Relation between BSIC and CELLID


#1

Hi!
I’m doing a survey of the existing cellular antenna towers in my city. Using a 2G chip (SIM800L) and with an AT command (AT + CENG) I get a list of the closest towers.

Analyzing the data of a single cellular company I see the following:

-I read the LAC, BSIC and the CELLID, among other data.
-The LAC is unique in the whole area. So it’s not a problem
-I need to identify a tower with a unique code, so I assume that the BSIC should be a unique number for each tower. And that there could be several CELLID in each tower.
-I see in the obtained data that there are CELLID’s that are repeated in different BSIC.

I do not understand the relationship between BSCI and CELLID.
Any help with this?


#2

Hi Mariano,

The Base Station Identity Code is a component of Synchronization Channel (SCH) that provides information needed to search base stations, identify them and synchronize with them.

BSIC = NCC + BCC (Network Colour Code + Base Colour Code)
It contains 8 bits and is Primarily used to differentiate between operators utilizing the same frequencies.

There are 4 basic parts of a cell identifier: MCC-MNC-LAC-CID
MCC-MNC is set by International Telecommunication Union. All telecom firms have access to this information as it is publicly available.
LAC-CID can be decided by the telecom firm. This is an internal decision and telecom firms don’t share this with each other

LAC:
This is decided by a telecom firm based on its own logic. Some telecom firms decide on LAC by region, others by a cluster. If a large amount of CID’s belonging to a particular telecom firm are in a particular area, all these will likely have the same LAC. This helps telecom firms organize information.
CID:
This is a unique id assigned to a physical cell unit.

If your survey isn’t related to frequency/ Synchronization channels, just looking at MCC-MNC-LAC-CID would be good enough.


#3

Mariano,

Refer to Sagar’s information. These are correct in general.
However, how BSIC are planned is dependent of the strategy of the operator.
Not always a site will hv the same BSIC.
When MAIO hopping is used, we may or not maintain similar BSIC for same site.
At the same time if SYNC hopping is used, we either maintain BSIC or change the HSN or vice versa.
Thats how the planning is done for 2G systems.

The trick of using these database is to know an detect these changes and then there will be historical changes seen in terms of operator strategy. I am doing a research on this as well.

As for LAC, it is always keep large however certain times it will be smaller. This is dependent on traffic pattern. If loading is high it is wiser to keep it small as lots of location updates occur especially at the border. Wherever there is 3G or 4G present the situation get more difficult.
There is a measure called Inter-RAT to measure these occurrences. We keep this counter as small as possible.
The LAC border is a crucial setting for billing purpose.
Good luck