lte imp

1. LONG TERM EVOLUTION (LTE)
25.2 INTRA-FREQUENCY AUTOMATIC NEIGHBOUR
RELATIONS
 Intra-frequency neighbours can be defined automatically as part of the normal intra-frequency handover procedure. The
addition of a neighbour increases the handover signalling requirement but once added, the neighbour can be used by all
other UE
 The intra-frequency handover procedure starts when the serving eNode B sends an RRC Connection Reconfiguration
message which instructs the UE to start intra-frequency measurements. This is illustrated in Figure 121
 Intra-frequency measurements for handover could be based upon reporting event A3, i.e. triggering the UE to send a
Measurement Report when a neighbouring cell becomes better than the serving cell by a specific offset
UE in RRC Connected mode with serving eNode B
RRC Connection Reconfiguration
(configure measurements)
eNode B
PCI = 3
Measurement Report
(report PCI=9 and RSRP)
RRC Connection Reconfiguration
(request Global Cell Identity)
Measurement Report
(report Global Cell Identity)
eNode B
PCI = 9
UE identifies PCI=9 and
measures RSRP
UE reads Global Cell Identity
from SIB1 on PDSCH
PCI
1
2
4
7
eNode B checks whether or not PCI=9
is already within neighbour database
Neighbour
database
Neighbouring eNode B
UE
UE in RRC Connected mode with serving eNode B
RRC Connection Reconfiguration
(configure measurements)
eNode B
PCI = 3
Measurement Report
(report PCI=9 and RSRP)
RRC Connection Reconfiguration
(request Global Cell Identity)
Measurement Report
(report Global Cell Identity)
eNode B
PCI = 9
UE identifies PCI=9 and
measures RSRP
UE reads Global Cell Identity
from SIB1 on PDSCH
PCI
1
2
4
7
eNode B checks whether or not PCI=9
is already within neighbour database
Neighbour
database
Neighbouring eNode B
UE
Figure 121 – Intra-frequency automatic neighbour relation definition (part 1)
 The UE searches for neighbouring cells, identifies their Physical Layer Cell Identities (PCI) and measures their RSRP
(and/or RSRQ). The UE then follows the instructions of the eNode B in terms of reporting, e.g. when a reporting event is
triggered
 The eNode B receives the neighbour cell measurements and decides whether or not the UE should complete a handover. If
a handover is to be completed, the eNode B checks whether or not the reported PCI is included within its existing
neighbour database
o if the PCI is included then the eNode B proceeds with the handover procedure in the normal way (as described within
section 23.5)
o if the PCI is not included then the eNode B proceeds with the automatic neighbour relation definition procedure
The remainder of this section assumes that the automatic neighbour relation definition procedure is initiated
 The eNode B uses a further RRC Connection Reconfiguration message to instruct the UE to read the Global Cell Identity
from the target cell. The UE is also instructed to read the Tracking Area Code and list of PLMN Identities
 The UE reads the requested information from SIB1 on the PDSCH. This requires the UE to first read the MIB on the
PBCH and then the Downlink Control Information (DCI) on the PDCCH. The information is reported back to the eNode B
using a Measurement Report message
 The serving eNode B uses the Global Cell Identity to request the X2 Tunnel Configuration from the MME (assuming an
X2 connection to the neighbouring eNode B does not already exist). The information is requested using an S1 Application
Protocol (S1-AP) eNode B Configuration Transfer message (shown in Figure 122)
 The MME uses the Global Cell Identity to interrogate the target neighbouring eNode B for its X2 Tunnel Configuration.
This is done using an S1AP: MME Configuration Transfer message
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2. IN BULLETS
 The neighbouring eNode B responds to the MME, which then allows the MME to forward the requested X2 configuration
information to the serving eNode B
Serving eNode B
S1AP: eNode B Configuration Transfer
- SON Information Request
- X2 TNL Configuration Info
eNode B
PCI = 3
eNode B
PCI = 9
S1AP: MME Configuration Transfer
- SON Information Request
- X2 TNL Configuration Info
MME
S1AP: MME Configuration Transfer
- SON Information Reply
X2 TNL Configuration Info
S1AP: eNode B Configuration Transfer
- SON Information Reply
X2 TNL Configuration Info
Neighbouring eNode B
X2AP: X2 Setup Request
X2AP: X2 Setup Response
Update
Neighbour
DatabaseUpdate
Neighbour
Database
IPSec Tunnel Establishment
SCTP Connection Establishment
Serving eNode B
S1AP: eNode B Configuration Transfer
- SON Information Request
- X2 TNL Configuration Info
eNode B
PCI = 3
eNode B
PCI = 9
S1AP: MME Configuration Transfer
- SON Information Request
- X2 TNL Configuration Info
MME
S1AP: MME Configuration Transfer
- SON Information Reply
X2 TNL Configuration Info
S1AP: eNode B Configuration Transfer
- SON Information Reply
X2 TNL Configuration Info
Neighbouring eNode B
X2AP: X2 Setup Request
X2AP: X2 Setup Response
Update
Neighbour
DatabaseUpdate
Neighbour
Database
IPSec Tunnel Establishment
SCTP Connection Establishment
Figure 122 – Intra-frequency automatic neighbour relation definition (part 2)
 The serving eNode B proceeds to establish an IPSec tunnel and an SCTP connection towards the neighbouring eNode B.
Once this has been completed, the two eNode B are able to signal to one another using the X2 Application Protocol (X2-
AP)
 The serving eNode B forwards an X2-AP: X2 Setup Request to the neighbouring eNode B. This message specifies
neighbour cell information in terms of Global Cell Identity, PCI and RF carrier. Upon reception, the neighbouring eNode
B adds the specified neighbour information to its database
 The neighbouring eNode B responds using an X2AP: X2 Setup Response message which allows the serving eNode B to
update its own neighbour database
 An X2 connection then exists between the two eNode B and the intra-frequency handover can proceed as normal
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