RF Planning & Optimisation
RF Design Requirements
The RF design inputs can be divided into Capacity requirements: – Erlang per subscriber during the busy hour – –Quality Quality of service for the air interface, in terms GoS – GoS –Network Network capacity Coverage requirements: – Target coverage areas. These should should be marked geographically – –Coverage Coverage area probability – –Penetration Penetration Loss of buildings and in-cars
RF Design Requirements
The RF design inputs can be divided into Capacity requirements: – Erlang per subscriber during the busy hour – –Quality Quality of service for the air interface, in terms GoS – GoS –Network Network capacity Coverage requirements: – Target coverage areas. These should should be marked geographically – –Coverage Coverage area probability – –Penetration Penetration Loss of buildings and in-cars
Propagation Models
The prediction of propagation loss in a mobile radio environment is very difficult given multiple factors, such as:
Irregular configuration of the terrain
Various shapes of architectural structures
Weather changes.
An easy analytic solution to the problem does not exist. Combining both statistics and electromagnetic theory helps to predict the propagation loss.
Models
There are few theoretical models and many empirical models to predict the propagation path loss.
The Okumura-Hata model The Walfisch-Ikegami model.
Okumura-Hata model
The Okumura-Hata radio wave propagation prediction is based upon empirical information obtained from measurements in Japan(Okumura, 1965).
The Hata formula is a mathematical fit for the Okumura graphical measurement data.
Okumura-Hata model
The Okumura-Hata model predicts the path loss L between the transmitter and receiver, taking into consideration the frequency, the height of antennas, the propagation distance, and the terrain type.
The model predictions correlate reasonably well with measurements, especially in urban and suburban areas.
This is not the case in rural areas with irregular terrain.
Correction factors are used for irregular terrain types such as: rolling hills, isolated mountains, general slopes (up or down), and mixed land-water paths.
General formula
L = a0 + a4·logf - a2·loghb - a·hm + [a1 – a3·loghb]·logd - Lc,
where a0, a1, a2, a3, and a4 are adjustable parameters.
Comparison of two models
The Walfisch-Ikegami is preferably used for microcells because it takes into account the effects of diffraction and scattering
The Okumura-Hata model is based on quasi-smooth terrain with no obstacles and therefore it is best applicable for macrocells.
LINK BUDGET
Link Budget Elements of a GSM Network
BTS Antenna Gain
Max. Path Loss
Fade Margin
Feeder Loss
Diversity Gain
BTS Receiver Sensitivity
LINK BUDGET
BTS Transmit Power
Penetration Loss
MS Antenna Gain,
Body and Cable Loss
Mobile Transmit Power
Mobile Receiver Sensitivity
Typical Link Budget
TRANSMITTING END END TRANSMITTING
MS (UL) (UL) MS
BTS (DL) (DL) BTS
33 dBm dBm 33
43dBm 43dBm
-2 dB dB -2
00
COMBINAR LOSS LOSS COMBINAR
00
00
FEEDER LOSS LOSS (@2dB/100M) (@2dB/100M) FEEDER
00
-1.5dB 1.5dB
CONNECTOR LOSSES LOSSES CONNECTOR
00
-2dB 2dB
TRANSMITTER ANTENNA ANTENNA GAIN GAIN TRANSMITTER
00
17.5dB 17.5dB
31dBm 31dBm
57dBm 57dBm
TRANSMITTER POWER POWER OUTPUT OUTPUT TRANSMITTER BODY LOSS LOSS BODY
EFFECTIVE ISOTROPIC ISOTROPIC RADIATED RADIATED POWER POWER EFFECTIVE
Typical Link Budget
RECEIVING END
BTS (UL)
MS (DL)
-115 dBm
-112 dBm
17.5 dB
0
ANTENNA DIVERSITY GAIN
3 dB
0
CONNECTOR LOSS
-2 dB
0
INTERFERENCE DEGRADATION MARGIN
-3 dB
-3 dB
BODY LOSS
0
-3 dB
DUPLEXERLOSS
0
0 dB
-4 dB
-4 dB
-126 dBm
-102 dBm
RECEIVER SENSITIVITY RECEIVE ANTENNA GAIN
FADE MARGIN REQUIRED ISOTROPIC RECEIVE POWER
Antenna Selection
Gain of antenna
Height of antenna
Beamwidths in horizontal and vertical radiated planes
VSWR; Nominal impedance
Frequency range
Radiated pattern (beamshape) in horizontal and vertical planes; Polarisation
Downtilt
RF Planning Tool
Map with Clutters and Heights
Map with Vectors
Site Properties
Transmitter Properties
TRXs Properties
Neighbours List
Different Levels of Signal Coverage
Optimization ?
W hat is Optimization ? Activity of achieving and maintaining the required quality as designed
W hy Optimization ? Deviations between plan and reality
W hat is Optimization
W hy Optimization ?
I naccuracy of radio planning Statistical variations in the path loss characteristics
I mplementation Antenna radiation pattern and effective radiated power
Environment Seasonal environmental changes, e.g trees, leaves and other environmental changes such as new highways, new buildings
Performance Determinants
Coverage
Interference
Handover Behaviour
Traffic Distribution
Performance Determinants
Coverage - Good signal level across the whole cell, coverage holes within a cell’s service area must be minimized.
I nterference - A reasonable level of interference must be contained at cells service area in order to provide a quality air-interface.
Performance Determinants
Handover Behavior - The quality of the airinterface in a cell with respect to handover behavior is good, no unnecessary handovers, Rxquality at acceptable level, BTS & MS use minimum transmit power.
Traffic
Distribution - The quality of the air-interface
in a cell with respect to traffic distribution is good, maximum amount of traffic can be handed.
Drive Tests for Optimization
Initial network coverage verification and benchmarking
Verification before and after changes
Locating and measuring interference
Locating areas where traffic problems exist
Locate coverage holes
Preventive maintenance
Drive Test Data Collection
CELL ID including BSIC, LAC, and time slot
RXLEVEL for the serving and the neighbour cells
RXQUALITY for the serving cell
BCCH, BSIC for the serving and the neighbour cells
TRANSMIT POWER
GPS POSITION DATA
Drive Test Route Planning
Primary route (street level) includes all major roads, highways and wide thoroughfares
Secondary route (street level) includes all streets, subdivisions and compounds when accessable
Miscellaneous routes (in-building and special locations) includes golf courses, beach resorts, shopping mails, department stores, convention centers, hotels and resorts
Drive Testing and Analysis
Performance Problems that often encountered:
Cell Dragging
Dropped Calls
Ping-Ponging
System Busy
Handover boundary
Drive Testing and Analysis
Cell Dragging - Calls may drag a cell beyond the desired handover boundary. This might result dropped calls or bad Rxquality.
Suggestions:
Create an appropriate neighbour cell list Check serving cell’s cell identifier in the neighbour cell’s neighbour list Check neighbour cell’s BCCH, BSIC, LAC, Cell ID, etc
Drive Testing and Analysis
Dropped Calls - Caused by either RF environments or incorrect system parameters
Suggestions:
Check if an appropriate neighbour cell list is defined Check HO parameters Existing or new coverage holes Abnormalities such as call setup failure
Drive Testing and Analysis
Ping Ponging - Serving keep changing and as a result of bad audio quality
Suggestions:
Check if an appropriate neighbour cell list is defined Check HO parameters Poor coverage No optimal antenna configuration
Drive Testing and Analysis
System Busy - System busy on several call attempts and site appears consistently on the traffic report
Suggestions:
Short Term : Reduce the traffic on the congested cell/site. re-design the antenna configuration, Change BTS configuration Long Term: Build a new cell site to off-load traffic
Drive Testing and Analysis
Handover Boundary - Handovers do not occur at the desired HO boundary, the result is an imbalance in traffic distribution across the system
Suggestions:
Check if an appropriate neighbour cell list is defined/Check HO parameters Inappropriate antenna configurations of the serving and neighbour cells No TCH available (neighbour cells congestion)
Drive Testing and Analysis
Typical example of drive test equipment components:
Test Mobile phone
Scanning receiver
Transceiver system
Antennas
GPS
Visual display unit
Laptop computer
Drive Test Equipment
AGILENT TECHNOLOGIES(HP) Test 4 networks simultaneously
Fast scanning receiver, UL & DL
Frequency Hopping Table
Spectrum Analysis
Channel Power
Interference Measurement
GSM Broadcast Channel Analysis
Any Questions?
