Drive Test

                                                                                                                                  

  

Contents

•What is RF Drive Test?•Why RF Drive Test is Done?•Tools & Equipment required•How RF DT is carried out?•Cases & Analysis                                                                                                                             

RF Drive Test

• Contents

•What is RF Drive Test?

•Why RF Drive Test is Done?

•Tools & Equipment required

•How RF DT is carried out?

•Cases & Analysis

RF Drive Test

 • Drive Test is one of the most comprehensive procedures of testing and analyzing a Radio Frequency Network

 – Coverage evaluation  –System availability  –Network capacity  –Network retainability  –Call quality

RF Drive Test

• Let us understand the meaning of the terms mentioned in the previous slide

– Coverage Evaluation 

Coverage Evaluation is the process of measuring the Received Signal Level of the Radio Frequency Signals from a Base Station

 RF Drive Test

•Coverage Evaluation:-

•A cellular mobile network in a city/town or a rural area is made up of several RF transmitting and receiving stations called Base Stations or Base Transceivers.

RF Drive Test

•Coverage Evaluation:

- Each cell has its own transmitting and

receiving equipment that covers a certain

geographic area.

RF Drive Test

 •Coverage Evaluation:

•A group of cells together form a cluster.

•The demography of the cells, for example, the type of terrain – whether hilly or plain, vegetation or buildings etc., is known as clutter.

RF Drive Test

 Coverage Evaluation: - Clutter data of a cell and of the geographic area to be covered is very important to estimate the actual area that will be covered by a Base Station.

RF Drive Test

 Coverage Evaluation:

- Radio Frequency signals from a Base

Station towards the mobile station and

those from the mobile station towards

the base station suffer due to the clutter.

RF Drive Test

Coverage Evaluation: - Let us examine some of the situations occurring due to the clutter

• Deflection - Deflection is the result of the Radio Frequency wave

encountering obstructions with much larger dimensions than the wavelength of the radio wave. This results in the wave rebounding.

 RF Drive Test

Coverage Evaluation:

• Diffraction - Diffraction occurs when radio waves encounter the edges and corners of obstacles. These act as secondary sources re-radiating beyond what is known as line-of- sight into the shadow region of the obstacle.

 RF Drive Test

Coverage Evaluation:

Diffusion (Scattering) - Scattering occurs when the dimensions of the object (usually vegetation) interacting with the radio wave are similar to the impinging wave’s wavelength. This causes the signal to disperse.

 RF Drive Test

•Coverage Evaluation:

- Therefore in practical scenarios, the signal level from a Base Station at any two points in the cell even being at the same distance from the Antenna, will not be the same due to the clutter variations

RF Drive Test

• Tools

- NEMO Drive test tool NEMO-Outdoor.

- GPS

- Inverter ±input 12V, Output 220 V ac, 400 W

- NEMO-Outdoor 5.40 Software

- Post processing tool Gladiator

RF Drive test

•   Work Process

- Collect OMC Parameter  - Database RF N/W  - Design BTS File (Nemo .nbf) - Drive Test Measurements - Analysis Programs - Coverage - Dropped Calls - Call Setup Success - Handover Perf. - Speech Quality

RF Drive test

Test Mobile Measurements• Collect Rx Lev measurements together with GPS co-ordinates• Analyze on planning tool - Reasons for poor coverage:- serving cell not best server/  handover problems - best server signal low check site / network design• Analyze in terms of relevant thresholds:- - indoor level  - in-car level  - outdoor level

RF Drive Test

•   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

RF Drive Test

• Collect / Analyze Drive Test Measurements• Test measurement (NEMO etc. together with a GPS) - Signal Strength - Co-channel and adjacent interference  - Handover relations• Test types  Continues drive test (Trace mode)  Spot test ±Network performance test (Statistical mode)• Test Measurement - Collect MS measurement report data (Downlink only!!)•

RF Drive Test

• Analysis Programs • Coverage:-  Analysis for Fulfillment 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

•  

RF Drive Test

•   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 synchronization 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 - Minimize local interference at the cell edge - Traffic load sharing between cells  - Compared to other optimization measures improvement potential is limited • Affected by - Measurement averaging - Power control parameters

Neighbors should in general be mutual

•   Speech Quality Analysis• Parameters:- - RxQual - Frame Erasure rate (FER) - Sppech Quality index (SQI)• Measurements:- - Drive Test (probably continuous call) - OMC statistics • Cause for poor quality - low signal strength (Coverage related) - interference - low signal strength and interference• Cause of interference - Co-channel interference - Adj.-channel interference - intermodulation - multipath interference

  Location Area Codes• Purpose  - identify location area - in incoming call is paged to all BTSs 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 signaling due to ping-pong cell reselections

•   Reporting (example)

RF Drive Test

 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

RF Drive TestAntenna Configuration• General points to check  - antenna type - 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 - space diversity, - polarisation diversity

RF Drive Test

Antenna Tilting• Antenna downtilt often used to minimize

interference  - Minimum: Vertical main lobe pointing at cell edge 

- Maximum: First null angle pointing at cell edge•

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