Shared RAN deployment scenarios are an excellent opportunity for mobile network operators to lower their investments on both, network hardware and operational costs by sharing resources.
The MORAN approach where each operator continues to have its dedicated spectrum (= radio network cells) is easy to understand.
However, the Multi-Operator Core Network (MOCN) is a bit more complex, especially if one of the involved operators asks for service assurance KPIs that apply to its - and only its - subscribers. In this case it is a prerequisite to find out which "call" belongs to which core network operator to enable further KPI correlation and aggregation.
The figure below illustrates how this works:
The MORAN approach where each operator continues to have its dedicated spectrum (= radio network cells) is easy to understand.
However, the Multi-Operator Core Network (MOCN) is a bit more complex, especially if one of the involved operators asks for service assurance KPIs that apply to its - and only its - subscribers. In this case it is a prerequisite to find out which "call" belongs to which core network operator to enable further KPI correlation and aggregation.
The figure below illustrates how this works:
(click on picture for larger version)
In the System Information Block (SIB) 1 of the cell a list of PLMN-IDs is broadcasted followed by a single Tracking Area
Code (which can be combined each of the PLMN-IDs to get multiple TAIs) and a single Cell Identity.
Encoding is specified in 3GPP 36.331 (RRC) as follows:
SystemInformationBlockType1
::= SEQUENCE {
cellAccessRelatedInfo
SEQUENCE {
plmn-IdentityList
PLMN-IdentityList,
trackingAreaCode
TrackingAreaCode,
cellIdentity
CellIdentity,
The spec further defines that the ECGI is the CellIdentiy
combined with the first (!!!) PLMN-ID from the PLMN-ID List:
CellGlobalIdEUTRA field descriptions
|
cellIdentity
Identity of the cell within the context of the PLMN.
|
plmn-Identity
Identifies the PLMN of the cell as given by the first PLMN entry in
the plmn-IdentityList in SystemInformationBlockType1.
|
So there is one and only 1 ECGI per radio cell in the
network, but multiple PLMN-IDs and hence, multiple TAI, one fore each core network operator, are broadcasted.
During RRC establishement a particular UE signals on behalf on the selected PLMN-ID information element in the RRC Connection Setup Complete message to which core network operator shall be used.
This information is "translated" by the eNB into ECGI and TAI with different PLMN-IDs. While the ECGI displays the PLMN-ID of the operator that owns the RAN equipment the TAI shows the selected PLMN-ID of the UE's core network operator.
Related Posts:
- The 3G4G Blog: Quick tutorial on Mobile Network Sharing Options
- The 3G4G Blog: Mobile Network Infrastructure Sharing in Japan over Electric Power Infrastructure
- The 3G4G Blog: A practical use of MOCN in ESN
11 comments:
Ah - realised how it works. There can be a maximum of 12 different PLMN identities across the up to 12 sets of up to 12 identities. So presumably, valid examples would be: 3 operators each with 4 PLMN codes, 1 operator with up to 12 PLMN codes, or 12 operators with only one PLMN code each.
Your scenario is valid in case that the max number of PLMN Identities is 12. They all could belong to the same or different operators. At the end of the day it is a matter how the transport network and/or signalling traffic routing is designed between RAN and core.
According to 3GPP 36.331 the max number of PLMN-IDs in the PLMN-ID-List is 15 since Rel. 11. See ASN.1 encoding:
PLMN-IdentityList3-r11 ::=SEQUENCE (SIZE (1..16)) OF PLMN-Identity
Thanks for this blogger, it's very useful.
One question related to RPLMN and HPLMN in the shared network, RPLMN!=HPLMN. In this case, based on TS23.122, the RPLMN should be selected. How UE or eNB can route the attach/Registration request to the HPLMN's core? Thanks again.
When the MS reselects to a cell in a shared network, and the cell is a suitable cell for multiple PLMN identities received on the BCCH or on the EC-BCCH the AS indicates these multiple PLMN identities to .....The MS shall choose one of these PLMNs. If the registered PLMN is available among these PLMNs, the MS shall not choose a different PLMN.
Thanks for this blog, it's very useful.
One question: if both RPLMN and HPLMN in a shared network, and RPLMN!=HPLMN. In this case, based on 23.122. The RPLMN should be selected when sends out attach/registration request message, is it eNB routing this message to HPLMN core? Thanks.
Spec 23.122：
When the MS reselects to a cell in a shared network, and the cell is a suitable cell for multiple PLMN identities received on the BCCH or on the EC-BCCH the AS indicates these multiple PLMN identities to the NAS according to 3GPP TS 44.018 [34], 3GPP TS 44.060 [39], 3GPP TS 25.304 [32], 3GPP TS 36.304 [43] and 3GPP TS 38.304 [61]. The MS shall choose one of these PLMNs. If the registered PLMN is available among these PLMNs, the MS shall not choose a different PLMN.
TAC value is set by the RAN owned operator but in the example above the TAI value might overlap with the second operator values. How do the RAN operator configure TAC values in such scenarios and share them with other operators.
@Anonymous: There is contractual (legal) agreement between the two operators to share RAN/radio resources and how to do it.
According to this agreement there are two (or more) PLMN-IDs+TAC broadcasted (RRC SIB - see my older comment above) in the same cell.
The UE (depeding on the IMSI PLMN-ID on its SIM card) indicates in RRC Connection Setup Complete which PLMN-ID+TAC it belongs to and hence, to which MME/HSS it shall be connected while using the same radio/RAN resources as UEs belonging to other PLMNs.
@无茗茶舍: Sorry for my late answer. RAN-Sharing and Roaming are two different, decoupled processes. This is true also for the legal contracts between operators. There is one contract for RAN sharing and other contracts for roaming.
Does anyone know if in the 5G NR we can support multiple cell Identities per cell? Which means can we have one cell identity per PLMN in the same cell?
Yes, it should work in 5G SA Networks in the same way as described in this blogpost. You can Broadcast multiple PLMN IDs in each physical cell.
For Implementation of MORAN. If Guest Operator has 15MHZ frequency Band and Host operator has 20 MHZ frequency band. Can guest Operator's RRU support for both operator's frequencies with same Bandwidths i.e 15 & 20. If Yes How? and If not ? what HW level changes need to be made to fully utilized the frequency bands of both operators.
I am preparing a new Blog Post dealing with MORAN implementations. Stay tuned.
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