Collect RxLev measurements together with GPS co-ordinates
• Analyse on planning tool •
Reasons for poor coverage: – serving cell not best server • handover problems – best server signal low • check site / network design
• Analyse in terms of relevant thresholds: – indoor level – in-car level – outdoor level
Test Types •
Continuous drive test – setup a test call and drive over an area for detecting lack of coverage, missing handovers, interferences etc.
•
Spot test – detail measurement to be taken at dedicated problem spots for detail analyzing of specific problem
Collect / Analyse Drive Test Measurements
•
Test measurement (TEMS etc. together with a GPS) – Signal Strength – Co-channel and adjacent interference – Handover relations
•
Test types – Continuos drive test (Trace mode) – Spot test – Network performance test (Statistical mode)
•
Test Measurement – Collect MS measurement report data (Downlink only!!)
Analysis Programs Coverage:
Analysis for Fulfilment of Coverage Requirements (Urban, rural ... areas, outdoor, in-car, indoor)
Dropped Call:
Analysis for Dropped Calls due to Interference, SW/HW failures, Transmission Network Failures
Call Setup:
Analysis for Blocking and Capacity Limitations, Analysis for Resource Allocation Procedures
Handover:
Analysis for Efficient Handover Performance
Speech Quality:
Analysis for Interference
Dropped Call Analysis •
How to measure – drive tests • repeated call setups (preferred) • continuous calls – OMC measurements
•
Reasons for dropped calls – lack of coverage – interference problems – handover problems – lack of synchronisation in network – problems with other parts of the network
Call Setup Analysis •
Reasons for failed call setups – lack of coverage – database problems • database inconsistencies • parameter settings, e.g. – RXLEV_ACCESS_MIN, RACHBT, RACH_MAX_RETRANS – cell reselection related parameters – network congestion
Handover Parameters •
Fine-tuning of handover parameters – Moving cell boundaries in order to • Enhance success rate for critical handovers • Minimise local interference at the cell edge • Traffic load sharing between cells – Compared to other opimisation measures improvement potential is limited – Affected by • Measurement averaging • Power control parameters
PS! Neighbours should in general be mutual
Speech Quality Analysis •
•
Parameters
Causes of interference
– RxQual
– co-channel interference
– Frame Erasure Rate (FER) – Speech Quality Index (SQI)
Cause for poor quality – low signal strength (coverage related – interference – low signal strength and interference
• mainly on one link only – multipath interference
Location Area Codes •
Purpose – identify location area – in incoming call is paged to all BTS’s within LA
•
Large location area – advantage: less location updates (reduced SDCCH load) – disadvantage: more paging traffic
•
Boundaries should not cross high traffic areas
•
Cell reselection across LA boundaries – Parameter Cell_Reselect_Hysteresis (typ. 4 dB) used to avoid unnecessary signalling due to ping-pong cell reselections
Problem Symptoms
Reporting (example)
Advantages over test drives
– Less labor intensive and time consuming – More comprehensive, based on large number of users – not limited to time of test drive – Uplink and Downlink analysis possible – Subscriber behavior mix of outdoor, indoor, incar use
FINE TUNING
Tools • Digital Tilt Meter • GPS • Compass • Spanner • Screw Driver Set • Safety Belt • Adjustable Wrench • Cutting Pliers • Mesuring Tape • Safety Shoe • Map Info • Map Source • Google Earth
Antenna Configuration •
General points to check – antenna type, e.g. • omni • directional 60, 90 or 120 degrees • electrical downtilt • cross-polarised – antenna azimuth angle (for directional antennae) • coverage targets – antenna tilt angle • electrical + mechanical – diversity & isolation • e.g. space diversity, • polarisation diversity
Site Check •
Verify that site is implemented according to plan
•
Check installation e.g. – antenna spacing (diversity, isolation) – antennae in one sector are installed in the same plane
Omni
Tx
– antennae alignment k1
– omni antenna installation – cable installation
k2
Rx
k2
Rxd
Antenna Fine Tuning
•
Horizontal Plane: – Possible coverage weakness between sectors – Interference reduction – Traffic load distribution
•
Vertical Plane: – Interference reduction – Possible coverage weakness in the short to medium distance range – Traffic load distribution
Omni vs. Sectorised
•
OMNI cells - more difficult to optimise – Electrical downtilt possible, however • same for entire cell – Parameters same for entire cell
•
Directional antennae – narrower beam
easier
to control interference
– tilting less efficient with wider beams
Sectorised cell site with different downtilt angles
Tilting • Antenna downtilt often used to minimise interference – Minimum: Vertical mail lobe pointing at cell edge
h
BS
– Maximum: First null angle pointing at cell edge
Tilting
•
Electrical vs. Mechanical downtilt 0
°
Electrical
0
Mechanical
– Advantages: • Better back lobe characteristics • Better lower side lobe characteristics
