Rf Cellular Optimization

RF & NETWORK OPTIMISATION

Network WHY?Optimization  Delight Customer with Good Quality – Differentiating Factor  Full utilization of Network & its various subsystems CHALLENGES:  Frequent Change in Usage Patterns (Market dynamics)  Managing Scarce spectrum to maximize profits Types: 

Soft Optimization



Physical Optimization

Why optimize a network every time? Hasn’t everything been done during planning phase or during the Last Quarter Excellence exercise?

• Parameters set during NO! 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

What is Network Quality ? O P E R A T O R

C U S T O M E R

NETWORK

• • • •

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 • Mail Box, Data, Fax • HSCSD, GPRS, WAP • Customer Care • Faulty H/W or S/W • Mobile Quality • Misuse of Equipment

SERVICES MOBILE COST

• 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 It´s far too late when customers complain!

customer complaints

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

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 Process Young 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

MMAC

GPS NMS X

Optimization Process Mature 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 Drop Call Rate (%)

3.5 3

• Drive test measurements are used

2.5

– 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 Call Bids / 10000

2

Average

1.5

Busy Hour

1 0.5 0 Mon

Tue

Wed

Thu

Fri

Sat

Sun

Mon

Tue

Wed

Repeaters/ IBS – Quality to Customer Extending Coverage – Indoor

Various Access Methods

CDMA Architecture Overview PSTN/PLMN MSC/VLR

HLR/AUC

SC

Abis BTS -1X Um

Abis

IS2000 TE/MS

WIN

Voice Only E1 STM-1

IP

HA

BSC/ PCF (1X)

OMC

E1

BTS - 1X

Ethernet

Router

(V+D) E1 STM-1

BTS - HSIA

BSC/ PCF HSIA

Router

IP

Ethernet

Abis

Internet

PDSN/FA AAA

AN-AAA

Server

CDMA Channels (Forward - Downlink) Forward CDMA Channels

Pilot Channels

Pilot

Sync Channel

Auxiliary Pilot

Traffic Channel RS1,RS2

Paging Channels

F-BCCH

F-QPPH

F-PCH F-CCCH

Traffic Channel RS3 to RS6

Fundamental Code Channel

Fundamental Code Channel

Supplemental Code Channel

CDMA Channels (Reverse - Uplink) Reverse CDMA Channels

Pilot

Access R-CCCH

Traffic Channel RS1,RS2

Traffic Channel RS3 to RS6

Fundamental Code Channel

Fundamental Code Channel

Supplemental Code 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 System RF 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 settings Downtilt the antenna Reorient the antenna to a different bearing. Replace the antenna with a lower gain model. Lower the antenna Move or eliminate the cell/sector Add 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

Common Pilot Pollution Scenarios • Terrain



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 PN Conflict Scenarios IV

– 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 Solution: of sector A, Sectors D and E share the same PN • Change PN plan if both sectors should provide C B service • Remove one of the pilots A from problem area by site reconfiguration if the E sector should not provide service

D

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 Management Benchmark Existing Performance Dropped Call %, Access Failure %, traffic levels

Identify Problem Cells and Clusters Weigh cells and clusters against one another

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

Traffic Trending and Projection Track 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