Solution to GSM and WCDMA Interworking for the RNPS GSM V0.75

7/16/2019 Solution to GSM and WCDMA Interworking for the RNPS GSM V0.75

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Product Name Confidentiality level: INTERNAL

GSM Drafted by: Wireless Network Research Department

Product VersionTotal pages: 100 pages

Solution to GSM and WCDMA

Interworking for the RNPS GSM

(V0.75)

(For internal use only)

Prepared by Date

Reviewed by Date

Reviewed by Date

Approved by Date


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Revision History

Date Version Description Author

2008.03.12 V0.7 Draft completed. Chen Shuai, Chen Jun

2008.08.30 V0.75 The document is modified

according to the GBSS V9.0

version planning.

Chen Shuai


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Contents

1 Overview ...................................................................................................................................... 7

2 Fundamental Theory ................................................................................................................... 8

2.1 Location Area Planning ....................................................................................................... 8

2.1.1 GSM Paging Scheme ............................................................................................... 8

2.1.2 WCDMA Paging Scheme ......................................................................................... 9

2.1.3 Principles of LA Planning ....................................................................................... 112.1.4 LA Planning Policy ................................................................................................. 15

2.1.5 LA Planning Scheme for Inter-PLMN Network........................................................ 18

2.2 RA Planning ...................................................................................................................... 18

2.3 Cell Selection and Cell Reselection .................................................................................. 18

2.3.1 Condition of Normal Camping On a Cell ................................................................. 18

2.3.2 Process of Cell Selection ....................................................................................... 21

2.3.3 Cell Reselection from 2G to 3G .............................................................................. 21

2.3.4 Camping on a 3G Cell Preferentially After a Call .................................................... 25

2.4 Handover Between Cells .................................................................................................. 25

2.4.1 Handover Process .................................................................................................. 25

2.4.2 Handover Process .................................................................................................. 28

2.4.3 Introduction to EMR................................................................................................ 33

3 Interworking Scheme in Different Scenarios .......................................................................... 38

3.1 Densely Populated Urban Areas ....................................................................................... 38

3.1.1 Cell Selection and Cell Reselection ........................................................................ 39

3.1.2 Handover ............................................................................................................... 40

3.1.3 Handover Area Division .......................................................................................... 43

3.2 Common Urban Areas ...................................................................................................... 43


3.2.2 Handover ............................................................................................................... 45

3.3 Major Highway or Railway ................................................................................................ 47


3.3.2 Handover ............................................................................................................... 48

3.4 Suburban and Rural Areas ............................................................................................... 49


3.4.2 Handover ............................................................................................................... 49

3 5 Dual Band GSM Network 49


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5 Case Study ................................................................................................................................ 68

5.1 2G/3G Hybrid Network of the Egypt Third License Project ............................................... 68

6 References................................................................................................................................. 707.Appendix ................................................................................................................................... 72


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Figures

Figure 2-1 LA division .................................................................................................... 12

Figure 2-2 LA division based on 2G-3G frequency bands .............................................. 15

Figure 2-3 LA division based on the geographical location ............................................ 16

Figure 2-4 Process of cell selection ............................................................................... 20

Figure 2-5 Process of cell reselection from GSM to WCDMA ........................................ 24

Figure 2-6 Process of handover decision ....................................................................... 28

Figure 2-7 Process of inter-RAT load handover ............................................................. 30

Figure 2-8 Process of a handover to a better 3G cell ..................................................... 32

Figure 2-9 Configuration of added EMR filter length ...................................................... 37

Figure 3-1 Distribution of 2G BTSs/3G NodeBs in dense urban areas and common urban

areas .......................................................................................................................38

Figure 3-2 Distribution of BTSs and NodeBs at the middle and end stage of WCDMA

network development ..............................................................................................44

Figure 3-3 Distribution of BTSs/NodeBs along major railways and highways ................ 47

Figure 5-1 Networking structure of MSCs in the network of the Egypt third license project

................................................................................................................................ 69


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Tables

Table 2-1 Comparison between the intra-PLMN and the inter-PLMN schemes .............. 13

Table 2-2 Cell priority ..................................................................................................... 20

Table 2-3 System messages to be modified ................................................................... 21

Table 2-4 Description of external 3G cells ...................................................................... 22

Table 4-1 External 3G cell description ............................................................................52


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1 Overview

The 2G/3G interoperability feature enables an MS to be handed over to or

reselected to the GSM network for normal communication if the serving cell of the

MS is not covered by the WCDMA network or if the communication quality within

a WCDMA cell is poor. On the other hand, an MS can be handed over to or can

reselect the WCDMA network if the MS requires data services.

When a dual-mode MS moves into the WCDMA network again or finds aWCDMA cell with good communication quality, the MS can be handed over to or

reselected to the WCDMA network if handover or reselection conditions are met.

In this way, mobile subscribers can enjoy a variety of services provided by the

third-generation mobile communication system.

At the initial stage of network construction, the third-generation communication

network cannot contribute to a wide coverage area as the GSM network does and

the WCDMA network has not been a mature communication system. Therefore,

the WCDMA network, in a long time, cannot totally replace the GSM network.

In this condition, the system interworking functions, such as handover and

reselection, can be used to ensure service continuity and availability. If a GSM

network is connected to the border of a WCDMA network, the wireless network

coverage is enlarged and network extension is implemented.

When an MS moves from a pure-GSM network to a WCDMA-GSM overlapped

area, the MS can be reselected to or handed over to the WCDMA network. In thisway, subscribers can experience better 3G services.

Telecom operators plan and design a 3G network according to the following

conditions:

z Service development requirements

z Distribution of 3G subscribers

z Investment costs and benefits

Network construction plans also vary with scenarios for the same area. Usually,

an area can be divided into the following sub-areas:

z Densely populated urban area

A special plan is carried out for the dual-band network.

z Common urban area


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z Reducing the number of handovers and reselections between systems

z Providing 3G subscribers with 3G services

z Using a 2G network to extend the 3G coverage and ensuring the continuity

of 3G services

2 Fundamental Theory

2.1 Location Area Planning

The 2G network telecom operators face the problem of constructing a shared

location area (LA) for both 2G and 3G networks.

z If a telecom operator plans to construct a 3G network at one time and does

not plan to extend or maintain the 2G network, the problem does not exist.

z If a telecom operator requires the function of 2G-3G handovers, this problem

must be solved.

In the case of LA planning, 3G network operators can refer to the configuration of2G LAs and routing areas (RAs). Alternatively, 3G network operators can

combine LAs according to the BSC traffic and try to align the border of 3G LA with

that of 2G LA, thus reducing the number of location updates upon inter-RAT

handover and reselection.

In some areas, 2G subscribers may be transferred to a 3G network.

Consequently, the number of subscribers within a 2G LA is reduced and the

paging capability overtakes the actual demand. Thus, location areas must beplanned again.

The principles of LA planning are as follows:

z Ensuring that the capacity of paging channels is not limited.

z Minimizing the overheads of location updates at the border.

z Simplifying the management .

When an MS in an LA is paged, the MSC sends a paging request to all the cells

within the corresponding LA through the BSC/RNC.

2.1.1 GSM Paging Scheme

Two paging modes, TMSI paging and IMSI paging, can be used for a GSM

system.


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When the IMSI paging mode is used for a paging channel on the Um interface,

the paging request message includes only two IMSIs. When the TMSI paging

mode is used, the message includes four TMSIs. The analysis shows that the

paging load in IMSI paging mode is twice that in TMSI paging mode.

The procedure for a successful wireless paging is as follows:

(1) After obtaining the current LAI of an MS from the VLR, the MSC sends a

paging message to all BSCs within the LA.

(2) After receiving the paging message, the destination BSC sends a paging

command request to all the cells within the LA of the BSC.

(3) After receiving the paging command message, the BTS sends a paging

request message over the paging sub-channel of the paging group. The

paging request message carries the IMSI or TMSI of the called MS.

(4) After receiving the paging request message, the MS requests an SDCCH

through the RACH.

(5) After the BSC confirms that the BTS has activated the desired SDCCH, it

allocates the SDCCH to the MS over the AGCH by sending an immediate

allocation command message.

(6) The MS sends a message (Paging Resp) to the BSC over the SDCCH.

(7) The BSC forwards the message (Paging Resp) to the MSC.

A successful wireless paging is complete.

Two configuration modes are available for the CCCH according to the GSM

specification:

z Shared CCCH-SDCCH (also called combined BCCH)

Every multiframe transmits three paging groups.

z Not shared CCCH-SDCCH (also called non-combined BCCH)

Every multiframe transmits nine paging groups.

2.1.2 WCDMA Paging Scheme

The 3GPP protocol specifies two paging types for the WCDMA system: Paging

type 1 and Paging type 2.

In terms of paging causes, a paging is required in the following cases:

z The following paging is related to the service model:

The MS in the idle state is called (initiated by the PS/CS domain).

The MS in the connection state is called or required to receive the

downlink data (initiated by the PS domain).


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The paging initiated when the MSC sends the security mode command

(the command includes the MSC encryption or completion protection

parameters).

The connection between only service module-related paging and paging capacity

is described in the following parts.

To increase the paging success rate, the WCDMA system often sends a paging

message for several times.

The theory of increasing the paging success rate is explained as follows:

z For the MSC

Before receiving a paging response from the MS, the MSC sends a

maximum of five paging messages to the MS. The number of paging

message is fixedly configured and cannot be changed.

If the MS is allocated with a TMSI, the first two messages are sent in TMSI

mode and the last three messages are sent in IMSI mode. The first four

messages are sent at the interval of t-1 seconds and the last message is

sent in t seconds. The upper limit of the interval is set to 5 (seconds) and the

default value is 3 (seconds).z For the WCDMA

The WCDMA network supports the retransmission of paging messages on

the Uu interface. The default number of paging retransmissions is 1. You can

use an MML command to set the number of paging retransmissions to any

integer from 0 through S. The upper limit of S is 2. In other words, the

maximum number of paging transmissions is 3.

Paging Type 1

For an MS in the state of Idle, CELL_PCH, or URA_PCH, the WCDMA network

sends the PAGING TYPE 1 message over the PCCH to initiate the paging

process and monitors the corresponding paging channel according to the PICH

indication and DRX requirements.

The PAGING TYPE 1 message is sent over the PCCH. The protocol, however,

specifies that every SCCPCH has a maximum of one PCH and corresponds to

one PICH (an MS selects a suitable PICH according to the algorithm specified by

the protocol 25.304). Therefore, the network paging capability is limited by the

size of a paging area. The paging area planning aims to plan the size of LA, RA,

and URA for Paging type 1.

Paging Type 2


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2.1.3 Principles of LA Planning

Principle 1

An LA cannot be too large. The maximum size of an LA is determined by the

capacity of the paging channel.

A paging message for an MS is sent to all cells within the LA. Therefore, the

paging area is too large, which increases the load of the paging channel and

increases the signaling traffic on the Abis/lub interface. In addition, the surplus

paging messages are discarded if the number of sending attempts exceeds what

is preconfigured in the BSC or RNC. As a result, the MS that is powered on within

the service area cannot be paged (the MS is out of service).

The upper limit of a paging area (namely the maximum of cells supported by a

paging area) is limited by the bandwidth of the paging channel. It changes with

the traffic. The size of an LA is configured according to the estimated result of the

paging area. At the initial stage of 3G network construction, the traffic is light and

many unknown factors exist. A 3G network, however, needs to be expanded and

adjusted eventually. Therefore, location areas also must be adjusted.

If an LA is too small, the location update overhead is great and the paging load

supported by the system decreases. If an LA is too large, the paging load

increases. Therefore, it is necessary to monitor the traffic and paging capacity of

an LA.

Principle 2

The LA division should contribute to lowest cost of location update at the border

of an LA and follow the geographical distribution.

If the coverage of an urban area and that of a suburban area are discontinuous,

the location of an MS may not be updated periodically. After the protection time

(set on the MSC) expires, the system conceives that implicit IMSI detach occurs

to the MS.

Suppose a mobile subscriber moves to an urban area and the LACs of the urban

area and the suburban area are the same, the MS sometimes does not send a

request for LA update immediately. Consequently, the MS may be out of serviceeven if it can receive signals.

In the case of LA division, a suburban area is allocated with an individual LA. That

is, the LA of an urban area is different from that of a suburban area. In this case,

the LA distribution is similar to a concentric circle, as shown in Figure 2-1. Thus,

the preceding problem is avoided


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Figure 2-1 LA division

In addition, if more than two LAs are allocated for a metropolitan with heavy traffic,

a mountains or river can be used as the border of an LA, thus reducing the

overlapping depth of different cells for the two LAs. If conditions do not permit,

remember not to locate the border of an LA on a street or a place with heavy

traffic (such as a shopping mall). Usually, the border of an LA should not be

parallel to or vertical to a street but oblique crossed with the street.

For the juncture between an urban area and a suburban area, locate the border of

an LA around the peripheral BTS rather than the juncture that is characterized by

heavy traffic to avoid frequent location update.

The telecom operator who has a complete 2G system and plans to construct a

WCDMA network can refer to the GSM LA planning scheme, especially the

scheme of border selection.The capacity of an RNC in a 3G network is greater than that of a BSC in a 2G

network. Thus, the number of RNCs is less than that of BSCs. In normal cases,

one LA cannot span several BSCs.

In the case of LA planning for a 3G network, the LA configuration and the BSC


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According to the protocol, one LA can span several MSCs that share a VLR. But

in actual conditions, one MSC is bound with one VLR. Thus, an LA can span

several BSCs/RNCs but cannot span several MSCs.

In actual network application, if one LA/RA spans several BSCs/RNCs, the MSC

sends a paging message to multiple BSCs/RNCs. Consequently, the signaling

traffic and processing difficulty are increased, and paging channels are blocked

and paging messages are discarded more frequently.

At the initial stage and mature stage of network construction, two schemes

(intra-PLMN and inter-PLMN) can be used for network construction according to

different network operation policies.

If the 2G equipment supports the R99 protocol, the intra-PLMN scheme is

recommended.

If the 2G equipment does not support the R99 protocol, only the inter-PLMN

scheme can be used. Alternatively, you can upgrade the 2G network so that 2G

equipment can support the R99 protocol.

For an inter-PLMN network, a UE cannot be reselected to a 3G network

automatically when it is served by a 2G network. The UE can be reselected to a3G network only through the manual network selection or periodical PLMN

location update.

In normal cases, the interval of 3G network reselection ranges from six minutes to

eight hours. The step is six minutes. Thus, the intra-PLMN scheme is

recommended.

For the network that can support the R99 protocol after being upgraded, you can

reduce the signaling (such as location update) related to the system interworking.

Table 2-1 lists the comparison between the intra-PLMN and the inter-PLMN

schemes.

Table 2-1 Comparison between the intra-PLMN and the inter-PLMN schemes

Intra-PLMN and

inter-PLMNIntra-PLMN Inter-PLMN

Mode of reselection

from 2G to 3GCell reselection HPLMN reselection

Interval of

reselection from 2G

t 3G

Short (at a second-level)Long (at least at a six-minute

level)


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Intra-PLMN and

inter-PLMNIntra-PLMN Inter-PLMN

Subscriber service

experience

Cell reselection

The time of reselection is

short.

When a subscriber moves back tothe 3G network, the subscriber,

acting as the called party, initiates

3G specific services because the

PLMN reselection period does not

arrive.

The service has losses.

Requirements for 2G

network

The 2G network is

required to support the

R99 protocol.

The 2G network is not required to

support the R99 protocol.

Whether the original

card needs to be

changed into a USIM

card

The original card does

not need to be changed

into a USIM card. Keep

the subscriber numberunchanged.

The original card must be

changed into a USIM card.

Change the subscriber number.

Whether a new

roaming protocol is

needed

No Yes

MS power

consumption

HPLMN reselection is

not required. Therefore,no MS power is

consumed for this

purpose.

When a subscriber stays on a

pure-2G network for a long time,

the MS initiates HPLMN

reselection requests periodically,

which causes MS power

consumption.

The preceding analysis shows that the intra-PLMN scheme outshines the

inter-PLMN.

If the current 2G network does not support the R99 protocol, it is recommended

that you upgrade the current 2G equipment. When the 2G network cannot be

upgraded, use the inter-PLMN scheme.

Both the replaced and newly constructed 2G networks support the R99 protocol.


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2.1.4 LA Planning Policy

The intra-PLMN scheme is recommended for the 2G network deployed with the

equipment supporting the R99 protocol. A unified LA planning is conducted on thesame PLMN.

If a GSM network and a WCDMA network use their own MSCs, LAs of the GSM

network and the WCDMA network must be different. By setting parameters, the

following objectives can be achieved:

Ensure that MSs can enjoy 3G services when they roam within cells of the

WCDMA network.

Reduce the number of handovers and reselections.

Design signaling channels considering the system load caused by location

update.

At the initial stage of network construction, the WCDMA system requires little

capacity and telecom operators want to reduce the network scale for saving costs.

In that case, the RNC can be configured in the MSC of a GSM system to achieve

that the GSM and the WCDMA systems share an MSC.

At the initial stage of network construction,

If the system capacity permits, the GSM and the WCDMA systems can share an

LA.

If the paging capacity is limited, the GSM and the WCDMA systems use more

than two LAs. In this case, two schemes for LA division (based on the

geographical location and based on the frequency band) are available as the

dual-band GSM network.

Figure 2-2 shows the LA division based on the frequency band.


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Figure 2-3 LA division based on the geographical location

For the LA division based on the frequency band, the original GSM network does

not need to be adjusted.

The location registration needs to be performed in the case of inter-RAT handover

or roaming.

For the LA division based on the geographical location, the location registration is

not required. The number of paging messages and the load of paging channels,

however, are increased.

For a hybrid 2G-3G network, if LAs are divided based on the 2G-3G frequency

bands, you need to:

z Periodically monitor the traffic and paging capacity of LAs of 2G and 3G

networks at the network development stage.

z Analyze the load of LAs and implement adjustments according to the system

traffic, location update, and collected paging data and performance counters.

During the adjustment, try to keep the GSM LA the same as the WCDMA LA.

For a mature network, the number of subscribers should grow stably.

Most of the new 3G subscribers are transferred from the 2G network. If

service-based handovers are not implemented, GSM LAs will be enlarged

when the number of GSM subscribers decreases with the development of

the network. At the same time, WCDMA LAs, however, will be gradually

reduced.

In the case of LA division for dual-band network, follow the policy included in

the solutions to the dual-band network.

Comparisons of LA division for the intra PLMN networks are as follows


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z At the border of a WCDMA network, 3G UE can be handed over to the GSM

network without location update because the number of 3G subscribers is

small and the coverage of the WCDMA network is not as good as that of the

GSM network at the initial stage of WCDMA network construction.

z The number of 3G subscribers increases stably at the initial stage and the

subsequent stage of network construction. Most of the new 3G subscribers

are transferred from the 2G network. Therefore, for an LA division, the

increase of subscribers need not be taken into consideration in a short term.

The LA division based on the frequency band has great advantages at the mature

stage of network construction.

z Continuous coverage is implemented at the mature stage of network

construction. The number of 3G subscribers increases with the general

increase in the number of subscribers.

If LAs are divided based on the geographical location, the subscriber density

grows and consequently the paging load increases.

If an LA is reduced, the number of reselections between LAs increases and

consequently the number of location updates increases.

In such a case, if LAs are divided based on the frequency band, subscribers

are distributed dispersedly, the LA is enlarged, and the probability of LA

updates is decreased.

z With continuous 3G network coverage at the mature stage, 3G subscribers

within the WCDMA coverage are provided with services by using the policy

of 3G subscriber preference. In this way, the number of handovers between

LAs decreases and service requirements of 3G subscribers can be met.

The preceding analysis shows that you can use different LA division principles for

different network structures. At the same time, you need to communicate with

telecom operators.

If LAs are divided based on the geographical location, the LA planning is not

required at the initial stage of network construction. You can use the LA planning

of the 2G network.

For a small city, the BSC and the RNC have clear boundaries, which overlap each

other. If the capacity permits, LAs can be divided based on the geographical

location. Thus, the number of location updates is decreased and the network load

is lightened.

The LA division based on the frequency bands has more advantages. Continuous

coverage is implemented either at the initial stage or mature stage of network


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In such a case, if the BSC and RNC are allocated based on the geographical

location, every LA has one RNC and several BSCs to avoid one LA spanning

several RNCs. Consequently, small paging capacity and heavy load cause

service losses. Therefore, the LA division based on the 2G-3G frequency bands is

recommended.

2.1.5 LA Planning Scheme for Inter-PLMN Network

If the protocol version of a 2G network is earlier than R99 and is not upgraded to

R99, an MS cannot be reselected or handed over to a WCDMA network when it is

served by a GSM network. In this case, only the inter-PLMN scheme can be used.

The MS is reselected to a WCDMA network through a periodical HPLMN

reselection.

According to the 3GPP protocol, if the PLMN and the HPLMN of an MS use the

same CC but different MNCs, the MS tries to be reselected to the HPLMN by

initiating PLMN reselection requests periodically. The reselection period is

specified by the parameter related to the USIM card.

In the EFHHPLMN file, the minimum value of the reselection period is set to six

minutes and the maximum value is set to eight hours. The step is six minutes.

The exact value is specified by telecom operators.

For a telecom operator that has multiple PLMNs, the scheme of LA division in a

WCDMA network is based on the LA division in a 2G network.

At the initial stage of network construction, two or more GSM LAs can be

combined into one WCDMA LA because the number of 3G subscribers is small.

At the mature stage of 3G network construction, some 2G subscribers aretransferred to the 3G network. When the number of 2G subscribers decreases,

separately re-plan the LAs for the 2G and 3G networks according to the telecom

operator's scheme.

2.2 RA Planning

For a hybrid 2G-3G network, the principle of RA division is the same as that of LA

division. In normal case, the size of an RA is smaller than or equal to that of an LA.

An LA has one or more RAs. Two subscribers in the same LA may not be in the

same RA. But, two subscribers in the same RA must be in the same LA.

The number of RAs in an LA is determined by the PS service traffic. An LA with

heavy PS service traffic can be configured with multiple RAs.


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(2) Register with the PLMN to receive the system messages of the PLMN,

receive paging messages, and initiate calls.

The process of selecting a suitable cell to obtain normal services is called normal

camping on.

A cell on which an MS camps meets the following requirements:

z The cell belongs to the selected PLMN.

z The cell is not set to Barred.

z The LA of the cell is not in the Barred Location List of the MS.

z The wireless path loss from the MS to the BTS is lower than the preset

threshold. That is, the receive level of the MS is higher than the preset

minimum receive level of the cell.


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Figure 2-4 Process of cell selection

The cell priority is determined by CELL_BAR_QUALIFY (CBQ) and

CELL_BAR_ACCESS (CBA) together.

Table 2-2 Cell priority


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CBQ CBA Cell Selection Priori ty Cell Reselection Status

1 1 Low Normal

2.3.2 Process of Cell Selection

When an MS is powered on or moves from a blind area to a network coverage

area,

The MS searches for all frequencies permitted by the PLMN and selects a

suitable cell to camp on.

The MS sorts out the cells in a descending order according to the receive level

and searches for a suitable cell that meets the requirement of camping on.

After the MS finds a suitable cell, the MS camps on this cell and makes necessary

registration.

An MS searches for a suitable cell in two modes: standard cell selection and

storing-list cell selection. When a 3G subscriber powers on a dual-mode MS in a

3G blind area or moves from a pure blind area to a pure-GSM network, the MS

selects a GSM cell if it fails to find a suitable 3G cell for camping on.

2.3.3 Cell Reselection from 2G to 3G

2.3.3.1 System Messages to Be Modified and Added

Table 2-3 lists the system messages to be modified.

Table 2-3 System messages to be modified

Data Value Range Default Value

Qsearch I 0-15 15

Qsearch C InitialAlways searching for

Use Qsearch IUse Qsearch I

FDD Q Offset 0-15 8

FDD Qmin 0-7 0

Qsearch P 0-15 15


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Table 2-4 Description of external 3G cells

Data Value Range Default Value.

Cell Index 5048-8047 5048

Cell Name 0-32

Cell Layer 1-4 3

MCC 0-

MNC 0-3

LAC 0-65535

CI 0-65535

RNC Index 0-4095

DL UARFCN 0-16383

Scrambling Code 0-511

Sync Case Sync case1/ Sync case2 Sync case2

Diversity Yes/No None

RSCP Threshold for Layer

Of 3G Cell0-63 30

Ec/No Threshold for Layer

Of 3G Cell 0-49 30

Min RSCP Threshold 0-63 10

Min Ec/No threshold 0-49 10

UtranCell Type FDD/TDD FDD

1. Adding System Message SI2quater

The system message SI2quater includes more information about cell

reselection, measurement, and reports. SI2quaterhas only SI2quater Rest

Octets IE besides the common message header of the Um interface. The

t t l l th f SI2 t i 23 b t hi h i th th t f th SI2


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BSIC. The occasion and method of sending SI2quater are the same as

those of sending other SI2 system messages (SI2, SI2bis, and SI2ter).

2. Modifying System Message SI2ter

The system message SI2 and SI2bis provide only the neighboring GSM cell

list of the current camping on cell. After a handover between GSM and

WCDMA is complete, the MS needs to be informed of the neighboring

WCDMA cell of the current camping on cell.

Compared with the definition ofSI2terin GSM 04.08, the definition ofSI2ter

in 3GPP 04.18 is added with cell reselection parameters related to the

frequency of neighboring 3G cells. Therefore, the mode of writing SI2ter

needs to be modified.

The message SI2ter is sent from the BSC to the BTS.

Before SI2ter is modified, the bytes (four bytes in total) contained in "Rest

Octets"IE ofSI2terare all idle ones according to the GSM 04.08 protocol.

AfterSI2ter is modified, the length of "Rest Octets"IE ofSI2ter does not

change according to the 3GPP 04.18 protocol, but the contents are changed

into the information about 3G cell reselection.

Because of the limitation on the byte, IE of every SI2ter contains the

description about only one frequency of the neighboring 3G cell according to

the protocol.

In the case of configuring external neighboring 3G cells, add the frequency

of neighboring 3G cells.

3. Modifying System Message SI3

"Rest Octet"IE of SI3 defined in the 3GPP 04.18 protocol includes thefollowing information:

Whether the SI2tquatermessage exists.

Whether the MS reports UTRAN CLASSMARK CHANGE.

Therefore, SI3 must be modified. If UTRAN FDD CELL BA1 TABLE is

configured, SI3 contains Support Send 2 QUATER Flag. Set Support

Send 2 QUATER Flag to Yes. When the BSC supports 2G/3G

interoperability and Outgoing -RAT HO Allowed is set to Yes, the setting isvalid.

When the BSC sends SI3 to the MS, the message Send 3G Class Flag is

used to inform the MS whether the early classmark message includes the

3G classmark information.


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For a GSM-WCDMA hybrid network, if a dual-mode MS is served by a GSM cell,

the MS performs inter-RAT WCDMA signal measurement when measuring the

signal level of neighboring GSM cells.

Qsearch_I indicates that the CS domain is in the Idle state. Qsearch_C indicates

that the CS domain is in the connection state. Qsearch_P indicates PS services.

These parameters determine whether to start the inter-RAT measurement.

If the 3G cell reselection list (composed ofSI2 terand SI2 quarter) has only one

UTRAN frequency, MSs can identify and reselect a new WCDMA cell within 30

seconds. The time allowed for cell reselection is extended by 30 seconds when

the list adds one different FDD frequency. If the added frequencies are the same,

the time allowed for cell reselection does not change.

In normal cases, a dual-mode MS can monitor 64 WCDMA cells (the number is

determined by the MS capability). A FDD cell has a maximum of three FDD

frequencies. Every frequency can support a maximum of 32 cells.

Process o f Cell Reselection from GSM to WCDMA


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If RSCP > RLA_C+ FDD Q OFFSET and Ec/No > FDD Qmin, the MS is

reselected to the FDD cell within five seconds when the following requirements

are met:

RSCP of the WCDMA cell is FDD Q OFFSET greater than RLA_C of the serving

GSM cell and all non-serving GSM cells.

Cpich_Ec/No of the 3G FDD cell is greater than FDD Qmin.

If an MS is already reselected to a cell 15 seconds ago, FDD Q OFFSET adds by

5 dB. The preceding three conditions are fixed in the program of a dual-mode MS.

FDD Qmin and FDD Q OFFSET are obtained from the BCCH broadcast of the

serving cell.During the five seconds in which an MS is reselected to a suitable GSM cell from

a FDD cell, the MS cannot be reselected back to the FDD cell.

If more than one FDD cell meets the preceding requirements, the MS is selected

to the cell that has the greatest RSCP value.

2.3.4 Camping on a 3G Cell Preferentially After a Call

At present, the cell reselection principle is as follows: An MS in the idle state

preferentially camps on a 3G cell.

Generally, after a dual-mode MS terminates a call in a 2G cell and returns to the

idle state, the MS camps on the 2G cell. Then, the MS is reselected to return to a

3G cell according to the network strategy. The channel release message of the

MS contains the IE "Cell selection indicator after release of all TCH and SDCCH",

instructing the MS to preferentially camp on a UTRAN cell after channel release.

If the parameter Preferential Camp-on 3G Cell After Channel Release

Al lowed is set to Yes, the MS checks whether the history measurement reports

contain neighboring 3G cells before it sends a Channel Release message. If

neighboring 3G cells exist, the MS selects the best neighboring 3G cell to camp

on. If the measurement reports do not contain neighboring 3G cells, the MS

camps on the serving 2G cell. The parameter Preferential Camp-on 3G Cell

After Channel Release Al lowed is a BSC-level parameter. The 3G cell camp-on

function will be implemented in GBSS V9.0 in the second quarter of 2009. For

details, consult the marketing department.

2.4 Handover Between Cells

2 4 1 H d P


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(3) Handover decision

(4) Handover implementation

The MS and BTS implement the measurement and measurement result report.

z The MS measures and reports the following information:

Downlink receive level, signal quality, and TA of GSM cells

Downlink RSCP value and Ec/No value of WCDMA cells

z The BTS measures and reports the uplink signal strength and receive level.

The BSC processes the measurement report (when the BTS pre-processing

mode is used, the measurement report is processed by the BTS). The BSC

provides basic functions, such as wave filtering and interpolation, for thesubsequent handover decision algorithm.

This process is the basis of the handover decision algorithm.

Two types of measurement reports are available:

z Enhanced measurement report (EMR)

z Measurement report (MR).

An EMR is a new type of downlink measurement report from an MS to the

network. Compared with an MR, an EMR provides more measurement

information such as BER and FER. An MS can report the measurement

information about a maximum of 15 neighboring GSM/WCDMA cells in an EMR

and about a maximum of 6 neighboring GSM cells in an MR.

The EMR is used for inter-RAT handovers between 2G and 3G.

The handover decision consists of the following processes:

z Handover protection for the initial accessz Handover penalty for the initial access

z 16-bit queuing

z Forced handover

z Various kinds of handover decision

z Processing of target cells for 2G/3G handovers

z Starting of consecutive handover protection

The 2G/3G interoperability supports the following inter-RAT handovers from 2Gto 3G:

z TA handover

z Bad quality handover

z Rapid level drop handover


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z Fast movement handover

In the inter-RAT load handover algorithm, the load conditions of the serving 2G cell

and neighboring 3G cells are measured, and then a handover decision is made on the

basis of the load conditions. If the load information of neighboring 3G cells is valid, the

system obtains the load levels of neighboring 3G cells and determines whether to perform

a handover according to the following process:

If the specified conditions for an inter-RAT load handover are met, candidate 2G cells

and candidate 3G cells are listed. Then, based on the setting of the parameterInter-RAT

HO Preference, the system determines whether the MS should be handed over to a 2G cell or to a

3G cell. If the specified conditions for an inter-RAT load handover are not met, a better 3G

cell handover should be performed. Note that the parameterBetter 3G Cell HO Allowed

should be set to Yes. If suitable cells for a handover exist, the 2G/3G inter-RAT handover

procedure is started. The inter-RAT load handover function will be implemented in GBSS

V9.0 in the second quarter of 2009. For details, consult the marketing department.

For the algorithm, the MS determines whether a suitable neighboring 2G cell

exists. If such a cell exists, the MS performs the following handover decision

according to the 2G cell list and 3G cell list:

Figure 2-6 shows the process of handover decision.


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Start

Interpolation and filteringprocessing of MRs

No downlink MR

handover decision-taking

Protection of

minimum handover

interval triggered?

HOInterTimer

protection triggered for

consecutive handover

interval?

HOInitTimer protection triggered for

minimum handover interval at initial

access phase

HOInitTimer:

Min Interval for TCH Hos

Min Interval for SDCCH Hos

SDCCH HO Allowed

Penalty

processing

Basic queuing of

candidate cells

Network characteristics

tuning for candidate cells

Forced handover processing

Other handover

decision-takings

HOInterTimer:Min Interval for Consecutive Hos

Determines target

handover cell based

on 2G/3GHOOPtSel

and 2GOrdThres

Starts consecutive

handover protection

timer: HOInterTimer

End

High-speed railway fast

handover decision-taking

TA handover decision

Interference handoverdecision

Rapid level drophandover decision

Emergency handover

Min Interval for

Emerg Hos triggered

Enhanced dual-band

handover decision

Load handover decision

Edge handover decision

Hierarchical

handover decision

PBGT handover

decision

Concentric

handover decision

Normal handover

AMR handover decision

Better 3G cell

handover decision

Tight BCCH

handover decision

2G/3GHOOPtSe:FDD: Inter-RAT HO Preference

TDD: TDD Inter-RAT HO Preference

2GOrdThres:

FDD: HO Preference Threshold

for 2G Cell

TDD: TDD HO Preference

Threshold for 2G Cell

End

Yes

Yes

No

No

Fast-moving microcell

handover decision

Bad quality handover

decision


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(2) The dual-mode MS performs inter-RAT measurement over idle timeslots and

reports the measurement result.

(3) The BSC determines whether to start the signaling process of an inter-RAT

handover according to the measurement result.

The GSM system adopts the time division multiple access (TDMA) technology.

Therefore, the inter-RAT measurement is conducted over idle timeslots and the

GSM system is not involved with the compressed mode.

The WCDMA system adopts the code division multiple access (CDMA)

technology. Therefore, the MS in the connection state works at a specified

frequency all the time. To keep a continuous call during the inter-RAT

measurement, both the WCDMA system and the dual-mode MS need to start the

compressed mode.

If the MS has only one transceiver, the compressed mode must be started. If the

MS has two transceivers, the MS can measure GSM cells without starting the

compressed mode.

A handover from GSM to WCDMA occurs when a mobile subscriber moves from

a pure-GSM network to a WCDMA-GSM overlapped area. In such a case,

handovers from GSM to WCDMA must be allowed in the BSC.

Generally, a GSM network has better coverage than a WCDMA network. A

handover from GSM to WCDMA refers to the inter-RAT load handover when the

following handovers are not triggered:

z Express railway fast handover

z Emergency handover

z Enhanced dual-band network handover

Figure 2-8 shows the process of a handover to a better 3G cell.


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Figure 2-7 Process of inter-RAT load handover


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GSM-WCDMA overlapped area. In this case, the parameterInter-RAT Load Handover

Difference Threshold should be set properly according to the customer's requirement,

network conditions, and network strategy. Candidate cells are selected on the basis of the setting

of the parameterInter-RAT Load Handover Difference Threshold.

( Loads_2G) 10 Loadi_3G 10 (ThrL_delta 100)

Here, is the coefficient of 2G load adjustment, its value ranges from 0 to 100, and the step is 1; Loads_2G is the

load level of the serving 2G cell; Loadi_3G is the load level of neighboring 3G cells. The same load may have

different meanings for the 2G and 3G networks, and different networks process services in different ways.

The value of can be adjusted so that services are processed by the network with good communication

environment, thus achieving the optimum network performance.

After candidate cells are selected, handover decision is made. In a GSM-WCDMA

overlapped area, the handover decision can be made according to the Ec/No or RSCP. In

each cell, only one decision mode is used. A candidate cell can be the target cell only

when the Ec/No after filtering is greater than Ec/No Threshold for Inter-RAT Load HO or

when the RSCP after filtering is greater than RSCP Threshold for Inter-RAT Load HO.

The handover decision mode to be used depends on the application scenario. In an area

with strong interference, the Ec/No should be used for the handover decision. In an open

area with limited network coverage, the RSCP should be used for the handover decision.

In densely populated urban areas and common urban areas, weak coverage areas and blind areas

may exist because of insufficient BTSs. Suitable decision modes should be used in these areas.

The handover decisions are based on the measurement reports sent by MSs.

Following the handover decision, a load handover decision is made if the candidate

3G cell list contains a neighboring 3G cell. The load handover uses the step-by-step

outgoing mode so that the possibility of a sharp increase in CPU usage is eliminated and


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this parameter is set to a large value, only a small number of 3G MSs can be handed over

to the 3G network. If the Ec/No is used for the handover decision, the parameter Initial

Ec/No for Inter-RAT Load HO should be properly set. If this parameter is set to a small

value, many 3G MSs can be handed over to the 3G network. If this parameter is set to a

large value, only a small number of 3G MSs can be handed over to the 3G network. Then,

a handover decision is made according to the P/N criterion. For neighboring cell i, if

Inter-RAT Load HO Last Times (indicated by P) out of Inter-RAT Load HO Watch

Times (indicated by N) meets the previously mentioned conditions, an inter-RAT load

handover is triggered in the cell. The inter-RAT load handover function will be

implemented in GBSS V9.0 in the second quarter of 2009. For details, consult the

marketing department.

If none of the edge handover, fast-moving micro cell handover, hierarchical

handover, inter-RAT load handover, PBGT handover, concentric cell handover, and

AMR handover is triggered, a better 3G cell handover is started. See the following figure.

Start

Handover triggered?

HOSYS is set to No?

or are 3G better cell parameters set to 0?

FDD set to No?

and TDD is set to No?

MTYPE is RSCP andRSCPi_f is greater than RSCP?

or MTYPE is Ec/N0 andEcNoi_f is greater than Ec/No?

FDD: Better 3G Cell HO Allowed

TDD: TDD Better 3G Cell HO Allowed

Processes

candidate 3G

cell list

Current cell type is FDDand MS supports FDD

MTYPE: FDD REP QUANT

RSCP: FDD RSCP Threshold for Better 3G CELL HORSCPi_f: measured value of FDD RSCP after filterin

Ec/N0: FDD Ec/No Thresho ld for Bet ter 3G CELL HO

EcNoi_f: measur ed value of FDD Ec/No after filtering

TDDRSCP:T DD RSCP Threshold for Better 3G CELL HO

TDDRSCPi_f: measured value of TDD RSCP after filteringTDDRSCPi_fTDDRSCP

Current cell type is TDD?

and MS supports TDD?

Are t he FDD P/FDD criteria

met?

Are t he TDD P/TDD N

criteria met?

FDD P: 3G Better Cell HO Valid Time

FDD N: 3G Better Cell HO Watch Time

End

No

No

Yes

No

Yes

No

No

No

No

Yes

Yes

Yes

YesYes

HOSYS: Outgoing-RAT HO Allowed


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For an FDD handover, FDD REP QUANT determines whether RSCP or Ec/N0 is

measured.

After the Ec/No or RSCP is measured and filtered, it is compared with the

corresponding threshold. If a neighboring 3G cell meets the previously mentioned

conditions and the P/N criterion, a better 3G cell handover is initiated.

After the inter-RAT load handover decision and better 3G cell handover decision are

made, a candidate 3G cell list is created. Then, a candidate 2G/3G cell is selected: If the

Service Handoverparameter is present, a 2G/3G target cell is selected according to the

value of the Service Handoverparameter; if the Service Handoverparameter is not

present, a target 2G/3G cell is selected according to the value of the Inter-RAT HO

Preferenceparameter in the data configuration. The decision procedure is as follows:

z IfInter-RAT HO Preference is set to Pre_2G_Cell and there are no suitable

neighboring 2G cells but with suitable neighboring 3G cells, a 3G cell is

preferred. Otherwise, a 2G cell is selected.

z IfInter-RAT HO Preference is set to Pre_3G_Cell , a 3G cell is preferred.

z If Inter-RAT HO Preference is set to Pre_2G_CellThres and there are no

suitable neighboring 2G cells but with suitable neighboring 3G cells, a 3G

cell is preferred. A 3G cell is also preferred if the receive level of the first

candidate 2G cell is lower than the value of HO Preference Threshold for

2G Cell.

If RSCP or Ec/N0 during a measurement period meets the measurement

requirements, the measurement is recorded as a valid measurement. If

consecutive measurement results meet the P/N criterion, a handover to a better

3G cell is triggered.

2.4.3 Introduction to EMR

2.4.3.1Technical Introduction

The 3GPP 44.018 protocol specifies that the system message MI/2QUATER

determines whether the MR or EMR is used for the MS to report the

measurement information about the serving cell and neighboring cells.

An EMR is a new type of measurement report which consists of more


34/100

For example, BEP, which is used to identify the channel quality, is

introduced. BEP is estimated one burst after another. Therefore, it

contributes to better precision than RXQUAL (BER) does. BEP reflects the

current C/I value, signal delay extension, and terminal speed.BEP uses the 5BIT coding mode (RXQUAL uses 3BIT coding mode)

especially when wireless signals are of poor quality. That is, the BEP can

improve the performance of algorithms that depend on the quality of wireless

signals. Therefore, the algorithms (such as the power control algorithm) that

useRXQUALto measure the quality of wireless signals must be replaced by

the BEP.

z The number of voice frames that are received correctly is added. This

parameter is used to measure the FER. The FER is used to measure the

performance of coding and decoding voice signals. RXQUAL is used to

measure the quality of wireless signals. Compared with RXQUAL, FER has

a better measurement effect for the voice quality.

(1) .Technical Restri ction

The EMR has the following technical restrictions:

z The BTS can pre-process the measurement report only after being informedof the exact information about neighboring cells. Therefore, if the current cell

supports the EMR and the measurement report is pre-processed by the BTS,

the CECHM must perform a forced outgoing handover for the calls in the

current cell when 2G/3G neighbor relation is dynamically deleted or added. If

the handover fails, the call is released.

z If the current cell can send an EMR and the switch of pre-processing the

measurement report is dynamically changed from ON to OFF, the BTS still

pre-processes the measurement report of the call. At this time, dynamically

adding or deleting 2G/3G neighbor relation does not cause forced outgoing

handovers for all calls in the current cell. Thus, when the BTS decodes the

EMR, a fault may occur. Therefore, do not dynamically change the switch of

pre-processing measurement report in the cell that supports the EMR.

(2). Assumption and Dependency

If an MS does not support the EMR, the MS sends an MR after receiving the

command of sending an EMR. If both the BSC and the MS support the EMR and

use the EMR, the measurement report without pre-processing has no faults. If the

measurement report is pre-processed, a fault occurs in the case of BTS

decoding.


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If the MS does not receive MI/2quater, the MS report an MR.

An MS in Idle mode receives the system message 2quater. 2quatercontains

Report Type. GPRS_BSIC Description in 2quaterdescribes the signal level of

the neighboring cell.

The MS does not receive a complete MI message at the initial stage of a call.

Thus, the MS reports the measurement according to 2quater. After receiving the

complete MI message, the MS reports the measurement according to MI.

For the current version, MI/2QUATER can be sent only when the license of

2G/3G handover and reselection permits. Therefore, the restriction needs to be

modified:

z Sending MI/2QUATER of non-3G neighboring cells is not controlled by the

license.

z Whether to send MI/2QUATER of 3G neighboring cells is controlled by the

license of 2G/3G handover and reselection.

(1) MI/2quater: REPORT_TYPE

Configure the call control on the LMT, 3G system message, and report type.

The report type can be set to MR(1) or EMR(0).

When MI/2quateris sent, set the value to REPORT_TYPE.

(2) Sending MI/2quater: Absolute_Index_Start_EMR

When sending an MR, an MS reports the neighboring cell information

according to 2G and 3G neighboring cell lists.

The MS sets up the 3G neighboring cell list according to MI or2QUTER.

Index_Start_3G (in normal cases, it is set to 0) is used as the index of

the 3G neighboring cell list.

In the Idle state, the MS sets up the BA table to obtain the 2G

neighboring cell list according to SI2, SI2bis, SI2ter, and SI2quater

(providing BSIC.)

In dedicated mode, the MS sets up the 2G neighboring cell list

according to SI5, SI5bis, SI5ter, and MEASUREMENT INFORMATION

(providing BSIC.)

When sending an EMR, an MS combines the 2G/3G neighboring cell lists

into one list. Absolute_Index_Start_EMR is added to the index of the 3G

neighboring cell and is used as the reported neighboring 3G cell index. If 2G

and 3G neighboring cells have the same index, a 2G neighboring cell is

preferred. In normal cases, Absolute_Index_Star t_EMR is set to the

number of 2G neighboring cells.


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For an EMR, the MS sets up a combined 2G/3G neighboring cell list and

uses 0-4 as the index of 2G neighboring cells. Absolute_Index_Start_EMR

is set to 5. The original 3G neighboring cell index 0-3 is separately added by

Absolute_Index_Start_EMR. Then, the indexes become 5-8.The MS reports the neighboring cell information according to the combined

2G/3G neighboring cell (the indexes are 0-8).

(3) MI-BSIC Description or2quater -GPRS_BSIC Description

If an MS is required to send an EMR, every index in the 2G BA table must be

specified with more than one BSIC in MI/2quater.

BSIC can be sent through one or more MI/2quater messages (if one

MI/2quatercannot hold BSIC).

BA_Index_Start_BSIC of every MI identifies the index from which BSIC of

MI starts in the BA table.

Number_Remaining_BSIC identifies the remaining number ofBSIC ofMI.

Frequency_Scrolling identifies what BSIC describes is the neighboring cell

described last time or the next index of the neighboring cell described last

time in the BA table.

2.4.3.3 Operation Instruction

To enable an MS to reports EMRs, you must correctly configure the measurement

report type.

(4) Choose Cell Attri bute > Call Control.

(5) Set Report Type EMR.

In this way, the MS can report an EMR according to the requirement of

2QUATER/MI.

If a cell supports the MS to send an EMR and the BTS pre-processes the

measurement report, the BSC must send the pre-processing information

structure.

The original pre-processing information structure is added by Mean Bit Error

Probability (MEAN_BEP)\Coefficient of variation of the Bit Error Probability

(CV_BEP)\REP_QUANT\NBR_RCV_BLOCKS (the number of correctly decoded

blocks) Voice\Filter Length.

The BTS uses Filter Length to process the interpolation filter for the original

EMR. The recommended configuration of

MEAN_BEP\CV_BEP\REP_QUANT\NBR_RCV_BLOCKS\Voice\Filter Length

is shown in Figure 2 9


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Figure 2-9 Configuration of added EMR filter length

An EMR sent by an MS may carry more information about neighboring cells than

an MR. After receiving the EMR, the BSC takes out six neighboring cells with best

signals to set up a candidate target queue for the implementation of subsequent

algorithms. In this way, the interpolation filter of the subsequent neighboring cell

queue is the same as that of the original neighboring cell queue.

Note:

Do not dynamically change the switch of pre-processing the measurement report

in cells that support the EMR.

If the switch of pre-processing the measurement report is changed from ON to

OFF in a cell that supports the EMR, the BTS still pre-processes the

measurement report for the original calls. At this time, dynamically deleting and

adding the 2G/3G neighboring cell relation does not cause forced outgoing

handovers for all calls in the cell. Then, a fault may occur when the BTS decodes

the EMR.


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3 Interworking Scheme in Different Scenarios

3.1 Densely Populated Urban Areas

The GSM network and WCDMA network can implement seamless coverage. The

distribution of BTSs and NodeBs is shown in Figure 3-1. For densely populated

urban areas, subscribers are densely distributed and the traffic is heavy.

z At the initial stage of 3G network construction, the number of 3G subscribers

is less, the 3G service traffic is light, and the system resource is sufficient.

z

For the 2G network, the number of 2G subscribers is great, services arecentralized in the CS domain, and the network capacity becomes limited with

the increasing number of subscribers.

With the network development and scheme changes,

z The number of 3G subscribers increases and that of 2G subscribers stably

decreases.

z The requirement of PS service increases.

In such a case, the 3G network load becomes heavy and the 2G network load

becomes light. Thus, the network load cannot reach the optimum value.


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3.1.1 Cell Selection and Cell Reselection

3.1.1.1 2G subscriber Selecting a 3G Network

For densely populated urban areas, the 2G network operates with the maximumcapacity or in the near-saturation state at the initial stage of 3G network

construction. In such a case, the scheme of traffic division is recommended. With

this scheme, 2G subscribers who use 3G MSs in a 2G network can reselect a 3G

network, thus reducing the 2G network load.

This scheme is also used when the following conditions are met:

z The 2G network temporarily has no limitation on the capacity.

z To make a fast profit from 3G network investments, the telecom operator

uses a 3G network to carry partial 2G services and does invest more on the

2G network.

For this scheme, you must,

z Register all GSM subscribers as 3G subscribers in the SIM card on the HLR.

z Consider the penetration rate of dual-mode MSs used by GSM subscribers.

If the penetration rate of dual-mode MSs is low, the effect of this scheme is

not obvious. If the penetration rate is high, the WCDMA network quality is

affected.

Therefore, before using this scheme, you must perform a detailed marketing

investigation and take the telecom operator's operation scheme into

consideration.

This scheme has the following risks:

z

In the case of changing the authority of 2G subscribers, the 2G subscribersneed to be automatically upgraded to 3G subscribers. If the tariff standard

cannot be increased to that of the original GSM, the telecom operator suffers

a loss from 3G investment.

This scheme is used when the GSM capacity cannot be expanded because

of the bandwidth limitation.

z The WCDMA network quality is affected when dual-mode MSs used by 2G

subscribers have a great penetration rate. All 2G subscribers who use

dual-mode MSs can camp on the WCDMA after cell selection or cell

reselection.

Therefore, this scheme is not recommended.

3 1 1 2 3G Subscr iber Selecting a 3G Network


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For densely populated urban areas, the GSM network has a perfect coverage.

Thus, selecting a 3G cell from a blind area to a densely populated area seldom

exists, but selecting a 3G cell from a pure-GSM network to a WCDMA-GSM

overlapped area exists. In such a case, to avoid 3G service losses and to reducethe GSM network load, the scheme of 3G subscribers selecting a WCDMA

through cell reselection is used.

Densely populated urban areas have complicated environment. Thus, the

parameter settings are affected by the multipath. To reduce the ping-pong

reselection that occurs when a 3G subscriber selects a WCDMA network from a

WCDMA-GSM overlapped area, set RSCP offset for a FDD cell reselection at

border areas in a WCDMA network to a great value and set FDD Qmin to a small

value.

The WCDMA cells inside the densely populated urban areas implement seamless

coverage and the coverage is good. When an MS is reselected to a 3G network

from a 2G network due to poor indoor 3G coverage or other causes, set RSCP

offset for FDD cell reselection to a small value and set FDD Qmin to a great

value. In this way, better 3G services provided by a WCDMA network can be

ensured in densely populated urban areas.

3.1.1.3 3G Subscr iber Camping on a 3G Network Preferentially

In a densely populated urban area, if a 3G MS stays in the blind area of a 3G

network or at an indoor place without 3G network coverage, the MS can make a

call only in the GSM network. During the call, the MS returns to the 2G/3G

overlapped area. If the inter-RAT handover function is not enabled, or if neither of

the inter-RAT load handover and better 3G cell handover is triggered, the MS

preferentially camps on the 3G network after the call is terminated, instead of

reselecting the 3G network through the cell reselection procedure. The "3G

subscriber camping on the 3G network preferentially" function requires the

support of the BSC version. In addition, the parameterPreferential Camp-on 3G

Cell After Channel Release Allowed should be set to Yes.

3.1.2 Handover

If a 3G subscriber is located in a 3G cell with good signals in a densely populated

urban area, do not hand over the MS to a GSM network.

In densely populated urban areas, the GSM network is mature and implements


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3.1.2.1 CS Service Handover

Better 3G Cell Handover

In a densely populated urban area, if a 3G subscriber initiates the CS service in a

GSM network or hands over the CS service from a WCDMA network to a GSM

network, which network will the MS be handed over to when the 3G subscriber

moves into a WCDMA-GSM overlapped area?

If the GSM network resource is limited but the WCDMA capacity is sufficient, the

CS service is handed over to the WCDMA network. In this way, the GSM network

load is reduced.

For densely populated urban areas with limited GSM capacity, it is recommended

that the CS service of 3G subscribers be handed over to the WCDMA network.

If the GSM resource has certain redundancy, the CS service is preferentially

handed over to the GSM network. After the service is complete, the MS reselects

a 3G cell and hands over to the WCDMA network.

When setting parameters, set Inter-RAT HO Preference to a 3G network and

decision condition to Ec/No because inside of densely populated urban areas,

the interference is great but RSCP has little difference.

Inter-RAT Load Handover

In densely populated urban areas, the traffic in the GSM network is heavy

and capacity expansion is difficult. In the early and development stages of the

WCDMA network construction, the traffic in the GSM network is still heavy.

Therefore, if the BSC version supports the inter-RAT load handover algorithm, theservices initiated in the GSM network or the 3G subscribers that are handed over

to the GSM network can be handed over to the WCDMA network through the

inter-RAT load handover decision procedure.

In the same conditions, the success rate of inter-RAT handovers is lower than that

of intra-RAT handovers. Therefore, the parameters related to inter-RAT handovers should

be properly set to improve the success rate of inter-RAT handovers. In addition, you

should properly set the parameters such as Initial Ec/No for Inter-RAT Load HOand Initial RSCP for Inter-RAT Load HO based on the traffic statistics related to

inter-RAT handovers. The inter-RAT handover parameters are cell-level parameters,

and thus you can set them according to the load conditions of cells. The initial

measurement threshold should be set according to the Load HO Threshold of


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Cell. If the inter-RAT load handover function is enabled, the better 3G cell

handover function can be disabled.

In the early and development stages of the WCDMA network construction, if the traffic in the GSM

network is not heavy, if the requirements of 3G services are met, and if the network quality is not affected,

it is unnecessary to hand over 3G subscribers back to the WCDMA network. 3G subscribers can

preferentially camp on the 3G network to retain 3G services.

3.1.2.2 PS Service Handover

For PS service handovers, use the same scheme as that used for CS service

handovers. If the GPRS has good coverage, the MS can continue to use the

GPRS network and implement intra-system handover and cell reselection in the

GPRS network.

The difference between PS services and CS services is that the PS services are

divided into dynamic resources and static resources during resource allocation

because telecom operators need to preferentially ensure CS services.

The PS services in some areas may be configured with only dynamic resources.

Therefore, the PS services are affected because of resource scarcity. Under this

condition, the PS services in densely populated urban areas are recommended to

be handed over to a WCDMA network with abundant resource.

If a subscriber initiates the PS service in a WCDMA network and then moves to a

blind area in the WCDMA network,

The network data rate can be adjusted to the one allowed by the GPRS network.

In this way, the subscriber can reselect the GPRS network.

The 3G subscriber directly initiates the PS service in the GPRS network. When

configuring the GPRS network capacity, reserve partial capacity for a 3G network

to meet the PS service requirements for 3G subscribers.

Set the parameters as follows:

Set Inter-RAT HO Allowed to Yes.

Set Inter-RAT HO Preference to a 3G network.

Set the decision condition to Ec/No.

Set the parameter related to cell reselection to Qsearch P because PS service


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inter-RAT NACC function will be implemented in GBSS V9.0 in the second

quarter of 2009. For details, consult the marketing department.

In sum,

The scheme used for 2G/3G handovers in densely populated urban areas is

made according to the traffic and network distribution.

An inter-RAT handover is not required if the 2G network capacity can temporarily

meet the requirement of 3G services during the time from that a 3G subscriber

initiates the service in a GSM network to that the 3G subscriber moves to a

WCDMA-GSM overlapped area.

3.1.3 Handover Area Division

The WCDMA and GSM coverage displayed in Figure 3-1 shows that border areas

of densely populated urban areas are the place where inter-RAT handovers occur

most frequently.

When a 3G subscriber is provided with the 3G service and moves from a densely

populated urban area to a common urban area, the MS is handed over to a 2G

network. These areas are the major areas for inter-RAT handovers. Thus, avoid aWCDMA border overlapped by a GSM border.

Good GSM coverage at the WCDMA border benefits successful handovers from

WCDMA to GSM. On the contrary, if the WCDMA border is improperly set, poor

GSM signals cause failures in the inter-RAT measurement and signaling

interaction. Consequently, call drops occur.

You need to make related adjustment on the GSM network for these areas, thus

ensuring successful handovers from WCDMA to GSM.

Handovers also occur when an MS moves from a pure-GSM network to a

WCDMA-GSM overlapped area. Thus, you need to enlarge the overlapping areas

between GSM BTS areas and WCDMA NodeB areas. In this way, a

complementation process between GSM and WCDMA is ensured. In addition,

add the inter-RAT handover duration and measurement time. In this way,

successfully handovers are ensured and ping-pong handovers are avoided.

When a 3G subscriber moves out of a house (3G network coverage is not

implemented inside of the house at the initial stage of 3G network construction),

the MS is handed over to the WCDMA network if the GSM network resource is

scarce. These areas are also inter-RAT handover areas. For these areas, use

Ec/No as the handover decision conditionand configure the neighboring cell of


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network is implemented only in the juncture areas between densely populated

urban areas and common urban areas or in major service areas of common

urban areas.

For common urban area,

Density of subscribers is comparatively high.

The major service is the CS service.

The PS service is required in only some scenarios.

The 2G network capacity is not a bottleneck of restricting the increase of 2G

subscribers. The number of 3G subscribers is small at the initial stage of 3G

network construction. Thus, the 3G network capacity will not be a restriction.

The common urban areas are also the major 2G/3G coverage areas. The number

of 2G subscribers increases with the development of cities, and so does the

number of 3G subscribers. The 3G network will develop increasingly and provide

seamless coverage for common urban areas.

Figure 3-2 shows that with further development of the 3G network, the 3G

network covers common urban areas and provides seamless coverage for

densely populated urban areas.

Subscriber distribution is sparser in common urban areas than in densely

populated urban areas. Thus, the hardware for the GSM network capacity has no

limitation. The requirement for 2G/3G network capacity in common urban areas is

lower than that in densely populated urban areas.

3 2 1 C ll S l ti d C ll R l ti


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The 3G network coverage over common urban areas must be taken into

consideration at the development stage of 3G network construction. The scheme

of cell selection and cell reselection used for common urban areas is the same as

that used for densely populated urban areas. That is, 3G subscribers

preferentially select a WCDMA network.

Common urban areas share the boundary with suburban and rural areas. If

suburban and rural areas have no WCDMA network coverage, the boundary of

WCDMA coverage is transferred from the edge of densely populated urban areas

to that of common urban areas. Thus, common urban areas are the places that

dual-mode MSs select a cell from a pure-GSM network to a WCDMA network.

The signal transmission environment in common urban areas is simpler than in

densely populated urban areas. Both the network coverage and capacity must be

taken into consideration for these areas. The coverage depth for some areas is

insufficient. Generally speaking, the environment of common urban areas is

stable and the multipath effect is less.

Set RSCP offset for FDD cell reselection to a great value but set FDD Qmin to a

smaller value than that set for densely populated urban areas.

If the BSC version supports the function that the a 3G subscriber preferentially

camps on the 3G network after the 3G subscriber terminates a call, the cell

reselection procedure is the same as that described in section 3.1.1 .

3.2.2 Handover



If a 3G subscriber moves from a pure-GSM network to a WCDMA-GSM

overlapped area of common urban areas, the MS performs an intra-system

handover inside of the GSM network rather than handing over to the WCDMA

network.

The GSM capacity is greater in common urban areas than in densely populated

urban areas. If the CS service initiated by a 3G subscriber in a GSM network is

handed over to a WCDMA network, the call quality is not improved. On the

contrary, the handover success rate is higher if the MS is handed over to the

mature GSM network

success rate At the completion of a call the 3G subscriber within the WCDMA


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success rate. At the completion of a call, the 3G subscriber within the WCDMA

network coverage reselects a WCDMA cell for 3G services.


Set HO Preference to a 2G network.

Set HO Preference Threshold for 2G Cell to a small value. Thus, handovers

from 2G to 3G become difficult.


In the early stage of the WCDMA network construction, the growth rate of

GSM subscribers in common urban areas are higher than that in densely

populated urban areas, and thus the capacity expansion requirements for the

GSM network in common urban areas are higher than those in densely populated

urban areas. Although the software for the capacity expansion of the GSM

network is not limited in common urban areas, the GSM network resources used

by 3G subscribers and also the GSM network capacity expansion should be

minimized so that the telecom operators can protect their investment. In the

2G-3G overlapped area of a common urban area, the inter-RAT load handover

function should be enabled and the parameterFDD REP QUANT should be set to

RSCP. To ensure the success rate of inter-RAT handovers, you should set the

parameter Initial RSCP for Inter-RAT Load HO to a value higher than the

WCDMA demodulation threshold and ensure that the handover band

requirements are met. In addition, the parameter Hierarchical Load HO Step

(RSCP) should be set properly so that a small number of subscribers are handed

over each time and the occurrence of call drops due to congestion is avoided.


In normal cases, telecom operators configure a small capacity for the GPRS

network in common urban areas. Thus, the PS service of 3G subscribers can

hand over to a WCDMA network rather than to a GPRS network through cell

reselection. In this way, the PS service of GPRS subscribers in a 2G network is

ensured.

The BTSs are distributed sparsely in common urban areas than in densely

populated urban areas. Thus, the signal strength in common urban areas is

stronger than that in densely populated urban areas.

Y t Q h P t ll l th th t t f d l l t d b


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3.3 Major Highway or Railway

Areas along major highways and railways are also the concerned areas for

telecom operators. For these areas, telecom operators concern about the

problem of GSM network coverage. If the problem of PS service continuity is

taken into consideration at the initial stage of 3G network construction, telecom

operators may implement the 3G network coverage over these areas to ensure

3G service continuity.

At the initial stage and further development stage of 3G network construction, the

3G network coverage is not as complete as the 2G network coverage. Only

densely populated urban areas implement 3G network coverage but suburban

and rural areas do not. The main roads in cities implement complete 3G coverage,

as shown in Figure 3-3.

Figure 3-3 Distribution of BTSs/NodeBs along major railways and highways


For the areas along major highways and railways, you can use the same

interworking scheme as that used for urban areas.

When setting parameters for cell reselection set FDD Q OFFSET to a smaller


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When setting parameters for cell reselection, set FDD Q OFFSET to a smaller

value for these areas than that set for densely populated urban areas and

common urban areas. But, the implementation of cell reselection must be

ensured.



reselection procedure is the same as that describes in section 3.1.1.3.

3.3.2 Handover



If a 3G subscriber moves from a pure-GSM network to a WCDMA-GSM

overlapped area along highways and railways, the MS does not need to hand

over from the GSM network to the WCDMA network.

For areas along highways and railways, handovers occur when the MS moves at

a high speed. In such a case, an intra-system handover is better than an

inter-RAT handover.

You can set the handover to one way intra-system handover from WCDMA to

GSM.


Set Outgoing -RAT HO Allowed to No.

Set HO Preference to a 2G network for areas with bad GSM network coverage.

Set HO Preference Threshold for 2G Cell to a small value. Thus, handovers

from 2G to 3G become difficult.


In the application scenarios of important highways and railways, the network capacity is

sufficient but coverage problems may exist. Therefore, the inter-RAT load handover

function is not required. If the network capacity for highways or railways is insufficient,

the inter-RAT load handover function in heavy-traffic cells should be enabled on the

basis of the traffic statistics.


Thus, you can set the PS service reselection to one-way reselection from


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, y y

WCDMA to GSM and do not set PS service reselection from GSM to WCDMA.

3.4 Suburban and Rural Areas

Suburban and rural areas have extensive land and the population is sparsely

distributed. The number of mobile subscribers is less. In these areas, only GSM

coverage needs to be implemented. If a 3G subscriber roams into these areas,

only the PS service needs to be ensured.

For some special areas, such tourist sights or places whose population varies

with seasons, telecom operators construct an individual WCDMA network. Thus,

one or more NodeBs form an isolated 3G coverage area. Only 3G services need

to be ensured in these special areas,


Some isolated 3G coverage areas may exist in suburban and rural areas. For cell

reselection, 3G subscribers must be ensured to successfully reselect the 3G

network over these areas.



reselection procedure is the same as that describes in section 3.1.1.3.

3.4.2 Handover

Both CS service handovers and PS service handovers in suburban and rural

areas are set to one-way handovers from WCDMA to GSM. Set Outgoing-RATHO

Solution to GSM and WCDMA Interworking for the RNPS GSM V0.75

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