6 - Parameter Optmisation_RAS51

1 © Nokia Siemens Networks Presentation / Author / DateFor internal use

3G RANOP 1Module 6 – Parameter Optimisation


3G RAN Optimization

RF Optimisation

and Neighbour Verification

• RF optimisation• New Site Integration• Neighbour plan

optimisation

Signalling Flows

• RRC Establishment• RAB Establishment• SHO• ISHO

Drive Test Analysis

• Drive Survey Analysis• System Performance

(RRC and RAB phases)

ClusterPreparati

on

• Cluster health checks• Parameter consistency

check• Neighbour list

verification• Uplink interference as

a problem indicator

Inter-System Working and Optimisation

• 3G<>2G Cell reselection

• Neighbour Planning• Handover Process and

compressed mode• 3G ISHO service

analysis (AMR and PS)• GSM ISHO Optimisation

Parameter

Optimisation

• Use of Parameters to optimise network performance

HSDPA Optimisati

on

• HSDPA Air Interface Capacity

• HSDPA Drive Test KPIs and Parameter Optimisation


Module 6 – Parameter Optimisation

Objectives

After this module the delegate shall be able to:-

• List some of the parameters that can be tuned for

improved performance

• Match these parameters to Call Setup and Call

Retention improvement areas

• Understand how new RAS05 & RAS51 PS features

effect for the throughput, file download time & PS

Call setup success

HSDPA parameter optimisation is included to module 7- HSDPA optimisation


Content

• Introduction

• Common Channel Power Settings

• Call Setup

• DL powers

• SHO optimisation

• Packet Scheduler


Parameter Optimisation Introduction

• The foundation of good network performance comes from a well optimised:• RF Plan• neighbour plan• Scrambling code plan

• The maximum benefits from parameter optimisation can only be realised if the above are in place.

• Although parameter optimisation can provide short term gains they do not correct underlying network problems. (E.g SHO <> Dominance)

• The UE types in the network needs to be taken into account during parameter optimisation

• There are always tradeoffs (e.g setup time versus success rate)

• Parameter values may be different from network to network due to NW plan and operator strategy and therefore these parameters should be tuned in every networkBasic Radio Platform (Site/Antenna Location,etc)

Scrambling Code Planning

Neighbour Definition

Parameterisation

Feature Strategy


Nokia Parameters an Introduction

• RNC = Radio Network Controller• WBTS = WCDMA Base Station• WCEL = WCDMA Cell• ADJ = Adjacency for WCDMA cell

• ADJS = intra-frequency adjacency

• ADJI = inter-frequency adjacency• ADJG = inter-system adjacency

• HOP = Handover Path• HOPS, HOPI, HOPG

• FMC = Frequency Measurement Control

• FMCS, FMCI, FMCG• COCO = Radio Network Connection

Configuration• WANE = WCDMA Authorized

Network• WSG = WCDMA subscriber Group• WLCSE= WCDMA Location service

entity• WSMLC= WCDMA Serving Mobile

Location Center

See RNC Parameter Dictionary

Managed Objects

RNCRNC

WBTSWBTS

WCELWCELADJSADJS

HOPSHOPS

ADJG

HOPG

FMCG ADJG

HOPG

FMCG

ADJI

HOPI

FMCI ADJI

HOPI

FMCIFMCI

FMCS

COCOCOCO

WANE

WSG

WLCSE

WSMLC


• Parameters to be tuned in case the problem is:

• For DL Coverage

• CPICHToRefRABOffset,

• For UL Coverage• Qrxlevmin, CPICH power

• High RRC Access failure• SCCPCH power

• Synchronisation T312 N312

• SRB rate

• High RAB access failure• ATO

Parameter Optimisation


Content

• Introduction


• Call Setup

• DL powers




Common Channel Power settings

• Common Channel power settings are critically important as they define the cell edge.

• The latest recommended settings are based on Nokia’s global experience and have been seen to work well. Care should be taken when optimising these parameters.

• The link budget of the PCCPCH and SCCPCH can be compared with Data on the DPCH.

• There tends to be plenty of margin in AICH and PICH.

• In general neighbouring cells should not have CPICH power differences greater than 3dB otherwise this can lead to soft handover radio link failures.

• Exceptions may occur between macro and indoor cells


DL Common Control Channel

• DL Common control channels must be heard over the whole cell.

• DL Common Channels does not have a power control.

• The power of the common physical channels are set relative to the CPICH

Parameters Default (Relative) Default (Absolute)

PtxPrimaryCPICH 33 dBm 33 dBmPtxPrimarySCH -3 dB 30 dBmPtxSecSCH -3 dB 30 dBmPtxPrimaryCCPCH -5 dB 28 dBmPtxSCCPCH 1 (SF=64) 0 dB 33 dBmPtxSCCPCH 2 (SF=256) -5 dB 28 dBmPtxSCCPCH 3 (SF=128) -2 dB 31 dBmPtxPICH -8 dB 25 dBmPtxAICH -8 dB 25 dBm



• Different quality requirement for the common channels make power planning a non-trivial task

• Different content and usage Different C/I requirement

Pilot coverageP-CCPCHcoverage

In this example the mobile "sees" the cell but cannot access it as it cannot decode the BCH



• Most common channel have fixed configuration and power• CPICH

• P-CCPCH

• P/S-SCH

• AICH

• PICH and SCCPCH power depends on selected configuration• PICH: depending on paging repetition used per radio frame (10ms)

• SCCPCH: depending on number of SCCPCH used

• Setting the DL Common Control Channel Power is a trade off between:• cell coverage: all the channels must be decoded at the cell edge

• cell capacity: the common channel power consume resources from the traffic channels


Pilot Channel Power Setting –PtxPrimaryCPICH • By default the CPICH consumes 2 W/ 33dBm of the WBTS power (20 W

PA)• For 40 W PA default is 4 W/ 36 dBm (10 %)

• For 8 W PA default is 29 dBm

• CPICH power is used to derive the power requirements of the other Common Control Physical Channels (CCPCH)

• The CPICH should be tuned on a per carrier per area basis as part of wide area parameter tuning following the radio network planning activity

Adjust CPICH transmit Power

Identify Cells with poor coverage

Identify Cells with excessive coverage

Evaluate Ec/Io and RSCP

performance


Ec/Io Array (1 dB increase)

Ec/Io Array (default powers)

Minimum requirement

Pilot Channel Power Setting

• Impact of increasing CPICH transmit power by 1 dB on two cells

• Improvement is sufficient to provide a CPICH Ec/Io > -15 dB in all pixels

• Does not require link loss calculations to be repeated

Any increase in CPICH will lead to reduction in (DCH) Capacity


Effects of CPICH Power Modification

CPICH Transmit Power

Increased soft handover overhead

Too much power

Too little power

Less Power Available for traffic

CPICH coverage holes

Unreliable scrambling code detection

Unreliable channel estimation

Early cell reselection /handover

Increased Eb/No requirement

Reduced system capacity


Reduced system coverage

Slow initial synchonisation

Non-ideal traffic distribution

Late cell reselection /handover


CPICH Transmit Power

Increased soft handover overhead

Too much power

Too little power

Less Power Available for traffic

CPICH coverage holes

Unreliable scrambling code detection

Unreliable channel estimation

Early cell reselection /handout too early

Increased Eb/No requirement



Reduced system coverage

Slow initial synchronisation


Late cell reselection /handout too late



Common Channel Power Configuration

• Soft Hanover is driven by the CPICH Ec/Io which means that CPICH power allocations are important

• If neighbouring cells have different CPICH allocations then radio links will be unbalanced during soft handover and radio links may fail

• Requirement to align CPICH allocations as much as possible

• Neighbouring WBTS with equal CPICH result in balanced radio links during soft handover

• Inner loop power control will be driven by both Node Bs

20 W 20 W

20 W 20 W

33 dBm CPICH

• Scenario results in unbalanced radio links during SHO. Inner loop power control will be driven by WBTS with 28dBm CPICH and therefore the radio link to the second WBTS may fail

33 dBm CPICH

33 dBm CPICH

28 dBm CPICH

30 dBm CPICH

28 dBm CPICH

• Slightly unbalanced radio links during soft handover

• Inner loop power control will be driven primarily by the 28dBm CPICH Node B

20 W 20 W


CPICH Imbalance

• RSCP from cell 1 = 27 - LinkLoss1

• RSCP from cell 2 = 33 - LinkLoss2

Cell A

CPICH = 27dBm Cell B

CPICH = 33 dBm

• For addition, LinkLoss2 - LinkLoss1 = 10 dB

• For drop, LinkLoss2 - LinkLoss1 = 0 dBIf we assume that both cells have the same UL link budget then, at the time of SHO addition, the UE transmit power will be controlled by cell1 because it's link loss is 10 dB less than the link loss to cell 2. This means that cell 2 will have 10 dB less power than it really needs. It is thus relatively likely that cell 2 will lose uplink synchronisation and the radio link to cell 2 will fail.

UE enters soft handover when (27 - LinkLoss1) - (33 -

LinkLoss2) < AdditionWindow

UE leaves soft handover when (33 - LinkLoss2) - (27 -

LinkLoss1) > DropWindow

Add window =4

drop window= 6


Secondary CCPCH Power Setting I

• The Secondary CCPCH (Common Control Physical Channel) carries FACH and PCH transport channels

• Parameter NbrOfSCCPCHs (Number of SCCPCHs) tells how many SCCPCHs will be configured for the cell. (1, 2 or 3)

• If only one SCCPCH is used in a cell, it will carry FACH-c (Containing DCCH/CCCH /BCCH), FACH-u (containing DTCH) and PCH. FACH and PCH multiplexed onto the same SCCPCH.

• If two SCCPCHs are used in a cell, the first SCCPCH will always carry PCH only and the second SCCPCH will carry FACH-u and FACH-c.

• If three SCCPCHs are used in a cell, the third SCCPCH will carry FACH-s (containing CTCH) and FACH-c idle (containing CCCH and BCCH ) . The third SCCPCH is only needed when Service Area Broadcast (SAB) is active in a cell.


Secondary CCPCH Power Setting II

• The power of SCCPCHs are set relative to CPICH transmission power, but it is based on the bitrate.

• The Spreading factor for SCCPCH, which is carrying FACH (with or without PCH), is 64 (60ksps)

• The Spreading factor for SCCPCH, which is carrying PCH only is 256 (15ksps)

• The Spreading factor for SCCPCH, which is carrying FACH-s/FACH-c idle for SAB, is 128 (30ksps)

• Recommended value of the transmission power of the SCCPCH is depended on the number of SCCPCHs . Default transmission power values for different SCCPCHs are as follow:

• PtxSCCPCH1 (SF=64) (default 0) For PCH/FACH or standalone PCH

• PtxSCCPCH2 (SF=256) (default –5) For Standalone FACH

• PtxSCCPCH3 (SF=128) (default –2) For SAB


Secondary CCPCH Power Setting III

• Some of the factors effecting the capacity requirements on the SCCPCH are:-• With increasing sizes of LA, RA or URA, traffic on the PCH will also

increase. • Paging message intended for a single specific UE will be distributed to all cells belonging to the registration area (LA, RA or URA) of the UE, causing extra paging traffic

LALA RA RAURAURA

SHRINKING LA’s

EXPANDING LA’s

• With increasing sizes of LA, RA and URA, the FACH traffic decreases.• the probability for a specific UE to cross the registration area border will decrease and thus LU, RU and URA update procedures due to the UE mobility will decrease.

Since FACH carries Location Updates, similar principle to

SDCCH capacity requirement in GSM.

Large LA > reduced LU traffic

Similar principle to paging capacity requirement in

GSM. Large LA > more paging

capacity > non-combined BCCH.


Total DL Common Channel Power

Service Type

Default

Power

Minimum

Activity

Minimum

Average Power

Maximum

Activity

Maximum

Average Power

CPICH 33 dBm

100 % 33 dBm 100 % 33 dBm

P-SCH 30 dBm

10 % 20 dBm 10 % 20 dBm

S-SCH 30 dBm

10 % 20 dBm 10 % 20 dBm

P-CCPCH

28 dBm

90 % 27.5 dBm

90 % 27.5 dBm

S-CCPCH

33 dBm

25 % 27 dBm 115 %* 33.6 dBm

PICH 25 dBm

96 % 24.8 dBm

96 % 24.8 dBm

AICH 25 dBm

0 % - 80 % 25 dBm

Total - - 35.5 dBm3.5 W

- 37.5 dBm5.6 W

* S-CCPCH control (TFCI) bits transmitted with higher power than data bits


Content

• Introduction


• Call Setup

• DL powers




Call Setup – Key Areas for investigation

• Cell Selection and Reselection• Initial cell selection to a good cell and subsequent cell reselections to

better cells is essential to increase the Call Setup Success Rate (CSSR) and speed up the call setup time.

• RACH Process• Improve the RRC Setup Performance

• Activation Time Offset• Improve PS Call Setup success rate by allowing more time for

Radio Bearer setup and Reconfiguration procedures

• SRB changes• Decrease call setup time by increasing the speed of the signalling

bearer


Cell Selection

• After the UE has switched on and a PLMN has been selected, the cell selection process takes place. A suitable cell is selected when the cell selection criterion S is fulfilled Squal > 0 AND Srxlev > 0.

Pcompensation= max(UE_TXPWR_MAX_RACH – P_MAX, 0)

Cell size defining parameters:• QrxlevMin (-115 … -25)• QqualMin (-24 … 0)

I am outsid

e

I am inside, but have not enough power

-50 .. 33 dBm

Squal = Qqualmeas – QqualMin > 0Srxlev = Qrxlevmeas - QrxlevMin – Pcompensation > 0


Cell Selection

Qrxlevmeas (dBm)CPICH RSCP

Qqualmeas (dB)(CPICH Ec/N0)

Qqualmin(–24...0)

Qrxlevmin(–115...–25)

Srxlev > 0Pcompensation(typ =>0 db)

Squal > 0S-Criterion

fulfilledSqual >0 AND

Srxlev > 0

• If the cell does not fulfill the suitable cell criteria (i.e. S-criteria) the UE cannot access the cell and therefore the UE is out of the coverage

• The Qqualmin and Qrxlevmin parameters should be tuned carefully as non optimum settings can have significant impact on CSSR, Call setup time and time on 3G


Cell Selection Example

Ec/Io distribution

0

10

20

30

40

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70

-25.0

-23.0

-21.0

-19.0

-17.0

-15.0

-13.0

-11.0

-9.0

-7.0

-5.0

-3.0

Ec/Io

Sam

ple

s

0%

20%

40%

60%

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100%

120%

Frequency

Cumulative %

• QualMin defines the minimum quality criteria for accessing the cell.

• With a setting of -18dB: the Ec/Io distribution at call Setup suggests that some 3-5% of call Setups are =< -18dB.

•For a WCDMA operator without an underlying GSM network this would suggest that upto 5% of potential traffic could be lost.

•Setting of this parameter is a compromise. Too high will reduce the amount of carried traffic. Too low will worsen the call Setup success rate.3-5% of call

Setups are =< -18dB


BLER for Each Ec/No

0%

10%

20%

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90%

100%

> -4 -4 to -

6

-6 to -

8

-8 to -

10

-10 to

-12

-12 to

-14

-14 to

-16

-16 to

-18

-18 to

-21

<-21

Ec/No [dB]

[%]

BLER for Each RSCP

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

> -60 -60 to -

70

-70 to -

80

-80 to -

90

-90 to -

100

-100 to -

112

-112 to -

115

< -115

RSCP (dBm)

[%]

These calls may be unable to setup the call after Qqualmin is changed to –18dB from current –20dB

Call Setup status statistics for each Ec/No rangeCall Setup status statistics for each RSCP range

• There is a tradeoff between maximizing 3G utilization and CSSR (end user experience)

• Even though the CSSR is ~ 70% successful in poor RF conditions (Ec/No<-18 dB)

• It is recommended to leave the Qqualmin and Qrxlevmin as -18 db and -111 dBm respectively

Cell Selection Example


Cell Reselection

• Intra / Inter-frequency or inter-RAT

Rs = Qmeas(serving cell) + Qhyst1 (or Qhyst2)

Rn = Qmeas (neighbour cell) – Adj(s/i/g)Qoffset1 (or Adj(s/i)Qoffset2)

Squal = Qqualmeas – Adj(s/i)QqualMin > 0Srxlev = Qrxlevmeas - Adj(s/i/g)QrxlevMin – Pcompensation > 0

Cell A Cell B

CPICH Ec/NoCPICH RSCP

CPICH Ec/NoCPICH RSCP

QqualMin = -20dB

Time

Cell Reselection

UE changes the serving cell to cell A from Cell B.UE changes the serving cell to cell A from Cell B.

UE starts neighbor cell measurements

near cell edge.

UE starts neighbor cell measurements

near cell edge.

Neighbour requirement = 4dB (Qhyst2)

Neighbour requirement = 4dB (Qhyst2)

5 seconds(Treselection)

5 seconds(Treselection)

QqualMin+Sintrasearch=-20dB + 4dB = -16dBQqualMin+Sintrasearch=-20dB + 4dB = -16dB


Cell Reselection Parameter• Treselection - Cell reselection triggering time – WCEL\Treselection = 2s

• Reselection takes place when the UE notices that there is difference between the cells’ Ec/No values (in worst case scenario there can be up to 3dB + Qhyst difference based on the measurement accuracy requirement)

• QHyst2 - Cell reselection hysteresis 2 – WCEL\Qhyst2 = 2 dB • This will add 2 dB hysteresis to the neighboring cell evaluation (target for the cell

reselection)

• AdjsQoffset2- Cell Re-selection Quality Offset 2 - HOPS\AdjsQoffset2 = 0dB• This parameter is used in the cell re-selection and ranking between WCDMA cells.

The value of this parameter is subtracted from the measured CPICH Ec/No of the neighbour cell before the UE compares the quality measure with the cell re-selection/ ranking criteria

• Sintrasearch - (WCEL-Sintrasearch = 12dB)• This parameter is used by the UE to calculate the threshold (CPICH Ec/No) to start

intra frequency (SHO) measurements (Sintrasearch above QqualMin value)

• Minimum required quality level in the cell (WCEL- QqualMin = -18dB)

• Minimum required RX level in the cell (WCEL- QrxlevMin = -111dBm)


Cell Reselection and Call Setup Time

• Poor cell reselection can lead to poor call setup time distribution (due to UE having to send several RRC Connection Requests

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

<3.

5s

3.5s

- 3

.7s

3.7s

- 3

.9s

3.9s

- 4

.1s

4.1s

-4.3

s

4.3s

-4.5

s

4.5s

-4.7

s

4.7s

-4.9

s

4.9s

-5.1

s

5.1s

-5.3

s

5.3s

-5.5

s

>5.

5s

Setup Time (seconds)

Call Setup Delay (PDF & CDF)

0

10

20

30

40

50

60

70

80

90

100

0 0 to 3000 3000 to 5000 5000 to 8000 8000 to 10000 > 10000Setup Time [ms]

PDFCDF

Call Setup Delay CDF

Poor Cell Reselection Performance Corrected Reselection Performance


• Default – ‘Normal’ conditions• Qqualmin = -20dB• Search when CPICH<-8dB, neighbours must be 2dB better, delay reselection by

3s• Set1 – Aggressive Reselection

• Start Searching Earlier (-6dB), no hysteresis to neighbour, change after 1s delay• Set2 – Faster Change

• Change ‘immediately’ but capped by hysteresis• Set3 – Search earlier with faster Change

• Searching starts at -6dB, hysteresis to neighbours but change ‘immediately’

Cell Reselection Test Case Example

Parameter Default Set1 Set2 Set3Sintrasearch 12dB 14dB 12dB 14dBQhyst2 2dB 0 2 2Treselection 3s 1 0 0


Cell Reselection Test Case Results

•Note: With common channel setting in this network: base Ec/No (own cell) is around -4 dB (that’s why not more than 1 cell at Ec/No > -4 dB)

Start the measurements at Ec/No ~-8dB -> with Qqualmin = -20 dB -> Sintrasearch >= 12dB -> test at least 12dB and 14dB

•If the reselection happens at about –16dB there is only 30% possibility that the second best server is >2dB lower than best server

Scanner data chart: •If the measurements for cell reselection happens at about Ec/No –8dB, there is 95 % possibility that second best server is >2dB lower than the best server


Cell Reselection

• Different network environments may require own parameter set

• Qhyst2 - add hysteresis to the neighboring cell evaluation

• 4 dB for 3G cells near different LA unless compensated by AddjsQoffset2 (per Adj)

• 2 dB hysteresis between 3G cells can be used in Urban environment to avoid Ping Pong

• 0 dB hysteresis can be used in the area of high mobility

• Treselection - Cell reselection triggering time

• 2s reselection time helps avoid too many cell reselections between cells and hence LA/RA updates when crossing LA/RA border. Thus there is less signaling and less call failures at LA/RA border due to LA/RA update.

• 0 s could be used in areas having high mobility like in highways.


RACH Process

• Optimum RACH performance is needed to ensure;

• High RRC Setup performance • In both cases the testing is concentrated on RRC Setup success rate, and

the number of RRC Connection Requests sent.

• Minimize the impact of UE Tx power (preamble power) to the cell capacity.

• Minimize call setup delay

• Different UE performance is taken into account


RRC Setup Phase

• This phase starts when UE sends the “RRC CONNECTION REQUEST” message using the PRACH channel

• It is completed when RNC, after reserving all the necessary resources for the RRC Connection (RNC, BTS, Radio and Transmission), replies with DL “RRC CONNECTION SETUP” message, carried over S-CCPCH (FACH sub-channel)

[RACH] RRC:RRC Connection Request

UEUE Node BNode B RNCRNC

ALCAP:ERQ

ALCAP:ECF

NBAP: RL Setup Request

Start TX/RXStart TX/RX


[FACH] RRC: RRC Connection Setup

NBAP: RL Setup Response

[DCH] RRC: RRC Connection Setup Complete

NBAP: Synchronisation Indication

L1 Synchronisation


PRACH Open Loop PC

• Purpose: To set the initial transmitted power of PRACH UL.

• UE determines the uplink preamble power of PRACH• UE PRACH First Preamble Power =

• Open loop PC is a part of the random access procedure for PRACH channel

Path loss calculatio

ns

Path loss calculatio

ns

Minimum received power at

BTS

Minimum received power at

BTS

Example:PtxCPICH=33dBm (Parameter per WCEL)

DL RSCP = -80 dBm (Measured by UE)UL_IF = –100 dBm

UL_Required_C/I = -25 dB (Parameter per WCEL)

UE PRACH First Preamble Power = 33 dBm – (-80 dBm) + (-100 dBm) + (-25 dB) = -12 dBm

Transmission power of CPICH (Broadcast on BCH, SIB 5)) -

Downlink RSCP measurement from active cell on CPICH (Measured by UE) +

Total received wideband interference power at WCDMA BTS (Broadcast on BCH, SIB 7) +

Required received C/I at the WCDMA BTS (Broadcast on BCH, SIB 5)


Required received C/I

• Because the accuracy of the UE Open Loop measurement, it is safest to start from a low power and increase it gradually until the acquisition is received.

• PRACHRequiredReceivedCI • This UL required received C/I value is used by the UE to calculate the initial

output power on PRACH according to the Open loop power control procedure.

• range: -35 ... -10 dB, step 1 dB default: -25dB

• If the value is too low then the RACH preamble ramping up takes a too long time. If it is too high, then it may cause blocking or high noise rise at BTS since the UE measurement on RSCP code power has a poor accuracy.

• This parameter can impact on the RACH coverage


DownlinkBS

L1 ACK / AICH

UplinkMS Preamble

1

Not detected

Message partPreamble2

PRACH_preamble_retrans# of PRACH preambles transmitted during one PRACH cycle without receiving AICH response

UEtxPowerMaxPRACH

… … … …

RACH_tx_Max# of preamble power ramping cycles that can be done before RACH transmission failure is reported

PowerRampStepPRACHpreamble

PowerOffsetLastPreamblePRACHmessage

Initial preample power:•Ptx = CPICHtransmissionPower - RSCP(CPICH) +RSSI(BS) + PRACHRequiredReceivedCI

RACH Process


Random Access Procedure Parameters

• Main parameters to improve the RRC Connection Setup performance are listed below

• PowerRampStepPRACHpreamble (Power Ramp Step)(Po)• The power ramp step on PRACH preamble when no acquisition indicator

(AI) is detected by the UE• range: 1 ... 8 dB, step 1 dB default: 2 dB• If the "power ramp step" is too low then the RACH preamble ramping takes

a too long time. If it is too high, then it may cause high noise rise at BS

• PowerOffsetLastPreamblePRACHmessage in PRACH(Pp-m)• The power offset between the last transmitted preamble and the control

part of the PRACH message (added to the preamble power to receive the power of the message control part)

• range: -5 ... 10 dB, step 1 dB default: 2 dB• The power offset between last preamble and message part should ensure

decoding the RACH message at BS with high probability. Still, it should be minimised to reduce UL interference



• RACH_preamble_retrans

• The parameter describes the number of PRACH preamble retransmissions in a preamble power ramping-up cycle

• range: -1 ... 64, step 1 default: 8

• Note: As the 3GPP requires almost certain detection of PRACH preamble at -19.5dB. The default of 8 retransmissions with 2dB power step, starting from -25dB should be sufficient

• RACH_tx_Max

• Maximum number of RACH preamble cycles defines how many times the PRACH pre-amble power ramping-up procedure can be repeated before UE MAC reports a failure on RACH transmission to higher layers

• range: 1,2...32 default: 8


• The RRC Connection success is highly dependent on the UE so all used UEs should be tested carefully before making any changes.

• Note, Some of the UEs (especially the ones with, early, Qualcomm chipset) could have fixed values for some parameters (an example from Sanyo):

• PRACH_preamble_retrans & RACH_tx_Max = 8 & 8

• PowerRampStepPRACHpreamble = 3dB



RACH Process testTwo values for PRACHRequiredReceivedCI tested (drive testing)• -20dB & -25dB : UL interference conditions are at the same level (reported in SIB 7 for both cases)

100%

0% 0% 0%

88%

2% 5% 6%

0%

20%

40%

60%

80%

100%

1 2 3 4

# RRC Connection Request Messages per call setup

%

PRACH req. C/I = -20dB PRACH req. C/I = -25dB

• Clear improvement in number of needed RRC Connection Request messages per call.

• For –20dB 100% of established calls are setup with only 1 RRC Connection Request message

• Clear improvement number of sent preambles per RRC Connection Request for –20dB case.

• For –20dB 50% of cases the needed number of preambles is <=4 where as for –25dB it is ~6.5

• There should also be improvement of the call setup time

0%

10%

20%

30%

40%

50%

60%

70%

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90%

100%

1 2 3 4 5 6 7 8

PRACH req. C/I = -25dB PRACH req. C/I = -20dB


RACH Process test• Two values for

PRACHRequiredReceivedCI tested (drive testing)

• -20dB

• -25dB

• Clear improvement in call setup delay for –20dB case. ~65% of the established calls are through with only 3.5 – 3.7s delay and the >5.5s delay “tail” disappears (in this case).

96.2%

100.0%

94%

95%

96%

97%

98%

99%

100%

-25dB -20dB

Call Setup Success Rate

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<3

.5s

3.5

s -

3.7

s

3.7

s -

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s

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s -

4.1

s

4.1

s-4

.3s

4.3

s-4

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4.5

s-4

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4.7

s-4

.9s

4.9

s-5

.1s

5.1

s-5

.3s

5.3

s-5

.5s

>5

.5s

Call Setup Delay (seconds) RRC Conn. Req. to Alerting

PRACH req. C/I = -25 PRACH req. C/I = -20


RACH Coverage ?

• The RACH coverage is influenced by:

• At cell edge this path loss should be compared with the one used for the nominal plan in order to have the same coverage for the DCH and the RACH preamble

• If RACH coverage is not good enough the RNC does not receive the RRC CONNECTION REQUEST message and RRC connection attempt fails without the RNC having any knowledge of the attempt

dCIredReceivePRACHRequi -RSSI -_Power Ue_Max_Tx LossPath isotropic dCIredReceivePRACHRequi -RSSI -_Power Ue_Max_Tx LossPath isotropic

Antenna gain and cable loss must be included

Antenna gain and cable loss must be included


RRC Setup & Access Phase

• When a physical dedicated channel establishment is initiated by the UE, the UE starts a timer WCEL-T312 (def=10 s) and waits for layer 1 to indicate WCEL- N312 (def=4) "in sync" indications

• On receiving N312 "in sync" indications, the physical channel is considered established and the timer T312 is stopped and reset

• On the BTS side after receiving synchronization indicators the BTS sends NBAP: synchronization INDICATION –message to RNC after which the closed loop and outer loop PC start to control the powers

RNC receives RRC Connection Setup Complete –message ->

RNC receives RRC Connection Setup Complete –message ->

RRC Connection Setup Complete –message SENT after 2 x 7 UL DPCCH frames from DL sync

RRC Connection Setup Complete –message SENT after 2 x 7 UL DPCCH frames from DL sync

L1 synchronisation established

BTS sends NBAP: synchronisation

IDICATION -message

L1 synchronisation established

BTS sends NBAP: synchronisation

IDICATION -message

UE initiates physical dedicated channel establishment before sending e.g. RRC Connection Setup Complete –message on DPDCH

UE initiates physical dedicated channel establishment before sending e.g. RRC Connection Setup Complete –message on DPDCH

Timer T312 startedTimer T312 started

“in sync” indicators on L1

“in sync” indicators on L1

Timer T312 stopped

Timer T312 stopped

N312 L1 “in sync” indicators

N312 L1 “in sync” indicators

L1 synchronisati

on established

L1 synchronisati

on established

N_INSYNC_IND indicators on

L1

N_INSYNC_IND indicators on

L1

1


RRC Setup & Access Phase

• In case UE is not able to establish synchronisation within timer T312 it stops TX on the DCH

• In case BTS is not able to establish synchronisation it does not send NBAP:synchronisation Indication –message to RNC

• The BTS tries to establish synchronisation until RNC sends NBAP:Radio Link Deletion message

[RACH] RRC:RRC Connection Request

UEUE Node BNode B RNCRNC

ALCAP:ERQ

ALCAP:ECF

NBAP: RL Setup Request



[FACH] RRC: RRC Connection Setup

NBAP: RL Setup Response

L1 Synchronisation


Radio Bearer Process

• Call Setup Success Rate (CSSR) depends on how well UE responds to the Radio Bearer (RB) Reconfiguration or RB Setup processes

• If UE does not have enough time to setup the lower layers for the new RB configuration then call setup will fail.

• This could be improved by increasing the Activation Time Offset (ATO) parameter:

• Used for delaying the bearer configuration change execution so that it will be performed simultaneously at both ends, based on the frame number.

• Connection Frame Number (CFN is used in NBAP and RRC messages when a radio link is reconfigured)

• This delay depends on the end-to-end transmission delay and must allow for RLC repetitions. If the delay is too short the repeated message may come too late and the transaction fails

• Call Setup time can be improved by changing ATO and/or changing the Signaling Radio Bearer (SRB) bit rate

• Both call setup delay and access performance should be considered and balanced.


ATO – Activation Time Offset

1 2 3 4 5 6 7

1 2 3 5 6

RAN

UE 4

7

7

Timer_poll

1-way RAN/UE delay

Timer_poll

7

7

RRC message of 7 blocks

Transmit fail Transmit fail

SignalingDelayOffset ActivationTimeOffset

• Total Activation offset consists of ActivationTimeOffset parameter part and fixed SignallingDelayOffset part

• The SignalingDelayOffset is an RNC internal parameter

• ActivationTimeOffset part represents the processing delay of RNC and BTS. This is extra delay is needed to allow for lost messages that cause AM RLC level repetitions and compensate for the processing delays in RNC, BTS and UE

The recommended value for ATO is 500-700 ms but even the lowest recommended value 300ms tolerates two RLC repetitions

•The CFN, which is set to the "activation time" field in L3 messages, is: (the CFN provided by FP +(ActivationTimeOffset + SignalingDelayOffset)/10) mod 256


ATO

• Signaling Delay Offset values are planned so that, together with the value 300 ms of the ActivationTimeOffset parameter, two AM RLC retransmissions are enabled during the activation time

• The SignalingDelayOffset is an RNC internal parameter that implies a required offset based on the SRB bit rate, the actual procedure and the length of a RRC message. The fixed values set in RNC are below (ms)

• The recommended value for ActivationTimeOffset is 700 ms. Increased delay will show up directly on the RB setup delay and consequently on call setup time (twice for UE to UE calls).

Service SRB 3.4 SRB 13.6 SRB 3.6 SRB 16.6AMR 280 70 240 60CS 280 70 240 60PS 200 50 160 40

SRB 3.6 SRB 16.6All Services 80 20

Physical Channel and Measurement procedures

RB Procedures Tranport CH procedures


ATO change case

AMR_701

0

200

400

600

800

1000

1200

1400

1600

1 2 3 4 5 6 7 8 9 10 11 12

Tim

e(m

s)

1500 500 200 1 RRCConnectionRequest <=> RRCConnectionSetup2 RRCConnectionSetup <=> RRCConnectionSetupComplete3 RRCConnectionSetupComplete <=> MM CM Service Request4 MM CM Service Request <=> MM Authentication Request5 MM Authentication Request <=> MM Authentication Response6 MM Authentication Response <=> SecurityModeCommand7 SecurityModeCommand <=> SecurityModeComplete8 SecurityModeComplete <=> CC SetUp9 CC SetUp <=> CC Call Proceeding

10 CC Call Proceeding <=> RadioBearerSetup11 RadioBearerSetup <=> RadioBearerSetupComplete12 RadioBearerSetupComplete <=> CC Alerting

1300ms

1000ms

The difference in call setup time to the previous page is almost the difference between the RadioBearerSetup and RadioBearerSetupcomplete messages (part 11).


SRB Change Case – CS Call Setup

• SRB 13.6 gives roughly 1-2 sec faster call setup than 3.4 but also require more capacity on Iub

• The Activation Time Offset (ATO) was 700ms in the tests. Previous tests indicate that the use of ATO=300ms would decrease the setup time by 400ms for each leg (for 3G to 3G case this means 2*400ms = 800ms). Using ATO values close to 300ms can bring some decline (0.2-0.4 %) to call setup success rate.

Call setup time (s) SRB 3.4 SRB 13.6

Mobile originating call 3.5 2.5

MOC with mobility 3.7 2.6

Mobile terminating call 3.4 2.2

MTC with mobility 3.8 2.2

Mobile to mobile call 7.5 5.1

M2M with mobility 8.2 5.5

Measured AMR call setup

times (RAS5.1 E4)


SBR Change Case- PS Call Setup

• SRB 13.6 gives 30% faster GPRS attach time and PDP activation time than SRB 3.4.

• GPRS attach time was measured between RRC Connection Request and ATTACH ACCEPT

• PDP context activation time was measured between messages RRC Connection Request and RADIO_BEARER_RECONFIGURATION_COMPLETE.

Parameters: ATO=700ms, ToAWE/ToAWS=10/25ms. P-TMSI reallocation was used.

• In above measurements the ToAWE/ToAWS default value of 10/25 ms was used. •Too Small value may cause lost messages when Iur Connection are in use or adjacent sites have different transport delay on Iub. SHO success rate may be used for monitoring this effect.

•If ToAWE is decreased the data may in some cases arrive in time to be transmitted without the need of timing adjustment which reduces the average RTT.

•In practice the measured RTT values with ToAWE/ToAWS=7/15ms were 10-20ms shorter.

SRB 3.4 SRB 13.6GPRS attach time (s) 2 1.3

PDP context session activation time (s) 5.5 3.5

PDP context session activation time with mobility (s) 5.6 3.6

Measured PS call setup

times (RAS5.1 E4)


SRB Change Case

94

95

96

97

98

99

100

RRC Setup SuccessRate RRC Access SuccessRate RRC Setup & Access SuccessRate

SRB 13.6kbpsSRB 3.4kbps

• RRC Connection Access phase Success Rate should be evaluated when changing the SRB bit rate

• Example of RRC performance with SRB 3.4 kbits/s and 13.6 kbits/s

!


Content

• Introduction


• Call Setup

• DL powers




Downlink power allocation of a radio link

PtxTotalMax (Max total power of WBTS)

CPICHtoRefRABOffset (def 2 dB)SF_adjustment

+PTxDPCHmin (default -28 dB)

+ PtxDPCHMax (def -3 dB)

Ptx_CPICH (def 33 for 20W WPA)

PCrangeDL (default 15 dB)

The maximum DL power is the lowest of these three values for NRT and Multirab

The minimum DL power is the maximum of these value

PCrangeDL

PtxDLabsMax (Maximum planned DL power of a radio link) – This parameter sets the maximum power for radio link, only NRT and Multirab.

PCrangeDL

In most cases we are operating in this range for

voice. For PS data the PtxDLabsMax can be

lower than the upper limit dictated by this


How it is actually done ?

• Define maximum radio link power:• RT: Ptx_max_rl = min{P_CPICH–CPICHtorefRABoffset+SF_adjustment, PtxTotalmax-

PtxDPCHmax}

• NRT & Multirab: Ptx_max_rl=min{P_CPICH-CPICHtorefRABoffset+SF_adjustment, Ptxtotalmax-PtxDPCHmax, PtxDLabsMax}

• Define minimum radio link power:

• Ptx_min_rl=max{Ptx_max_rl-PCrangeDL, Ptxmax-PTxDPCHmin}• SF_adjustment is the mapping of the max power to the actual bearer based on

spreading factor and downlink Eb/No compared to the reference service (12.2 kbps AMR)

• If the radio link includes multiple bearers then the numerator of this equation should include the sum of the Eb/No, bit rate products for all bearers

refref

CCTrCHDCHDCHDCH

REbNo

REbNoadjustmentSF

_


Maximum DL Power

• If call setups are attempted and are failing in bad Ec/No or RSCP conditions then one solution to improve the call setup success rate might be to tune CPICHtoRefRABOffset

• The max DL power is determined by Admission Control as

EbNoref is the (linear) value of the planned downlink Eb/No of the reference service which is defined with parameter Downlink BLER target of the reference service (DLreferenceTargetBLER).

EbNoDCH is the (linear) value of the planned downlink Eb/No of the service transferred on the DCH

RDCH is the maximum transport channel bit rate of downlink DCH.

Rref is the maximum DCH bit rate of the reference service (parameter DLreferenceBitRate).

Ptx,DPCH,max is the value of PtxDLabsMax – PtxDPCHMax.

Ptx,off defines the power of the primary CPICH in relation to the maximum code power of the ref. service (WCEL-CPICHtoRefRABoffset)


• 64 kbit/s CS Data service multiplexed with a 3.4 kbps SRB

• 64 kbps service DL Eb/No: 4.5 dB = 2.82

• 3.4 kbps SRB DL Eb/No: 8.0 dB = 6.31

• Reference service: 12.2kbit/s speech with Eb/No: 5.5 dB = 3.55

• CPICHtoRefRabOffset = 2 dB

• PtxCPICH: 33 dBm

• SF_Adjustment= (2.82*64 + 6.31*3.7)/(3.55*12.2) = 4.7 = 6.7 dB

• PtxCPICH - CPICHtoRefRabOffset = 33 dBm - 2 dB = 31 dBm

• Ptx_DPCH_max = PtxDPCHMax =3dB below the maximum power = 40dBm

• Ptx_max_rl=min(31+6.7 dBm, 40 dBm) =37.7 dBm

Maximum DL Ptx of the Radio LinkExample

SF Adjustment


• Recommended RNW value for CPICHtoRefRABOffset=0. This change means that the maximum link power for a connection is increased

by 2 dB to improve the DL coverage. This change means also that the minimum power is increased as well (as the minimum power is Max power – DL PC Range) which might lead to the situation where too high powers are allocated even in the good coverage conditions as a result power is wasted

So if CPICHtoRefRABOffset=0 dB then it is recommended to set PCRangeDL= 20dB to compensated increase of CPICHtoRefRABOffset

Maximum DL power

• Example Maximum and Minimum Power for different services• WCEL/CPICHtoRefRABOffset = 2dB and RNC/PCrangeDL = 15dB

Service Type

3. 4 kbps standalone SRB

13.6 kbps standalone SRB

12.2 kbps speech + 3.4 kbps SRB

64 kbps data + 3.4 kbps SRB



Maximum 27.8 dBm 31.8 dBm 32.2 dBm 35.2 dBm 38 dBm 40 dBmMinimum 15 dBm 16.8 dBm 17.2 dBm 20.2 dBm 23 dBm 25 dBm


Content

• Introduction


• Call Setup

• DL powers




SHO Optimization

• The main emphasis in SHO optimization is related to SHO overhead, SHO success rate, call drop rate and average Active Set size.

• Neighbour planning is more important than SHO parameter optimization, so it should be done properly

• Acceptable SHO overhead in this case is 50 % or less, one example below

0 50 100 150 2000

100

200

300

400

500

600

Soft handover overhead [%]

An average active set size of 1.75 corresponds to a SHO

overhead of approximately 50 %. It may be appropriate to

define different thresholds for different environment types, i.e.

according to the site density.


SHO Failures

• The SHO failures are mainly related to: • Initial Synchronization Failure of the new added RL

• Active Synchronization Failure of the existing RL(s)

• Different soft handover parameters can help with synchronization problems between radio links.

• When new radio link is added to the Active set the L1 synchronization between the UE and the new BTS must be achieved. The UL/DL synchronization procedures are needed to establish reliable new connection between BTS and UE.

• Some of the initial synchronization failures are due to the fact that there can be difference in the UL noise rise levels of the adjacent cells (check Noise rise from Module1)

• If a lot of initial synchronization failures for SHO links are seen then one possibility is to try to reduce those by delaying the additions.


• If there are many Active synchronization Failures detected, one action could be to advance the SHO activity (e.g. using cell individual offsets) or in general use different FMCS (usually these conditions are improved when addition is done earlier)

If UE does not have enough level to receive Active Set Update message it is possible that call drop happen because of HO failure.

Call drop be avoided by setting earlier timing (timing for sending out Measurement report) of HO between targeted cells.

Use FMC parameter Use AdjsEcNoOffset

Impact all of FMC targeted areas

Impact only between 2 targeted

cells

SHO Failures


SHO Optimisation

• Different sets in different Network environment could improve SHO performance

• Dense Urban/Urban Area has typically lot of Overlapping/Capacity Problems

• Areas with good CPICH EcNo levels in Active Set, smaller SHO overhead could be done with low Add/Drop window (2/4 dB)

• Rural Area/Poor Coverage Area: Reliable set with cost of SHO OH

• Rural areas/Highways with low CPICH EcNo –13…-16 in Active Set, more loose add/drop window (4/6 dB) could be used to have more reliability for SHO synchronisation


SHO Optimisation

Scenario Goal Main adjs affected Minor adjs affected

Deep fading Anticipate the addition

• FMCS parameter related to addition/replacement

• adjsEcN0offset > 0

Temporary Strong Neighbour

Increase the stability of the active set

• FMCS parameter related to addition/replacement and deletion (depending on drop_ho%)

• adjsDERR


• adjsDERR

Ping pong Increase the stability of the active set

• FMCS parameter related to addition/replacement and deletion (depending on drop_ho%)

• synch parameter in case of high rl_fail_AB% and p_fail_ini_radio%

• adjsDERR with low SHO_duration_ave%


• adjsDERR with low SHO_duration_ave%


SHO Parameters

• The most important FMCS parameters to be used for SHO optimization are

AdditionWindow

Too wide soft HOarea

Too small soft HOarea

+ Soft HOOverhead

UL macrodiversitygain decrease

- UL Troughput

too high

too low

unnecessary softHO branch

addition- DL Troughput

frequent HOs+ signallingoverhead

Parameters Default value

CPICH Ec/No Filter Coefficient 600 ms

Addition Window 4 dB

Addition Time 100ms

Drop Window 6dB

Drop Time 640ms

Drop Window

unnecessary softHO branches

remain undropped

+ Soft HOOverhead

too high

too low

too wide soft HOarea

- DL Troughput

frequent HOs+ signallingoverhead


Individual Ncell Offset

time

P CPICH 1

P CPICH 2

P CPICH 3

Reporting Range

Reporting Event

1B

Reporting Event

1A

AdjsEcNoOffset

Enlarging Cell 3 by x dB

Ec/Io


Case 1: SHO Parameter test in dense Urban Area• Following SHO parameter scenarios used during test


Nokia Voice Call Performance In Dense Urban Area• Highest soft handover overhead was observed with window add/drop parameters 3.5/5 dB, 4/6 dB and 2/6 dB.

• Nokia UE ASU efficiency is always higher than 60%. Samsung UE achieves this level only in single mode.

-40.00

-20.00

0.00

20.00

40.00

60.00

80.00

Ref

Ref, n

ew n

eighb

or lis

t

Ref, n

ew n

eighb

or lis

t

Filter C

oeff=

1

Filter C

oeff=

1

Add T

ime=

60ms

Filter C

oeff=

5

Add T

ime=

160m

s

Drop T

ime=

240m

s

Drop T

ime=

1280

ms

W a

dd/d

rop=

1.5/

3dB

W a

dd/d

rop=

3.5/

5dB

W a

dd/d

rop=

2.5/

5dB

W a

dd/d

rop=

4/6d

B

W re

place

ment=

1dB

W re

place

ment=

3dB

T repla

cem

ent=

640m

s

Filter C

oeff=

2

W a

dd/d

rop=

3/4d

B

W a

dd/d

rop=

2/6d

B

Power,dBm Time between MR,s SHO,% ASU eff,% ASU time,s Drops


• ASU time is lowest when Filter Coeff=1. This result is confirmed by counters.

• ASU time is highest when Filter Coeff=5 and window add/drop= 2/6 dB.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

Ref

Ref, n

ew n

eighb

or lis

t

Ref, n

ew n

eighb

or lis

t

Filter C

oeff=

1

Filter C

oeff=

1

Add T

ime=

60m

s

Filter C

oeff=

5

Add T

ime=

160m

s

Drop T

ime=

240m

s

Drop T

ime=

1280

ms

W a

dd/d

rop=

1.5/

3dB

W a

dd/d

rop=

3.5/

5dB

W a

dd/d

rop=

2.5/

5dB

W a

dd/d

rop=

4/6d

B

W re

plac

emen

t=1d

B

W re

plac

emen

t=3d

B

T repl

acem

ent=

640m

s

Filter C

oeff=

2

W a

dd/d

rop=

3/4d

B

W a

dd/d

rop=

2/6d

B

Time between MR,s ASU time,s

Nokia Voice Call Performance In Dense Urban Area


Case 2: SHO Parameter test in various areas

• The following parameter sets are tested in City Center, Highway and Suburban Area using Nokia 6630


-60

-40

-20

0

20

40

60

80

Filter

Coef

f=2,

Wre

place

=1dB C

ity C

ente

r

Filter

Coef

f=2,

Wre

place

=1dB H

ighway

Filter

Coef

f=2,

Wre

place

=1dB S

uburban

are

a

Filter

Coef

f=1,

Wre

place

=1dB C

ity C

ente

r

Filter

Coef

f=1,

Wre

place

=1dB H

ighway

Filter

Coef

f=1,

Wre

place

=1dB S

uburban

are

a

Wadd

/dro

p=4/6

dB,Filt

erCf=

2,W

repl=

1dB C

ity C

ente

r

Wadd

/dro

p=4/6

dB,Filt

erCf=

2,W

repl=

1dB H

ighway

Wadd

/dro

p=4/6

dB,Filt

erCf=

2,W

repl=

1dB S

uburban

are

a

Wadd

/dro

p=3/4

dB,Filt

erCf=

2,W

repl=

1dB C

ity C

ente

r

Wadd

/dro

p=3/4

dB,Filt

erCf=

2,W

repl=

1dB H

ighway

Wadd

/dro

p=3/4

dB,Filt

erCf=

2,W

repl=

1dB S

uburban

are

a

Wadd

/dro

p=4/6

dB City

Cen

ter

Wadd

/dro

p=4/6

dB Hig

hway

Wadd

/dro

p=4/6

dB Suburb

an a

rea

Power,dBm Time between MR,s SHO,% ASU eff,% ASU time,s Drops

• Highest soft handover overhead was observed with window add/drop parameters 4/6dB.

Nokia Voice Call Performance in various areas


0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

Filte

r Coef

f=2,W

repl

ace=

1dB C

ity C

ente

r

Filte

r Coef

f=2,W

repl

ace=

1dB H

ighw

ay

Filte

r Coef

f=2,W

repl

ace=

1dB S

uburb

an a

rea

Filte

r Coef

f=1,W

repl

ace=

1dB C

ity C

ente

r

Filte

r Coef

f=1,W

repl

ace=

1dB H

ighw

ay

Filte

r Coef

f=1,W

repl

ace=

1dB S

uburb

an a

rea

Wad

d/dro

p=4/6

dB,Filt

erCf=

2,W

repl=

1dB C

ity C

ente

r

Wad

d/dro

p=4/6

dB,Filt

erCf=

2,W

repl=

1dB H

ighway

Wad

d/dro

p=4/6

dB,Filt

erCf=

2,W

repl=

1dB S

ubur

ban

area

Wad

d/dro

p=3/4

dB,Filt

erCf=

2,W

repl=

1dB C

ity C

ente

r

Wad

d/dro

p=3/4

dB,Filt

erCf=

2,W

repl=

1dB H

ighway

Wad

d/dro

p=3/4

dB,Filt

erCf=

2,W

repl=

1dB S

ubur

ban

area

Wad

d/dro

p=4/6

dB City

Cen

ter

Wad

d/dro

p=4/6

dB Hig

hway

Wad

d/dro

p=4/6

dB Sub

urban

are

a

Time between MR,s ASU time,s

• Highest ASU activity with Filter Coefficient=1.



• Least number of drops in all areas is achieved with W add/drop= 4/6dB.


0

0.005

0.01

0.015

0.02

0.025

0.03

Filter C

oeff=

2,W

repla

ce=1d

B

Filter C

oeff=

1,W

repla

ce=1d

B

Wadd

/dro

p=4/6d

B,Filte

rCf=

2,Wre

pl=1d

B

Wadd

/dro

p=3/4d

B,Filte

rCf=

2,Wre

pl=1d

B

Wadd

/dro

p=4/6d

B

Drops/min,CityCenter

Drops/min,Highway

Drops/min,SuburbanArea


• Typically during drive test drops were caused by rapid radio signal degradation.



Conclusions from SHO parameter Test

• Significant drop call ratio improvement, can be achieved using parameter set Wadd= 4dB, Wdrop=6dB, Wreplacement= 1dB, Filter Coefficient=2.

• It has drawbacks as increased soft handover overhead, increased number of DCH setup rejections due to lack of DL resources.

• Wadd= 1.5dB, Wdrop=3dB shows highest drop call ratio.

• Influence of Filter Coefficient to drop call ratio remains unclear since majority of terminals in the network have hard coded value. Subsequent one week long tests couldn’t confirm drop call ratio improvement.

• No positive influence of Wreplacement= 1dB has been found.

• The following parameter set showed the best drop call ratio after setting back Filter Coefficient and Wreplacement values back to default:

• Wadd= 4dB, Wdrop=6dB, Wreplacement= 2dB, Filter Coefficient=3.


Content

• Introduction


• Call Setup

• DL powers




Packet Scheduler Parameters

• The focus for PS data tests is to minimize the PS call drop and keep the throughput high

• The performance depends on the usage of certain bit rate and different RRC states of the connection.

• New RAS05 & RAS51 Optional features has impact the throughput and PS call setup success (PBS) if activated

• Dynamic Link Optimization (DyLo) feature could impact the achieved throughput

• Maximum allowed bitrate in certain cells (e.g. Rural, Highway) could be set to a lower value if there is risk of capacity shortage (Radio, Iub)

• Further performance/throughput could be optimized with different bearer activity/inactivity timers and traffic volume parameters.

• The optimum set of parameters depend on the used application (FTP, MSS, email) and amount of data.


Initial and Minimum bit rate (UL/DL)

• In RAS05 there is one parameter for Initial and Minimum: MinAllowedBitRateDL/UL (Initial and minimum allowed bit rate in down/uplink)

• In RAS5.1 there are own parameters for both : InitialBitRateDL/UL (Initial bit rate in down/uplink) and MinAllowedBitRateDL/UL (Minimum allowed bit rate in down/uplink)

• InitialBitRatexL is the "the initial bit rate that can be allocated by the PS in schedule situation. PS does not schedule NRT DCH bit rates that are below the value of this parameter."

• MinAllowedBitRatexL is "the minimum allowed bit rate that PS can downgrade to the NRT DCH bit rate in congestion situations“

• Setting high bit rates already from the initial Radio Bearer allocation gives not only higher peak bit rate but also lower RTT and faster TCP slow start.

• But high initial bit rate can be problematic from the service accessibility point of view since if there is not enough AIR interface, BTS HW or Iub capacity the RAN will reject the capacity allocation

See Priority Based Scheduling feature


Traffic Volume measurements

• In the call setup phase RAN allocates 0/0 RB without any traffic volume reports

• Traffic volume report is required to upgrade 0/0 RB to initial bit rate (e.g. 64kbps)

• Note that once reporting event has been triggered TrafVolThresholdLow, the traffic volume report is put on hold and is sent only if the condition is still fulfilled after parameter TrafVolTimeToTrigger

time

Transport Channel

Traffic Volume(= UE Ruffer

Load) 4A

UE in CELL_FACH: TrafVolThresholdULLow (128 Bytes)

UE in CELL_DCH: TrafVolThresholdULHigh (1024 Bytes)

4A 4AMeasurement

report has information about

currentUE buffer load


• One option to favor high initial bit rate is to set “high traffic volume threshold” equal to “low traffic volume threshold”

TrafVolThresholdULHigh = TrafVolThresholdULLow

• Then the RAN allocates highest possible bit rate (Air interface, Iub and BTS HW taken into account) in the direction (UL or DL) which triggered the high traffic volume threshold

• The other direction gets initial bit rate. Note that the same threshold is used for DCH upgrade unless the feature Flexible Upgrade of the NRT DCH Data Rate is in use.

• Allocating highest possible bit rate using this method can delay RB allocation since Iub and BTS HW resources are typically the bottleneck, and those resources are allocated based on attempt and failure.

Traffic Volume measurements

Note that the same threshold is used for DCH upgrade unless the feature Flexible Upgrade of the NRT DCH Data Rate is in use.


Bit rate upgrading

• The NRT DCH can be upgraded due to• 1) High amount of data in buffer – Capacity request/ Bit rate upgrade • 2) High utilisation/throughput – Flexible upgrade of the NRT DCH data rate

• It is possible to upgrade the NRT DCH data rate • If the feature flexible upgrade of the NRT DCH data rate is activated

• From any bit rate below the maximum allowed bit rate to the maximum allowed bit rate

• By default (Nokia recommended parameter set) flexible upgrade is always used together with high throughput measurements

• If the feature flexible upgrade of NRT DCH data rate is not activated• The lightweigth flexible upgrade (FlexUpgrUsage =“off”) has already been

available from RAN 04ED onwards and allows upgrade from any bitrate below the maximum allowed bitrate to the maximum allowed bitrate

• The dedicated channel upgrade procedure is performed in CELL_DCH state and it requires the reconfiguration of radio link, transmission and RNC internal resources


Bit rate downgrading

• The dedicated channel of a non-real time (NRT) radio access bearer (RAB) can be downgraded or released due to multiple causes

• 1) Excessive downlink power – Dynamic link optimisation – DYLO- for NRT traffic coverage feature

• 2) Different congestion situations – Enhanced priority-based scheduling and overload control – RAS05 feature

• 3) Low utilisation/throughput – Throughput-based optimisation of the packet scheduler – RAS51 feature

• 4) Maximum bit rate limitation – Another RAB is setup for the same UE - MultiRAB

• 5) Inactivity of the radio bearer

• The dedicated channel downgrade procedure is performed in CELL_DCH state and it can be performed by

• Reconfiguration of radio bearer (also transmission, WBTS and RNC resources)

• Limitation of the maximum transport format combinations (temporary)


• RAS05 bring new load balancing features which can downgrade or release NRT DCH in congested situation

• Enhanced Overload Control• In an overload situation PS start modification or reconfiguration of existing NRT DCHs radio

bearers to be able to decrease loading.

• Prx/PtxTotal > Prx/PtxTarget+ Prx/PtxOffset (Overload Area)

• Priority Based Scheduling - PBS• Existing NRT allocations can be downgraded or released if there are other users requesting

initial capacity in the congested situation

• Prx/PtxTotal > Prx/PtxTarget (Marginal Load Area)

Load Margin

Normal load

Overload

Priority Based SchedulingEnhanced Overload Control

Prx/Ptx Target [dB]

Prx/Ptx Target+Prx/Ptx Offset

RB downgrades due the congestionRAS05 Optional features


Enhanced priority based scheduling RAS05 Optional feature

• The feature Enhanced priority based scheduling (PBS) allows the operator to select alternative methods for the packet scheduling

• PBS is based on the radio bearer reconfiguration procedures

• Existing NRT allocations may be downgraded or released if there are users requesting initial capacity in the congested situation

• Congestion of the following resources can trigger the enhanced priority based scheduling function

• Downlink power

• Uplink interference

• Downlink spreading code

• BTS HW (WSP)

• Iub AAL2 transmission

RT traffic

NRT RB 1NRT RB 2

time

bit rateReconfiguration of RB1Reconfiguration of RB1

Capacity request RB2Capacity request RB2

Increase PS call setup success and decrease

throughput of existing RB


Throughput Based Optimisation

• Throughput based optimization of the PS algorithm adapts the DCH resource reservation to meet the actual utilization (or used bit rate) of the DCH.

• The upper and lower thresholds trigger the DCH downgrade when the throughput decreases below the corresponding threshold

• If the throughput decreases below the release threshold, the DCH is released

• DCH adaptation can be performed independently for UL and DL direction

• Release of the NRT DCH can be performed only if both uplink and downlink direction utilisation is low enough in the same time.

100%

downgrade_upperthreshold

downgrade_lowerthreshold

release_threshold

ave_throughput

send release request to PSsend downgrade request to PS

There is three type of measurements related to feature:

•Upper throughput measurements

•Lower throughput measurements

•Release Measurements

Throughput based

optimisation


Throughput based optimisation - example

1 2 3 4 5

1. Initial bitrate 64

2. Max bitrate 384

3. Downgrade UL to 8

4. Downgrade 256

5. Downgrade to 128

6. To Cell FACH

6

256 also SF 8

Upper Averaging window=2s

Upper time to trigger=4s

Lower Averaging window=2

Lower time to trigger=1.4

DCHutilGuardtime=6s

UL downgrade from 64 to 8 is ~ 7sec after initial. Downgrade is happening due the lower measurement but DCHutilguardtime (6s) is delaying downgrade

UL Downgrade ~7s

DL Downgrade ~7s DL Downgrade ~7s

DL

Throughput based

optimisation


02.8

30.2

02.8

07.1

07.1

14.6

03.2

04.4

04.5

19.5

02.8

13.1

13.1

03.3

0%

20%

40%

60%

80%

100%

Thput "Off" Thput_Set 1default

Thput_Set 2"fast"

Thput_Set 3"slow"

128

256

384

64

Picture below shows distribution of RB’s during download with 4 different parameter set

• Set2 “fast” shows most optimal use of resources with UDP

* Times are calculated between “RB Reconfiguration complete” Messages

When Throughput based optimisation is “off”, there is RB upgrade from initial (64) to maximum (384) – but no downgrades

Changed parameters during test

Throughput based

optimisationRB distribution with different parameters sets


• As we can see from previous slide, the throughput-based optimisation decreases the capacity loss (mainly BTS HW, transmission and downlink spreading code capacity loss) which too high bit rate allocation causes in the network.

• Example below shows average capacity reservation for different sets

• The Iub reservation is proportional to the allocated bit rate

• Resource utilization is ratio between used resources and allocated resources

Throughput based

optimisationHW Capacity Reservation


The flexible upgrade of the NRT DCH data rate

• Algorithm for upgrading the NRT DCH bit rate from any bit rate up to the maximum bit rate of the radio bearer

• The usage of the feature is controlled with the RNW configuration parameter FlexUpgrUsage

• ‘On’ = Flexible upgrade of the NRT data rate is applied• High bit rate upgrades allowed from any data rate to the maximum allowed bit

rate of the radio bearer AND also high throughput indication is received

• ‘Off’ = Flexible upgrade of the NRT data rate is not used• High bit rate upgrades allowed from any data rate to the maximum allowed bit

rate of the radio bearer

• Algorithm is based on uplink and downlink• Traffic volume measurements (TVM) Trigger upgrade algorithm• High throughput measurements Allow upgrade

• Flexible upgrade of the NRT DCH data rate is allowed only if• The high throughput measurement information indicates high throughput

Flexible Upgrade


The flexible upgrade of the NRT DCH data rate

• Flexible upgrade (FlexUpgrUsage =“on”) together with high throughput measurements can be used for allowing NRT DCH upgrades only when the already allocated NRT DCH capacity is fully used

• When traffic volume measurement report indicates that the volume is above the DCH bitrate specific high threshold for UL or DL then the high throughput measurement is triggered.

Parameters (TrafVolThresholdUL/DLHighBitRate) are in use if the Flexible Upgrade of NRT DCH Data Rate feature is activated by the FlexUpgrUsage parameter. Otherwise the traffic volume threshold for the uplink/downlink direction is defined by the TrafVolThresholdUL/DLHigh parameter.

If the throughput stays above the high threshold (default 6% means 94%

utilization) for the time of the supervision period then the DCH bitrate

is upgraded

When FlexUpgrUsage is set “on” and DCHUtilHighAveWin > 0, high Throughput

measurement are activated

Flexible Upgrade


Flexible upgrade “On”

Flexible upgrade “Off”

3.6s

2s

Effect of flexible upgrade can been seen

here

Flexible Upgrade

• Based on test done in NTN - Flexible upgrade together with High throughput measurements, delays the upgrade from initial to maximum bit rate and thus increases to file/page download time for www applications

Flexible Upgrade


Flexible Upgrade

HTTP 200k download times are calculated

• TC 1, is reference case when both Flexible upgrade and Throughput based optimisation were OFF

• TC 2, Both were ON – In this case the flexible upgrade clearly delay upgrade from Initial to Maximum

• TC 3, Flexible upgrade OFF (theory this is suppose to show same value as TC1, but UL is downgraded due the throughput based optimisation which is expected to cause delay for the download time ?)

• TC 4 Initial bit rate was set same than Maximum bit rate = 384, this case shows best performance.

Flexible Upgrade

HTTP 200k download time

7574.8

10432

8650.4

6340.5

0

2000

4000

6000

8000

10000

12000

1 2 3 4

Flexi upgrade on Initial bit rate was set same as Max bit rate 384

Flexib

le u

pgra

de

ON

Flexi upgra

de

OFF

Both

O

ff


DyLO Improves NRT traffic coverage

Dylo restrictions• Radio link conditions under DRNC cannot trigger DyLO• The reconfiguration of Iub AAL2 transmission resources is not

performed due to DyLO• DyLO is not allowed during compressed mode measurement

UE384kbps

128kbps

BTS

Radio link is modified to use lower bit rate (with physical channel reconfiguration

message) when Tx power is getting close to maximum, in order to ensure sufficient

quality


Triggering of DyLO

time

Ptx, RLdistance

Ptx, ave

Triggering of DyLO

Ptx, maxOffset

Ptx, ave is averaged radio link power, measured and reported to RNC by BTS

Ptx, max is determined by Admission Control

The value of the Offset is fixed at 2 dB

DyLO is triggered if

Ptx, ave > Ptx, max – Offset

Dylo can be started only if the current bitrate is higher than Maximum Allowed DL User Bitrate in HHO


Dylo Test example- compare throughput with the coverage

CPICH RSCP and RB Status (Set2)

0

100

200

300

400

16:4

1:39

:209

16:4

1:44

:736

16:4

1:49

:754

16:4

1:57

:764

16:4

2:05

:265

16:4

2:14

:159

16:4

2:21

:229

16:4

2:25

:084

16:4

2:33

:295

16:4

2:40

:816

16:4

2:50

:761

16:4

2:53

:485

16:4

2:58

:402

16:4

3:07

:605

16:4

3:16

:879

16:4

3:22

:396

16:4

3:28

:805

16:4

3:34

:344

16:4

3:39

:451

16:4

3:45

:459

16:4

3:49

:866

16:4

3:53

:491

16:4

3:54

:864

16:4

3:59

:009

16:4

4:05

:037

16:4

4:13

:620

16:4

4:19

:109

16:4

4:23

:935

16:4

4:25

:667

16:4

4:28

:191

16:4

4:34

:199

16:4

4:41

:209

16:4

4:44

:274

Time

RB

_S

tatu

s

-130

-120

-110

-100

-90

-80

-70

-60

StatusID

RSCP

CPICH Ec/No and RB Status (Set2)

0

100

200

300

400

16:4

1:39

:209

16:4

1:44

:245

16:4

1:49

:252

16:4

1:56

:252

16:4

2:02

:351

16:4

2:11

:234

16:4

2:19

:786

16:4

2:21

:789

16:4

2:28

:799

16:4

2:35

:809

16:4

2:43

:821

16:4

2:51

:702

16:4

2:54

:256

16:4

2:59

:204

16:4

3:07

:875

16:4

3:16

:387

16:4

3:21

:895

16:4

3:27

:894

16:4

3:32

:901

16:4

3:37

:549

16:4

3:43

:416

16:4

3:48

:454

16:4

3:51

:289

16:4

3:54

:502

16:4

3:56

:325

16:4

4:00

:220

16:4

4:06

:039

16:4

4:15

:594

16:4

4:19

:619

16:4

4:23

:935

16:4

4:25

:637

16:4

4:28

:111

16:4

4:32

:206

16:4

4:39

:717

16:4

4:44

:114

Time

RB

_S

tatu

s

-24

-19

-14

-9

-4

StatusID

Ec/No

Sf8

sf16

sf32FACHIdle

Sf8

sf16

sf32FACHIdle

RB Status Statistics(vs EcNo)

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

> -4 -4 to -6 -6 to -8 -8 to -10 -10 to -12 -12 to -14 -14 to -16 -16 to -18 < -18

Ec/No [dB]

sf8

sf16

sf32

100.00%

0.00%0.00%

51.03%

38.30%

10.67%

40.72%

47.55%

11.73%

30.34%

56.40%

13.26%

17.03%

57.16%

25.81%

11.54%

56.09%

32.37%

11.32%

37.74%

50.94%

5.21%

18.75%

76.04%

6.98%

4.65%

88.37%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

> -4 -4 to -6 -6 to -8 -8 to -10 -10 to -12 -12 to -14 -14 to -16 -16 to -18 < -18

Ec/No [dB]

RB Status Statistics(vs EcNo)

sf32

sf16

sf8

384 128 64

RB Status for each Ec/No

≒-7 ～ -8 ≒-14 ～ -15


Module 6 – Parameter Optimisation

Summary

• Parameter optimisation is not a substitute for RF

Optimisation

• In optimisation we have to consider the balances

between power (resources) and success/speed

• Call Setup can be improved by improving Cell Selection

and Reselection, SRB Rate and ATO

• Call retention can be improved by adjusting SHO

parameters at the expense of resource usage


Version control

Version Date Status Owner

RAN04 2006 Base version Mike Roche, Steve Hunt, Gareth Davies, Pekka Ranta

RAS051_v1.0 24. 04. 2007 Updated some performance results to RAS51 benchmake values

Added many Packet Scheduler test results.

Added SHO test results

Checked for RAS051 level

Kirsi Teräväinen

Documents

6 - Parameter Optmisation_RAS51