3G RF Optimisation Basics

WCDMA Basics & Generic 3G

Optimisation Process1-WCDMA Basics

Frequency Reuse

Scrambling Codes

Signal Strength/Quality Measurements in WCDMA

Pilot PollutionSoft/Softer Handover

Missing Neighbours2-Generic 3G Optimisation Process

Process overview

RF KPIsIn Call KPIs

Tools for the job

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

Scrambling Codes & CPICH

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

the cell

• The Common Pilot Indication Channel (CPICH) is

broadcast from every cell

• It is this “beacon” that is used by the phone for its cell measurements for network acquisition and handover

purposes (Ec, Ec/Io).

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 measurementsThree 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)

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

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

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

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, 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

Handovers in WCDMA

Various handover types exist in WCDMA

Those between WCDMA sites (intra-system HO)

Those between WCDMA and GSM (inter-system HO)

Handovers in WCDMA - Softer HO

▪Softer handover occurs between sectors of the same site

Handovers in WCDMA - Soft HO

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 - 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

Handovers - Inter system HO

Inter system handover occurs between 3G and 2G sitesAs with all handovers, accurate adjacencies will be required

Optimisation Basics

1-Coverage Optimisation2-Neighbour Optimisation

3-Pilot Pollution Optimisation

4-SHO Optimisation

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 coverageLink budgets should be used to determine both the planning

targets and the drive survey level targetsNote that the planning and drive survey level targets will be

different

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

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

NMISSINGBESTNMISSINGinMEcNoEcNo

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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.

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

Pilot Pollution Optimisation

Best server CPICH_Ec >= Ec target

(dBm)

And

Best server CPICH EcNo < Ec/Io

target (dB)

▪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

Pilot Pollution Optimisation

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?

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

Optimisation Basics

•Coverage Optimisation•Neighbour Optimisation

•Pilot Pollution Optimisation

•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