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Frequency Planning

This topic contains 15 replies, has 0 voices, and was last updated by  majid 2 months ago.

Viewing 15 posts - 1 through 15 (of 16 total)
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  • #50812 Reply

    Abdel

    Hi guys,

    I would like to know whether the below mentioned paragraph is possible or not.

    GSM900 Band
    There are 42 channels, starting from 83 to 124. They will be divided into 2 parts for different purposes as below:
     BCCH channels (84, 86, …124) 21 even channels.
     TCH channels (83, 85, …123) 21 odd channels.
    And then Frequency hopping is activated. Therefore is it possible to mix the BCCH and TCH together? In my opinion I think it is not recommended better to isolate the BCCH channels from any adjacent TCH. What do you think guys?
    Thanks

    #50813 Reply

    Huawei RF

    Well, it depends on several parameters..
    1- You should make sure that the 21 channels can support a BCCH plan pattern looser than 4X3
    2- Mixing the BCCH and TCH channels in adjacent way will expose them to adjacent channel interference. While if you isolate them you will not have this problem, besides a small interference with 4X3 pattern.
    3- remmember that the number of TCHs should be more than 2 times the number of TRXs in a cell to get good frequency hopping gain.

    rnp_rno_engineer@yahoo.com

    #50814 Reply

    Abdel

    Hi Huawei RF,

    Thanks for ur reply. Yes the frequency re-use is much looser it is 7×21 but the problem is the sites are very close together and may generate interference so it needs a sharp optimization on all the coverage of all cells to avoid interference.But I am wondering if you still can isolate the TCH from the BCCH why I use this technique?
    “remmember that the number of TCHs should be more than 2 times the number of TRXs in a cell to get good frequency hopping gain.” I think 50% Frequency hopping load is not bad but it is recommended not more than 35% for a better quality.

    Thanks

    #50815 Reply

    m@u

    It is possible to mix BCCH with TCH channels, but not recommended.

    As “Huawei RF” says It’s better to reduce the BCCH channels to 4×3 to have more TCH hopping channels with that you can even create more lists of hopping for different purposes.

    #50816 Reply

    Huawei RF

    I didn’t really get what you mean by 7×21… may be u mean 21×3?
    Which means that there is no reuse at all??

    What is the average distance between two sites for this network?

    #50817 Reply

    Pix

    Abdel,

    It looks like you’re going to perform a manual frequency planning, right ? That’s why you’re trying to find a way to split your frequency band in two parts : BCCH & TCH.

    If you choose to alternate BCCH and TCH, as you said, the main problem I can see is that you have to be extra-careful : it might be easy to make a mistake and plan adjacent BCCH/TCH in the same site, or even in the same cell.
    Otherwise, if you are extra-careful (and i’m sure you are), this is an interesting approach.

    Quite original, but that might actually work, if you can ensure that your C/I stays above -6dB (limit of adjacent interference impacting the radio quality). In other words, you need a good cell planning with sharp borders.

    But additionally (that’s what everybody is talking about in this post), it is surprising to see as many BCCH’s as TCH’s frequencies. Unless you have only 2 TRX per cell, this can’t work : your BCCH quality is going to be too good, and your TCH quality too bad.

    As a rule of thumb, if you plan 1 trx BCCH + 3 trx TCH per cell, you should have 2.5 to 3 times more frequencies for TCH than for BCCH (approx.). For “easy” manual planning, it should be 3 times more.

    I hope it helps… regards,
    pix

    #50818 Reply

    Abdel

    Hi pix and Huawei RF,

    One guy came up with this proposal to mix up the TCH and BCCH and I don’t know why he is trying to use these technique. That is why I asked you guys. Planning manual is a bit difficult but I often use the ILSA automatic Frequency planning tool from Aircom which is part of their enterprise suite. After that I make some adjustments of the ILSA output.
    “I didn’t really get what you mean by 7×21… may be u mean 21×3?” No I made a mistake we are using fractional reuse 1×3 pattern.
    The distance between our sites are 200-400m.

    #50819 Reply

    zoy

    Hi Abdel,

    Would it be possible to have the ILSA automatic Frequency planning tool from Aircom.

    #50820 Reply

    zoy

    This tooL ILSA is part of the Asset3G the planning tool of aircom. This tool greatly depends on the planning parameters and radio propagation. Therefore, ILSA needs the ASSET3G.

    #50821 Reply

    ZAPH

    can anyone explain what is this 4×3, 7×21, 21×3, 1×3……..

    is it related to frequency planning as “freq x no.of sites” or something else

    plz explain clearly so that funda may be clear in one reading..

    thanx

    #50822 Reply

    Shaon

    7×21-is it posssible?

    #50823 Reply

    Pankaj

    I we have less BCCH frequency available and there is more sites to plan BCCH frequency,then hw could i reduce the inetrference…..???

    #50824 Reply

    Mickey

    Hey Pix,

    Hope you are doing good,Thanks for your valuable answers.

    Below you mentioned TCH Freq should be 3 times more than BCCH, does it means, Suppose i have total 75 Channels,And my Avg TRX per cell is 6, then TCH should be 6*3, i.e minimum 18.
    I want to know what is the exact calculation for No.of BCCH if there is any Technical Calculation to this.
    Can i keep like this : Out of 75 Channels – BCCH 28, TCH 47 (it will also fulfill (No. of TRX * 3) crieria.

    What you say ?

    #50825 Reply

    Pix

    Hi Mickey

    With so many ARFCN available, you don’t need to worry. It would be interesting to keep 5 to 8 ARFCN not used, for future TRX extension, or new cell integration.

    The way to split the band between BCCH and TCH depends on how many TRX per cell.
    My example was for 4 TRX per cell, in which case you give 30% of band to BCCH and 70% of band to TCH.
    In your case, with 6 TRX per cell, I would give 20% to BCCH band, 72% to TCH band, and 8% free, reserved for future use.
    There is now several automatic frequency planning tools, based on radio measurements. It’s usually a tool provided by the vendor (EFO for Ericsson for example). I’m currently using extensively EFO for creating frequency planning on ALU, Huawei, Ericsson on Nokia networks. The results are just incredible.
    It’s way more efficient to do a FP using such tool rather than doing it manually. And the resulting KPI… well, they are amazing 🙂

    Rgds, Pix.

    #50826 Reply

    APZ

    One thing I am not clear, in BCCH planning the carrier spacing between
    the cells among intra cells of same site and inter cells of adjcent sites should be 400 Khz , some say
    1 Mhz to avoid Co-channel and adjacent channel interference. How about TCH channal assignments ?
    In principle, the spacing between
    BCCH and TCH of same sites must be
    at least 400Khz, Is there any principles of TCH frequency planning
    among the cells of same site and inter cells of adjacent cells of adjacent sites ? If have, I would pleasure to learn it

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