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Seemless handover between cell of the different bands is the basis for this article.It is intended to provide a cost effective and quality migration from dual band site to dual band cells.In particular i will be making reference to Ericsson’s RBS 2206.A full cabinet of RBS 2206 can be configured to allow dual band cells to share the same PCM link thus making handover between these cells on different band (900band and 1800band)seemless.A typical example is achieving 444/888 cofiguration using dual Band cabinets.3 cabinets are used each cabinet representing a cell for both bands( 900A & 1800DA),900B & 1800DB), 900C &1800DC).
Each cabinet use 1 PCM link (in this case the LAPD will be concentrated to take the maximum 12trxs permissible by a DXU in a cabinet. TG synchronisation across cabinet will not be necessary because the TG synch is done internally in individual DXU in each cabinet.I have personally integrated this and the result is fantastic.
I will do an update on this later.
ThanksI am very interested, waiting for your updates. Thanks.
Michael,
I’ve optimized such networks, with dualband cells. The “logical” principle is :
1800 cells are considered “inner zone”
900 cells are considered “outer zone”Are those the same thing than what you’re referring too ?
Since you’ve explained about the physical part, I’ll tackle the logical part.
Those cells are basically concentric cells, and the handovers between the 2 zones are seamless (but the HO thresholds are a bit tricky to find). The GSM1800 zone has naturally a smaller coverage than the GSM900 zone, because of radio propagation properties of those two different frequency bands. This is the reason why the 1800 zone is the “inner” zone.
The BCCH and SDCCH are always located in the outer zone (gsm 900), on top of TCH. The inner zone contains only TCH. Therefore a call can be setup only in the GSM900 zone.
HO from outer to inner is based on RX_LEV of the outer zone, it is a “better condition” HO. The level of the outer zone is too high, so the MS is handovered to the inner zone, for capacity purpose.
HO from inner to outer is based on RX_LEV of the inner zone, and it is an emergency HO (too low RxLev in inner zone, so the MS has to jump back to the outer zone to receive a good rx lev).
A MS in the inner cell will preferably make a HO to the outer zone, rather than to a neighbor cell, even if there is such a possibility.
Pix,
Just few things from my side:
Generally, for Nokia it is possible to use Common BCCH feature, which gives us opportunity to have only one cell with 2 bands. Usefull.
And I had official info from E/// and Nokia about SDCCH allocation for dual-band cells. It is possible to allocate SDCCH/8 at 1800 and 900 as well. So usage of SDCCH at inner cell also possible, if it required for some reasons(like traffic optimization for example).
I am not sure that allocating an SDCCH in the inner zone based only on the level of the RACH is reasonable, but it’s a decision you could make.
What do you think about quality HO from inner zone? In siemens HO based on Quality from inner to outer are not possible. You only could go to adjacent cell. does other vendors allow Q HO from inner to outer?SDCCH on inner zone is not recommended, but yeah, i guess that’s possible (not in alcatel though).
Vand’, in alcatel, the quality HO are available only when going from inner zone to neighbor cells, not inner to outer.
IMO, what is missing is the measurements of the RX_LEV(OUTER) when in the INNER zone, and the measurements of the RXLEV(INNER) when in the OUTER zone. Because of this, the inter-zones HO are based on an assumption of the RxLev in the target zone. In multiband cells, the inner zone (1800) is about 6dB to 10dB weaker than the outer zone (900), but it can’t be known precisely. And that’s a problem…
Plus, you can have different antennas/tilts between 1800 and 900 zones. It further increases the uncertainty of the rx_lev in the target zone (inner or outer).
The difference is more like 14 to 16 as you have 3 db from max power 30/33 and at least 10 db from propagation.
I was thinking in the DL way, but it’s correct that the MS will loose an additional 3 dB in uplink. That’s something I never thought about…
Which is the reason why I tend to observe a higher number of inner-outer HO due to UL level, than due to DL level. hmmm.. now all is clear 🙂Vanderley, could you explain that more clear:
“The difference is more like 14 to 16 as you have 3 db from max power 30/33 and at least 10 db from propagation.”
Thanks
Javi,
There is 10dB “natural attenuation” when you switch a transmitting source from 900MHz to 1800MHz (cf. free space propagation law). On top of that, keep inmind that a typical mobile station will emitt at a power of 30dB in 1800MHz and 33dB in 900MHz.
Therefore, in a dual band cell, in the uplink path, there is a loss of 13dBm (theory) between 900MHz and 1800MHz zones. In downlink, there is a 10dB loss (the BTS is still emitting at the same power).
Thank Pix.
I have another question and maybe you can help me.I’m working in a GSM 900/1800 network planification, so I have channels in both bands.
I’ll use GSM900 for coverage and GSM1800 for capacity. That’s ok, isn’t it?
The thing is, should I do concentric cells with the same structure in GSM and DCS? (number of sectors, azimut, height…)
Or should I put Omnis in 1800 band to give capacity to my network?
Thanks
hi javi,
omnis for capacity ? omnis are not really for capacity, they are mostly for cheap coverage (initial roll out, rural areas, etc…)
what i recommend you to do is to make dualband concentric cells :
for each site, you’ll have 1 or 2 chained BTS, with a mix of 900MHz and 1800MHz TRX.For instance, you can have a 3×2 in 900 and a 3×4 in 1800. For each cell:
Cell’s outer zone = 2 x 900MHz TRX (BCCH + SDCCH + TCH)
Cell’s inner zone = 4 x 1800MHz TRX (only TCH)And you connect each cell to a dualband crosspolar antenna (900/1800). So in the end, you have only 3 BCCH (=3 sectors), only 3 antennas, and a 3×6 site.
Hi Pix,
first of all, thanks a lot.I’ll do it in that way, but I have a restriction, I can only use up to 4 TRX per sector. SO, I’ll put 2 TRX in Outer zone and 2 TRX in the inner zone.
Thanks Pix
Hi All,
My network is E/// platform with 2×06 equipment. Our network have dual band as well. Majority are G1800 band but very few G900 band. Thus we use G900 for Coverage and G1800 for Capacity. I have sites use dualband with G18 max 12+12+12 but G9 max 2+2+2(due to limited G9 spectrum to be re-used). G9 congested easily due to set up calls being done G9 cells before HO to G18 cells (G18 band higher priority than G9 band). I had change the cell reselection criteria of the G9 cell to “disguise” the G9 cell 12dbm lower than the actual SS during idle mode so that majority call setup in G18 cells. What other setting can be done to offload the G9 cells to G18 cells beside expending the G18 cells by setting lower Layer Thres?
Can any Guru give any ideas?I think you can define seperate BCCH/SDCCH for 1800 so that calls may be setup directly in the Inner Cell when MS lies in the inner cell. You’ll have to define seperate cells for 900 and 1800 then.
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