3G overlapping cells in massive events

[Mdaf]

Hello, In events with massive number of outdoor users, is it useful to have more than 1 cell having same frequency serving the area? well for me I guess not because if you have high overlapping between two cells you will be forced that both cells will be in the active set most of the time which means same UEs are using SF128 from two cells at the same time....no resources saved
I have debate regarding this point and one of my colleagues suggested to make active set size=1 to save codes but for me it will cause interference since the overlapping is high and SHO will not take place....
Please help me and if anyone has experience I would be glad if you share...high number of users with 2 cells same frequency serving massive event with high overlapped area between the two cells.
note: the distance between the two cells is 150 meters and the users are located between two cells
Many thanks.

[khurrambilal01]

Hello, In events with massive number of outdoor users, is it useful to have more than 1 cell having same frequency serving the area? well for me I guess not because if you have high overlapping between two cells you will be forced that both cells will be in the active set most of the time which means same UEs are using SF128 from two cells at the same time....no resources saved
I have debate regarding this point and one of my colleagues suggested to make active set size=1 to save codes but for me it will cause interference since the overlapping is high and SHO will not take place....
Please help me and if anyone has experience I would be glad if you share...high number of users with 2 cells same frequency serving massive event with high overlapped area between the two cells.
note: the distance between the two cells is 150 meters and the users are located between two cells
Many thanks.

Hi,
You have to keep balance between Soft Handover Factor and interference.
SHO should be around 30-40% then you would have a balance between the two overlapping cells, resources would not be over-utilized because of SHO & interference would also be under control.

[Mdaf]

Many thanks but I'm talking about two cells separated by 150 meters only so I think it would be difficult to compromise between interference and SHO overhead where users are located between two cells....what do you think?
one more thing I have a very basic question but if you think about it it's really strange...for me :-)
if you have 2 cells with scrambling code x and another cell with scrambling code y, why when they are in active set they won't interfere each other ( I'm talking about DL not UL, UL is very clear and simple) in other words why SC x is interfering SC y in DL and if they are not together in the active set but they don't interfere each other if they are in the same active set. For example same rf conditions for x, and y , same cpich, rscp, same point in the field. If x and y not in AS we will have interference, x and y in AS no interference ......what is happening what am I missing.

[khurrambilal01]

Many thanks but I'm talking about two cells separated by 150 meters only so I think it would be difficult to compromise between interference and SHO overhead where users are located between two cells....what do you think?
one more thing I have a very basic question but if you think about it it's really strange...for me :-)
if you have 2 cells with scrambling code x and another cell with scrambling code y, why when they are in active set they won't interfere each other ( I'm talking about DL not UL, UL is very clear and simple) in other words why SC x is interfering SC y in DL and if they are not together in the active set but they don't interfere each other if they are in the same active set. For example same rf conditions for x, and y , same cpich, rscp, same point in the field. If x and y not in AS we will have interference, x and y in AS no interference ......what is happening what am I missing.

Actually when two SC x & y are in Active set, still they are creating some interference for each other but it's less as compared when they are not in AS; The reason is when SC x is there in AS and UE moves into coverage area where SC y is stronger or almost same, So power of SC x would be increased to continue the services (Power control) but if SC y is too in AS then the best serving cell would change and SC x power would be optimized (would not increase) so lesser interference would be there because of SC x.
I hope you understand.

[Weiland86]

Mdaf,

Don't get me wrong but you are missing the whole CDMA theory... a general view is like this... IS-95, CDMAOne, WCDMA are called self interference systems... this because they transmit at the same frequency and time... in these systems we have 2 kind of codes... channelization (orthogonals) and scrambling (quasi-orthogonals) codes which are use in different way in DL and UL... lets focus in DL from now on.
We use scrambling codes in order to identify cells while we use channelization codes in order to identify channels (control or traffic ones), so regarding your question... Basically we always have interference does not matter if you have 1,2 or 3 cells (SC) in the active set, this interference is called EcIo or EcNo usually the mean the same but in fact are not the same... anyways which is equal to

No SHO EcIo = 10 log10 ( RSCP "SC1" / sum (RSCP "all other SC which have presence in that point").

So we always have interference... if you only have 1 cell in the active set and the other cells have strong presence in that point the EcIo will have a bad value what happened when we are in SHO considering 2 cells in the active set we have 2 Radio links 2 different sources of information 1 link with each cell (SC) so the other cells are not causing you too much interference as before, now 2 cells are providing you resources and the EcIo calculating is a little bit different as follows:

SHO EcIo = 10 log10 ( RSCP 'SC1' + RSCP 'SC2' / sum RSCP 'all other SC which have presence in that point' )



key summary: we always have interference, So in SHO or not every SC is causing interference one to each other, if we are in SHO the advantage is that you have more than 1 Radio link at same time...which is better than just have one from a RF point of view.

Sorry i am about to sleep I wrote very fast I hope this clarify or help you in something

BR,
Weiland