Page 309 - From GMS to LTE

Long Term Evolution (LTE) and LTE-Advanced Pro 295

The following excerpt from an LTE SIB 1 message shows how the list of networks that
share an LTE base station looks in practice. It is interesting to note that the Tracking
Area Code and the Cell Identity are the same for both networks.

SystemInformationBlockType1:
[…]
CellAccessRelatedInfo:
PLMN Identity List
PLMN-Identity
MCC 310
MNC 260
cellReservedForOperatorUse notReserved
PLMN-Identity
MCC 311
MNC 660
cellReservedForOperatorUse notReserved
trackingAreaCode ‘10100101 00000001’
cellIdentity ‘00000100 11101011 10110000 0010’
cellBarred notBarred
[…]
When a mobile device connects to the base station it includes information as to which
core network it would like to communicate with. In UMTS this is done in the Initial
Direct Transfer message in which the first NAS message (Location Update Request) is
embedded as described in 3GPP 25.331, 10.2.16c. In LTE, the mobile device includes
the information in the RRCConnectionSetupComplete message, as shown in the
following excerpt:

rrcConnectionSetupComplete:
rrc-TransactionIdentifier 1
selectedPLMN‐Identity 2
registeredMME
mmegi ‘00000001 01011110’B
mmec ‘00010111’B
dedicatedInfoNAS ‘1704E61DA36[…]’

Based on the ‘selectedPLMN‐Identity’ field, the eNode‐B then decides which core
network and MME to establish a signaling connection to for this subscriber. This means
that the eNode‐B is connected to several core networks simultaneously. In practice only
one IP‐based backhaul connection is used and an IP router closer to the core network
infrastructure then provides connectivity to the MMEs and Serving‐Gateways of the
different core networks. Further details can be found in 3GPP TS 23.251 [29].

4.15.3 MORAN (Mobile Operator Radio Access Network)

Another approach to radio network sharing is to share the digital part of a base station,
the passive antennas and backhaul connectivity while each network operator uses their
own radio channels. This way, each network operator can use their own spectrum,