Unicom

CPICH Ec/Io 2D Threshold

2D quality threshold CS dB –13 -13

PS dB –13 -13

CPICH RSCP 2D Threshold

2D strength threshold CS dBm –95 -95

PS dBm –95 -105

Hysteresis2D Delay range for 2D judgment

CS/PS dB 4 4

TimeToTrigger2D Timer to trigger Event 2D

CS/PS ms 640 640

CPICH Ec/Io 2F Threshold

2F quality threshold CS dB –5 -5

PS dB –5 -5

CPICH RSCP 2F Threshold

2F strength threshold CS dBm –80 -90

PS dBm –80 -100

Hysteresis2F Delay range for 2D judgment

CS/PS dB 4 4

TimeToTrigger2F Timer to trigger Event 2F

CS/PS ms 640 640

CPICH Ec/Io 3A Threshold

3A quality threshold CS dB –6 -6

3A quality threshold PS dB –6 -6

CPICH RSCP 3A Threshold

3A strength threshold CS dBm –95 -92

PS dBm –95 -102

Hysteresis3A 3A delay window CS/PS dB 4 4

TimeToTrigger3A Timer to trigger Event 3A

CS/PS ms 100 100

Note:

The values of Unicom are different according to the different requirements from each city.

The values above are only for reference, the values for each project depend on the

actual.

3.4 Setting for 2G/3G Inter-RAT Neighbor Cells

To set the 2G/3G inter-RAT neighbor cells, the general methods are as follows:



The setting for the neighbor cell is based on the different interoperability strategies

of 2G/3G.

When the coverage is not continuous within the UMTS network, the interoperability

between the whole network and 2G system should be taken into account. The

method of configuring 2G neighbor cells for the whole network is the same as the

method of configuring neighbor cells within the system, and the traffic congestion of

the neighbor cells should also be taken into account.

When the coverage is continuous within the UMTS network, and it only switches

between the edge of the UMTS system and 2G system, it only needs to configure

the neighbor cells for the edge base stations, and the principles below should be

considered:

The co-location and co-direction cells are set to be the neighbor cells.

Generally, GSM900 is preferred, and the traffic-balancing and capacity of

GSM900/1800 also should be considered.

The congestion GSM cells are not to be set as far as possible.



4 Interoperability Problems Analysis and Optimization

The main points for evaluating the quality of inter-RAT interoperability is that, dual-mode

terminal can move smoothly from one network to another network, without off the network

or calls dropped. The key to achieve a smooth migration is how to adjust the relationship

between GSM and WCDMA, after a long period of optimization, the signal distribution of

GSM network has become more reasonable, so the adjustment should be primarily

focused on the WCDMA side. Specific adjustment principles are as follows:

Avoid a sudden decline of the signal in the border area of WCDMA coverage, if

there is a sudden decline in the border area of ECDMA, it is suggested to optimize

the network, increase the signal strength or reselect the WCDMA signal. This

principle also applies to the signal of internal WCDMA for different frequency

handover.

Avoid the overlap between the borders of WCDMA and GSM. if GSM has a good

coverage in the border of WCDMA, it helps to handover from WCDMA to GSM

successfully, on the contrary if the border of WCDMA is not set properly, the signal

strength of GSM network is not enough while handing over, it will increase the

failure possibility of inter-RAT measurement or signaling interaction, which causes

the dropped call.

Continuous signal coverage in WCDMA should be implemented as much as

possible, reduce the signal blind and weak zones, especially in the places with

many people, The WCDMA signal usually declines suddenly in these place, and it is

too late to handover and measure between systems and leads to a higher failure

probability of the system handover. By increasing the coverage, the inter-RAT

handover can be pushed to the edge of 3G coverage, which reduces the number of

inter-RAT handover.

The border of WCDMA network should be chosen in the area of low density people,

avoiding the area of higher density (stations, terminals, etc.). This will not only

reduce the number of inter-RAT handover, but also avoid signaling exchange

delay/failure due to lack of processing power, and eventually leading to dropped

calls. In addition, according to the specific environment, optimizing WCDMA

measurements and switching algorithm parameters to further improve the success

rate of inter-RAT handover.

Table 4-1 Optimization Methods of Typical Scenarios

Scenario FAQ Optimization Method

General scenario

Rapid changes in local signal or high-speed

1. First to improve the coverage through network planning and optimization.



Scenario FAQ Optimization Method

mobile users, easily dropped calls

2. Trying the optimization method in the scenario of fast signal changing, but pay attention to the optimized performance of the whole network

Still, low-speed

If you use CPICH RSCP measurement of the whole network, indoor still scenario prone to frequent handover of PS / reselection

1. Using Ec / Io measurement, 3A events reporting

2. Lower PS handover threshold, reducing the probability of frequent handover / reselection.

Fast signal changing

Elevator coverage scenario, better coverage outside the elevator, it does not meet the inter-RAT measurement conditions, the coverage of the elevator after closing is poor, leading to high rate of dropped calls

1. Increasing 3G coverage in the lift, 2G-3G handover needs to be avoided.

2. Increasing 2D/2F threshold, 3A handover quality threshold appropriately or reducing 2D delay, so that UE (outside the elevator) can start the inter-RAT measurement as soon as possible.

3. PS service can rebuild automatically, in this scenario, rebuilding is not obvious for the users after calls are dropped, and it does not need to optimize specially.

The analysis of typical reselection and handover problems are described below.

4.1 Reselection Problems Analysis and Optimization

Avoid the problems of excessive and failed reselections from WCDMA to GSM/GPRS for

dual-mode terminals in the edge of a WCDMA network, which decreases the inter-RAT

reselection probability and increases the paging success rate of the system.

The solution is to set the inter-RAT parameters of cell reselection reasonably, such as the

SsearchRAT parameter, if this parameter is set to be too small, the reselection from

WCDMA to GSM/GPRS may fail. However, it also cannot be set to be too higher,

otherwise the users in some places will reselect GSM/GPRS network too early or

ping-pong reselection may occur between systems, which does not meet the 3G

preferred strategy. So the inter-RAT parameters of cell reselection should be set

reasonably.

The parameters SsearchRAT of WCDMA and FDD_Qmin of GSM/GPRS should have

the interval of more than 4 dB. Additionally, the edge of WCDMA network reselection

cannot be set in the densely populated areas, in order to reduce the probability of cell

reselection between WCDMA and GSM/GPRS. At the same time it also reduces the

signaling interaction between systems and saves the resource of air interface, and the

terminal will save more energy. In the update period of the location area and routing area

after system reselection, the terminal will be barred for the outgoing calls as the calling

party, and barred for the incoming calls as the called party, so reducing the inter-RAT



reselection probability can improve the paging success rate of the system

correspondingly.

4.2 Handover Problems Analysis and Optimization

The prerequisite is that the cell phone is set to dual-mode automatic network selection.

This configuration can be queried through the multiRAT_CapabilityList.supportOfGSM

and multiRAT_CapabilityList.supportOfMulticarrier parameters in the

RRCCONNECTIONSETUPCOMPLETE message. Generally, the dual-mode is set to

True. The reason for the inter-RAT failure handover is as shown in the table below.

Table 4-2 Inter-RAT Handover Failure

Information Element/

Group Name Need Multi Type and Reference

Semantics Description

Inter-RAT handover failure cause

MD

Enumerated(Configuration unacceptable, physical channel failure, protocol error, inter-RAT protocol error, unspecified)

Default value is "unspecified".

11 spare values are needed.

The returned message cell shows that gsm_MessageList is 06 28 XX. XX refers to the

GSM information as follows.

Figure 4-1 RR Cause Information Element



4.2.1 Physical Channel Failure

If interRAT_HO_FailureCause.t = 2, it corresponds to the physical channel failure. This

phenomenon is due to the access failure on the air interface when the UE attempts to

access 2G interface. It may be caused by wrong configuration (handover to a cell that

does not exist) of neighbor cell (CGI), poor 2G signal (The threshold set in RNC for

handover to 2G is too small), external interference, or UE natural defects (Qualcomm cell

phones of Version 4240 have such kind of problem).

Currently the most common failure is that, the timer T3124 times out, the 2G RACH

channel cannot be accessed. If the neighbor cell is configured correctly, there are three

possible reasons as follows:

1. Uplink interference

Analysis

The GSM channel cannot be synchronized, and the engineers should check the

handover success rate of each 2G cell at the same time.

Solution

Delete the poor 2G neighbor cells. In some areas different frequencies vary widely,

the poor frequencies interfere a lot. If the handover success rate is lower than 80%,

it needs to summarize the rule of the deleted neighbor cells, and perform the RNC

neighbor cell deletion according to the rule.

2. Handover destination was refused before.

Analysis

For the operator's business marketing strategy, a part of the users are not allowed

to subscribe to 2G network.

Solution

Fundamental solutions: CN supports the service handover based on IUEI, which the

user attribute can be known by the access network.

Avoidance solution: Cancel the inter-RAT handover.

3. Abnormal cell phone

Analysis

The problem is related with the cell phone.



Solution

If it is PS domain, avoid the handover of such kind of users, if it is CS domain, no

handle it or communicate with the cell phone users.

4.2.2 Wrong Configuration

Analysis

interRAT_HO_FailureCause.t = 1, corresponding to Configuration unacceptable

handoverFromUTRANFailure.interRATMessage.gsm_MessageList = 06 28 6f

This phenomenon is the most common failure in the foreign countries; it shows that most

inter-RAT handovers have failed, only individual cell phones with better compatibility are

successful: encryption configuration information is not filled completely.

Solution

Upgrade BSC or adopt with the CN from ZTE.

4.2.3 Protocol Error

interRAT_HO_FailureCause.t = 3, corresponding to protocol error. There is protocol error

in the location update request message received; the network sends location update

refuse message, the reasons are as follows:

Mandatory information unit error

Information unit does not exist or cannot be achieved

Invalid information unit content

Protocol error

interRAT_HO_FailureCause.t = 3, corresponding to inter-RAT protocol error

"inter-RAT protocol error" or "configuration unacceptable": UE does not accept the

HANDOVER FROM UTRAN COMMAND message issued by RNC, the message format

issued by RNC may have problem, or maybe UE does not support the inter-RAT

handover.

4.2.4 Parameter Configuration

2D event threshold is not set reasonably, generally the threshold is not advised to

set to be too high, it is recommended to set more than 100 dBm, in order to assure

the handover success rate; 2D event delay also should be set reasonably.



3A event parameter is not set reasonably.

When UE is moved from outdoor to indoor, WCDMA signal declines sharply,

however the signal in GSM cell is still very strong due to it has indoor distribution

system. In this scenario, if the parameter of inter-RAT handover in the WCDMA cell

is not set reasonably, it also can lead to the failure of inter-RAT handover.

Relocation failure: Check whether the LAC set by CN is complete; check the radio of

relocation failure, if it is more than 20%, please ask CN to check together.

4.2.5 Neighbor Cell Configuration

The configuration of neighbor cell is missing; the current WCDMA cell misses the

destination GSM neighbor cell (The detected most powerful GSM cell is not the

neighbor cell of the current service cell).

The configuration of neighbor cell is excessive: the configuration of GSM neighbor

cell in for the current WCDMA is excessive, agreement: the maximum quantity of

GSM cells measured by UE is 32.

4.2.6 Resource Refusing

There is no available radio resource in the current destination GSM cell.



5 Cases Study

5.1 PLMN Selection and Reselection

5.1.1 Case 1

Phenomenon

In the A network, the handover from 3G->2G and reselection could not be performed by

using MOTO, NOKIA cell phones.

Case analysis

1. The voice could be handed over from 3G to 2G, but after hooking on, it returned to

3G from 2G at once, it could not reside in 2G even if it met the condition to reside.

2. The handover failed when the data service met the condition to hand over from 3G

to 2G.

3. UE in the 3G IDLE mode could not reselect 2G even if the condition was satisfied.

A network adopted different PLMN schemes for 3G/2G, The current 2G did not need to

change, and 3G adopted the different PLMN from that of 2G.

Network reselection scheme: While UE is residing in 3G, it can reselect 2G through the

normal cell reselection; while UE is residing in 2G, it can reselect 3G through equivalent

PLMN reselection.

Network handover scheme: The voice can be handed over from 3G to 2G, and it

reselects 3G back through equivalent PLMN after hooking on. PS data service can be

handed over from 3G to 2G, and it reselects 3G back through equivalent PLMN.

Problem location

The equivalent PLMN was used in PLMN selection, cell selection, reselection and

handover. When UE was reselecting, it could access normally only when it detected that

the cell was the permitted PLMN; for the case of different PLMNs, if 2G‘s PLMN was not

set to be equivalent PLMN in 3G, the following phenomenon shows:

The voice could be handed over from 3G to 2G successfully, but after hooking on in

2G, the cell phone would not update location at once, but research PLMN, the

phenomenon was that the cell phone was off the network temporarily.



When the data service met the condition to handover from 3G to 2G, after receiving

the CELL CHANGE ORDER issued by RNC, UE failed to search the 2G network,

and it returned CELL CHANGE ORDER FAIL.

UE in the 3G IDLE mode could not reselect 2G.

Solution

Set 2G‘s PLMN to be equivalent PLMN on both 3G‘s UEC and SGSN, the handover from

3G to 2G and reselection were normal.

Experience

Understand the restrictions of different PLMNs networking, and set the parameters

reasonably.

5.2 Cell Selection and Reselection

5.2.1 Case 1

Phenomenon

It could not reselect from 3G to 2G due to the measurement for different system was not

enabled by UE.

Problem location

If it was not set to enable the measurement for different systems in the FACH (MOD

CELLMEAS), RNC would not issue the information of GSM neighbor cell in SIB 11, even

if it already met the condition to enable the measurement for different systems in 3G, it

would not reselect due to there was no neighbor cell in the different systems.

Solution

Enable the measurement for different systems.

5.2.2 Case 2

Phenomenon

UE could not reselect from 2G to 3G due to 3G neighbor cell relationship was not set.

Problem location

After setting the reselection parameters for 2G=>3G, the radio signal had met the

condition for reselection to 3G, but the cell phone still could not reselect. The most direct

method was to use the background software of the cell phone to track the 2G message



issued by the network and signal quality measured by UE. If the neighbor cell relationship

of 3G was not set in 2G, then there was no 2quater (2ter) message in the system

message.

Solution

Add the 3G cell as the neighbor cell of different systems for 2G cell on the 2G BSC.

5.3 Inter-RAT Handover

5.3.1 Case 1

Phenomenon

Frequent handover from 3G to 2G in the cell was caused by the handover parameters

configuration for RNC1 and RNC10.

Case analysis

We performed coverage test for this site by using Agilent tester, but the result showed

that the 3G signal of the three cells in the site was good, so the coverage problem was

excluded.

We performed CQT dialing test in one cell at TRI722W, in the process of test, both

parties called in 3G, and handed over to 2G within several seconds, and the call must be

ended for handing over to 3G, This 3G/2G handover always occurred in the tests of

dozens of times.

While moving from one cell (12552) of TRI255W which was the neighbor site of TRI722W

to another cell (17223) of TRI722W, in the soft handover area, UE remained in 3G

network when 12552 was the best cell, when 17223 became the best cell, UE handed

over to 2G network after 3 seconds. So we doubted that the problem existed in the 3 cells

of TRI722W.

Problem location

From the analysis above, we doubted that the inter-RAT handover parameters or

strategies of the 3 cells in TRI722W had problem, which speeded up the handover from

3G to 2G. We found that the judgment method of different system event of the 3 cells in

TRI722W was ―3C Event Trigger‖, and the absolute threshold value of 3C event was -90

dBm, thus the 2G signal was very easy to achieve -90 dBm in the 3G coverage of the 3

cells in TRI722W, so the handover from 3G to 2G was easy to occur.

Solution

We modify the judgment method of different system event of the 3 cells in TRI722W to be

―3A Event Trigger", in this way, the handover from 3G to 2G could happen only when the



3G signal RSCP tested by UE was below -95 dBm and the 2G signal RSCP was above

-90 dBm, this method was hard to achieve. we tested afer the modification, there was no

handover from 3G to 2G in the call process within the coverage of TRI722W3G.

For the whole network

We found that the handover from 3G to 2G was very easy for the configuration 3C Event

Trigger and the 2G neighbor cell was configured, thus many call traffic volume of 3G was

absorbed by 2G, then we checked the sites distribution of 3C and 3A handover trigger

parameters for the whole network, as shown in the table below.

Table 5-1 3C Handover Trigger Parameters for the Whole Network and Sites Distribution of 3A Handover Trigger Parameters

RNC ID

Number of NodeBs With “3A Event

Trigger” for Inter-RAT Handover

Number of NodeBs With “3C Event

Trigger” for Inter-RAT Handover

Number of NodeBs With “3C Event

Trigger” for Inter-RAT Handover (Configured

With 2G Neighbors)

RNC1 68 106 20

RNC10 40 50 36

RNC2 120 0 0

Sum 228 156 56

1. If the judgment method of different system event was ―3C Event Trigger‖, and the

absolute threshold value of 3C event was -90 dBm, thus the base station of 3C

different system trigger (2G neighbor cell was configured) could achieve -90 dBm

very easily, so the handover from 3G to 2G occurred very easily, from the statistic

form we could see that RNC1 had 20 base stations, and RNC10 had 36 base

stations, which belonged to this case, the 56 base stations totally were very easy to

handover from 3G to 2G, These sites mainly located around the airport highway and

TRIPOLI, but also there were some sites locating in the places where there were

high internal call traffic volume in TRIPOLI (for example, Fatah University, Libya's

largest university). Fortunately, it was better for the border sites; the handover to 2G

was easy, which could ensure the success rate of handover from 3G to 2G and

reduced the call drop rate due to the handover from 3G to 2G; However, for the

places where had relative densely 3G sites within TRIPOLI, the frequent handover

from 3G to 2G would result in the loss of many users and a decline in traffic. For this

case there were 2 methods to suggest:

The first method was to remove the 2G neighbor cells of the base stations which

has relative high call traffic volume in TRIPOLI, and ensure the users within the city

reside in the 3G network, but this method would lead to that 3G could not handover

to 2G in case of call drop for the indoor places where the signal was not good.

The second method was to change the judgment method of different system event

from ―3C Event Trigger‖ to ―3A Event Trigger" for cells of base stations which had



relative high call traffic volume in TRIPOLI, which also could ensure that the users in

the city reside in the 3G network.

2. The judgment method of different system event was ―3A Event Trigger", which

made the handover from 3G to 2G occur only when the 3G signal RSCP tested by

UE was below -95 dBm and the 2G signal RSCP was above -90 dBm, this method

was hard to achieve.

3. The current locations of ―3A Event Trigger" sites and ―3C Event Trigger‖ sites in

RNC1 and RNC10 were disordered.

The locations are shown in the figure below.

Figure 5-1 Sites Locations of 3A Event Trigger and 3C Event Trigger

is ―3A Event Trigger" site; is ―3C Event Trigger‖ site; is ―3C Event Trigger‖ with 2G neighbor

sites configured (56).

Experience

For the ―3C Event Trigger‖ sites with 2G neighbor sites configured, we determined to test

2 sites in the dense area, on 28th Aug we tested the ―3C Event Trigger‖ sites with 2G

neighbor sites configured, RNC10‘s TRI101W and RNC1‘s TRI119W, in the test process

we found that the RSCP on the ground is around from -81 dBm to -86 dBm, which met

the requirement in the contract, it is around from -90 dBm to -100dBm in the car when UE

is in the different locations, thus 3C event is easy to be triggered by compression mode,

so it is easy to enter 2G, as the dense areas are the sensitive places for the customer

and there are many users, the 3G signal is the room is easy to be below -95 dBm, and

the users often enter 2G, which will cause the dissatisfaction of the 3G users, so change

the judgment method of different system event from ―3C Event Trigger‖ to ―3A Event

Trigger", which ensures that the users reside in the 3G network.



5.3.2 Case 2

Phenomenon

3G neighbor cells were missed to configure for 2G, which resulted in the low call traffic

volume in the far 3G sites and no 3G signal.

Case analysis

To resolve the customer complaint, we added the site TRI358, the nearest 3G site from

the site was 16 km away, after the site operated normally, by observing KPI we found that

CS call traffic volume of each cell was lower, it was around 0.1 erl, and the customer

complained that there was no 3G signal, as shown in the figure below.

Figure 5-2 TRI358 Site Location

Problem location

Firstly we checked the cell parameters configuration in the 3G site, and there was no

error and alarm.

3G signal was normal by testing on site, and CS and PS services are normal.

For the test of inter-RAT handover, we found that 2G cannot handover to 3G, and it

We contacted with the engineer for 2G, and confirmed that the cell was missed to be

configured as neighbor cell in 2G.

The site was a single site, and there was only 2G site around within 16km, many local

users use 3G/2G terminals, the cell was missed to be configured as neighbor cell in 2G, it

caused that the cell phone in 2G cell cannot reselect to 3G cell, so the user complained

that there was no 3G signal, and there were few 3G users under the site.



Solution

The configuration of 2G neighbor cell was completed and the problem was solved.

Experience

For the scenario of single 3G site or few sites, DO configure the 2G neighbor cells

reasonably, at the same time the information of 3G sites should also be configured

reasonably in 2G.

5.3.3 Case 3

Phenomenon

A failure 2G/3G handover case in Unicom of Chongqing Wanzhou

Case analysis

In the 2G/3G handover test, the cell phone did not hangover regularly, the data

configuration was correct by checking, but we found that no increment synchronization

was performed after data configuration, which led to the failure handover due to no data

issued to RNC.

Problem location

After the increment synchronization, the handover remained to fail, we captured the

signaling of RNC, and we knew that the 2G/3G handover switch of core network was not

enabled.

Solution

Perform increment synchronization for the data configuration, and issue the

configuration to RNC.

Enable the 2G/3G handover switch of core network

5.3.4 Case 4

Phenomenon

The success rate of 3G/2G handover was low due to the wrong configuration of neighbor

cell.

Case analysis

The success rate of handover for RNC1 was around 89%, after troubleshooting we found

that each of the three sectors in TRI119W was configured a wrong 2G neighbor cell, so

the success rates of handover were low for the site and the sites around, it was around



18%, which resulted in that the success rate of handover was only 89% for the whole

network.

Problem location

1. We checked the handover parameters configuration of the relative sites, the

strategy was 3A event, the 2D threshold was -95dBm; the absolute threshold of the

cell was -95 dBm/-4; the absolute threshold of 2G cell was -90 dBm, so there was no

problem with the parameter configuration.

2. We checked the configuration of the neighbor cell, and found that a wrong 2G

neighbor cell TRI191 was configured for the site TRI119W, as shown in the figure

below.

Figure 5-3 Relative Location of TRI119W and TRI191

So far, the low success rate of handover was founded.

At the same time we found that TRI006W-1, TRI006W-3, TRI007W-1, TRI007W-2,

TRI007W-3 and TRI011W-3 were the 3G neighbor cells of TRI119W and the 3G cells in

the same active set could handover with the commutative 2G cells, so the success rates

of handover were low for these cells, too.

Solution

After the 2G neighbor cells of TRI119W were removed, the success rate of handover

increased to 93.5% for the whole network, as shown in the figure below.

Figure 5-4 Success Rate of Handover after Deleting 2G Neighbor Cells



Experience

For the success rate of 3G/2G handover, we not only need to pay attention to the

neighbor cell of 3G cell , but also need to check whether the configuration of 2G neighbor

cell is correct as the neighbor cell of 3G cell.

5.3.5 Case 5

Phenomenon

The information of 2G LAC was missed in CN, which lead to the inter-RAT handover

cannot be performed.

Case analysis

For one new 3G site in Indonesia, the service was normal by testing, but the terminal

could not handover from 3G to 2G, finally the 3G signal turned to be weak and the call

was dropped. The information of 2G neighbor cell could be tested from TEMS; for the

handover between 2G/3G systems, generally we analyze it from the points below:

Missed/Wrong configuration for 2G neighbor cell

Problem of GSM network equipment

Problem of parameters (UEC, GSM) configuration

Problem location

1. We got the list of 2G neighbor cells from the customer and compared it with the

actual configuration, they were identical.

2. The number of sites without inter-RAT handover were around 4 or 5, the other sites

were normal, handed over to the cells under the same BSC, so the parameters

problem could be excluded; from the sites location figure we could see that, the sites

could not handover normally were from the same area, the related 2G sites

belonged to one LAC area, and there was no wrong configuration for LAC.

3. We traced the signaling of the cells which could not handover normally in the OMC

network management, and found that CN would fail to relocate directly each time

after RNC sent the request of relocation, as shown in the figure below.



Figure 5-5 Relocation Failure

Figure 5-6 Signaling Flowchart of Inter-RAT Handover

From the signaling above we could find that after RNC sent the request of relocation, CN

refused directly, the reason was TRANAP_semantic_error, it is a kind of syntax error,

generally it is due to that the data does not match, so the problem was located at CN or

2G, finally the LAC codes of these related cells were not added in CN.

Solution

We created these LACs again in CN and the problem was solved, from OMC traffic

statistics, we could see the handover related specifications and the value of counter, the

figure below shows the chart of a typical site for inter-RAT handover.



Figure 5-7 Inter-RAT Handover

Experience

If the GSM parameter were modified in the 2G system, the GSM parameters in the

3G system must be modified synchronously.

The problem analysis follows the principle from the whole to the part, and gradually

narrows the range until the problem is solved.

5.3.6 Case 6

Phenomenon

WCDMA system could not use PS and CS at the same time due to the configuration of

encryption algorithm in PS domain.

Case analysis

When a user used CS voice service firstly, then he used PS service simultaneously in the

process of calling, at this time the two services could be used at the same time; but when

the user used PS service first, and used CS voice service simultaneously (no matter

calling or called), the voice service could not be used, and it was busy tone in the

telephone, there was the RNAP_SECURITY_MODE_REJECT message in the traced

signaling.

Problem location

After the user used PS service first and made voice call simultaneously, there was the

RNAP_SECURITY_MODE_REJECT message found in the traced signaling, as shown in

the figure below.



Figure 5-8 Failure Signaling of Security Mode

The detailed reason was as follows.

Figure 5-9 Value of Failure Reason

The value of failure reason showed that the latest issued integrity protection or encryption

information did not match the previous configuration; according to the analysis above, the

two services should be configured with different encryption algorithm; Then we checked

the encryption algorithm of each service separately: For PS: two encryption algorithms

were configured — No Encryption and UEA1.

Figure 5-10 Encryption Algorithm for PS Service

For CS: Only one encryption algorithm UEA1 was configured here.

Figure 5-11 Encryption Algorithm for CS Service

According to the protocol:



The CN initiates the procedure by sending the SECURITY MODE COMMAND message.

The message may contain the Encryption Information IE and shall contain the Integrity

Protection Information IE, specifying, in preferred order with the most preferred first in the

list, which ciphering, if any, and integrity protection algorithms may be used by the

UTRAN.

RNC will give priority to the first encryption algorithm in the list issued by core network.

The user first used PS service, so RNC chose the first encryption algorithm (No

Encryption) directly in the list issued by CN. Then at the same time he used voice service,

but UEC encryption algorithm for CS is UEA1. But before that RNC has recorded that the

user's encryption algorithm was No Encryption, then it was UEA1 at this time, the two

were founded to be different, so the RNAP_SECURITY_MODE_REJECT message was

issued, which led to that the voice service cannot be established. But PS service always

could be used.

Solution

We adjusted the order of encryption algorithm for PS service, ranked UEA1 at first as

follows.

Figure 5-12 Encryption Algorithm

Encryption algorithm UEA1 ranked first or only UEA1 was configured. When only using

only one service, no matter what encryption algorithm was configured for PS or CS, the

rejection phenomenon security mode would not appear, but there would be such problem

when using the concurrent services.

Experience

Why was it possible to use CS service first and then use PS service in the process of

calling? The reason is as follows:

For the case of using CS voice service, RNC will choose the first encryption algorithm

directly in the list issued by CN, and there is only one encryption algorithm UEA1. Then

use PS service in the process of calling, at this time RNC will not choose the first

encryption algorithm directly in the list issued by CN as above, because PS is not the first

service, so it will not choose the first encryption algorithm in the list, but it checks what

encryption algorithm has been configured for PS service and compares, then it finds that

UEA1 has indeed been configured for PS service, So PS is available. As the rule of RNC

choosing the first encryption algorithm in the list issued by CN, it is only for the first

service.

umts rno subject-2g3g interoperation analysis guide_r2.0

Documents

zte corporation address

zte confidential proprietary

followup document

document structure

author date document

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