Location Area Update in Cell_pch/URA_PCH

[rosan]

Hi There,

When a UE is in URA_PCH or Cell_PCH and crossing a RNC boundary then at which point it does the location area update?
Only after SRNS RELOCATION stated for PS or independent of PS?

Thanks.

rosan

[tarek_gara]

Hi Rosan, Try to search for MIB sig contining TAG flag... and Sib1

[rosan]

TAG flag changed when SIB got changed in a cell. How it relates to this?

rosan

[tarek_gara]

Ues may not try to decode all the SIBs, so to decode SIB1 (containing PLMN, LAC, RAC...) MIB (BCCH) should have diff TAG values, to perform cell update and if new LAC to also perform LAC update, that is why if same TAG value into 2 inter-lac Cells, Ue could not perform LAC update.

[rosan]

Ok. I'll check that. But I could see it was decoding the SIB-3,5,7 etc from neighbouring RNC cell. Have you seem a case where inter RNC cells had same value Tag?

[tarek_gara]

yes, it is coming from wrong TAG list planning...

[rosan]

Never heard of TAG list planning.

rosan

[tarek_gara]

whuch vender ? in huawei and ericson it exists.
and you can check in 3GPP.

Description :

Minimum PLMN tag value corresponding to a RAC. It is defined by the operator.The PLMN value tag is contained in the Master Information Block (MIB) and System Information Block 1 (SIB1) as an information element. The PLMN value tag in the MIB changes after an SIB1 is updated. After the UE detects the change in the PLMN value tag, it automatically reads the new SIB1.
When a UE moves between neighboring cells that belong to different LAs or RAs, the UE needs to read the SIB1 of the destination cell to initiate a location update procedure, which requires that the two cells have different PLMN value tags.
Therefore, during network planning, different value ranges should be allocated to the PLMN value tags of any two geographically neighboring areas (including scenarios where one area is part of the other area). The two areas can be two LAs, two RAs, or one LA and one RA.
During parameter configuration, the PLMN value tags of different value ranges should be assigned to any neighboring areas after negotiation. There is no intersection between the value ranges. The area can be an LA or RA. The PLMN value tags of LAs or RAs vary within the specified range. As a result, a UE can always read different PLMN value tags when moving across the areas and thus correctly reads the SIB1.
Note:
In practice, if a cell supports PS services, the PLMN value tag of the cell varies within the specified value range of the RA to which the cell belongs. If a cell does not support PS services, the PLMN value tag of the cell varies within the specified value range of the LA to which the cell belongs. For detailed information of this parameter, see 3GPP TS 25.331.

[rosan]

That is a very good explanation. Is it from a vendor documentation? My vendor is Nokia.

rosan

[tarek_gara]

this from Huawei description.
the only thing that we can find in Nokia is :

There is a huge amount of SIBs, which have to be read by the UE. This requires a lot of battery power. Therefore, a Master Information Block (MIB) was introduced, which gives references and scheduling information about the SIBs. The MIB is transmitted in every 8th radio frame on the P-CCPCH (on position SFN mod 8 = 0, and with a TTI of 20 ms). For most of the SIBs used within the system, the MIB may carry a value tag. The only exceptions are SIB 15.2, SIB 15.3 and SIB 16. If a value tag is unchanged, the corresponding system information has not been modified. Thus, there is no need for the UE to read the SIB. SIB 7 has no value tag. It changes with each occurrence. Scheduling information is used to inform the UE, where and when a specific system information is transmitted.