How UE can distinguish b/w two eNBs for intra frequency measurement in LTE

Question

If two carrier frequencies are same then based on what does UE distinguish between them. Is there any UMTS kind of distinction based on a separate pilot channel or separate D/L scrambling code ?

Answer 1

In case of intra frequency measurement, UE reports PCI(physical cell Indenity) of neighbor enodeb and also tell about CellGlobalIdentity to eNB. All the possible target enodebs around source eNB will use different PCI value. In LTE frequency reuse factor is 1, means all enodeb can use same frequency then only PCI is the parameter which helps to differentiate among eNBs over the air and from core network point of view every eNB is identified by CellGlobalID (PLMN+ cell Identity).

Comments

As in this case it is intra frequency ,So whether ENB externally need to configure measurement object for other ENB or..... UE can detect these cells (As same frequency) and Report to ENB about the detected PCI and his RSRP and RSRQ as part of neighboring cells ???

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As part of normal attach procedure, eNB configures measConfig for an UE within the rrc connection reconfiguration. In something gets changed at the network side and eNodeB get to know new neighbor list. It again configures a measConfig for the UE and sends within the rrc connection reconfiguration message.

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"If something gets changed at the network side and eNodeB get to know new neighbor list"

How ENB came to know about new neighbor (Only way if OAM is goving him info) otherwise UE can measure the cells as Other cells are operating with the same frequency with different PCI.

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Yes OAM or EMS can inform to eNodeB about the new list of neighbors .

Answer 2

On decoding PSS (Primary synchronization signal) and SSS (secondary synchronization signal) the UE can identify the cell IDs of the eNBs. The cell-specific reference signals (pilot signals), which are used by UE for measurements, are different for different cell IDs. So based on the cell ID, UE can generate the correct cell-specific reference signals. There is more information in 36.211 section 6.10.1.1.