4G/LTE - Non 3GPP Access

 

 

 

Non-3GPP Based Technology

 

In the past, most of the technologies implemented and commericalized are based on 3GPP specification. Meaning there are explictely defined specification first and then chipset maker/UE maker implement those features based on 3GPP specification. But recently I see the requirement in the market or from network operators are going even faster than formalization of 3GPP specification. So quite often I see some advanced chipset maker and UE makers are working on a lot of projects that is not even described in the 3GPP specification. When I say '3GPP' in this case, it means 3GPP 'TS' specification. There may be something going on in 3GPP at the level of discussion/forum or even at the level of 'TR' (Technical Report).

Followings are some of the features/technologies that belongs to this category as of my writing (Aug 2014)

  • Dual SIM/Multi SIM
  • U-LTE (LTE in Unlicensed Spectrum)
  • SON (Self Organizing Network)

The picture has changed since 2014. All three technologies later entered 3GPP TS specifications. LAA brought LTE into unlicensed spectrum in Release 13, and 36.300 now describes the SON functions in clause 22. Multi-USIM support followed in Release 17. Each section below keeps the original note and adds where the technology ended up in the specifications.

Followings are the topics to be covered in this page.

Dual SIM/Multi SIM

A dual SIM phone holds two subscriptions, but it usually has only one receiver chain. While it listens to one network, it can miss a page from the other. For years each chipset maker handled this in its own way, and that is why the page counted dual SIM as a non-3GPP technology.

3GPP addressed this in Release 17 under the name Multi-USIM. 23.401 v20.0.0 clause 4.3.33 defines a Multi-USIM UE as a UE with several USIMs that keeps a separate registration state with a PLMN for each of them. The UE uses a separate IMEI for each USIM when it registers. On the radio side, 36.331 added MUSIM support for LTE in v17.0.0.

The standard does not remove the single receiver. Instead, it gives the UE ways to tell each network about the conflict. The UE indicates the Multi-USIM features it supports in the Attach or Tracking Area Update, and the MME answers with the features the network supports. The UE may use only the features that the MME confirmed.

Clause 4.3.33 lists the features. With Connection Release, the UE asks to go back to ECM-IDLE on one USIM because of activity on the other. With Reject Paging Request, the UE answers a page with an indication that it will not accept it. Paging Cause Indication for Voice Service adds a Voice Service Indication to the page when it is for the MMTel voice service. Paging Restriction lets the UE limit the pages it wants to receive. Finally, a Requested IMSI Offset moves the paging occasions of one USIM, so that they do not collide with those of the other.

  • Multi-USIM since Release 17 : 23.401 clause 4.3.33 and MUSIM in 36.331 v17.0.0.
  • One IMEI per USIM : each registration is separate.
  • Features are negotiated : the UE uses only those the MME confirms.
  • Paging collisions solved by signalling : IMSI offset, reject paging, paging restriction.

U-LTE - LTE in Unlicensed Spectrum

Operators wanted more capacity than their licensed spectrum could give, and the 5 GHz band was free to use but already full of Wi-Fi. The question in 2014 was how LTE could share that band without harming Wi-Fi. The links below are from that time, before 3GPP had settled the answer.

The answer was Licensed-Assisted Access, or LAA, which 36.300 introduced in v13.2.0 for Release 13. 36.300 v19.2.0 clause 5.7 defines LAA as carrier aggregation with at least one SCell in unlicensed spectrum. So the licensed PCell always stays in the configuration, and the unlicensed carrier only adds capacity. The LAA SCell uses frame structure type 3, which 36.211 v19.3.0 defines in clause 4.3.

The key difference from plain LTE is Listen-Before-Talk. Before the eNB or the UE transmits on an LAA SCell, it senses the channel and transmits only if the channel is free. Clause 5.7.1 defines four Channel Access Priority Classes and maps the standardized QCIs onto them. The channel access procedures themselves are now in TS 37.213.

Later releases added uplink LAA. 36.213 schedules it with DCI formats 0A, 0B, 4A and 4B, and the uplink grant tells the UE which type of channel access to use. The same ideas carried over to NR in unlicensed spectrum, which also uses 37.213 for channel access.

  • LAA since Release 13 : 36.300 clause 5.7, introduced in v13.2.0.
  • Unlicensed SCell, licensed PCell : carrier aggregation keeps the anchor in licensed spectrum.
  • Listen-Before-Talk : four channel access priority classes, procedures in 37.213.
  • Frame structure type 3 : 36.211 clause 4.3.

SON - Self Organizing Network

SON automates work that engineers used to do by hand. That covers configuring a new eNB, building neighbour lists, and tuning handover and load. The question the author raises is how much of that work 3GPP has actually standardised, and the answer below shows it is only part of it.

You may not agree that I call SON as 'Non 3GPP based technology' because you might have heard about this for so many years and you might have beeing testing some of SON feature. I agree that some of the component technology that can be a 'PART' of SON like ANR, but SON as a fully integrated technology has not reached 'TS' level specitication. Even the latest 3GPP document 36.902 is 'TR', not 'TS'.

36.902 is still a TR, as the author notes. However, 36.300 v19.2.0 clause 22, Self-configuration and self-optimisation, now describes the SON functions in the stage 2 TS. Self-configuration covers the dynamic set-up of the S1 and X2 interfaces, the ANR function in clauses 22.3.2a to 22.3.4b, and a framework for PCI selection in clause 22.3.5. Self-optimisation covers Mobility Load Balancing in clause 22.4.1 and Mobility Robustness Optimisation in clause 22.4.2.

The author's point still holds in part. The specification defines the procedures and the information that eNBs and UEs exchange, but the decision logic stays with the implementation. For example, the PCI can come from a centralized or a distributed assignment through OAM, and clause 22.4.1.1 states that triggering the load balancing functions is optional and depends on implementation. So SON as a complete product is still built by each vendor on top of these standard parts.

  • 36.902 is a TR : the use cases.
  • 36.300 clause 22 is TS : self-configuration and self-optimisation.
  • ANR, PCI selection, MLB and MRO : standard procedures and signalling.
  • Algorithms left to vendors : triggering and decisions depend on implementation.

Reference

[1] 3GPP TS 23.401 v20.0.0 - clause 4.3.33, Support for Multi-USIM UE

[2] 3GPP TS 36.300 v19.2.0 - clause 5.7, Licensed-Assisted Access, and clause 22, Self-configuration and self-optimisation

[3] 3GPP TS 36.211 v19.3.0 - clause 4.3, Frame structure type 3

[4] 3GPP TR 36.902 - Self-configuring and self-optimizing network use cases and solutions