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BCCH Adjacent frequency

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  • #53154 Reply
    Alex
    Guest

    In some cases I see adjacent frequecies of BCCH frequency by TEMS pocket which is whitout any Cell ID.When I lock on these frequency,MS couldn’t find the network.Also RxLev of them are very good.
    My question is :
    1-Why there is such this adjacent freauency?
    2-If it is because of a faulty in hardware,which part of RBS may cause it?

    Thanks

    #53155 Reply
    pix
    Guest

    TEMS can measure the adjacent frequencies of the serving frequency. It will just measure the RXLEV, not taking care about which cell uses this frequency (as far as i know !).

    When you lock on this frequency, you should be to camp on it and setup a call … if this is a BCCH frequency !

    Are you sure it’s BCCH ?

    If it is BCCH, then which cell is it ? maybe the cell is too far, or suffer very very bad interference in the area where you try to perform this drivetest.

    #53156 Reply
    Alex
    Guest

    Thanks Pix,
    Suppose we are near a cell with a TEMS and we know the BCCH of it,for example BCCH=25.
    I mean MS not only measures this ARFCN(25)and camps on this cell but also MS measures two adjacent frequencies which are 24 and 26.
    There is no any external interfernce.I found it by changing the BCCH (for example to 32) so I could see two adjacent frequencies again (which are 31 and 33).
    What is your idea now?

    #53157 Reply
    Pix
    Guest

    Alex,
    What you are explaining is correct. I don’t really understand your problem ๐Ÿ™‚

    What do you mean by external interfernce ?

    Adjacent channels will interfer the BCCH 25 only if they are received 6 to 9dB stronger than the freq. 25.

    #53158 Reply
    resonance
    Guest

    dear alex

    if interference is high than you r not able too decode the bsic of any particular bcch and you will not be able to make call on that bcch. is that explain your problem

    #53159 Reply
    Alex
    Guest

    I mean two adjacent frequencies(ARFCN-1,ARFCN+1)of BCCH frequency(ARFCN)propagate from antenna so I can visit them by TEMS but I couldn’t camp on.
    I guess there would be a problem with Antenna or RBS(but I don’t know which part of RBS also).
    Hi Pix,
    this site is a stand-alone site and there is no any interference around it.

    #53160 Reply
    rf fan
    Guest

    Hi Alex,
    Frist you must check your measurement equipment. May be you phones are broken …

    If everything is OK and this happening only few BTS’s , may be there is a problem with BCCH TRX. (Bad RF fiter or someting else).

    Do you have declared adjacent’s with ARFCN +/- chanel on this cell ? If you don’t have, but your phone measure ARFCN +/- , problem is clear ๐Ÿ™‚

    #53161 Reply
    pix
    Guest

    alex, can you give some numerical values :
    rxlev(arfcn-1)=
    rxlev(arfcn)=
    rxlev(arfcn+1)=

    if there is no other GSM cells than this cell, then there are three possibilities :
    – external interferer (army radars ?)
    – faulty BTS (leaky rf filter, as suggested by rf fan)
    – faulty TEMS (or TEMS with undesired behaviour, to be politically correct…)

    #53162 Reply
    Alex
    Guest

    Thanks rf fan and Pix,
    I am sure that problem comes from faulty RBS because I changed the BCCH number but the situation was the same.
    By the way,Which part of RBS may cause this peroblem?

    BR,
    Alex

    #53163 Reply
    rf fan
    Guest

    I suspect BCCH TRE – but next step (if this doesn’t resolve problem) are to replace ANC ….

    #53164 Reply
    pix
    Guest

    i’ll not answer any other question if you don’t give me the rxlev values ๐Ÿ˜€

    but i’m surprised that radio frequency leaks so strongly on adjacent channels… that’s why i’m asking the values..
    when you check out other BTS, the adjchannels are weaker ?

    #53165 Reply
    Alex
    Guest

    Hi,

    Pix,
    Suppose I am under BTS and measuring the BCCH’s frequency,so results are as belew:

    BCCH Freq.(ARFCN=25) ….RxLev=-37 dbm
    Adj1 Freq.(ARFCN-1=24)…RxLev=-41 dbm
    Adj2 Freq.(ARFCN+1=26)…RxLev=-40 dbm

    rf fan,
    What do you mean about “ANC” ?

    #53166 Reply
    rf fan
    Guest

    Combiner + Equalizer + SomeFilters and control blocks in our vendor is in Block called “ANC”.

    Wich is your vendor ?

    #53167 Reply
    Alex
    Guest

    Hi rf fan,

    Ericsson is vendor here.

    #53168 Reply
    Pix
    Guest

    Alex,

    ANC meanss Antenna Network Combiner (in alcatel-lucent).

    Thx for the values… interesting problem.

    Have you activated the SFH perhaps ?

Viewing 15 posts - 1 through 15 (of 20 total)
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