UMTS-RNO-0005 - Drive Test Analysis

7/31/2019 UMTS-RNO-0005 - Drive Test Analysis

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Title:

Drive Test Analysis

Date:

05/07/2006

Page Number:

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Created by:

Alexandre Silva

Approved by: Doc Ref.:

UMTS-RN0-0005

Drivetel Servios e Projectos de Telecomunicaes Lda

Confidential Document

Drive Test Analysis


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Contents

1 Measurements on a drive test............................................................................ 3

1.1 Radio measurements .........................................................................................4

1.1.1 Spectral measurements on UTRA carrier ...........................................4

1.1.2 Measurements on common channels .................................................. 5

1.1.3 Measurements on dedicated channels ................................................. 8

1.2 Higher-layer measurements ............................................................................ 10

1.2.1 Transport channels ............................................................................ 10

1.2.2 User-data measurements ...................................................................11

1.3 Load simulation .............................................................................................. 12

1.3.1 Uplink radio load 12

1.3.2 Downlink radio load.......................................................................... 13

2 Radio optimization based on drive tests ......................................................... 14

2.1 Call set-up failure............................................................................................15

2.1.1 Coverage problem............................................................................. 16

2.1.2 Admission Control problem..............................................................17

2.1.3 Interference problem......................................................................... 18

2.1.4 Active Set Management ....................................................................19

2.2 Call drop 19

2.2.1 Coverage problem............................................................................. 19

2.2.2 Interference problem......................................................................... 22

2.2.3 Active Set Management problem......................................................22

1.1.4 RLC problem ....................................................................................241.1.5 RL problem .......................................................................................25

1.3 Higher-layer performances on User plane ...................................................... 25

1.3.1 Offered bit-rate.................................................................................. 26

1.3.2 Transport Channel BLER.................................................................. 27

1.3.3 Performances for RLC AM............................................................... 27

1.4 Higher-layer performances on Control plane ................................................. 27

Abbreviations ..............................................................................................................29


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1.Measurements on a drive test

In this section, we are listing the different measurements that could be taken on a drive test,

while using either a 3G scanner or a trace mobile or both.

The purpose of this document is not to tackle with implementation-specific measurements

for commercial 3G scanners or trace mobiles.

On a drive test, one tester can take following measurements:

Radio measurements Higher-layer measurements (RLC and over)


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1.1 Radio measurements

The 3GPP25.215 and the 3GPP25.133 are specifying the UE

measurement capabilities required in UMTS FDD.

3G scanner versus trace mobile

The main advantage of a 3G scanner is that the user can specify the

UTRA carrier to monitor, whereas a trace mobile will only measure the

various UTRA carriers at the cell selection without reporting this

measurement to the system.

Then, the user can specify the cells to monitor on a 3G scanner, whereas

a trace mobile will only measure the various cells at the cell selection in

idle mode and the active cells together with the declared neighboringcells in connected mode.

A 3G scanner may also give some measurements onto the P-SCH and S-

SCH.

1.1.1 Spectral measurements on UTRA carrier

UTRA carrier RSSI

The UTRA carrier RSSIis the key measurement for the DL interferenceseen by the UE.

From the 3GPP TS25.215, theReceived Signal Strength Indicatoris the

wide-band received power within the relevant channel bandwidth. In

wide-band systems, the spreading of the power by code channels do not

ensure a perfectly homogeneous power level over the spectrum. The

PAR (Peak to Average Ratio) gives an indication of the homogeneity of

the power level over the 5MHz bandwidth. The higher the number of

codes mixed the lower the PAR.

From 3GPP TS25.133, the reporting range forUTRA carrier RSSIis

from 100dBm to -25 dBm.The UTRA carrier RSSImainly encompasses the intra- and inter-cell

load on the UTRA carrier. But, interference due to adjacent channels or

other radio transmitters are also included.

The intra-cell contribution Iintra to the UTRA carrier RSSIcan be

extracted from the Transmitted Carrier Powermeasured at the Node B

antenna connector and the path-loss measured by the drive test chain on

the CPICH as:

Iintra = Transmitted Carrier Powercell, Node B- Pathloss cell, UE


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In the same way, the contributions of the neighboring cells for which

the CPICH can be demodulated can be analyzed.

1.1.2 Measurements on common channels

Cell detection

On one UMTS carrier, a cell is identified by its PSC (Primary

Scrambling Code). There are 512 scrambling codes grouped into 64

groups of each 8 different scrambling codes.

To detect a cell, the UE searches sequentially for:

the universal 256-chip primary synchronization code, being

identical for all cells and repeated at the beginning of each slot

of the P-SCH. Once the peak is detected, the slot boundary is

known.

the largest peak from the secondary synchronization code

word based on the slot boundary. The UE needs to check the

64 possible scrambling code group for the secondary

synchronization code word, beginning at each of the 15positions, since only the slot boundary is known and not the

frame boundary.

the current PSC in the identified scrambling code group by

scanning the CPICH: the correlation peak obtained while

descrambling the CPICH with the current PSC allows the

detection of the PSC.

RAKE measurements

The RAKE receiver performs the multi-path combining at the mobile

side. The 3GPP definitions for measurements are always after RAKErecombining. It does not make sense to analyze each path for radio

optimization for following reasons:

The RAKE coefficients are not configurable

The RAKE algorithm is proprietary

Multi-path profile changes from one test to the other


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CPICH measurements

The CPICH is emitted continuously with a fixed power level, so that it

serves for the cell evaluation and downlink channel estimation at the

UE.The reference point for the CPICH measurements is the antenna

connector of the UE, even though the RAKE receiver combines

measurements.

The CPICH measurements are the key radio measurements for cell

optimization.

CPICH RSCP

The CPICH RSCPis the key measurement for DL coverage. The

CPICH RSCPis an RXLEV measurement. This measurement is for:Cell re-/selection

UL open loop power control

From the 3GPP TS25.215, the CPICH RSCP(Received Signal Code

Power) is the received power on one code measured on CPICH.

From the 3GPP TS25.133, the reporting range is forCPICH RSCPis

from 115dBm to -25 dBm.

As a rule of thumb, one can say (for dense urban):

-108dBm CPICH RSCP < -105dBm

Uncertain CS64 coverage on unloaded network


Uncertain CS64 coverage on 50%UL-loaded network


CS64 coverage on 50%UL-loaded network for outdoors


CS64 coverage on 50%UL-loaded network for in-car


CS64 coverage on 50%UL-loaded network for indoor daylight

-62dBm CPICH RSCP

CS64 coverage on 50%UL-loaded network for indoor first-wall


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Downlink path-loss

The path-loss measured on the CPICH is defined as:

Pathloss = CPICH TX Power - CPICH RSCP

With a typical value of 33dBm for the CPICH TX power, the range for

path loss is then 58dB to 148dB.

One should be careful with the figures for the path-loss, since this

definition does not correspond to the pure radio loss.

3GPP Pathloss = CPICH TX power @ NB antenna connector -

CPICH RSCP @ UE antenna connector

Pure Radio Loss = CPICH TX power @ NB antenna output -

CPICH Rx power @ UE antenna input

3GPP Pathloss = Pure Radio Loss + feeder losses - NB antenna

gain + UE antenna gain

With typical values of feeder losses (3dB), NB antenna gain (17dBi)

and UE antenna gain (0dBi), 3GPP Pathloss = Pure Radio Loss 14dB

and the range for radio loss is then 72dB to 162dB.

CPICH EC/I0

The CPICH EC/I0 is the key measurement for radio optimization for

CDMA. The CPICH EC/I0 measures the soft radio capacity. This

measurement is for:

Cell re-/selection

Radio admission control

DL open-loop power control

Soft HO and inter-frequency Hard HO

From the 3GPP TS25.215, the CPICH EC/I0 is the received energy per

chip divided by the power density in the band. The EC/I0 is identical toRSCP/RSSI.

From the 3GPP TS25.133, the reporting range forCPICH EC/I0is from

24dB to 0dB.

The typical distribution of the CPICH EC/I0 highly depends on the cell

load. Requirements in term ofCPICH EC/I0 depends on:

The non-limitation in UL and DL coverage

The number of cells that can be recombined


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The mobile sensitivity

As a rule of thumb, one can say:

-15dB CPICHEC/I0 -18dB

Preferred situation is more than 1 active RL


Good value for 60%-loaded network


Preferred situation is not more than 1 active RL

CPICHEC/I0 -8dB

Only 1 active RL for high-quality best server

1.1.3 Measurements on dedicated channels

Per definition, a 3G scanner does not perform measurements on

dedicated channels.

Uplink

UE TX power

The UE TX poweris the key measurement to analyze UL coverage.

It is the only uplink measurement that is available at the UE side. It is

defined in the 3GPP TS25.215 as the total UE transmitted poweron one

carrier at the UE antenna connector.

From the 3GPP TS25.133, the reporting range forUE transmitted power

is from -50 dBm to 33 dBm. But, the Power Class of the UE bounds the

upper limit (defined in 3GPP TS25.101).

Power Class Maximum TX power

1 +33 dBm

2 +27 dBm

3 +24 dBm4 +21 dBm

Test mobiles in R1 and R2 were Power class 3 only.

UE Tx power = PDPCCH,UL+ PDPDCH,UL

PDPCCH,UL = (D/C)2 x PDPDCH,UL

CandD are parameterized,D being fixed at 15


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As a rule of thumb, one can say:

16dBm UE TX power < 24dBm (shadowing and fading)

9dBm UE TX power < 16dBm (in-car penetration)

0dBm UE TX power < 9dBm (indoor day-light)

-10dBm UE TX power < 0dBm (indoor first-wall)

UE TX power < -10dBm(deep indoor)

Downlink

Signal-to-Interference Ratio

The Signal-to-Interference ratio is not standardized for the UE.

This internal measurement should be used in the DL outer-loop power

control. The SIR target for DL is defined through UE-proprietary

algorithms to achieve the BLER Quality Value assigned by the UTRAN

(see Downlink Transport Channel BLER).

Therefore, one should be cautious when analyzing such measurements

in a mobile trace, since various definitions are possible.

Metrics for synchronization

The UE Rx-Tx time difference, the CFN-SFN observed time differenceand the SFN-SFN observed time difference are concerning

synchronization issue at the UE side over the radio interface.

The SFN-SFN observed time difference is for identifying time

difference between two cells.

The CFN-SFN observed time difference is for handover timing

purposes to identify active cell and neighbor cell time

difference.

The UE RX-TX time difference is used for RL set up purposes

to compensate propagation delay of DL and UL in order to getTPC commands on DL with the right timing for the UL power

control.


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1.2 Higher-layer measurements

1.2.1 Transport channels

Downlink BLER

The Transport Channel block error rate (BLER) is based on evaluating

the CRC of each transport block associated with the measured transport

channel after RL combination (performed by the Rake receiver). It is

computed as the ratio between the number of received transport blocks

resulting in a CRC error and the number of received transport blocks

over the measurement period.

Transport channel BLER value shall be calculated from a time window

with following size:

if periodical reporting mode is specified by the UTRAN, the size

should be equal to the IE Reporting interval in mentioned SIB11 or

12 (see 3GPP TS 25.331)

otherwise, this is an internal measurement at the UE side and the

window size is freely designed

The Transport channel BLER reporting range is from 0 to 1.

The BLER Quality value is a target indicated by the UTRAN at the

RRC CONNECTION SETUP and at the RADIO BEARER SETUP for

the initiated service. Therefore, the follow-up of the BLER helps

assessing whether the UE is performing according to the quality

requirements or not.

If the BLER is lower than the targeted Quality value, the QoS

offered by the UTRAN is sufficient, as far as the data integrity is

concerned.

If the BLER is higher than the targeted Quality value, the radio

interface is not able to satisfy the required QoS. This could be due

to:

Shortage of power to be dedicated to the UE on DLPower limitations due to radio parameter settings

Power limitations due to high traffic on DL

High interference level on DL

Poor performances of the DL outer-loop power control

Logically, the Transport channel BLER and the SIR are bound through

the DL outer-loop power control, which is a mobile-proprietary

algorithm.


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Poor performances could be following:

Bad or slow convergence

RLC statisticsThree RLC modes are available for Radio Bearers: Transparent,

Unacknowledged and Acknowledged.

For all RLC modes, statistics can be done on traffic volume and data

rate.

In the RLC Acknowledged Mode, several algorithms manage packet

retransmission, mainly:

Transmission and reception windows

Polling and Status signaling

In the RLC Acknowledged Mode, following measurements can be done:

Transmitted but not acknowledged PDU (UL)

Retransmitted PDU (UL)

Received erroneous PDU (DL)

Window follow-up (UL and DL)

1.2.2 User-data measurements

TCP statistics

Mostly used assessments are the FTP throughput and the PING round-

trip time.


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1.3 Load

We are not dealing with stress of network elements to determine critical

load in terms of processing capacity. Radio load consists only in

interference on radio interface. Therefore, no signaling or data

processing is generated. Radio load is critical for W-CDMA systems.

1.3.1 Uplink radio load

The main concern on uplink is to figure out the increase of the

interference level due to the traffic available on the cell. The

interference level can be expressed as the noise rise in dB and depends

on the cell load in % of the pole capacity.

Cell load, XUL , is in term of % of pole capacity and impacts the noise

rise as follows:

NoiseRise = -10log (1- XUL)

Following reference values can be used:

Cell load Noise Rise

50% 3dB

75% 6dB

Noise rise a s a function of the Cell load

0

5

10

15

20

25

30

35

40

45

0.00% 20.00% 40.00% 60.00% 80.00% 100.00%

Cell Load

No

ise

Ris

e

in

dB



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1.3.2 Downlink radio load

The limiting factor on downlink will be the maximum TX power for the

Node B. Therefore, the power usage on DL is expressed as the

percentage of the maximum TX power for the cell.

Maximum output power

Others traffic

Trace Mobiletraffic

Other mobiles

Trace mobile

OD settings dBm dB related

to CPICH

Activity factor

(% time)

CPICH 33,0 1

P-SCH 28,0 -5 0,05

S-SCH 28,0 -5 0,05

PCCPCH (BCH) 31,0 -2 0,9

SCCPCH (FACH, PCH) 31,0 -2 1

AICH 24,0 -9 1

PICH 28,0 -5 1

Total power (common channels) 37,3

MAX cell power 43,0

(total power for 60% cell load) 40,8(OCNS = 60%cell load - CCH) 38,2

dBm Total cell power

MAX DL power for AMR 31,0 41,2

MAX DL power for CS64 37,0 42,3

MAX DL power for PS128 39,0 43,0



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2 Radio optimization based on drive tests

The analysis of drive test measurements allows the detection and eventually the localization

of radio problems over the coverage area. Generally, radio problems are sorted into:

Coverage issues Mobility-management issues Best-server issues Interference issues

In this section, we are analyzing following aspects:

Call set-up failure Call drop Higher-layer performances


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2.1 Call set-up failure

Here, we only consider call set-up failures that are due to the radio.

Following call set-up failures are not considered:


Invalid USIM

Unavailability of the network (CN, UTRAN, transport)

Investigations on call set-up problems should go through the following

list:

Coverage problem

Admission Control problem

Interference problem

Active Set Management problem

Following questions should drive the investigations:

Are the CPICH measurements for the selected cell at normal values

with regard to the path loss?

What is the load status of this cell at the Call set-up?

At which stage of the call set-up did the procedure fail?

UE Node B RNC CN

Initial NAS message transfer

Authentication Procedure

Security mode command

Iu

RAB assignment request

Iu UP initialisation

RAB Assignment Response

DCCH Radio Link set-up

RB setup request

RB setup complete

Synchronised Radio Link reconfiguration

Initiate AAL2 Iub dataconnection for DCCH

Initiate AAL2 Iub dataconnection for DTCH

RRC connection request

RRC connection setup

RRC connection setup complete

IubUu


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2.1.1 Coverage problem

Call set-up may fail because of Coverage limitation when:

The RACH message can not be sent: the RRC CONNECTION

REQUEST can not be addressed (UL, PRACH power settings)

The UE can not serve the power required after the UL Open-Loop

Power Control

The UE does not receive the Paging message for MTC (DL, PICH

and S-CCPCH power settings)

In case of repeated errors, further investigations must be driven,

respectively on:

RRC CONNECTION REQUEST sending can be checked at the

mobile side

Path loss on DL can be assessed based on scanner or mobile

measurements (CPICH RSCP). This should be done on the UE-

selected cell. Then, the UL Open-loop power result can be checked.

Reception of PAGING notification can be checked at the mobile

side

UL and DL MAPL for call set-up

In case of errors repeated over an area, further investigations must be

driven, especially on:

Feeder installation for RX diversity for UL limitation

Feeder losses

Antenna azimuth

PRACH , PICH, S-CCPCH power setting

RACH parameters

UL MAPL for call set-up

When establishing the DPCCH, the proprietary SRNC calculation for

initial DPCCH power will require from the UE a given power level for

the DL DPCCH, which should be lower than the maximum Tx power ofthe UE power class.

DPCCH_Initial_power = (CPICH_TX_power - CPICH_RSCP) +

(UL_SIR_target 10log(UL_SF=256)) 97

AND

DPCCH_Initial_power < UE_Max_Tx_Power


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Following default values are given as indications for R2:


UL_SIR_target (on a per-service basis, DCCH: 2dB)

UL_SF (on a per-service basis, DCCH: 256)

UE_MaxTxPower (on a per-mobile basis: 24dBm)

CPICH_TX_power (on a per-cell basis: 33dBm)

DL MAPL for call set-up

When establishing the DL DPCCH, the proprietary SRNC calculation

for initial DPCCH power will require from the Node B a given power

level for the DL DPCCH, which should be lower than the maximum

allowed Tx power on DPCCH.

10/, 104.01__

MarginiCPICH

mm,i

m PtSFIoCPICH_Ec

etDL_SIRTargpowerinitialDPCCH =

AND

DPCCH_Initial_power < MaximumDLpower+CPICH_Tx_power

Following default values are given as indications for R2:

UE_MaxTxPower (on a per-mobile basis:24dBm)

DL_SIR_target (on a per-service basis,DCCH:5dB)

DL_SF (on a per-service basis,DCCH:256)

Margin (on a per-service basis,0dB)

MaxDLpower (on a per-service basis,DCCH:-2dB)

2.1.2 Admission Control problem

Call set-up may fail because of Admission Control limitation when:

DL radio resources are overloaded (RAC issue)

UL radio resources are overloaded (RAC issue)

Node B processing resources are overloaded (RAC issue)Transport resources are overloaded (CAC issue - tbc)

RNC resources are overloaded (CAC issue - tbc)

RAC issue can be assessed by monitoring NBAP messages for RADIO

LINK SETUP FAILURE with the associated cause.

UL and DL radio overload can be due to:

High cell load due to user traffic for UL a/o DL


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OCNS activation for DL

Interference problem for UL a/o DL

2.1.3 Interference problemInterference problems may be due to:

Surrounding cells of the operating UTRAN

Other radio sources than the operating UTRAN

Call set-up failure may be due to Interference problem when the RAC

rejects the call, while the effective cell load is not at maximum:

The RTWP on UL in Node B measurements are high but with a

small number of users, i.e. not only cell users are contributing to

the noise rise.The RSSI on DL is higher than the Transmitted Carrier Power on

DL of the detected cells decreased by the Path Loss seen on CPICH

for each detected cell.

Intra-network interference

Intra-network interference can be analyzed with the help of the scanner

on DL.

See Pilot pollution

See Missing adjacencies in the neighboring cell list

External interference

Specific investigations with a spectrum analyzer have to be performed

for interference coming from other radio sources than the operating

UTRAN.

This becomes a Spectrum Clearance issue.

Two kinds of problems may then be distinguished:

Interference that is due to out-of-band emissions from other

transmitters. In this case, filters must be set at the interfering

transmitter.

Interference that is due parasite transmitters that should not

transmit in this band. In this case, parasite emissions must be

stopped in the UMTS band.


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2.1.4 Active Set Management

The mobile can not synchronize on the Radio Link due to high pollution

2.2 Call drop

Here, we only consider call drops that are due to the radio. Following

call drops are not considered:

Mobile auto-reset, power-off, etc.

CN-generated reasons (to be analyzed in RANAP IU RELEASE)

Failure in transport network

Possible reasons for radio call-drop are:

Coverage problem

Interference problem

Active Set Management problem

RLC unrecoverable error

RL failure

Following questions should drive the investigations:

Are the CPICH measurements for the Active Cells and the UE TX

power at normal values with regard to the path loss seen on the

cells?What are the last messages that the UE sent or received? (CELL

UPDATE, MEASUREMENT REPORT, ACTIVE SET UPDATE)

What are the last BLER measurements from the UE?

2.2.1 Coverage problem

Call drop may be due to Coverage limitation when:

The UE TX power reached the maximum value at the end of

the call (UL limitation)The UE SIR or the UE Rx power or the UE BLER on DL did

not reach its target value at the end of the call (DL limitation)

See Call set-up failure, Coverage problem


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On unloaded networks

On unloaded networks, coverage problem on UL a/o DL reveals RNP

defects a/o tradeoffs (propagation model, database accuracy, calibration

settings, etc.) or errors in RNP implementation.Path loss on DL can be assessed based on scanner measurements

(CPICH RSCP). This should be done on the cells of the Active Set only.

In case of errors repeated over an area, further investigations must be

driven, especially on:

Feeder installation for RX diversity for UL limitation

Feeder losses

Antenna azimuth

CPICH power setting

On radio-loaded networks

On loaded networks, coverage problems may be linked to radio

limitations on DL. Indeed, the cell may not be able to serve the power

required by the Radio Link if the cell is already emitting at full power.

Cell TX power can be assessed based on Node B measurements on DL

Transmitted carrier power.

Drop Calls examples with explanation

As all sites are co-channel, if the RF is present, it will be used (for better

or worse). Therefore, it is imperative that each sector is carefully RF

controlled. Ideally each serves its intended area but not beyond.

Controlling and managing the RF environment is central to

optimization.

Problem Maps Solution

COVERAGE: Bestserver CPICH RSCPbelow required level

- Best RSCP Scanner/Mobile- Tx Power Mobile (note that high mobilepower can mean either coverage or

interference problem)- Best SC regarding CPICH Ec/Io

Check antennas and feeders are OK, with nothing obscuringview of antenna, like block building, rooftop effect or anyradiating object nearby the antenna pattern radiation,

consider reducing the antenna down-tilt to improvecoverage. As a last resort, increase pilot power.

QUALITY:Best

CPICH Ec/Io belowrequired level

- Best CPICH Ec/Io Scanner/Mobile- RSSI CPICH from Scanner

- Best SC regarding CPICH Ec/IoScanner/Mobile- Best RSCP 2

nd, 3

rd, 4

th, 5

th, () Scanner

- Tx Power Mobile

IfEc/Io lower than -9 db (network without load), the best-server RSCP is at expected levels, and the RSSI is high, need

to reduce Interference from other cells.

Check Best RSCP 2nd

, 3rd

, 4th, 5

th, () in order to decide

which cells to remove from the interference area.

Can the azimuth of other cells be changed to reduce number


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of servers in that area? Can neighbouring cells be down-tilted? Avoid facing sectors shooting against each other.

QUALITY/CAPACITY:Active set toolarge, Soft handovers

area too high and toomany handovers along

routes

- Number of link in the AS Mobile

- Number of link in the AS simulatedScanner

- Best SC regarding CPICH Ec/IoScanner/Mobile- Number of link in the AS Excel Graph(desired values for Urban environments

will be 10 to 20% of soft HO areas)

(Generally this will correspond also to areas with low Ec/Io,

but not always). Check that the cell best server areas areconfined, not excessive, but big enough to guarantee a small

overlap between cells in order to allow the soft handover.

Can the azimuth of neighbouring cells be changed? Balancecoverage levels with other cells using down-tilts?

Optimizing capacity will be important when traffic grows.AS < 4 pilots, for 5dB window (ReportingRange) relative tothe best Ec/Io should be used to calculate the number of cellin the active set.

Based on IS-95 experience, the best performing networks arethose that are designed for three-way hand-off or less.

Site with coverage farbeyond desired area

- Best SC regarding CPICH Ec/Io Scanner- Best RSCP SC Scanner

Cell appears inneighbour list of cells

beyond the areadesired

- Best SC regarding CPICH Ec/Io Scanner- Best RSCP SC Scanner

Typical of high sites. Ensure electrical down-tilt is sufficient.Increase combined down-tilt, but not below 10 to 12o

(depending on antenna type). Be aware that once off themain lobe of the antenna, increasing tilting will be unlikelyto reduce interference, hence consider maintaining tilt tocover desired area.

Can antennas be lowered? As a last resort, reduce pilot

power; however be aware that this will also reduce in-building coverage of the cell: hence reduce power just

sufficiently to keep the cell out of active sets or raise Ec/Novalues.

CAPACITY: Cellsfrom the same siteappear at similarcoverage levels

- Number of link in the AS Mobile- Number of link in the AS simulatedScanner- Best SC regarding CPICH Ec/Io Scanner

Check azimuths between co-site cells: where possiblemaintain the azimuth between cells to 100-120

ofor 3 sectors

site. Check antennas have unobstructed views, including atroof edges to minimise scatter.

Call Performance:Neighbour Lists

If the correct cell is not used in softhandovers, the Ec/No and BLER willdegrade and Ue_Tx_Power will increasein Mobile Plots.

Compare also:- Best SC regarding CPICH Ec/Io Scanner- Best SC regarding CPICH Ec/Io Mobile

Tuning neighbour lists is a major aspect of optimisation.Check ACTIX options to find quickly missing neighbourcells between Mobile and Scanner measurements.

Check correct values for parameters:ReportingRangeEvent1A_1B_1C andHysteresisEvent1A_1B_1C.

Check Active Set Management problems, mainly:The UE

is sending repetitive MEASUREMENT REPORT withoutgetting an ACTIVE SET UPDATE;The UE can notmanage as many radio links as present in the Active Set (e.g.

in case of Rake limitations)-PILOT POLLUTION.


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Call Performance:Voice/PS performance

ForAMR, any areas where the voicequality degrades or the call drops happenshould be noted and analysed.

ForPS, it should note areas where the

throughput of the application reduces andidentify any parameter or RF related issuesthat may be causing this.

Analyse also:- BLER Mobile- BLER Statistics

Check BLER Exit Criterias:- Voice AMR 12.2: BLER


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Reason for the non-reception of ACTIVE SET UPDATE from the

RNC

MEASUREMENT REPORT are not received at the RNC

ACTIVE SET UPDATE are not received at the UEMaximum numbers of RL a/o Node B in AS are reached

RAC on target cell rejects the RL establishment

Time-to-trigger and Hysteresis, Antenna tilt to cancel resurgence

UE radio capabilities and maximum AS size

Missing adjacencies in a cell neighborhood

The UE is evaluating the radio quality of neighboring cells to detect

potential cells to add to the Active Set. The UE does not reportmeasurements on other cells that may be detectable but only on the list

of neighboring cells signaled by the S-RNC.

The list of neighboring cells is compiled at the S-RNC and transmitted

to the UE in RRC MEASUREMENT CONTROL messages. The

compilation of this list is proprietary. It mainly consists in assembling

the different sets of neighboring-cell lists for all the cells of the Active

Set.

The operator parameterizes the neighboring-cell list for each cell. The

first computed list is inherited from the RNP, which runs proprietary

algorithms to list neighboring cells. These lists may be not optimizeddue to used algorithms or due to inappropriate methods for

neighborhood follow-up in deployment/densification phases.

Drive tests may help detecting missing adjacencies on a live network.

Criteria for Event 1A

10Log(MNew) Wx10Log(MBest)+(1-W)x10Log(MI) -(R1a+H1a)

MNew : measurement on the cell entering the reporting range

Mi : measurement on a cell in the active set

NA: number of cells in the current active set

MBest: measurement result of the strongest cell in the active setR1a : reporting range for the event 1a

H1a : hysteresis parameter for the event 1a

Criteria for Event 1B

10Log(MOld) Wx10Log(MBest)+(1-W)x10Log(MI)-(R1b +H1b)

MOld: measurement on the cell leaving the reporting range



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NA: number of cells in the current active set

MBest: measurement result of the strongest cell in the active set

R1b : reporting range for the event 1b

H1b : hysteresis parameter for the event 1b

Criteria for Event 1C

10Log(MNew) 10Log(MI) + H1c

MNew : measurement on the cell leaving the reporting range


H1c : hysteresis parameter for the event 1c

Pilot pollution

Soft handover is working well, when:

Radio links have a non-negligible life time and no Ping-Pong

overloads the signaling,

Radio links can be recombined in an effective manner at the

Rake receiver.

A polluter transmitter is a transmitter that checks all criteria to enter in

active-set but which is not admitted due to the active-set limit size.

One can distinguish different levels of criticality for pilot pollution:

A non-potential candidate cell for soft handover

A potential candidate cell for soft handover but with poor

performance

A potential candidate cell for soft handover but not declared in

the neighboring cell list

To limit pilot pollution, further investigations must be driven, especially

on:

Antenna azimuth and tilt

CPICH power setting

Cell maximum TX power

Neighboring-cell list and Monitored Set

2.2.4 RLC problem

The Radio Link Control protocol can engender call drops, when errors

in this protocol can not be recovered. Errors do only concern the

Acknowledged Mode. In an error case, the UE drops the call and sends


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a RRC CELL UPDATE message on the RACH with the cause RLC

unrecoverable error.

Possible deadlocks in RLC AM are:

Not acknowledged PDU in the Sending Window (UL)Not received error-free PDU in the Receiving Window (DL)

Not received Status

Not received Polling result

2.2.5 RL problem

The Radio Link maintenance can engender call drops, when

unrecoverable RL failures occur. In a failure case on DL, the UE drops

the call and sends a RRC CELL UPDATE message on the RACH withthe cause RL failure.

RL failures are described in 3GPP TS25.331. They consist in L1

synchronization loss. In CELL_DCH State, after receiving N313

consecutive "out of sync" indications from L1 for the established

DPCCH physical channel, the UE starts T313. If N315 successive "in

sync" indications from L1 are received before T313 expiry, the RL

failure is recovered and T313 is stopped. Otherwise, this is a RL failure.

L1 reports "out of sync" if one of these criteria is fulfilled:

The UE estimates the DPCCH quality over the previous 160ms

period to be worse than a threshold Qout

The 20 most recently received transport blocks with a non-zero

length CRC have been received with incorrect CRC. In addition,

over the previous 160ms, all transport blocks with a non-zero

length CRC have been received with incorrect CRC.

2.3 Higher-layer performances on User plane

The offered end-user QoS should also be monitored upon drive-tests.

However, one should separate Application Optimization from RadioOptimization. Indeed, the assessment of the QoS offered by the UTRAN

should only restrict to QoS that the UTRAN can actually offer, this

mean RAB QoS.

Optimization of end-user QoS should be driven next and if the

subjective end-user QoS is not sufficient, following changes could

apply:

Modify the Application settings for a better use of the RAB


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If it not sufficient, higher the RAB QoS requirements. This will

trigger further Radio Optimization with the new RAB

implementation

The RAB QoS is described in 3GPP TS23.107 with following

attributes:

Maximum bit-rate (kbps)

Guaranteed bit-rate (kbps)

SDU error ratio a/o Residual bit error ratio

Delivery order (y/n)

Maximum SDU size (octets)

Delivery of erroneous SDU (y/n/-)

Transfer delay (ms)

Traffic handling priority

Allocation/Retention Priority

Following attributes are taken into account for the choice of the Radio

Bearer:

Maximum bit-rate for PS and Guaranteed bit-rate for CS

SDU error ratio a/o Residual bit error ratio for RB BLER for CS

RLC mode is Transparent for CS and Acknowledged for PS (in-

order delivery, max SDU size, delivery of erroneous SDU)

Therefore, the monitoring of the QoS offered by the UTRAN relies on:

Offered bit-rate

Transport Channel BLER

Performances for RLC AM (Acknowledged Mode)

2.3.1 Offered bit-rate

For CS services, the offered bit-rate can only be the requested one. The

bit-rate is guaranteed.

For PS services, the UTRAN can apply service downgrade, if the RAC

can not admit the requested bit-rate. The downgrade is then reconsider

at each Cell-FACHCell-DCH transition. Once a bit-rate is attributed,

a channel with the corresponding bandwidth is allocated over the radio

interface.


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2.3.2 Transport Channel BLER

For CS services, the Transport Channel BLER is the Frame Error Rate

for the service, since no retransmission is allowed.

For PS services, the Transport Channel BLER is a tradeoff between theeffort in terms of bandwidth to support retransmission and the effort in

terms of radio to limit errors.

2.3.3 Performances for RLC AM

For PS services, the RLC performances in terms of retransmission rate

and delay impact the higher-layer QoS.

2.4 Higher-layer performances on Control planeFor the proper working of the Telecom procedures, minimal

performances on Control plane are required, especially in terms of

delay. But, the delay introduced for the Telecom procedures definitely

impacts the end-user perception of the network quality, especially at the

Call set-up.

Performances in terms of delay on the Control Plane depend on:

The buffering and the processing times in the nodes

The quality offered by the Transport Network

The quality offered by the Radio Links for signaling

This is on this last item that the Radio Optimization can bring

improvement. The quality offered by the Radio Links can be mainly

monitored through:

Access to common channels

Offered bit-rate

Transport Channel BLER

Performances for RLC AM (Acknowledged Mode)

Radio optimization is done in the same way as for traffic channels.

End-user assessment will rely on Procedure times, such as:

Attach time

Paging time

Call set-up time (MOC, MTC, MTM)

Time for PDP context establishment


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Other Procedure Times, such as the time for SHO completion, may only

impact call set-up failure rate and call drop rate from an end-user point

of view.

Other Procedure Times, such as the Detach time, may only impact the

network performances from an operator point of view.

Events for the definition of the time interval are often specific for each

operator and related to commitments.


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Title:

Drive Test Analysis

Date:

05/07/2006

Page Number:

29/30

Created by:

Alexandre Silva

Approved by: Doc Ref.:

UMTS-RN0-0005



Abbreviations

AM Acknowledged ModeAS Active Set

BLER Block Error Rate

CAC Connection Admission Control

CFN Connection Frame Number

CN Core Network

CPICH Common Pilot Channel

CRC Cyclic Redundancy Check

DL Downlink

DPCCH Dedicated Physical Control Channel

DPDCH Dedicated Physical Data Channel

FTP File Transfer ProtocolHO Handover

MAPL Maximum Allowable Path Loss

MOC Mobile Originating Call

MTC Mobile Terminating Call

MTM Mobile To Mobile

NB Node B

NBAP Node B Application Protocol

OCNS Orthogonal Channel Noise Simulation

PDU Protocol Data Unit

PSC Primary Scrambling Code

QoS Quality of ServiceRAB Radio Access Bearer

RAC Radio Admission Control

RANAP RAN Application Protocol

RLC Radio Link Control

RNP Radio Network Planning

RRC Radio Resource Control

RSCP Received Signal Code Power

RSSI Received Signal Strength Indicator

RTWP Received Total Wide-band Power

SCH Synchronization Channel (Primary: P-SCH, Secondary: S-SCH)

SFN Sequence Frame Number

SIR Signal to Interference Ratio

SRNC Serving RNC

TPC Transmit Power Command

TX Transmitted

UE User Equipment

UL Uplink

UTRA UMTS Terrestrial Radio Access


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C fid ti l D t

END OF DOCUMENT

Documents

UMTS-RNO-0005 - Drive Test Analysis