3g rf optimisation basics

January 2005

AIRCOM International 2005

3G RF Optimisation Basics

Robert Joyce

January 2005


WCDMA Basics & Generic 3G Optimisation Process

▪ WCDMA Basics

▫ Frequency Reuse

▫ Scrambling Codes

▫ Signal Strength/Quality Measurements in WCDMA

▫ Soft/Softer Handover

▫ Pilot Pollution

▫ Missing Neighbours

▪ Generic 3G Optimisation Process

▫ Process overview

▫ RF KPIs

▫ In Call KPIs

▫ Tools for the job

January 2005


UK 3G Spectrum Allocations

From (MHz) To (MHz) From (MHz) To (MHz) From (MHz) To (MHz)

A Hutchison 3G 1920.0 1934.9 2110.3 2124.9 1914.9 1920.0 2x15 + 5 = 35

B Vodafone 1944.9 1959.7 2134.9 2149.7 N/A N/A 2x14.8 = 29.6

C O2 1934.9 1944.9 2124.9 2134.9 1909.9 1914.9 2x10 + 5 = 25

D T-Mobile 1959.7 1969.7 2149.7 2159.7 1899.9 1904.9 2x10 + 5 = 25

E Orange 1969.7 1979.7 2159.7 2169.7 1904.9 1909.9 2x10 + 5 = 25

Total (MHz)

TDD

Licence Operator

FDD DownlinkFDD Uplink

1905

1910 1960

FDD Uplink

Licence A - Hutchison 3G

Licence B - Vodafone

1935

Licence C - O2

Licence D - T-Mobile

FDD Downlink

21502110

Licence E - Orange

1915

1920 1945 1970 1980 2125 2135 2160

TDD

January 2005


Frequency Reuse

▪ Initially operators have been launching with just a single carrier

▪ Network will initially be FDD only

▪ e.g. Operator X will launch using only the FDD carrier (F1 =10588)

▪ All launch cells will use F1 & therefore Operator X’s 3G network will have a frequency reuse of 1

UARFCN

Frequency

(MHz)

FDD Uplink F1 9638 1927.6

F2

F3

FDD Downlink F1 10588 2117.6

F2

F3

January 2005


Scrambling Codes & CPICH

▪ The Common Pilot Indication Channel (CPICH) is broadcast from every cell

▪ It carries no information and can be thought of as a “beacon” constantly transmitting the Scrambling Code of the cell

▪ It is this “beacon” that is used by the phone for its cell measurements for network acquisition and handover purposes (Ec, Ec/Io).

CPICH

January 2005


3G Coverage Measurements

▪ The majority of 3G coverage measurements are based upon measurements of the CPICH

▪ Golden Rule: If the UE can’t see the CPICH the UE can’t see the cell.

▪ Initial 3G network optimisation will be performed purely from CPICH measurements

▪ Three key related measurements for 3G optimisation are

▪ Ec - The Received Signal Level of a particular CPICH (dBm)

▪ Io - The Total Received Power (dBm)

▪ Ec/Io - The CPICH Quality (The ratio of the above two values)

January 2005


Total Received Power Io

▪ In a WCDMA network the User Equipment (UE) may receive signals from many cells whether in handover or not

▪ Io* = The sum total of all of these signals + any background noise (dBm)

▪ *Note: Sometimes Io is referred to as No, RSSI or ISSI

Io

January 2005


Received Power of a CPICH Ec

▪ Using the properties of SCs the UE is able to extract the respective CPICH levels from the sites received

▪ Ec* = The Received Power of a Particular CPICH (dBm)

▪ *Note: Sometimes Ec is referred to as RSCP

Ec1 Ec2

January 2005


The CPICH Quality (Ec/Io)

▪ From the previous two measures we can calculate a signal quality for each CPICH (SC) received

▪ Ec/Io = Ec - Io (dB)

▪ *Note: Sometimes Ec/Io is referred to as Ec/No

Ec1 Ec2

January 2005


Example

▪ From the above three measurements we can calculate for each pilot the Ec level for that particular pilot

▪ Ec1 = -80 - 5 = -85dBm

▪ Ec2 = -80 - 10 = -90dBm

Ec/Io1=-5dB Ec/Io2 =-10dB

Io=-80dBm

January 2005


Ec, Io and Ec/Io Measurement

▪ All commercial scanners and test UEs are capable of making Ec, Io and Ec/Io measurements

▪ It is these measurements that are used for cover analysis and basic optimisation

January 2005


3G Scanners

▪ Many types of 3G scanners on the market

▪ Agilent’s 3G Scanner & Nitros Software

▪ Anritsu’s ML8720B 3G scanner

▪ DTI Seagull (Dual band 3G/2G) scanner

▪ From experience the Anritsu scanner is the better of the all three with a higher sampling rate and greater flexibility

▪ However DTI scanner has added benefit of 2G scanning, ideal for 3G-2G neighbour optimisation as well as 2G optimisation

January 2005


Handovers in WCDMA

▪ Various handover types exist in WCDMA

▪ Those between WCDMA sites (intra-system HO)

▪ Those between WCDMA and GSM (inter-system HO)

January 2005


Handovers in WCDMA - Softer HO

▪ Softer handover occurs between sectors of the same site

January 2005


▪ Soft handover occurs between sectors of the different sites

▪ For both softer and soft it is the Ec/Io levels used to determine whether a cell should be added or removed from the active set

Handovers in WCDMA - Soft HO

January 2005


Handovers - Inter frequency HO

▪ Inter frequency handover occurs between two WCDMA carriers

▪ Will be used once operator deploys its second carrier, for microcell layer or capacity purposes

January 2005


Handovers - Inter system HO

▪ Inter system handover occurs between 3G and 2G sites

▪ As with all handovers, accurate adjacencies will be required

3G 2G

January 2005


Optimisation Basics

▪ Coverage Optimisation

▪ Neighbour Optimisation

▪ Pilot Pollution Optimisation

▪ SHO Optimisation

January 2005


Coverage Optimisation

▪ As with 2G if the coverage is inadequate then the call quality will be inadequate

▪ Therefore this first stage in 3G optimisation is ensuring adequate coverage

▪ Link budgets should be used to determine both the planning targets and the drive survey level targets

▪ Note that the planning and drive survey level targets will be different

January 2005


Coverage Optimisation

Dense Urban Urban/Suburban Rail Road Rural Indoor

Deep Indoor - 95% Deep Indoor - 95% Indoor Window - 95% Indoor Window - 95% Outdoor - 90% 95%

12.2k Speech -71.0 -81.0 -88.0 -95.0 -102.0 -102.0

64k CSD -72.0 -82.0 -90.0 -96.0 -103.0 -102.0

64k PSD -73.0 -82.0 -90.0 -97.0 -103.0 -103.0

64k CSD Videophone -71.0 -80.0 -88.0 -94.0 -101.0 -101.0

144k CSD -69.0 -79.0 -86.0 -93.0 -100.0 -99.0

144k PSD -70.0 -79.0 -87.0 -94.0 -100.0 -100.0

384k CSD -65.0 -75.0 -84.0 -90.0 -95.0 -95.0

384k PSD -66.0 -76.0 -84.0 -90.0 -96.0 -96.0

Service

Environment

▪ These levels are the levels that should be achieved at the roof of the vehicle

▪ If these levels are not achieved then inbuilding coverage will be poor

▪ Further optimisation with lower coverage levels is very difficult

▪ Solutions: Downtilt, Azimuth, New Site

▪ Given below are example target drive survey Ec levels for the different 3G services

January 2005


Neighbour Optimisation

▪ Missing Neighbours was and still is the biggest cause of poor performance in most commercial 3G networks

▪ The majority of call drops in early cluster are due to missing neighbours.

▪ It is therefore essential that the initial neighbour list is thorough, ideally with neighbours ranked in order of importance

▪ In 3G the UE must be on the best cell at all times … otherwise it will drop the call – this is not the case in 2G

▪ 3G/2G neighbour lists must also be comprehensive, incorrect 3G/2G neighbour lists will lead to dropped calls when moving from 3G to 2G and poor 3G re-selection performance when on 2G

January 2005


3G/3G Neighbour Optimisation

▪ We declare a 3G missing neighbour as a a cell not declared as neighbour of the best active cell although it is eligible to be added in the active set.

▪ A practical margin of 5dB is recommended as an initial window … anything bigger and the neighbour lists become too large

▪ Solution: 3G Scanner Survey, Actix Analysis, Neighbours Added

NMISSINGBESTNMISSING inMEcNoEcNo __ arg

January 2005


2G/3G Neighbour Optimisation

▪ 2G/3G neighbour optimisation will require the use of both 3G and 2G drive survey equipment

▪ Dualband scanner files can quickly be processed to pair up the best 3G cells with the best 2G cells for every sample along the drive survey.

January 2005


Pilot Pollution Optimisation

▪ As more and more 3G sites are integrated, the pilot pollution within the network will increase

▪ With >4 pilots of a similar level it can be very difficult to establish even a voice call

▪ The higher the data rate the more susceptible the service is to pilot pollution (bad Ec/Io).

▪ Whilst 3G voice requires an Ec/Io of above -15dB, 384kbps will required Ec/Io levels of -9dB or higher !!

▪ Pilot pollution should not be confused with poor coverage, where there is poor coverage, there is generally pilot pollution/bad Ec/Io

January 2005


PS384 - Pilot Pollution Areas

▪ DL_PS384 is much more sensitive to pilot pollution or overlaps than lower bit-rates. Optimising pilot pollution for PS128 is already a challenge, for 384 might be an unrealistic target.

▪ Comparison of required EcIo:

Service Voice PS64 PS128 PS384

Min EcIo -15 -13 -13 -9.5

▪ Even with good Ec levels, some areas will never provide reliable PS384 simply due to cell overlaps. It seems unclear whether a mature network may ever provide a full 384 footprint.

Conclusion: 384 requires an optimised network

January 2005


Required EcIo

GPRS Attach Success Rate vs Serving CPICH Ec/Io

-20%

0%

20%

40%

60%

80%

100%

120%

-19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5

Serving Cell CPICH Ec/Io (dB)

GPRS Attach Success Rate

January 2005


PS384 - required EcIo

DL Application Throughput vs. Serving Cell CPICH Ec/Io

0

50

100

150

200

250

300

-14 -12 -10 -8 -6 -4 -2 0

Serving Cell CPICH Ec/Io (dB)DL

Ap

pli

ca

tio

n T

hro

ug

hp

ut

(kb

ps)

Mean DL Application Throughput

Mode DL Application Throughput

DL Application Throughput (Last Value)

January 2005



▪ To avoid confusing areas of poor coverage with areas of pilot pollution we can define an area of pilot pollution as somewhere where

▪ The Ec target is the target coverage = -100dBm

▪ The current recommended Ec/Io target = -10dB

▪ Actix is able to identify areas of pilot pollution and display the locations on a map

Best server CPICH_Ec >= Ec target (dBm)

And

Best server CPICH EcNo < Ec/Io target (dB)

January 2005



▪ There are various means of reducing pilot pollution

▪ New Sites: Additional sites may reduce pilot pollution by bringing dominance to an area (before optimising for pilot pollution, always check that a new site is not about to be brought on air in the locality)

▪ Antenna Downtilts: By adjusting tilts on the best servers, or worst interferers, pilot pollution can be removed

▪ Solution: 3G Scanner Survey, Analysis, Downtilts, New Sites?

January 2005


Handover Optimisation

▪ Softer, Soft, Inter-frequency & system HOs have all been optimised on Nokia’s trial and other customers networks

▪ Therefore initial HO Optimisation should not require any changes to the UTRAN parameters ….

▪ Instead initial HO optimisation will involve studying how much HO occurs in the network and where this HO occurs.

▪ For 3G/3G HO, Actix is able to display areas where Softer & Soft HO is occurring and calculate the percentage of a drive route in SHO

▪ Typically we should be aiming for a SHO area of less that 40%

▪ Optimisation of SHO area should be performed using downtilt and azimuth changes

▪ Solution: 3G Scanner Survey, Analysis, Downtilt and Azimuth changes

January 2005


Optimisation Basics




▪ SHO Optimisation

▪ Everything is based around Ec/Io, to improve this we need to

▫ Increase Ec (improve the best server(s))

▫ Reduce Io (reduce pilots not eligible for the active set)

▫ Get all neighbours optimised

▪ In call drive runs should only take place once Radio Optimisation is complete

January 2005


Overview of Generic Optimisation Process

January 2005


3G Optimisation Process

▪ This section will cover the following;

▪ Overview a generic 3G Optimisation Process

▪ Key Performance Indicators

▪ Analysis Tools & Processes

▪ Next Steps

January 2005


Key Performance Indicators (KPI)

▪ In order to benchmark the performance of a 3G network a basic set of KPI targets are required

▪ The 3G KPI targets fall into two categories, RF KPIs and in-call KPIs

January 2005


RF KPIs

▪ The RF targets are defined in terms of: -

▫ RSCP of the Common Pilot Channel

▪ -89 dBm in >= 95% of bins for dense urban

▪ -94 dBm >= 95% of bins for urban

▪ -99 dBm >= 95% of bins for suburban

▪ -104 dBm >= 90% of bins for rural

▫ Ec/Io of Common Pilot Channel in unloaded network

▪ Ec/Io >= –10 dB in >= 95% of bins for DU, U, SU

▪ Ec/Io >= –10 dB in >= 90% of bins for Rural

▫ Ec/Io of Common Pilot Channel in loaded network

▪ Ec/Io >= –14 dB in >= 95% of bins for DU, U, SU

▪ Ec/Io >= –14 dB in >= 90% of bins for Rural

▪ Test case to be agreed

▫ SHO Overhead: 30-40%

January 2005


RF Optimisation

▪ Basic RF analysis checking the following




▪ SHO Optimisation.

▪ First stage is to run the KPI reports, then follows this with more detailed analysis.

▪ If the route meets the RF KPIs there’s no point doing further analysis

January 2005


Actix RF KPI Report

▪ Run the basic RF KPI report – check the KPIs

RF Scanner KPI Analysis

Scanner File 05Jan27 141458 Vodafone NZ RF KPIs

Coverage (Ec) Coverage

Target Ec(dBm) Achieved % Environment Target Ec(dBm) Target % Target Ec/Io(dB) Target %

Ec >= -89 96.68% Dense Urban -89 95% -10 95%

Ec >= -94 99.49% Urban -94 95% -10 95%

Ec >= -99 100.00% Suburban -99 95% -10 95%

Ec >= -104 100.00% Rural -104 90% -10 90%

Quality (Ec/Io)

Target Ec/Io(dB) Achieved %

Ec/Io >=-10 96.15%

Achieved % Target

SHO Overhead 41.11% SHO Overhead 40%

Other Achieved % Target

Pilot Pollution Area 3.85% Pilot Pollution <=5% 5%

January 2005


Actix RF KPI Report

▪ Run the basic RF KPI report – check the RSCP (Ec)

Scanner Best RSCP

-20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120

RSCP (dBm)

Perc

en

tag

e

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

RSCP PDF

RSCP CDF

January 2005


Actix RF KPI Report

▪ Run the basic RF KPI report – check the Ec/Io

Scanner Best Ec/Io

-2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 -15 -16

Ec/No (dB)

Perc

en

tag

e

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Ec/Io PDF

Ec/Io CDF

January 2005


Actix RF KPI Report

▪ Run the basic RF KPI report – check the Ec/Io vs Ec distribution

Ec/No vs RSCP

95.4%

3.3%

0.6%

0.7%

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

-120-110-100-90-80-70-60-50-40-30-20-100

RSCP (dBm)

Ec/N

o (

dB

)

DA

CB

-10dB

-100 dBm

Pilot Pollution Area

RSCP >= -100

Ec/Io <-10

Good Coverage Area

RSCP >= -100

Ec/Io >=-10

OK Coverage Area

RSCP < -100

Ec/Io >=-10

Poor Coverage Area

RSCP < -100

Ec/Io <-10

January 2005


Basic “Sites on air” analysis

▪ For each cell in the cluster check that coverage is seen for the sites expected to be on air

▪ Check correct SC is radiating in the expected direction (crossed feeders?)

▪ Highlight those sites not seen on air and any suspected crossed feeders

▪ But make sure your cell refs data is

accurate !!!

January 2005


Coverage (Ec) Analysis

▪ If KPI Report indicates good Ec - no further Ec analysis required !

▪ Otherwise analyse !!

▪ Solution: Tilts, azimuths, new sites

January 2005


Neighbour Optimisation

▪ If downtilts are to be made to any sectors, then additional neighbours should not be added to/or for these cells as they may not be necessary after downtilts

▪ Actix should be used to generate Missing Neighbour Report from Scanner data

▪ Remember until the cluster is complete, additional neighbours will come and go

January 2005


3G/3G Neighbour Optimisation (2)

▪ 3G Neighbour lists can be generated automatically by the Actix

▪ The tool runs through every point in the survey comparing the Ec/Io values of the SCs seen generating a neighbour list like the one given

▪ The number of missing neighbours found will be dependent on the quality of the initial neighbour list

▪ Don’t be scared of adding neighbours !!

Source

SC Site

Source

Cell Action

Target

SC

Target

Cell

Sample

Count

Intersite

Distance (km)80 Grey Lynn Shops 63136 Add 81 20 0.0

81 Grey Lynn Shops 63137 Add 80 19 0.0

108 St Lukes Carpark 65367 Add 138 23 2.9

117 Symonds St 64477 Add 507 17 1.3

138 Newton 65477 Add 98 20 0.8

138 Newton 65477 Add 108 20 2.9

January 2005


Pilot Pollution (Ec/Io) Analysis

▪ Run Pilot Pollution query to display areas of pilot pollution on map

January 2005


Pilot Pollution (Ec/Io) Analysis

▪ Identify worst “Pilot Polluters” on map

▪ Solution: tilts, azimuths, new site?

January 2005


SHO Analysis

▪ KPI report will indicate % of route in SHO

▪ Aim for SHO < 40%

▪ Run RE SHO query to display areas on a map - is this due to distant sites, is it in important high traffic areas?

▪ Solution: Tilts, Azimuths

January 2005


Cell Adjacency Planner - CAP

3G – 3G adjacencies

January 2005


Cell Adjacency Planner - CAP

3G – 2G Adjacencies

January 2005


3G/3G Neighbour Optimisation (3)

January 2005


Stage 3: In Call Optimisation

▪ Only once the RF Optimisation is complete should In Call analysis be undertaken

▪ In call analysis will also pick up

▫ Coverage Problems

▫ Pilot Pollution Problems

▫ Missing Neighbours

▫ SHO problems

▪ However if the RF Optimisation has been done correctly, none of the above should be seen at Stage 3 !

▪ In Call Optimisation will be similar to RF Optimisation

▫ Run In Call KPI report

▫ Analyse any problems seen

January 2005


Stage 3: Run Call KPIs Report

▪ Run RE Call KPI report

▪ Identify problem areas, Call Setup Success, Call Drop etc.

January 2005


Stage 3: Detailed In call analysis

▪ Detailed in call analysis

▪ Look for the basics first, Ec, Ec/Io, missing neighbours etc.

▪ Only then delve into the detailed L3 message flows.

January 2005


Process Summary

▪ Stage 0 Cluster Preparation - plots, site checks, neighbour checks etc.

▪ Stage 1&2 RF optimisation, Ec, Ec/Io, Missing Neighbours, SHO Area

▪ Stage 3 In Call Analysis (Speech, Video, PS, ISHO etc) – will be the subject of a further training session once Actix/RanOpt in place.

▪ And finally CLUSTER ACCEPTANCE !!

▪ Any questions: [email protected]

January 2005


3G RF Optimisation Basics

Robert Joyce

3g rf optimisation basics

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