2g to 3g handover v1.0

8/12/2019 2G to 3G Handover v1.0

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2 NOKIA Centra.PPT / 04-03-2003 / BGu, JMa Company Confidential

Cegetel (VF CBT) has set a high priority on inter-system inter-working A must for commercial opening (Q3/03) In a multi-vendor context

But is concerned about any impact on live GSM/GPRS networkperformance

A 5 months consultancy Define the strategy

Evaluate the architecture Explain the mechanisms Propose parameters Identify the risk areas for the mechanisms Prepare testing Decode the roadmaps

Identify impacts on GSM Suggest solutions to alleviate the risks on GSM

Discussion on our conclusions has only happened little with Cegetel, socomments and critics are welcome now ! (and later :-)

Context


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Define the strategy

Propose parameters Identify impacts on GSM

Suggest solutions to alleviate the risks on GSM

Agenda


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Strategy

Objectives Ensure service continuity Obtain maximum use of WCDMA

Better quality (AMR, PS bit rates) Investment efficiency

Avoid ping-pongs

Analysis

WCDMA coverage does not just end at the edge of roll-out, it also stopsindoor before GSM

GSM

WCDMA


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StrategyWhat gain brings 2G->3G Voice ISHO ?

At what Dual-Mode UE penetration level P can we see a visible gain onGSM capacity ?

Arbitrary threshold : A gain of 1 Erlang in GSM load

At high load levels, Erlang B can be approximated by

is the traffic in Erlang blockingthe blocking target C is a constant

We estimate a mobility factor M, ratio of calls setup in GSM-only coverageand ending in WCDMA coverage (good guess 3% ?)

A gain in GSM load is visible if

Therefore no gain is visible if the penetration is below

CblockingErlB ),(

1 PM

MPthreshold

1



Define the strategy



Agenda



ParametersShould we use HCS for 3G2G reselection?

HCS with the same priority on WCDMA and GSM Allows to introduce a temporary offset on R-criterion

Introduces latency, risk to set-up a call in a bad cell Allows to discriminate neighbor selection depending on server quality

If Qsearch_RAT > 0 dB: Very poor serverTake any neighbor Poor serverBe more demanding on the neighbor quality

-16 dBQsearch_RAT(s)=4dB

QHCS(s)=-18dB

QqualMin(s)=-20dB

Qhcs(n)=-85dBm

AdjgQrxLevMin(n)=-102dBm

WCDMAEc/No

GSMAV_RXLEVNCELL(

n)



ParametersShould we use 3G2G HCS ?

HCS with different priorities on WCDMA and GSM

Then GSM must have a lower priority than WCDMA Otherwise, reselection will occur preferentially to GSM, which is not the

objective

Allows to introduce a mobility evaluation criterion, but Mobility is not a suitable trigger for reselection (coverage is) It introduces ping-pong, as mobility is not evaluated in GSMWCDMA

reselection

Reselect WCDMA

WCDMA WCDMA WCDMA WCDMA WCDMA WCDMA

GSM GSM GSM GSM GSMGSM

Reselection Ncr=1 Ncr=2

Ncr=3Fast Moving state detectedstart GSM measurements for reselection

Reselect GSM withdifferent priorities

Reselection to WCDMA shall not occur within 5 secsafter UE hasreselected a GSM cell from a WCDMA cell if a

suitable GSM cell can be found [05.08]Priority (HCS_PRIO)=3

Priority (HCS_PRIO)=4


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ParametersUse of GSM thresholds

Operators have worked on thresholds for access to the cell, and they haveproved successful, therefore they must be re-used

Reselection AdjgQrxLevMin (n) = RxLevAccessMin (n)

Handover 3G2G ISHO is an emergency handover (coverage) Therefore the minimum threshold could be applied

AdjgRxLevMinHO (n) = rxLevMinCell (n) However this threshold is in general very low and not sufficient to hold

the calldrop in GSM Besides at these levels a subsequent handover should occur

immediately Therefore handover thresholds are good references to use

AdjgRxLevMinHO (n) = hoThresholdsLevDL (n) This increases call drop in WCDMA but reduces it in GSM


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Parameters3G2G ISHO triggers

Activating all five triggers may cause unwished handover

Principle to activate triggers one by one upon requirements AMR

Normally the uplink direction should limit UL Quality trigger activates only when the Outer Loop PC is already

out due to UE Tx Power limitation Because of UL DTX a downlink direction trigger can also be checked

Either CPICH Ec/No or CPICH RSCP

PS Power triggers are not very useful due to rate adaptation

MAC layer Transport Format selection in the UL Dynamic DL bitrate Adaptation in the DL

PS Coverage is therefore best measured with CPICH coverage Either CPICH Ec/No or CPICH RSCP

CPICH Ec/No or CPICH RSCP ? CPICH Ec/No is a better measure of coverage But the CPICH Ec/No trigger may cause unexpected ISHO in the

polluted middle of a good WCDMA coverage: Is that good ? Trials are required to decide on the proper trigger


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Inter-system neighbor definition (1/7)Environment

Problems: Manage the different site densities : more sites in GSM than in WCDMA

macro-layer Therefore more than 32 neighbors could be required

Take into account the different site configuration GSM and WCDMA collocated/not collocated M900 and M1800 collocated/not collocated

Define simple and deployable processes

Make use of the existing neighbouring definition rather thansimulating

Avoid handovers to bad quality cells Rather drop the call in WCDMA than increase counters in GSM

Assumptions WCDMA and M1800 coverage are equivalent

M900 coverage wider and deeper than WCDMA and M1800 Traffic is higher on GSM1800 (due to Cegetels strategies)


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Inter-system neighbor definition (2/7)Principles

When WCDMA and M900 are collocated Use the underlying M900 cell as the basis for neighbor definition Ignore the underlying M1800 cell if it exists

When WCDMA and M1800 are collocated Use the underlying M1800 cell as the basis for neighbor definitions

If the WCDMA site is standalone Simulate a virtual collocated M1800 cell and use existing processes

for neighbor definitions (2G simulation)

Use all M900 neighbors of the underlying neighbor M900 provides a continuous coverage

Use M1800 neighbors of the underlying neighbor only when standalone If they are cosited with WCDMA SHO should occur If they are cosited with M900 it covers further than M1800


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Inter-system neighbouring definition (3/7)3G2G

Tri-band collocated site (WCDMA site collocated with dual band siteM900/M1800)

900

M900

WCDMA

Collocatedtri-band site

M900

M1800

Neighbour

Neighbour

M1800

Neighbour

Isolated

M1800 site


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WCDMA site collocated with M900 site only

900

M900

WCDMA


M900

Neighbor

Neighbor

M1800

Isolated

M1800site

Neighbor


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WCDMA site collocated with M1800 site only

900

WCDMA


M900

M1800

Neighbor

Neighbor

M1800

Neighbor

Isolated

M1800site


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Isolated WCDMA site

900

WCDMA

Standalone WCDMA

site

M900

Virtual Neighbor

Virtualcollocated M18

00

Virtual Neighbor

M1800

Virtual Neighbor

Isolated

M1800 site

I i hb i d fi i i ( / )


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Collocated 2G/3G site The WCDMA cell must be declared as neighbour cell of

The GSM collocated M900/M1800 All the GSM neighbours of all the collocated GSM cells

This does not raise the same issues as 3G2G as the site density ishigher in GSM

Isolated 3G site Use M1800 virtual

colocated site

Follow existingneighbouringdefinitionprocess

WCDMA

StandaloneWCDMA site

M900

Virtual collocated M1800

Virtual Neighbor

M1800

Virtual Neighbor

900

Virtual Neighbor

WCDMA

StandaloneWCDMA site

M900

Virtual collocated M1800

Virtual Neighbor

M1800

Virtual Neighbor

900

Virtual Neighbor


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Define the strategy



Agenda

Si lli T f T ffi (LU)


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Signalling Transfer Traffic (LU)

Impact:

Each inter-system reselection will cause a Location Update to occur Increases greatly the SDCCH load

Possible solutions:

Redimension SDCCH

Redesign LA borders to reduce 2G-2G LAU

Introduce Gs interface to have combined LAU/RAU over GPRS If not yet done due to PBCCH

Introduce BSS8 Dynamic SDCCH

Use a common LAC in a common 2G/3G-MSC

M bil di t ib ti & GSM Q S


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Mobile distribution & GSM QoSImpact

All Dual Mode terminals will go to WCDMA in the centre of a GSM/WCDMAcollocated cell

But they will return or remain in GSM at the borders

Modified C/I distribution Mean speech quality may be degraded Mean rxLev/rxQual may be degraded GPRS CS1/CS2 use proportion may be degraded : lower bitrate

0 %

10 %

20 %

30 %

40 %

50 %

60 %

70 %

80 %

90 %

100 %

0 5 10 15 20 25 30 35

Without 2G/3G interworking

With 2G/3G interworking

M900

Distance

Density

WCDMA

DM UE

Penetration

M900

Distance

Density

WCDMA

DM UE

Penetration

M bil di t ib ti & GSM Q S


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Mobile distribution & GSM QoSPossible solutions

Develop a weak C/I design methodology Work on site configurations ro reduce overlapping Introduce this mobile distributions in the frequency plan production tools Introduce interference management features

RF Hopping DL Power Control

Change parameters to manage this interference


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GSM Indicators

Impacts:

Here the focus is on existing GSM KPIs, andwhether they are affected by interworking

New HO table (004000) counters are created, andthe existing ones are not incremented

Therefore ISHO has not impact on HO KPIs However new formulas or new KPIs are

required

Existing TCH table (001000) counters areimplement by ISHO

Therefore the HO Failure KPIs will be degraded(except if ISHO performance is better than 2G-2G HO performance)

Possible solutions:

Tune the 3G2G capture levelAdjgQrxLevMinHO to keep unevitable drop calls inWCDMA while ensuring executable ISHOs areperformed

M1800

WCDMA

adjQrxLevMinHO

MA900

M1800

WCDMA

adjgQrxLevMinHO

MA900


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GPRS service degradation: SGSN queuing


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GPRS service degradation: SGSN queuingsystem

Impact

Data transfer after a PS 3G

2G cell reselection risks to overflow the 2G-SGSN buffers

Possible solutions

Increase 2G-SGSN capacity

Provide 2G-only subscribers a higher QoS priority than 3G subscribers

A paradoxal solution to safeguard the lowest bitrates

(source)

3GSGSN

(target)

2GSGSN

Dual mode MS

Dual mode MS

moves

(source)

RNC

(target)

BSC

Forward unsent dat a

OldGTPTunnel

GGSN

New

GTPT

unnel

Forward

(source)

3GSGSN

(target)

2GSGSN

Dual mode MS

Dual mode MS

moves

(source)

RNC

(target)

BSC

Forward unsent dat a

OldGTPTunnel

GGSN

New

GTPT

unnel

Forward

A l GSM i hb ll


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Actual GSM neighbour cells amount

On Nokia system, when ISHO feature is activated, the amount ofneighbouring GSM cells is reduced by 1

The maximum number of neighbouring cells for a BTS/SEG object is:

32 without any ISHO or CBCCH feature activated 31 if ISHO or CBCCH is activated

30 if ISHO and CBCCH are activated

In dense urban environment this does represent a heavy constraint forCegetel, because no satisfying neighbouring cleaning solution.

2g to 3g handover v1.0

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