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)
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