rf cellular optimization

RF & NETWORK OPTIMISATION

WHY?

Delight Customer with Good Quality – Differentiating Factor

Full utilization of Network & its various subsystems

Network Optimization

CHALLENGES:

Frequent Change in Usage Patterns (Market dynamics)

Managing Scarce spectrum to maximize profits

Types:

Soft Optimization

Physical Optimization

• Parameters set during the planning phase must be reviewed according to network statistics

• As number of users increase, network expansions must be considered as well as new strategies

• Frequency plan/ PN Plan may have to be altered in order to avoid interference and network quality degradation during network growth

Why optimize a network every time? Hasn’t everything been done during planning

phase or during the Last Quarter Excellence exercise?

NO!

What is Network Quality ?

OPERATOR

CUSTOMER

NETWORK

SERVICES

MOBILE

COST

• Mail Box, Data, Fax• HSCSD, GPRS, WAP• Customer Care

• Faulty H/W or S/W• Mobile Quality• Misuse of Equipment

• H/W Failure• Network Configuration• Network Traffic• Spectrum Efficiency

• Coverage yes/no• Service Probability• Quality• Call Set Up Time• Call Setup Success Rate• Call Completion Rate

• H/W Costs• Subscription/Airtime costs• Additional Services Costs

• Network Equipment Costs• Maintenance Costs• Site Leasing Costs• Transmission Link Costs

OPTIMIZATION FLOW

• QUALITY DEFINITION

• QUALITY TARGETS

• QUALITY MONITORING

• ALARM ANALYSIS

• CONFIGURATION ANALYSIS

• TROUBLESHOOTING

• CHANGE REQUEST

• QUALITY IMPROVEMENT

Network Quality Cycle

Performance Monitoring• Network is under permanent change

detect problems and symptoms early!

OMC

field tests

customer complaints

It´s far too latewhen customers

complain!

Performance Monitoring Key Performance Indicators

• KPIs are figures used to evaluate Network performance– Post processing of NMS data or – Drive test measurements data

• Usually one short term target and one long term target– Check the network evolution and which targets are achieved

• KPIs calculated with NMS data– Network performance on the operator side.

• KPIs from drive test – Performance on the subscribers side

Performance Monitoring With NMS

• KPIs to evaluate the network performance with NMS are:– SDCCH and TCH congestion– Blocking percentage [%]– Drop call rate [%]– Handoff failure and/or success rate– Call setup success rate – Average quality DL and UL– BHCA per Sub– Busy Hour Traffic Utlisation– ASR– Paging Success Rate

Performance Monitoring With Drive Tests

• Evaluate network performance from the subscriber point of view

• KPIs information

– Quality, CDR, Interference, Missing neighbors, Call setup time, Data throughput

• Added value of drive test measurement

– Find out the geographical position of problems like bad quality to look for a possible interference source in the area

– Compare the performance of different networks (benchmarking)

– Display the signal level on the digital maps to individuate areas with lack of coverage eventually improve the propagation model

Various Optimizations

• Hardware

• Parameters

• Transmission

Hardware Optimisation

• Hardware for Optimising

– Capacity Augmentation to meet varied usages Currently >60% usages are tracked & Augmentation happens @ ~ 80% utilisation

– Interim Augmentation to meet excegencies. Hardware is shifted from one location to the other to meet unexpected spurt in usages

– Antennae Optimisation for right footprint.

Parameter Optimisation

• Relevant parameters for Optimising

– Frequency– Transmit power– Handoff Matrix– LA/LAIs– Handoff/handover Thresholds– Power control parameters– PN offset– Timer Value Optimisations

Tx resource Optimisation

• Transmission Resources for Optimising

– Inter BSC/ Inter MSC Connectivities– MPLS Connectivities– Capacity utilisation based optimisation

Optimization ProcessYoung Network Case

• In a young network the primary target is normally the coverage

• In this phase usually there is a massive use of drive test measurement – check the signal and

– the performance of the competitors

GPS

NMS X

MMAC

Optimization ProcessMature Network Case

• In a mature network the primary targets are quality indicators– CDR, FER, Handoff failures, Interference, MTx

• Important use the information from NMS– a general view of the network performance

• Drive test measurements are used – In areas where new sites are on air Where interference and similar problems are pointed out by

NMS data analysis– In areas where new sites are on air

Drop Call Rate (%)

0

0.5

1

1.5

2

2.5

3

3.5

Mon Tue Wed Thu Fri Sat Sun Mon Tue Wed

Call Bids / 10000

Average

Busy Hour

Repeaters/ IBS – Quality to CustomerExtending Coverage – Indoor

Various Access Methods

CDMA Architecture Overview

TE/MS

Abis

Abis

Abis

PSTN/PLMN

BSC/ PCF (1X)

Internet

Router Router

IP

IP Um

IS2000E1 STM-1

E1 STM-1

Ethernet

MSC/VLR HLR/AUC

PDSN/FA

AAA

HA

OMC

SC

WINBTS -1X

Voice Only

BSC/ PCF HSIA

BTS - 1X

(V+D)

BTS - HSIA

E1

Server

Ethernet

AN-AAA

CDMA Channels (Forward - Downlink)

PilotChannels

AuxiliaryPilot

Pilot

Forward CDMAChannels

SyncChannel

PagingChannels

F-QPPH

F-PCHF-CCCH

F-BCCH

Traffic ChannelRS1,RS2

FundamentalCode Channel

Traffic ChannelRS3 to RS6

FundamentalCode Channel

SupplementalCode Channel

CDMA Channels (Reverse - Uplink)

Pilot

Reverse CDMA Channels

AccessR-CCCH

Traffic ChannelRS1,RS2

FundamentalCode Channel

Traffic ChannelRS3 to RS6

FundamentalCode Channel

SupplementalCode Channel

GSM Channels (U/L & D/L)

RF Optimization

Objectives of RF Optimization

Purpose of RF Optimization:

Fine tune network elements

Ensure performance and quality of network in preparation for live traffic

• Document system performance against exit criteria• Ensure acceptable coverage

• Minimize dropped calls, and lower originations and terminations failure.

Starting Optimization on a New SystemRF Coverage Control

• Contain each sector’s coverage, avoiding gross spillover

into other sectors

• Tools: PN Plots, Handoff State Plots, Mobile TX plots

Search Window Settings

• Find best settings for SRCH_WIN_A, _N, _R

Neighbor List Tuning

• Groom each sector’s neighbors to only those necessary

but be alert to special needs due to topography and traffic

• Tools: diagnostic data, system logs

Access Failures, Dropped Call Analysis

• Iterative corrections until within numerical goals

Pilot Pollution• Pilot pollution is the number of pilots(in addition to the best serving pilot)which

have a Signal Strength within a preset dB level(Pilot pollution threshold-usually 6dB) of the best serving sector

Correcting Corrections::::

Reduce Pilot,Page,Sync,Tch_max and Tch_Min settingsDowntilt the antennaReorient the antenna to a different bearing.Replace the antenna with a lower gain model.Lower the antennaMove or eliminate the cell/sectorAdd new site.

Common RF Optimization Scenarios I

• Pilot Pollution– Low Ec/Io caused by the presence of numerous, poor quality, non-

dominant pilots

Symptoms

Low Combined Ec/Io No dominant pilot Above average mobile received

power High drop rate High access failure rate

• Terrain

Common Pilot Pollution Scenarios

Pilot Pollution can be a symptom of rapid changes in elevation or areas with very high elevations as the RF power is more difficult to control

Problem:

Inadequate downtilt on the highest site causes an overshoot Inappropriate choice of antenna vertical beam and/or inadequate downtilt

for the lowest sites causes multiple pilot reception by the mobile Solution:

The proper antenna type, orientation and downtilt

Common Pilot Pollution Scenarios

• Water Features– Problem:

• Multiple pilots arrive at the mobile due to increased propagation over water

• Downtilt alone may not be enough to maintain the coverage in the network core whilst effectively reducing the propagation over the water

– Solution:• Control of the cross-water

propagation by correct site configuration:

– Antenna Type– Orientation– Downtilt

Common RF Optimization Scenarios II

• Slow/Missed Handoff– Problem: Mobile requests a handoff to a Neighbor Pilot

but due to slow searching • Handoff not completed as a stronger PN arrives causing interference • Handoff completed but new pilot has poor Ec/Io

– Solution: • Minimization of the Active and Neighbor search windows

– Statistical Analysis of pilot delays using a detailed drive of each sectors’ coverage area

• Removal of unnecessary non-serving neighbors

Common RF Optimization Scenarios III• Forward Link Interference

– Problem: A mobile with adequate received power, normal mobile transmit power that has a high Ec/Io with high FFER

– Two Possible Scenarios:• Pilot not in neighbor list

– Add neighbor if pilot should be providing service– Remove pilot from the problem area by changing site configuration if it should not be

providing service

• Pilot in neighbor list but outside search window– Re-optimize search windows if pilot should be providing service– Remove pilot from the problem area by changing site configuration if it should not be

providing service

Common RF Optimization Scenarios IV• PN Conflict

– Problem: The merged neighbor list of a mobile in soft handoff contains a reference to two sectors with the same PN

– Symptoms are similar to forward link interference– Example:

• Mobile in three-way soft handoff with sectors A, B and C• Sector D is a neighbor of sector B and sector E is a neighbor of sector A,

Sectors D and E share the same PN

A

E

D

BC

Solution:• Change PN plan if both

sectors should provide service

• Remove one of the pilots from problem area by site reconfiguration if the sector should not provide service

RF Optimization Issues: Network Design and Configuration Coverage holes, excessive coverage overlap

Call Processing Problems due to misconfiguration Neighbor Lists Search Windows Power control parameters

Physical Problems/Hardware Problems Mismatched multicarrier sector coverage

Capacity Issues Forward and Reverse Power Control Overload Physical resource congestion – Channel elements, packet pipes – IP network congestion

Managing A New Dimension: circuit-switched and IP traffic blend QoS-related competitive issues

Performance Monitoring/Growth ManagementBenchmark Existing Performance

Dropped Call %, Access Failure %, traffic levels

Identify Problem Cells and Clusters

Weigh cells and clusters against one another

Look for signs of OverloadTCE or Walsh minutes -- excessive ? Soft handoff excessive? Required number of channel elements -- excessive? Forward Power Overloads, Originations, Handoffs blocked

Traffic Trending and ProjectionTrack busy-hour traffic on each sector; predict exhaustion Develop plan for expansion and capacity relief – split cells, multi-sector expansions, multiple carriers

Call Quality Problem List

Call Dropped – CHECK HANDOFF/HANDOVER

Speech Clipping – FER/ FAULTY HARDWARE IN MGW

Humming Sound – FAULTY HARDWARE IN MGW

No Service – FAULTY HARDWARE

Disturbance in voice - FER/ FAULTY HARDWARE IN MGW/ L3 STACK