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cell Reselect Offset

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  • #53222 Reply
    m@u
    Guest

    Hi guys,

    What is the recommended (default) cell reselect offset value?
    In my Nortel Network I have it at 4dB and for some traffic balancing the high band (1900) was changed to 8dB.
    Of course during a drivetest with TEMS I noticed that too that the difference between C1 and C2 is the same offset, but. Shouldn’t it be 0dB for 850 and then only 4dB for 1900?

    Please advise.

    m@u…

    #53223 Reply
    pix
    Guest

    m@u,

    you are right, what matters in the cell reselect offset is just the difference between one cell and the other.

    whether CRO(A) = 30 and CRO(B) = 34

    or

    CRO(A) = 0 and CRO(B) = 4, in the end, it still means that cell B is seen 4dB stronger than cell A.

    So whether you put 4dB and 8dB, or 0dB and 4dB, it will not change anything. But perhaps you missed out some cells which are set at CRO=0 dB or 2dB ?

    #53224 Reply
    m@u
    Guest

    I knew that you were going to answer pix, hehehe. U tha man.

    OK but here is the real problem:

    At the edge of the cells when the real signal RxLev(A)=-100dBm (measured with a scanner and CRO(A)=8 we will have -92.

    And there is another cell with RxLev(B)=-94dBm, CRO(B)=0dB from which we will have, then the phone will go to cell A and setup calls with A instead with the real best server cell.

    And I also noticed that the HandOvers are also affected by this offsets, so, your call will handover to a probably worst cell (due to the CRO) than to a good one.

    Is there any other way to do traffic balancing between bands?
    I’ve tried CRO and HO params to move or keep more traffic in the 1900 cells than the 850. But seems that the performance is affected.

    #53225 Reply
    pix
    Guest

    no, cro cannot affect HO detections. In your example, after call setup, it’s highly probable that the call will HO to cell B. If it doesn’t, it means your HO parameters were modified.

    What you say in the end is already the answer. When you introduce 1900MHz within a 850MHz network, you expect the new band to capture the traffic. So you put higher CRO’s, force HO from 850MHz to 1900MHz and restrain HO from 1900 to 850.
    1900 provides better capacity and cleaner frequencies, normally..

    But by doing such a “1900” oriented network, you might certainly degrade your radio quality. So you must find a compromise : push most traffic to 1900 (not all), in order to load this frequency band in such a way that the radio quality in both bands are equivalent.

    See, loading 1900 at 80% and loading the 850 at 50% might provide equivalent radio quality. (the more you use the frequency band, the more interference)

    Optimization of such multiband network is driven by traffic sharing first, and radio quality in second.

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