intersystem operability svu

For internal use only1 © Nokia Siemens Networks

Multivendor projectCapability Management

Intersystem Operability SVU Session


Title Intersystem Operability SVU Session, Ericsson RAN

Reference NSN MS, CM, MV team

Target Group NPO UTRAN/GERAN

Technology WCDMA, GSM, Ericsson

Software Release WCDMA P7, GSM 10A

Service RAN Tuning and Optimisation

Service Item Intersystem Tuning and Optimisation

Version Ver. 1.0

Version Date 31 August 2010

Version Date Section Comment

1.0 31 August 2010 All Final

Document Info


Contents

Mobile Network Architecture IRAT Strategies Features related to IRAT Idle mode and common channels IRAT Deployment and tuning in idle mode Connected mode IRAT Deployment and tuning in connected mode


Mobile Network Architecture


Contents



IRAT Strategies

The Inter-system strategies, or as Ericsson like to call it Inter-Radio Access Technology (IRAT) strategies are implemented through parameters in both GSM and WCDMA.

Idle mode: WCDMA users in state IDLE, CELL_FACH and URA_PCH

GSM users in state Idle and Packet transfer mode

In these states the IRAT cell reselection is controlled by the UE.

Connected mode: WCDMA users in state CELL_DCH (CS and PS)

GSM speech users (CS)

Dedicated

Cell_DCH

Dedicated

Cell_DCH

Dedicated

Cell_DCH

Dedicated

Cell_DCH

Common

Cell_FACH

Common

Cell_FACH

Common

PDCH

Common

PDCH

Dedicated

TCH

Dedicated

TCHCS

PS

Idle

WCDMA GSM

GPRS/EDGE

Handover

Network controlled

Cell Change

Network controlled

Cell Reselection

UE controlled

Cell Reselection

UE controlled


Idle mode

Camp on WCDMA whenever there is coverage, allowing immediate access to higher bit rates for PS services whilst maximizing possibility to set up and receive video calls

Connected mode

Calls set up in WCDMA (Speech, CS and PS) should be kept there as long as possible

Speech calls set up in GSM

• Move the call from GSM to WCDMA when the quality is acceptable and keep it on WCDMA as long as possible (pro - ability to set up multirab, cons – risk of drop during IRAT handover and a risk for ping pong handover)

• Keep the call in GSM until it’s terminated (pro - no IRAT handover and more capacity left for PS data in WCDMA)

Packet calls set up in GSM should be handed over to WCDMA as soon as coverage and quality are acceptable. The same parameters manage connections in GSM idle mode and packet transfer mode so they must be tuned to satisfy both strategies. Furthermore, parameters must be set to avoid ping pong handover

IRAT Strategies

The main strategy is to minimize number of system transitions and to get highest possible throughput for PS services


IRAT Strategies

Main goals of tunning and optimizing IRAT Prevent/minimising ping pong HO or cell change in idle and connected mode

Keep users away from entering in CPM unless absolutely necessary

Maximizing the WCDMA coverage by applying as low trigger levels to GSM as possible without performance degradation

Improve IRAT success rate and decrease IRAT return rate in connected mode

Lower WCDMA drop rate and IRAT HO activity rate in connected mode

Minimized time spent in CPM

Decreasing the number of CPM periods without IRAT HO or CC

Ping pong HO/CC and needlessly entering CPM can seriously damage user’s performance experience and degrade network capacity as well as throughput for PS connections.

Pre-requisites for a successful IRAT tuning Both the WCDMA and the GSM network must be properly tuned. The neighbour lists have to be satisfying in WCDMA and GSM separately and the pilot pollution in WCDMA has to be minimized.

Proper IRAT neighbours must be defined and implemented.

UE brand commonly used in the operators network should be used for drive testing


Contents



GSM features related to IRAT

GSM-UMTS Cell Reselection and handover (mandatory)

Fast Return to WCDMA at call release (recommended)

Handover with usage of Service Indicator (recommended)

Combined Cell Reselection Triggering GSM to WCDMA (recommended)

Combined Handover Triggering GSM to WCDMA (recommended)

Optimized Throughput at GSM to WCDMA Cell Change (optional, based on NC2)

Smooth GSM to WCDMA unloading (optional)

Queuing of WCDMA calls in BSS (optional)



GSM - UMTS Cell Reselection and HandoverFeature “GSM - UMTS Cell Reselection and Handover” allows UEs multi-RAT (GSM and WCDMA) to roam between UMTS and GSM radio access network without the loss of service. It supports mobility in idle mode, handover of CS connections and cell reselection/update for PS connections.Provides the basic mechanisms for handover and cell reselection from GSM to UMTS. Various parameters are used to control when a multi-RAT MS in idle or connected mode shall start measuring on WCDMA cells. A WCDMA cell will only be considered as a candidate for cell reselection or a handover if the signal quality in the target cell is good enough. It is also possible to prioritize of UMTS or GSM. In addition to the radio criteria, the traffic load of the GSM cell can be used as a criterion for handovers towards UMTS.

Fast Return to WCDMA after Call ReleaseFeature “Fast Return to WCDMA after Call Release” significantly reduces the period of time until a UE becomes reachable in WCDMA after call release in GSM. This feature is very beneficial if the objective is to push voice calls to GSM in these places in order to, for example, save WCDMA capacity for mobile broadband connections.

Handover with Usage of Service IndicatorFeature “Handover with Usage of Service Indicator” allows modification of the GSM-UMTS Cell Reselection and Handover criteria depending on the value of the Service Indicator (SI) and to direct MSs to preferred radio access network, GSM or WCDMA. The SI is a BSS internal parameter and it indicates whether the MSC has any preference in which system (GSM or WCDMA) a CS connection shall be served. SI is valid per CS connection.



Combined Cell Reselection Triggering GSM to WCDMA Feature “Combined Cell Reselection Triggering GSM to WCDMA” provides a capability of defining a threshold for CPICH RSCP measurements which is to be used at cell reselection. This will help in avoiding a cell reselection triggered by weak WCDMA cells which causes problems for the terminals to reach the WCDMA cell on the uplink and makes sure that the terminal performs cell reselection to the most suitable WCDMA cell.

Combined Handover Triggering GSM to WCDMA Feature “Combined Handover Triggering GSM to WCDMA” allows UE only to report WCDMA cells with a signal strength above a certain threshold. This decreases the risk of dropped calls because UE will only report cells with acceptable signal strength.

Optimized Throughput at GSM to WCDMA Cell ChangeBy allowing the terminal to reselect to a WCDMA cell only when the user is not transferring data, feature “Optimized Throughput at GSM to WCDMA Cell Change” avoids long interruptions for packet data services when users are moving from GPRS/EDGE to WCDMA.



Smooth GSM to WCDMA UnloadingFeature “Smooth GSM to WCDMA Unloading” regulates a load in a GSM cell by controlling the handovers of speech connections between WCDMA and GSM. A high load GSM cell is unloaded by limiting the number of handovers per second.

If there is a high traffic load in the GSM cell all incoming handovers from WCDMA will be rejected.

Queuing of WCDMA Calls in BSSWith feature “Queuing of WCDMA Calls in BSS” it is possible, for prioritised subscribers, to provide an enhanced network accessibility in GSM coming from the WCDMA network via the directed retry procedure.


WCDMA features related to IRAT

GSM Handover and Cell Re-selection (mandatory)

Directed Retry to GSM (recommended)

Service Based Handover to GSM (recommended)

IF/IRAT mobility on HSPA (recommended)

Improved DL Coverage (optional)



GSM Handover and Cell Re-selectionThe feature “GSM Handover and Cell Re-selection” provides support for IRAT handover, Cell Change and Cell Reselection for interoperability with GSM, whereby CS and/or PS calls can be transferred to and from GSM networks without loss of context. Transfer between GSM and WCDMA systems for the Multi-RAB is also supported where the procedure is essentially a handover of the CS part and cell re-selection of the PS part. In case that DTM is not supported in GSM, the PS transfer will be suspended. For PS connections on dedicated channel cell change to GPRS is done, while on common channel UE initiates the cell re-selection. Either way the UE performs RA update and re-initiates the connection in GPRS.

Service based handover to GSMFeature “Service Based Handover” redirects WCDMA speech-only users to GSM at call setup based on a Service Indicator (SI) as set by the Core Network .

SI could have following values:

“Should” (CM for GSM measurements should start immediately in order to perform IRAT transfer of the connection as soon as possible)

“Should not” (CM for GSM measurements nor IRAT transfer of the connection should not be initiated unless the IRAT transfer is not required to save the connection due to bad quality or low signal strength)

“Shall not” (CM for GSM measurements nor IRAT transfer of the connection should not be initiated regardless of any radio related reason)

Missing value



IF/IRAT mobility on HSPAThe feature “IF/IRAT mobility on HSPA” supports IRAT and Inter-frequency mobility for RAB combinations mapped on DCH/HS and EUL/HS without channel down switch to DCH before triggering Compressed Mode.

Compressed mode measurements will be triggered at a reception of the event 2d or 6d when on DCH/HS or EUL/HS. If IF nor IRAT measurements can’t be started the UE will remain on DCH/HS or EUL/HS without triggering a down switch to DCH/DCH.

The target cell for Inter Frequency handover must have the same capabilities as used in the source configuration (connection on EUL/HS can only be handed over to a cell that is capable of both EUL and HS). If this is not a case then down switch to DCH/HS or DCH/DCH have to be performed before IF HO.

Directed retry to GSMThe feature “Directed Retry to GSM” attempts to off-load speech traffic from a WCDMA cell to a co-sited GSM cell. This feature acts based on SIs, but also works when SI is missing and the decision for activating the feature is triggered by a RAB Assignment Request from the CN. If a call is chosen for Directed Retry to GSM, the request for the speech Radio bearer will be rejected with cause "Directed retry“. Then a request is made to the CN to relocate the UE to a specific GSM cell, using the IRAT HO procedure. This HO is blind (not based on UE measurement) and target cell must be co-located with the WCDMA cell.

Improved DL coverage Feature “Improved DL Coverage” allows UEs to access the system with CPICH RSCP coverage level of -119 dBm instead of -115 dBm without the feature. To benefit from the feature, cell reselection to GSM should be avoided and this is accomplished by disabling the start of GSM measurements.


Contents



qQualMin - minimum quality access level to the WCDMA network.qRxLevMin - minimum signal strength access level to the WCDMA network.Pcompensation - If there is a mix of 21dBm and 24 dBm UEs in the network there is a need for compensation factor. P - UE output power according to its class.

Tuning of idle mode IRAT thresholds is done with parameters sRatSearch and sHcsRat.

Recommended values are

qQualMin=-18, sRatSearch=4, qRxLevMin=-115, sHcsRat=3

Idle mode and common channels WCDMA

W2G Cell Reselection - Start of GSM measurementsWhen WCDMA coverage gets worse than one of the two criteria below, measurements on GSM start. The measurements are done for UEs in idle mode, CELL_FACH and URA_PCH.

P,0)max(oncompensatiP

oncompensatiPrxlevmeasQ

qualmeasQ

UlmaxTxpower

sHcsRatqRxLevMin

sRatSearchqQualMin



W2G Cell Reselection - Start of GSM measurements continuedParameter fachMeasOccaCycLenCoeff is used to set intensity or to switch off GSM measurements for UEs in CELL_FACH.

Parameter interFreqFddMeasIndicator indicates whether Inter Frequency (IF) measurements for idle and common channels are activated or not.

If IRAT and IFHO are wanted on CELL_FACH recommended values are:

IRAT only: interFreqFddMeasIndicator=FALSE and fachMeasOccCycLenCoeff=4

Both IFHO and IRAT: interFreqFddMeasIndicator=TRUE and fachMeasOccCycLenCoeff=3


Qmeas - quality value of the received signal, derived from the average CPICH Ec/No or CPICH RSCP level for WCDMA cells and from the average received signal level for GSM cells. (s) means serving and (n) is for the neighbour cell.

qHyst(s) - hysteresis value. Set by qHyst1 (for RSCP ranking) or qHyst2 (for Ec/No ranking).

qOffset(s,n) - offset between serving cell and neighbour cell, defined per cell relation. Can be used to move borders between two cells and is set by qOffset1sn or qOffset2sn.

Qofmbms and TO(n) - offsets for the features MBMS and HCS.

IRAT cell reselection to GSM takes place if a GSM cell is ranked as the strongest cell according to ranking criteria during treSelection seconds.

Recommended settings:

qOffset1sn=7, qHyst1=4, qHyst2=4 and treSelection=4


W2G Cell Reselection – Cell rankingParameter qualMeasQuantity determines if ranking should be RSCP or Ec/No (recommended). If both WCDMA and GSM cells are in the list, the first ranking based on signal strength is carried out. If a GSM cell is ranked as the best candidate, the UE performs cell reselection to that cell. Alternatively, a WCDMA cell is ranked as the best candidate and second ranking is executed according to Ec/No (excluding all GSM neighbours).

Criteria for ranking:

TO(n)offmbms

Qn)(s,meas(n)Q(neighbor) R

offmbmsQ(s)meas(s)Q(serving) R

qOffset

qHyst


Idle mode and common channels GSM

G2W Cell Reselection – MeasurementsWhen the multi-RAT UE enters an area without WCDMA coverage, it should camp on a GSM cell. While in the GSM network the UE should perform measurements on WCDMA neighbouring cells which is controlled with parameter QSI. The parameter QSI is set per cell and defines the signal strength thresholds for start of WCDMA measurements:

Always (QSI =7)

Never (QSI =15)

When signal strength of the GSM cell is above a certain value (QSI is from 8 to 14 – from -78dBm to -54dBm with 4dBm step)

When signal strength of GSM cell is below a certain value (QSI is from 0 to 6 – from -98dBm to -74dBm with 4dBm step)

The recommendation for GSM cells that have WCDMA neighbours is to have QSI=7 (“Always”) in order to enable cell reselection to WCDMA also in the areas with good GSM coverage.

In GSM cells outside WCDMA coverage, set QSI=15. This means WCDMA measurements are turned off, which saves battery in the UEs.



G2W Cell Reselection – Cell RankingCell reselection from GSM to WCDMA criteria:

CPICH Ec/No > FDDQMIN

and

CPICH RSCP > RLA + FDDQOFF

FDDQMIN is used to assure a sufficient quality of the candidate WCDMA cell, by defining the minimum Ec/No quality of a WCDMA cell for cell reselection.

RLA is the average of the received signal levels for all monitored GSM frequencies in the BA list, and it is measured in dBm.

FDDQOFF sets an offset between signal strength of GSM cells and the defined WCDMA neighbours.


FDDQOFF=0 (-inf), FDDQMIN=5 (-10dB)



G2W Cell Reselection – Cell Ranking when using the feature Combined Cell Reselection Triggering GSM to WCDMACell reselection criteria:

CPICH Ec/No > FDDQMIN - FDDQMINOFF

and

CPICH RSCP > FDDRSCPMIN - min((P_MAX - 21 dBm), 3 dB)

and

CPICH RSCP > RLA + FDDQOFF

FDDQMINOFF is used to make the requirement of signal quality less attractive for UEs that support the signal strength criterion. FDDRSCPMIN defines a minimum signal strength threshold for cell reselection to WCDMA. P_MAX is the maximum UE output power according to its class.


FDDRSCPMIN = – 102 dBm, FDDQMINOFF = 0 dB


Contents



Ping pong handoverFor good IRAT performance it is essential to avoid idle mode ping pong handover because it can lead to unnecessary LA and RA updates. Ping pong HO increases the processor load in the CN. Each system transition causes outage time during which the UE is not reachable from the system and paging success rate is impacted.

To avoid ping pong handover sufficient difference in CPICH Ec/No thresholds in GSM and WCDMA has to be ensured:

• qQualMin + sRatSearch ≤ FDDQMIN + 4dB

• Increase the difference in Ec/No thresholds with sRatSearch or FDDQMIN

• timeToTrigger parameters

To avoid too many unnecessary IRAT cell selections due to slow intra frequency cell reselection in WCDMA:

• qHyst2=2 dB

• Decreasing the timer treSelection

• qOffset1sn can be increased 10-15 dB

Difference between RSCP thresholds in GSM and WCDMA can be adjusted:

• FDDRSCPMIN

• FDDQOFF can be set to -28, -20 dBm or even higher for co-site

• sHcsRat

Tuning IRAT in idle mode


Contents



Connected mode WCDMA

Activating IRAT

On RNC level: fddGsmHoSupp

Per RAB: using the system constant gsmHoAllowed

Per cell: using hoType (for serving RNC) and defaultHoType (for drift RNC)

If all cells in AS have hoType (or defaultHoType) set to "NONE", then IRAT (and IFHO) measurements are not started

If at least one cell in the AS has hoType (or defaultHoType) set to "IF_PREFERRED" then the preferred HO type is IF

If at least one cell in the AS has hoType (or defaultHoType) set to "GSM_PREFERRED" and no cell in the AS has hoType (or defaultHoType) set to "IF_PREFERRED" then the preferred HO type is GSM

During IRAT activation there are two things that should be kept in mind:

- time in CPM should be minimized due to decreased network capacity

- number of PS ping pong handovers should be kept to a minimum since these might cause long outage times



Compress Mode (CPM) – Start of CPM measurementsBy entering CPM as late as possible (without causing the connections to drop prior to a handover) we are able to have the WCDMA coverage as far as possible.

Events 2d (the estimated quality of the current used frequency goes below Ec/No or RSCP threshold) and 6d (UE TX Power reaches its maximum value) trigger start of CPM measurements.

The UE will start measurements on the GSM system if any of these conditions are fulfilled for best cell in AS

CPICH Ec/No < event 2d Ec/No threshold or

CPICH RSCP < event 2d RSCP threshold or

UeTxPower = event 6d threshold

Event 2d Ec/No threshold: usedFreqThresh2dEcno + serviceOffset2dEcNo - hysteresis2d/2

Event 2d RSCP threshold: usedFreqThresh2dRscp + serviceOffset2dRscp - hysteresis2d/2

Event 6d threshold: parameter txPowerConnQualMonEnabled defines whether connection quality monitoring, using Tx Power Measurements is enabled or not.



Compress Mode (CPM) – Stop of CPM measurementsEvents 2f (the estimated quality of the current used frequency goes above Ec/No or RSCP threshold) and 6b (UE TX Power becomes less than a absolute threshold) trigger stop of CPM measurements.

The UE will stop measurements on the GSM system if all of these conditions are fulfilled for best cell in AS

CPICH Ec/No > event 2f Ec/No threshold and

CPICH RSCP > event 2f RSCP threshold and

UeTxPower < event 6b threshold

Event 2f Ec/No threshold: usedFreqRelThresh2fEcno + usedFreqThresh2dEcno + serviceOffset2dEcNo + hysteresis2f/2

Event 2f RSCP threshold: usedFreqRelThresh2fRscp + usedFreqThresh2dRscp + serviceOffset2dRscp + hysteresis2f/2

Event 6b threshold: ueTxPowerThresh6b


Handover and Cell ChangeIRAT HO and Cell Change is triggered by Event 3a (Estimated quality of the WCDMA is below certain threshold and estimated quality of GSM is above certain threshold)

IRAT HO/CC attempt will be triggered if

GSM RSSI with BSIC verified > gsmThresh3a

and any of these conditions are fulfilled for best cell in AS

CPICH Ec/No < event 3a Ec/No threshold or

CPICH RSCP < event 3a RSCP threshold or

CPICH RSCP < event 3a UE Tx Power threshold

during TimeToTrigger3a time.

Event 3a Ec/No threshold: usedFreqThresh2dEcno + serviceOffset2dEcNo + utranRelThresh3aEcno -

hysteresis3a/2

Event 3a RSCP threshold: usedFreqThresh2dRscp + serviceOffset2dRscp + utranRelThresh3aRscp -

hysteresis3a/2

Event 3a UE Tx Power (RSCP): usedFreqThresh2dRscp + serviceOffset2dRscp + utranRelThresh3aRscp + utranRelThreshRscp - hysteresis3a/2




Special treatment of speech callsWith two WCDMA RAN features Service based handover (SBHO) and Directed retry to GSM we are able to overrule the thresholds for CPM and IRAT HO/CC for the speech calls.

Decisions to make system transitions are based on the information from the core network sent to the UE at the call setup in the Information Element “Service Handover”. It includes the parameters called Service Indicators (SI). The UEs only act on the SIs if the features Service Based Handover and/or Directed Retry to GSM are activated.

SI could have following values:

“Shall not” – Never hand over to GSM

“Should not” – Handover to GSM is allowed only when loosing coverage (normal IRAT HO)

“Should” – Handover via Service based Handover. If SBHO is enabled Directed Retry to GSM is considered

IE is missing – Directed Retry to GSM. If load criterion is not fulfilled normal IRAT is triggered


Handover from GSM to WCDMAA WCDMA cell will become a handover candidate only if any or both of the urgency or load criteria are fulfilled in addition to the quality criterion for WCDMA cells to be added to the candidate list:

CPICH Ec/No >= MRSL (WCDMA quality criterion)

MRSL= 36 (-6dB) if RSCP is the main trigger for WCDMA compressed mode.

MRSL= 30 (-9dB) if Ec/No is the main trigger for WCDMA compressed mode.

Recommendation is to set MRSL = FDDQMIN in order to balance the behaviour in active and idle mode.

The urgency criteria may be due to large timing advance, bad downlink quality or bad uplink quality.

The load criterion is Percentage of idle TCH in the serving cell <= ISHOLEV

ISHOLEV is a traffic load threshold of the serving GSM cell that needs to be exceeded in order to evaluate WCDMA measurements for handovers.

ISHOLEV =99 (max. value), WCDMA will be always prioritized.

With different values of ISHOLEV handovers to WCDMA will be triggered only in case of high traffic in the serving GSM cell.

Traffic load in the serving cell is checked periodically according to the parameter COEXUMTSTINT.

TALLOC is used to prevent sending a new candidate list immediately with the same WCDMA cell in case of inter system handover failure.

Connected mode GSM


Connected mode GSM

Handover from GSM to WCDMAAll valid neighbouring WCDMA cells are sorted in decreasing order of CPICH Ec/No. A final candidate list is created only from GSM cells for non-urgency/non-load criterion, WCDMA cells added over GSM cells for non-urgency/load criterion, WCDMA cells added below GSM cells for urgency/non-load criterion and WCDMA cells added over GSM cells for urgency/load criterion.

QSC controls when the UE should measure on WCDMA frequencies.

To off-load GSM traffic and to extend UMTS coverage

ISHOLEV should be set to the wanted traffic threshold and QSC=7 (Always), or to values 8-14 if the cells are co-sited

To extend UMTS coverage with GSM

ISHOLEV=99. Both QSC=7 and QSI=7 (Always), or 8-14 if the cells are co-sited. FDDQOFF=0 (-inf)

To extend GSM coverage with UMTS

QSC has to be used as a threshold below which WCDMA measurements can commence. ISHOLEV=99


Contents



IRAT Deployment in connected mode

Some core WCDMA cells with poor coverage need GSM as fallback and they should have IRAT active.

Stand alone GSM

WCDMA hoType=NONE

WCDMA border cell with underlying GSM hoType=GSM_PREFERED

Selecting deployment area

Divide the WCDMA cells into border cells and core cells.

Border cells are cells that always have IRAT HO/CC activated, (hoType=GSM_PREFERED). They are at the edge of the WCDMA coverage.

Core cells are cells that usually do not have IRAT HO/CC active (hoType=NONE). In this area the coverage from both systems is good, and they are not adjacent to stand alone GSM cells.


Tuning IRAT in connected mode

Consistency CheckFor IRAT Handover performance it is crucial that GSM cells are well defined in WCDMA system and vice verse.

GSM Cell definition contains: Cell identity MCC MNC LAC NCC BCC BCCH Frequency Band Indicator MaxTxPowerUl

During consistency check, these properties must be compared with latest 2G cell database and External GSM Cells for UTRAN to GSM audit and with latest 3G cell database and External UTRAN Cells for GSM to UTRAN audit.

UTRAN External Cell definition contains: RNC Cell Identity MCC MNC LAC UARFCN UL MRSL Scrambling Code primarycpichpower qQualMin sRatSearch usedFreqThresh2dEcno



Consistency Check

Keeps UTRAN cell data consistent in the GSM radio network

BSS UTRAN

BSS

InternalGSM Cell

ExternalUMTS Cell

Sub Network

UTRAN Cell

GSM OSS – CNA DB RANOS – MIB UTRAN

UTRANBSS

BSS

InternalGSM Cell

Sub Network

UTRANCell

ExternalGSM Cell Relation

GSM OSS – CNA DB RANOS – MIB UTRAN

Keeps GSM cell data consistent in the UTRAN radio network

For consistency checks either OSS feature – IRATHOM (IRAT Handover Manager) can be used, or some in-house developed tool.

IRATHOM is used to synchronies the data between a GSM Radio Access Network and UMTS Radio Access Network (UTRAN) to support Inter-Radio Access Technology Handover.



WCDMA connected mode parametersFor WCDMA connected mode the recommendation is to deploy the same parameter values in all the cells, border or core.

Trigger Threshold Unit Value

Event 2d Ec/No [dB] -13

Event 2d RSCP [dB] -105

Event 2d Ec/No DRNC[dB] -13

Event 2d RSCP DRNC[dB] -105

Event 2f Ec/No [dB] -11

Event 2f RSCP [dBm] -102

Event 6b [dB] 18

Event 3a Ec/No [dB] -13

Event 3a RSCP [dBm] -105

gsmThresh3a [dBm] -95

If different thresholds are used in neighbour cells, UEs in soft/softer handover between them will use the highest threshold. In that case at least one cell has to have hoType=GSM_PREFERRED or IF_PREFERRED.

Parameters serviceOffset2dEcNo and serviceOffset2dRscp are used to change trigger thresholds for other UeRcs. If there is a need to disable IF and IRAT HO for some UeRc settings serviceOffset2dEcNo=-20 and serviceOffset2dRscp=-50 should be implemented.

Initial tuning of WCDMA connected mode For core network cells with IRAT HO/CC activated, the event 2d Ec/No and RSCP thresholds might be lower. In these cells load might be higher and the users might move with lower speed than in border cells.

The trigger thresholds for Speech (UeRc=2)



Tuning goalsThe proposed way of tuning is to set the thresholds on a cell level to a reasonable values for speech (UeRc=2) and to use those thresholds as a starting point for tuning services. This means that parameters usedFreqThresh2dRscp and usedFreqThresh2dEcno defined on a cell level should be tuned before serviceOffset2dEcNo and serviceOffset2dRscp defined all over RNC on UeRc level.

Maximizing time in WCDMA The main IRAT strategy is to keep the calls as long as possible in WCDMA without causing dropped connections. This can be done if event 2d is triggered as late as possible and the best settings for thresholds need be found by adjusting usedFreqThresh2dEcNo and usedFreqThresh2dRscp, after which adjusting serviceOffset2dEcNo and serviceOffset2dRscp individually, per service.

Minimizing unnecessary time in CPM Time spent in CPM is a waste of either power or throughput, so the aim is that all CPM sessions should result in successful IRAT HO or CC.

The decision wether an IRAT HO attempt or CC shall be made (events 2d and 2f) is made by parameters usedFreqRelThresh2fEcNo, usedFreqRelThresh2fRscp, utranRelThresh3aEcNo and utranRelThresh3aEcNo Rscp, together with TimeTotrigger3a.

The number of measurement reports containing event 2d and 2f can be reduced by adjusting the hysteresis2d/2f.


Preventing ping pong handover - SpeechToo many IRAT or ping pong handovers during a speech call can be dramatically reduced by tuning the parameters serviceOffset2dEcNo, serviceOffset2dRscp, MRSL and FDDREPTHR2.

The following condition must be fulfilled:

MRSL > usedFreqThresh2dEcno (the event 2d Ec/No threshold) + a hysteresis

The default setting of MRSL=30 (- 9 dB).

The feature Combined Handover Triggering GSM to WCDMA gives possibility to define a condition to prevent ping pong handover based on threshold for CPICH RSCP - FDDREPTHR2.

The following condition must be fulfilled:

FDDREPTHR2 > usedFreqThresh2dRscp (the event 2d RSCP threshold) + a hysteresis

If the feature is not active an increase of MRSL might be needed to gain difference of 6 dB between the Ec/No thresholds in GSM and WCDMA.

If the value of ISHOLEV is high, there is a possibility that slightly increased value of MRSL can easily switch off G2W handovers completely. In that case the performance indicator “Time in WCDMA” must be monitored carefully.




Preventing cell change ping pong – GPRS to PS (R99)IRAT cell reselection and IRAT CC lead to outage times and there is limited possibilities of decreasing the outage times with radio network parameters. Since the increased number of IRAT cell changes and especially ping pong cell change for PS services leads to poor throughput, the focus of the tuning should be on decrease of these.

The outage time is dependent on the network configuration, application and on the UE.

To avoid ping pong cell change sufficient difference in CPICH Ec/No thresholds in GSM and WCDMA should be ensured, and that is done by adjusting parameters in either/ both of the systems. In GSM PS connections are in packet transfer mode and so steered by the idle mode parameters, but it is preferred to tune the WCDMA parameters serviceOffset2dEcno and serviceOffset2dRscp which only impact selected UeRcs instead of tuning FDDQMIN in GSM which would also impact the idle mode.


HSDPAHSDPA connections do not support IRAT cell change and during HSDPA connection the system transition can occur either via a down switch to DCH followed by an IRAT cell change, or via dropped connection followed by a call set up in GSM again.

Recommended setting:

hsToDchTrigger.poorQualityDetected=OFF

By deciding to have hsToDchTrigger.poorQualityDetected=ON the number of dropped connections for users leaving HSDPA coverage might be reduced. and event 2d thresholds on HSDPA cells have to be tuned and lowered for cells having IRAT HO/CC inactive (hoType=NONE), to prevent poor user throughput due to unnecessary HS to DCH switches.




Recommended GSM handover parameter settings

SPRIO=YES FDDMRR = 1 if GSM cell have GSM neighbours in different GSM bands (GSM 900 and 1800) FDDMRR = 2 if GSM cell don’t have GSM neighbours in different GSM bands

Strategy GSM used to extend WCDMA coverage and off-load GSM system at certain traffic load threshold:

Set QSC = 7 (always) or QSC = 8 (above -78dBm) for UTRAN cell co-sited with GSM cell. Set ISHOLEV = traffic load at which the WCDMA handover shall start

Strategy GSM used to extend WCDMA coverage:Set QSC = 7 (always) or QSC = 8 (above -78dBm) for UTRAN cell co-sited with GSM cell. Set ISHOLEV = 99

Strategy GSM to be extended with UTRAN coverage :Set QSC = 1 (below -94dBm) Set ISHOLEV = 99

FDDREPTHR2 > usedFreqThresh2dRscp + a hysteresis; If the feature Combined Handover Triggering GSM to WCDMA is on, then FDDREPTHR2=16 (-100dBm).

QSCI = 1 (always) MRSL = 30 (-9dB) if Ec/No is the main trigger for WCDMA compressed mode MRSL = 36 (-6dB) if RSCP is the main trigger for WCDMA compressed mode


Thank You!

intersystem operability svu

Documents