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Quickly: The HSN is used to define the hopping sequence from one
frequency list, andMAIO is used to set the initial frequency on
this list.
It did not help? So come on and try to understand better ...
Note: The goal here is not to teach HSN and MAIO planning, since
this task involvesmany possible configurations and scenarios, which
would escape the scope of our
tutorial. The main goal today is to understand, in a planning
already deployed, what theymean values MAY HSN and assigns.
Frequency Hopping e MA List
To understand how HSN and MAIO are used in planning, we first
need to know somebrief concepts.
Frequency Hopping or FH: one of the great advantages of the GSM
system, in the constantsearch to reduce interference. More on the
FH due to a new tutorial.
MA List: set of frequencies (channels) assigned to a particular
sector, ie are those channelsthat can be used to attend calls from
users.
To illustrate, let's consider a sector with 4 TRX, where the
first TRX is used for BCCH andthe others are TCH TRX.
The MA List with the channels of traffic then would be:
HSN e MAIO
Sure, with the example in mind, let us return to our
parameters.
First, the definition of HSN: Hopping Sequence Number. It is a
number that defines thefrequency hopping algorithm, and can vary
from 0 to 63, ie there are 64 hoppingalgorithms to be used in
GSM.
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If HSN is zero, the frequency hopping sequence is cyclic, ie
without changes.
If HSN is greater than zero, then frequencies vary
pseudo-randomly.
When we enabled the Hopping - our case - all TRX in the SAME
SECTOR has the SAMEHSN. And if the we have 1x1 SFH it is
recommended to have the SAME HSN for ALLSECTORS of the BTS.
In our example, the MA List is small - just three frequencies.
The size of the MA List
should be taken into account in the planning of HSN: HSN should
be the designated soas to minimize the average probability of
collision, according to the designated MAIOs.
And how MAIO's are designed?
Well, first defining MAIO: Mobile Allocation Index Offset. It's
MAIO that designate the
initial position of frequency - among the frequencies available
in MA List, that list withthe frequency hopping. It is the
frequency that TRX uses so get hopping.
MAIO planning is straightforward if the number of TRX is small
compared to the length ofthe sequence of hopping.
For example, MAY 0 means that the TRX should use the first
frequency, or f1.
GSM Automatic Frequency Planning Tools
The concept of HSN and MAIO is important, and when the number of
TRX andfrequencies is small, we can even do planning 'byt
hand'.
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However, the best way - and always recommended - is to use
network planning toolssuitable for this purpose, as the AFP, from
Optimi, or Ultima Forte, from Scheme.
These tools can be configured with measurements collected from
the network (via BSSand / or Drive Test ), and with predictions
(calculations) built in that allow the creation
of a Interference Matrix. Based on this matrix, along with other
algorithms, it allow abetter design of parameters based on such
critical conditions in traffic load and access.According to
characteristics of each sector, they then provide the final
planning,including the possibility of simulations.
Conclusion
Knowing the concept of HSN and MAIO we can use them correctly in
our plans, and/or
do audits of our existing networks. For example, in two hopping
sequences, if we havethe same HSN and different MAIO, we guarantee
that they never overlap, or in otherwords, are orthogonal.
Another conclusion is that two channels with different HSN, but
with the same MA Listand at the same time slot, will interfere with
1 / n of bursts, where n equals the number
of different frequencies in the hopping sequence. This
conclusion is somewhat more
complex to see, and is due to feature pseudo randomly from HSN.
So if you haveinterest, deepen their studies of MAY and HSN.
Otherwise, just understand that it is why
we say that the Frequency Hopping somehow averages the
interference across thenetwork.
