19-03-2012, 12:58 PM
RF Planning and Optimisation Software
Overview
This document describes every aspect of frequency planning in Atoll, from high level description of the frequency planning
process to the practical level detail. Main topics covered in this document include AFP prerequisites, AFP usage, AFP minimisation
target and some possible problems that may come up during training.
This document begins with a basic user guide, a short operational introduction to the AFP process in Atoll, and goes on
to summarize most aspects of the practical planning process with detailed discussions on certain topics. It also explains
the means to evaluate a frequency plan available in Atoll. A chapter is dedicated to advanced topics and troubleshooting
in the end.
Four appendices contain in-depth information on technical aspects of the cost function, the BSIC allocation algorithm, the
IM calculation and the dimensioning process respectively. All in all, this document is almost self sufficient with respect to
the use of Atoll AFP.
1.1 Introduction to AFP
The main role of an Automatic Frequency Planner (AFP) is to assign frequencies (channels) to the network such that the
overall network quality is optimised. With the evolution of GSM over the years to integrate many improvements, additional
requirements have emerged in the process of radio network planning. The implementation of baseband and synthesised
frequency hopping, discontinous transmission and network synchronisation, for example, has led to higher sophistication
in the process of frequency planning. These enhancements require that an AFP also be intelligent and advanced enough
to help the frequency planner through out his tedious task.
The Atoll AFP considers a large number of constraints and directives; for example, ARFCN separation requirements
between transmitters, interference relations, HSN assignment methods, frequency domain constraints, a certain fractional
load to maintain etc. Hence, the AFP depends on a variety of input data, such as the interference matrix, neighbourhood
relations, traffic information and so on.
This document not only explains how to use the Atoll AFP, by describing the AFP GUI, but also includes detailed descriptions
of the various constraints, directives, and data sources. The primary target of this document is to explain the technical
background of the AFP.
1.1.1 Frequency Assignment as a Cost Minimization Problem
From the technical point of view, the Frequency Assignment Problem (FAP) is considered as a minimization problem. This
means that the AFP will generate a set of Frequency Plans (FPs), and propose the one that has the lowest cost as the
“Best Solution”. Therefore, the AFP cost is the equivalent of AFP quality estimation: the lower the cost, the better should
be the quality from the AFP point of view.
The approach of cost minimization is not only the most common approach to the FAP but probably also the easiest to
understand and control. It provides the user with means of guiding the AFP in its task. For example, by setting the cost of
interference violation low, the AFP will concentrate its efforts on resolving the separation violations.
There are AFP tools in which certain types of objectives are presented as “hard constraints”. If a hard constraint is not
satisfied, the AFP does not offer any solution or offers a partial solution (with fewer frequencies and satisfying hard
constraints). The philosophy of hard constraints vs. soft constraints has nothing to do with the quality of an AFP engine, it
is merely a behaviour convention. In Atoll, we prefer always offering a solution to offering partial assignments or violating
domain limitations. This ensures that you will always get a result when you launch the Atoll AFP. This result will very well
depict the difficulty of the FAP. The cost of this solution will clearly indicate if unacceptable violations have occurred or if
this plan has improved the current frequency plan.
The cost function definition permits you to place as much emphasis as required on certain elements of the cost function.
This manipulation will make the AFP behave as if it were guided by hard constraints, from the optimisation viewpoint, while
retaining its property of being a quality monitor and a hardness-of-assignment monitor both.
1.1.2 Abbreviations
Some abbreviations and terminologies used in the document are listed below:
GSM Global System for Mobile Communications (Groupe Speciale Mobile)
GPRS General Packet Radio Service
EDGE Enhanced Data rates for GSM (or Global) Evolution
EGPRS EDGE based GPRS
TSL Timeslot
TX Transmitter or sector
TRX Transceiver
BCCH Broadcast Control CHannel. A term usually employed in Atoll to refer to the TRX carrying this
channel.
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AFP Reference Guide
1.2 Architecture
The Atoll Automatic Frequency Planning (AFP) module is an optional module that enables you to generate frequency plans
for GSM and TDMA networks automatically. The Atoll AFP module can allocate the following parameters:
• Frequencies
• Frequency hopping groups (MAL)
• HSN, MAIO
• BSIC (TSC planning)
TCH Traffic CHannel. A term usually employed in Atoll to refer to a TRX carrying traffic with usually the
same coverage area as the BCCH.
TCH_INNER Inner Traffic CHannel. A term usually employed in Atoll to refer to a TRX carrying traffic but usually
having a coverage area less than that of a TCH.
HR/FR Half Rate/Full Rate
CS Circuit-switched
PS Packet-switched
HCS Hierarchical Cell Structure
Subcell An entity defined by the pair [TX, TRX Type]
HO Handover
kbps Kilobits per second
GoS Grade of Service
QoS Quality of Service
KPI Key Performance Indicators
TL Traffic Load
P Probability
C Carrier power (Signal strength)
C/I Carrier to Interference ratio
AFP Automatic Frequency Planner/Planning
DTX Discontinuous transmission
GUI Graphical User Interface
FP Frequency Plan
BBH Baseband Hopping
SFH Synthesized Hopping
NH No Hopping
MAL Mobile Allocation List. In the context of SFH, MAL is the group of frequencies used by the
frequency hopping TRX.
AMR Adaptive Multi-Rate
CC Concentric Cells
Transmitter Atoll synonym for cell or sector in conventional GSM jargon
FER Frame Erasure Rate
FH Frequency Hopping
DLPC Down Link Power Control
RRM Radio Resource Management
Synchronised
transmitters Transmitters that are synchronised and can, therefore, share the same HSN.
Data Model A project can be saved in a filename.ATL file or as a database. In both cases, most of the project’s
information is saved in database tables. We refer to these tables as the data model.
IM, IMco, IMadj Interference Matrix, Co-channel / Adjacent-channel Interference Matrix
FN Frame Number
CDF Cumulative Density Function
TSC Training Sequence Code
FAP Frequency Assignment Problem
# Number of
Chapter 1: Overview
© Forsk 2008 AT271_ARG_E4 15
• TRX rank (can be used to prioritise the use of good frequencies)
• Performance Indicators at Site/Cell/TRX levels
Atoll works with an open AFP interface. Any AFP built using this interface can be able to allocate the following additional
parameters. Future versions of the Atoll AFP module are planned to assign the following parameters as well:
• Group ID (better administration of the frequency resources)
• TN offsets
• FN offsets
Atoll AFP implements simulated annealing, taboo search, graph heuristics and machine learning. It manages its time
resources to match the users time directive. If allowed enough time, the AFP will employ a major part of this time in “learning”
the network. During the learning phase, the AFP tunes up its internal parameters. Towards the end of the user-defined
time, the AFP switches to a randomised combinatorial search phase.
Network learning is performed by executing numerous fast and deterministic instances of the AFP. The one that obtains
the best performance is memorized in the document and is, therefore, the most suitable for the specific network. The next
time an AFP is executed it will start where the learning process ended and it will use the parameter profile of the best solution
stored in the document.
The Atoll AFP is built based on a specified COM interface designed as a part of Atoll’s open platform strategy. The interface
is designed in such a way that puts aside elements that are not inherent to the AFP process. At the same time, through
the modelling capabilities of the planning tool, the AFP can support complete list of features expected from an AFP.
Note:
• The following scenario will demonstrate the usefulness of AFP learning capabilities:
- Create a GSM GPRS EGPRS project and import its network elements and maps.
- Create a copy of “Atoll AFP module” and name it “Atoll AFP module 2”.
- If the network has X transmitters, run “Atoll AFP module 2” for X / 10 minutes to obtain a
cost Y. (Short execution)
- Now run “Atoll AFP module 2” for a longer time (for example, X / 5 hours).
- Another cost, Z, is obtained, which is better than Y (i.e. Z < Y). The network dependent
information is memorized in the “Atoll AFP module 2” instance whereas the “Atoll AFP
module” instance remains unchanged.
- Now if you perform a short execution with “Atoll AFP module 2”, you can get the improved
result (Z) right away. While a short execution of the “Atoll AFP module” instance will give
the initial cost (Y).
- If X / 5 hours is too long, you can perform the “learning” on a small (representative) part of
the network.
Basic AFP Tutorial
Atoll AFP framework complies with its global open architecture strategy. Any AFP module, Atoll AFP or 3rd party AFP, can
be interfaced and made available to RF planning engineers through Atoll. Furthermore, different AFP modules are activated,
accept their main inputs and generate their main outputs in the same manner. This section teaches the basics of
activating an AFP in Atoll.
2.1 AFP Process in Atoll
The AFP process is a cycle in which the AFP is only one of its many steps:
The figure below gives a better view of interaction of the AFP with other elements in Atoll:
The following figure depicts the outputs of the AFP:
Figure 2.1: AFP Process in Atoll
Figure 2.2: Interaction of the AFP with Other Elements
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AFP Reference Guide
2.2 Loading and Validating the Network
To launch the AFP, choose the Automatic Allocation… command from the Frequency Plan menu of the Transmitters
folder context menu. This initiates a series of dialogs called the AFP wizard.
Figure 2.3: AFP Outputs
Figure 2.4: AFP Launch Wizard - AFP Session Tab
Figure 2.5: AFP Launch Wizard - Separations Tab
Chapter 2: Basic AFP Tutorial
© Forsk 2008 AT271_ARG_E4 21
Here you can,
• Specify the AFP module you would like to use and set its parameters,
• Choose the network parameters and AFP performance indicators you want the AFP to allocate,
• Specify the network’s default separation requirements,
• Consult the network’s “Exceptional Pairs” and define other separation constraints for them, and
• Indicate whether interferences are to be included in calculations or not.
For explanations of AFP performance indicators, refer to "AFP Performance Indicators" on page 38. The last wizard dialog
contains some global parameters that often vary from one AFP instance to another:
The most important option here is the one proposing the two sources of the traffic load information. Traffic load can be
read directly from the subcells table, which could have been filled manually, by the dimensioning process or by a KPI calculation.
You can also specify that the traffic load should be read from the default traffic capture (explained later).
Clicking Validate will start the data verification and storage optimisation aimed at providing fast access to data needed by
the AFP. This stage may generate many warnings for real-life networks (for example, values out of range). These are
displayed in the Event viewer. It is recommended to revise the network data according to these messages and continue
once all the data are clean and coherent. If a certain message is not clear or self evident, you can always contact Forsk’s
technical support. The figure below depicts the Event viewer with some sample messages:
Let us look at two of these messages:
Figure 2.6: AFP Launch Wizard - Global Parameters Tab
Notes:
• In case the traffic load is taken from the Subcells table, committed after a KPI calculation,
you must be aware of a certain difference: in the KPI calculation, Atoll divides the captured
traffic by the timeslot capacity of the existing number of TRXs, while the AFP requires it to
be divided by the timeslot capacity of the required number of TRXs.
• The traffic load is artificially increased to 0.1, if it is too low (less than 0.1), in order to
maintain the AFP robust against partial data conditions. Hence, the AFP cannot completely
ignore the existence of a frequency in a TRX.
Figure 2.7: Event Viewer - Sample Messages
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AFP Reference Guide
This means that the value entered in the AFP weight column of the Transmitters table for the transmitter 19941 is invalid.
In the database, this field’s name is “COST_FACTOR”. A value of –2 for the cost factor implies that the AFP should generate
the worst assignment possible for the transmitter. It would be interesting to investigate the origin of this erroneous value
as it may avoid possible errors in the future. Atoll automatically resets this value to 1 in order to avoid such calculation
errors.
This message informs that 3678 subcells were loaded successfully. The next section explains the significance of the term
‘effectively selected’ and why 3678 subcells were loaded and only 6 selected for the AFP process.
2.3 Definition of the AFP Scope
In the example above, the 6 subcells effectively selected for the AFP process had many potential interferers, neighbours,
neighbours of neighbours, and/or transmitters with exceptional separation constraints with them. No AFP can perform a
good allocation for these 6 subcells without “dragging in” a large part of the network. The AFP considers the part that is
“dragged in” to be “frozen”. On the other hand, there are many other ways to freeze network elements in Atoll. Some
precise definitions are provided in order to avoid misconceptions.
Let us define 4 groups of transmitters (ALL, NET, SEL, RING):
• ALL = All the transmitters in the project.
• NET = Active transmitters that pass the filters on the main Transmitters folder and on the main Sites folder.
• SEL = Transmitters belonging to the (sub)folder for which the AFP was launched and that are located inside the
focus zone.
• RING = Transmitters belonging to NET, not belonging to SEL and having some relationship with the transmitters
in SEL:
- If interferences are to be taken into account (see the dialog above), all transmitters whose calculation radii
intersect the calculation radius of any transmitter in SEL will be included in RING. For large calculation radii
(20 km for example), a single site can have a very large RING loaded.
- Neighbours are always included in RING.
- If one transmitter of an Exceptional Pair is included in SEL and the other is not, then the other will be included
in RING as well.
- If BSIC assignment is required, then all the second order neighbours (neighbours of a neighbour) will be
included in RING as well.
Both the RING and the SEL parts of the network are loaded. It is important to know which subcells are loaded as the cost
is calculated for all loaded subcells. The RING part is frozen for all assignments (BSIC, HSN, MAL, MAIO and channels).
The SEL part may be assigned some parameters but only the ones specified in the dialog above. For example, if the user
did not select BSIC, it will not be assigned.
In addition to the generic freezing options above, there are some finer freezing options available in the data structure:
1. Individual transmitters can be frozen for channel (and MAL), HSN and/or BSIC assignment.
2. Individual TRX’s can be frozen for channel (and MAL) assignment.
In an Atoll project, it is strongly recommended to avoid TRX’s without channels. For this reason, never create transmitters
automatically if there are no channels to assign to them. Therefore, if the user does not ask for MAL/MAIO assignment, all
SFH subcells are considered frozen and no TRX will be created for them. The same occurs when only a MAL/MAIO
assignment is requested. In this case, all NH and BBH subcells will be considered frozen and no TRXs will be created.
Figure 2.8: Message 1
Figure 2.9: Message 2
Note:
• See Developer Reference Guide for details on the TO_ASSIGN and FROZEN assignment
states available in the AFP API.
Chapter 2: Basic AFP Tutorial
© Forsk 2008 AT271_ARG_E4 23
2.4 Preparing to Launch the AFP
Once the network is loaded and all warnings resolved, the AFP launch dialog will appear. This dialog contains a short
summary of the state of the loaded network, SEL + RING.
Interference matrices can be managed through the Interference Matrices folder. You can have more than one interference
matrices in your document. The top most active interference matrices set is used by the AFP. You can either embed the
interference matrices in the document or store them in external files. Atoll compresses the interference matrices if stored
in the .atl document itself. It is not necessary to load IMs or look for them each time AFP is launched. You can view the
reports on different interference matrices available in the Interference Matrices folder. This report has a summary section
which indicates the current state of the IMs.
Figure 2.10: AFP Launch Window
Example 1: When partial IM info exists, we can see that 9 transmitters out of 24 do not have any
interferers.
Figure 2.11: Partial Interference Matrices - Report
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AFP Reference Guide
The AFP launch dialog also lets you define a generator initilialisation number. This number serves as a directive of
randomness for the AFP process being launched. If the generator initialisation is set to 0, the AFP will be fully random. An
integer other than 0 will define a given deterministic sequence for the AFP process. Each generator initialisation number
(other than 0) corresponds to a deterministic sequence. Therefore, each AFP instance launched with the same generator
initialisation number will yeild the same results.
You can use this option if you want to have the same set of solutions every time you launch the AFP for the same part of
the same network.
The Atoll AFP has a single algorithm with a number of steps. The AFP ignores some of these steps if the alloted target
calculation time is too short. One of these steps is deterministic, i.e. independent of the generator initialisation number,
while the other steps are initialized by this number.
• Generator Initialisation = 0 (default value) signifies that this intialisation number will be calculated randomly.
• Generator Initialisation 0 means that the number will be the one set by the user. Every time you define the same
number, the AFP algorithm will be initialised in the same way, and hence the set of solutions will be the same.
It is advised to set Generator Initialisation = 0, and let the AFP reach the end of the Target Computation Time defined.
However, you must keep in mind that all the AFP computations are deterministic in the start, independent of the generator
initialisation. The AFP must be allowed to compute during the target time to observe the effects of randomness.
Example 2: When complete IM info exists, observe that the IM topology is more or less normal.
Figure 2.12: Complete Interference Matrices - Report
Notes:
• Since the method chosen by the AFP depends on the target time provided, you might not
get the same results using the same generator initialisation number if the defined target
times are different. Therefore, to actually get the exact same results from the AFP process,
you must define a certain target time and a certain generator initialisation.
• The AFP may be perfectly deterministic during a portion of the target computation time (5 -
15%). During this period, the randomness seed will have no effect on the solutions. If you
want to see the effect of randomness, let the AFP calculate until the end of the target time,
or set a shorter target time.
Chapter 2: Basic AFP Tutorial
© Forsk 2008 AT271_ARG_E4 25
2.5 Launching the AFP and Monitoring its Progress
Provide a time quota and a generator initialisation number in the above dialog and launch the AFP by clicking Run. It is
important to set a long time quota from time to time to allow the AFP to calibrate itself. If not stopped, the AFP will usually
continue for a while before stopping by itself.
The window below opens when the AFP is started, and displays information about the AFP process:
The Progress section of this window in the top left displays the target time allocated to the AFP, the time elapsed and the
number of AFP solutions that have been evaluated so far.
The general information and interference matrices report section in the top right gives some general information about the
current solution in real time. This display depends on the selected AFP module. This section lists the status of the current
solution, the initial cost, the cost of the current best solution, the cost of the previous solution and whether the previous
solution was kept or rejected. You can use the >> button to switch to the report on the currently used interference matrices.
The Event viewer has been made accessible through the AFP progress dialog in order to help the user keep track of all
the important warnings and messages generated before and during the AFP process. This also enables you to export
these messages as an AFP log file.
If a solution is kept, a corresponding message appears in the Event viewer. Double-clicking the message in the Event
viewer will open a dialog with the full details of this message, which will look something like the following figure.
After the AFP is allowed to compute solutions and try to optimise the network for a while, the AFP progress dialog would
look somewhat like this:
Important:
• If only a short time is specified, the full optimisation potential of the AFP will not be utilised.
Figure 2.13: AFP Progress Window
Figure 2.14: Event Viewer Message - Solution Kept
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AFP Reference Guide
The Best Frequency Plan Costs section displays the current values of modifiable and total costs, and their respective separation
components. This section also displays the total weighted Erlangs of the network concerned in the AFP process,
i.e. the total cost of a 100% interfered frequency plan). It gives a general idea of how good the cost of a certain frequency
plan is. The cost of any solution remains between 0 and the Network Weighted Erlangs. The cost is as better as it is closer
to 0.
Apart from the above information, this section also contains a table listing the initial frequency plan and all the AFP solutions
kept so far sorted in ascending order of cost. This table can display:
• Modifiable costs
• Total costs
• Frozen costs
• Summed components
• Main components (separation violation cost component, interference component and modified TRX component)
• Additional taxes (corrupted, missing or out of domain TRXs)
For detailed description of modifiable and non-modifiable parts of the total cost, please refer to "Modifiable and Non-Modifiable
Costs" on page 51.
Using the buttons available in the Plan comparison section in the bottom right, it is possible to visually compare the initial
frequency plan and the current best solution (with the Best Plan column in the AFP cost details table checked). Clicking
these buttons opens dialogs containing graphs corresponding to ’Cost Distribution on Frequencies’ and ’Usage Distribution
on Frequencies’.
The cost of a frequency f is given as:
Where, FL(i) is the fractional load of frequency f in the MAL of i, and cost(i) is the AFP cost of TRX i in Erlangs.
Figure 2.15: AFP Progress Window
Costf FLi Costi
i TRXs using f
=
Chapter 2: Basic AFP Tutorial
© Forsk 2008 AT271_ARG_E4 27
You can pause or stop the AFP process any time to check the current best solution, and resume optimising the network
after you have checked it. Pausing the AFP process opens the AFP results window with the current best solution results
listed.
2.6 AFP Outputs
When calculations stop (completed or paused to view the current situation), Atoll displays the frequency plan proposed by
the AFP. All results/violations are listed in a dialog window. This window contains a table listing all the assigned resources.
Transmitters located within the Focus zone are listed in the results dialogue. If a Focus zone is not available, the results
are displayed for all the transmitters within the Computation zone. These resources and related items (transmitters,
subcells) are coloured differently to indicate different reasons:
• Arctic blue: frozen resource
• Red: resource modified compared to the previous allocation but with separation violation
• Green: resource modified compared to the previous allocation respecting the separation constraints
• Black: resource not modified
• Blue: resource assigned with no separation violation
• Purple: resource assigned but with separation violation
• Grey: items and resources involved in computation but not available for allocation
Positioning the cursor over a resource in the table displays the reason for its colour in a tool tip.
The AFP result dialog is a non-blocking dialog. It enables the user to access other Atoll windows while the AFP is still pending.
Thus, it is possible to view other data or warning/error messages in the Event viewer (for example, the history of AFP
solutions). From this stage, it is possible to commit, to resume or to quit the AFP. It is good practice to keep a report through
the export option before resuming the AFP. The user can also partially commit some of the results as explained in the next
section.
The results window displays all the results of the AFP session. It is possible to only display some of the results by checking/
un-checking the relevant choices in the Display options menu. You can choose to display the results related to:
• Cells (BSICs)
• Subcells (HSNs)
• TRXs (Channels/MAL, MAIO) and related separation violations
Selected AFP performance indicators (AFP TRX ranks, and total and separation costs at TRX, subcell, transmitter and
site levels) will also be available in the results window. These AFP performance indicators are also available to export.
You can choose whether to display the AFP indicators in the results as separate columns. The Show AFP Indicators
command in the Display options menu controls the display of AFP TRX ranks, and total costs and separation cost components
at TRX, subcell, transmitter, and site levels.
Figure 2.16: Cost Distributions on Frequencies
Figure 2.17: Frequency Usage Distributions
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AFP Reference Guide
As the network had been loaded according to both the items to assign and the ones they relate to, it is possible to display
the frequency plan of either:
• Items belonging to the selected transmitters (see the definition of SEL), or
• Items belonging to the loaded transmitters (see the definition of SEL + RING). In the preceding example, there
were no transmitters in the RING set, so the option is not available.
It is also possible to display detailed information about separation constraint violations, i.e. the co-channel and adjacent
channel collision probabilities for relevant TRXs. You can choose to display these separation constraint violations through
the Display options menu.
The Separation violations column lists each each type of separation constraint violation realted to a given TRX, i.e. exceptional
pair, co-transmitter, co-site, or neighbour. Another column titled ’With the TRX’ contains a button for each type of
separation constraint violation. This caption of this button shows the TRX with which the separation constraint violation
occurs. Clicking this button takes you to the corresponding TRX row in the table. Right-clicking a row with a separation
constraint violation opens a Separation Constraint Violations context menu, which opens a dialog mentioning the reason
of violation when clicked. For example:
Use the Commit button to assign the allocated resources and AFP performance indicators. The resume button permits
resuming the AFP optimisation from where it stopped the last time.
Figure 2.18: AFP Results Window
Figure 2.19: Separation Constraint Violation Details Message
Note:
• At the bottom of the AFP results window, messages related to the last solution are
displayed, which may list problems as well.
Chapter 2: Basic AFP Tutorial
© Forsk 2008 AT271_ARG_E4 29
2.6.1 Partial Commit Functionality
It is often required to commit only a part of the automatically generated frequency plan rather than committing it entirely.
The purpose is to avoid committing TRXs that violate separation constraints (sometimes referred to as “not closing the
frequency plan”). Future Atoll versions will incorporate advanced automatic filters for partial commit.
The dialog examples below depict a case where removing a TRX eliminates a separation constraint violation on neighbours.
Once a TRX is manually removed from the resulting plan, separation violations are recalculated (may take a few
seconds). If the TCH TRX of transmitter Site36_3, causing neighbour separation constraint violations, is removed from the
sample frequency plan below, the resulting frequency plan has no neighbour separation constraint violations on the TCH
TRX of transmitter Site36_1.
It is possible to specify the action to be taken with each TRX individually, or globally delete all TRXs with separation violations.
It is also possible to mix the old plan and the new plan. Though this is not recommended, since it can cause interferences
of which the user might be unaware. The dialog examples below depict how this operation can be carried out.
The Delete the TRX option implies that the resulting frequency plan will not respect the number of required TRXs. In the
above example, note than the neighbour separation constraint violations at transmitter Site36_1 vanished once the TCH
TRX at Site36_31 was deleted.
Figure 2.20: AFP Results Window - Partial Commit Feature
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AFP Reference Guide
2.6.2 Automatic Constraint Violation Resolution
Different types of constraint violations, i.e. co-transmitter, co-site, neighbour, and exceptional pair, can automatically be
eliminated from the propsed frequency plan using the Automatic Constraint Violation Resolution tool. This tool is accessible
from the Actions button menu.
The aim of this tool is to find the TRXs in the currently proposed frequency plan that cause constraint violations of any of
the four following types:
1. Co-transmitter
2. Co-site
3. Neighbour
4. Exceptional pair
Once it finds the TRXs that satisfy the criteria, it sets their corresponding values to Delete the TRX in the Channel Assignment
column of the AFP results window.
This tool lets you resolve any type of constraint violations for different types of TRXs, control or traffic. You can also define
a threshold of co-channel and adjacent channel collision probabilities. This restriction will only set those TRXs to Delete
the TRX, which have a co-channel or adjacent channel collision probability higher than the threshold you defined.
Figure 2.21: AFP Results Window - Partial Commit Feature
Chapter 2: Basic AFP Tutorial
© Forsk 2008 AT271_ARG_E4 31
2.7 Visualising and Manipulating Results
The Commit button copies the frequency plan to the data structure. It is not necessary to save the document or commit
the changes to the database right away as the AFP cycle has not yet ended. At this stage, various generic and specific
tools are available in Atoll, and can be used to inspect the candidate frequency plan. Interference and C/I prediction studies
and various consistency checks are described in the following chapters of document. In addition to these, a useful tool is
also available in Atoll, called the Search tool. Its function is to facilitate visualising co-channel and adjacent-channel transmitters.
This tool is explained in detail in the User Manual. Other means of inspection include the common grouping, filtering,
advanced filtering, display and tool tip management features.
2.8 Manual Frequency Allocation
This section describes quick and useful techniques for performing manual frequency allocations in Atoll.
2.8.1 Manual Frequency Allocation for SFH Case
It is possible to perform frequency allocations for irrgular pattern networks, i.e. patten allocation of type 1/N. The following
set of operations will results in a frequency allocation even if the network is not a 100% regular pattern network.
1. Run the AFP so that it creates the required number of TRXs.
2. Group the transmitters by azimuth and manually assign the MALs to the most important azimuth groups.
3. Filter out these azimuth groups and delete the TRXs of all transmitters that were not assigned a MAL manually.
4. Run the AFP again selecting MAIO assignment only. This will assign proper MAIOs to the TRXs to which MAL
was manually assigned.
5. Remove the filter and freeze the existing TRXs. Now use the AFP to complete the assignment (assigning all
resources).
2.8.2 Manual Frequency Allocation for NH Case
To carry out manual frequency assignment:
1. Create a Best Server map and display it,
2. Display neighbours of the transmitter for which you want to find a frequency manually,
3. Open the Search tool,
4. By scanning the spectrum a good frequency can easily be found and can be allocated to the transmitter.
Figure 2.22: Constraint Violation Resolution Tool
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AFP Reference Guide
In this example, frequency 11 is not a good choice since it is used as a neighbour co channel. Frequencies 10 and 12
present similar characteristics.
On the other hand, frequency 14 is a good one and can be possibly allocated. None of the frequencies {13, 14, 15} are
allocated at the selected transmitter of at its neighbours.