Mobility enhancement in E-UTRAN Release -16

Mobility enhancement in E-UTRAN Release -16

  November 16, 2020    tls123

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 Dual Active Protocol Stack (DAPS) handover

DAPS Handover is a handover procedure that maintains the source eNB connection after reception of RRC message for handover and until releasing the source cell after successful random access to the target eNB.

-    If DAPS handover is configured, the UE continues the downlink user data reception from the source eNB until releasing the source cell and continues the uplink user data transmission to the source eNB until successful random access procedure to the target eNB.

-    Upon reception of the handover command, the UE:

-     Creates a MAC entity for target cell;

-     Establishes the RLC entity and an associated DTCH logical channel for target cell for each DRB configured with DAPS;

-     For the DRB(s) configured with DAPS, reconfigures the PDCP entity to configure DAPS with separate security and ROHC functions for source and target and associates them with the RLC entities configured for source and target respectively;

-     Retains rest of the source link configurations until release of the source.

-     When DAPS handover fails, the UE falls back to source cell configuration, resumes the connection with source cell, and reports the DAPS handover failure via the source without triggering RRC connection re-establishment if the source link is still available; Otherwise, RRC re-establishment is performed;

Conditional Handover (CHO)

A Conditional Handover (CHO) is defined as a handover that is executed by the UE when one or more handover execution conditions are met.

-    UE maintains connection with source eNB after receiving CHO configuration, and starts evaluating the CHO execution condition(s) for the CHO candidate cell(s) and executes the HO command once the execution condition(s) are met for a CHO candidate cell.

-    To improve the robustness, the network can provide the up to 8 candidate cell configuration(s) associated with execution condition (s) to UE. If at least one CHO candidate cell satisfies the corresponding CHO execution condition, the UE detaches from the source eNB, applies the stored corresponding configuration for that candidate cell and synchronises to that candidate cell. UE stops evaluating the execution condition(s) for other candidate cells once the handover is triggered.

-    The UE accesses to the target eNB and completes the handover procedure by sending RRCConnectionReconfigurationComplete message to target eNB. The UE releases stored CHO configurations after successful completion of RRC handover procedure.

-    When initial CHO execution attempt fails or HO fails, if network configured the UE to try CHO after HO/CHO failure and the UE performs cell selection to a CHO candidate cell, the UE attempts CHO execution to that cell; Otherwise, RRC re-establishment is performed.

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DL MIMO efficiency enhancements for LTE

DL MIMO efficiency enhancements for LTE

  November 16, 2020    tls123

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MIMO is an effective technique to improve spectral efficiency and increase overall network capacity. SRS can be utilized to improve DL MIMO performance, especially for massive MIMO in TDD. In release-16 SRS capacity and coverage are enhanced by introducing more than one SRS symbol in a UL normal subframe and introducing virtual cell ID for SRS.

More than one symbol for SRS in a UL normal subframe

With the introduction of more than one SRS symbol in a UL normal subframe, the SRS capacity and coverage can be increased. These additional SRS symbol(s) are referred to as trigger type 2 SRS.

1 to 13 symbols of the first 13 symbols of a UL normal subframe can be configured to a UE for aperiodically triggered SRS transmission. Intra-subframe repetition, frequency hopping and antenna switching of the additional SRS symbols can be supported. A guard period of one SC-FDMA symbol can be configured for frequency hopping and antenna switching.

The number of repetitions can be configured from the set {1, 2, 3, 4, 6, 7, 8, 9, 12, 13}. If a UE has more receive antennas than transmit chains (e.g. 1T2R), the UE can be configured to transmit the additional SRS with antenna switching. And a UE can additionally be configured with frequency hopping for the additional SRS. The number of antennas (pairs) to switch is:

-    2 for 1T2R, or the number of pairs is configured as 2 for 2T4R

-    3 if the number of pairs is configured as 3 for 2T4R

-    4 for 1T4R

Both legacy SRS and additional SRS can be configured to the same UE, and transmission of legacy SRS and additional SRS symbol(s) in the same subframe for the UE is supported.

For sequence generation, per-symbol group hopping and sequence hopping are supported.

Independent open loop and close loop power control is supported for additional SRS, and DCI formats 3/3A/3B are used for close loop power control.

UEs not configured with SPUCCH/SPUSCH are not expected to be triggered with additional SRS in the same subframe as PUSCH/PUCCH in the same serving cell. UEs configured with SPUCCH/SPUSCH drop the SRS transmission in the symbols colliding with SPUCCH/SPUSCH in the same serving cell.

The additional SRS transmission in the symbols colliding with PUSCH/PUCCH of another serving cell in the same TAG, the same band and with the same CP, is dropped.

The additional SRS transmission in the symbols colliding with PUSCH/PUCCH of another serving cell in the different TAG is dropped if the total transmission power exceeds the PCMAX in any overlapping portion.

Virtual cell ID

Virtual cell ID within the range from 0 to 503 can be configured for SRS to increase SRS capacity.

The virtual cell ID can be configured to only additional SRS symbol(s) or both legacy and additional SRS symbol(s). If virtual cell ID is not configured, the physical cell ID is used.

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Network Slicing

Network Slicing

  November 16, 2020    tls123

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 Release 16 Network Slicing addresses two major limitations of Release 15 in 5GC:

(1) Enhancement of interworking between EPC and 5GC when UE moves from EPC to 5GC, the target serving AMF may not be able to serve all the PDU sessions that the UE intends to move to the 5GC.  More specifically, the following aspects needs to be addressed:

-              Selecting an AMF based on the slices associated to the active PDU connections that serve the UE in the EPC in Connected mode and during the Idle mode mobility

-              Selecting an appropriate serving V-SMF based on the slices associated to the active PDN connections that serve the UE in the EPC in Connected Mode

 (2) Support for Network Slice Specific Authentication and Authorization (NSSAA)

-              Enable the support for separate authentication and authorization per Network Slice.  The trigger of NSSAA in the 5GC is based on UE subscription information from UDM and also operator’s policy.  However, the UE shall indicate its support for NSSAA to its serving 5GC.

-              The AMF performs the role of the EAP Authenticator and communicates with the AAA-S via the AUSF. The AUSF undertakes any AAA protocol interworking with the AAA protocol supported by the AAA-S.

Enhancement of Interworking Between EPC and 5GC

During the mobility from EPS to 5GS, in case of CM-IDLE state, the PGW-C+SMF sends PDU Session IDs and related S-NSSAIs to AMF in Registration procedure. The AMF derives S-NSSAI values for the Serving PLMN and determines whether the current AMF is appropriate to serve the UE. If not, the AMF reallocation may need to be triggered. For each PDU Session the AMF determines whether the V-SMF need to be reselected based on the associated S-NSSAI value for the Serving PLMN. If the V-SMF need be reallocated, the AMF trigger the V-SMF reallocation.

In case of CM-CONNECTED state, during handover preparation phase the PGW-C+SMF sends PDU Session IDs and related S-NSSAIs to AMF. Based on the received S-NSSAIs values, the target AMF derives the S-NSSAI values for the Serving PLMN, the target AMF reselects a final target AMF if necessary and forwards the handover request to the final target AMF. When the Handover procedure completes successfully, the UE proceeds with the Registration procedure. For each PDU Session based on the associated derived S-NSSAI values, if the V-SMF need be reallocated, the final target AMF triggers the V-SMF reallocation. The final target AMF sends the S-NSSAI value for the Serving PLMN to V-SMF to update the SM context. The V-SMF updates NG RAN with the S-NSSAI value for the Serving PLMN via N2 SM message.

 

Network Slice-Specific Authentication and Authorization (NSSAA)

In Release-16, based on UE’s 5GMM Core Network Capability and subscription information, the serving AMF will trigger Network Slice-Specific Authentication and Authorization for the S-NSSAIs of the HPLMN. If a UE does not support this feature but requests these S-NSSAIs that are subject to Network Slice-Specific Authentication and Authorization, these S-NSSAIs will be rejected by the PLMN.

If a UE supports this feature and requests these S-NSSAIs, which are subject to Network Slice-Specific Authentication and Authorization, the UE shall leverage the corresponding credentials for these S-NSSAIs for the Network Slice-Specific Authentication and Authorization. As for how to these credentials in the UE are not specified.

To perform the Network Slice-Specific Authentication and Authorization for an S-NSSAI, the AMF invokes an EAP- based Network Slice-Specific authorization procedure for the S-NSSAI.

This procedure can be invoked for a supporting UE by an AMF at any time, e.g. when:

a.            The UE registers with the AMF and one of the S-NSSAIs of the HPLMN which maps to an S-NSSAI in the Requested NSSAI is requiring Network Slice-Specific Authentication and Authorization; or

b.            The Network Slice-Specific AAA Server triggers a UE re-authentication and re-authorization for an S-NSSAI; or

c.            The AMF, based on operator policy or a subscription change, decides to initiate the Network Slice-Specific Authentication and Authorization procedure for a certain S-NSSAI which was previously authorized.

Based on the outcome of the Network Slice-Specific Authentication and Authorization, the Allowed NSSAI for each Access Type will be updated accordingly.   It is network policies to decide for which Access Type to be used if both Access Types are subject for the Network Slice-Specific Authentication and Authorization. However, if the Network Slice-Specific Authentication and Authorization fails for all S-NSSAIs in the Allowed NSSAI, the AMF shall execute the Network-initiated Deregistration procedure with the appropriate rejection cause value for each Rejected S-NSSAI.

After a successful or unsuccessful UE Network Slice-Specific Authentication and Authorization, the UE context in the AMF shall retain the authentication and authorization status for the UE for the related specific S-NSSAI of the HPLMN while the UE remains RM-REGISTERED in the PLMN, so that the AMF is not required to execute a Network Slice-Specific Authentication and Authorization for a UE at every Periodic Registration Update or Mobility Registration procedure with the PLMN.

A Network Slice-Specific AAA server may revoke the authorization or challenge the authentication and authorization of a UE at any time. When authorization is revoked for an S-NSSAI that is in the current Allowed NSSAI for an Access Type, the AMF shall provide a new Allowed NSSAI to the UE and trigger the release of all PDU sessions associated with the S-NSSAI, for this Access Type.

The AMF provides the GPSI of the UE related to the S-NSSAI to the AAA Server to allow the AAA server to initiate the Network Slice-Specific Authentication and Authorization, or the Authorization revocation procedure, where the UE current AMF needs to be identified by the system, so the UE authorization status can be challenged or revoked.

The Network Slice-Specific Authentication and Authorization requires that the UE Primary Authentication and Authorization of the SUPI has successfully completed. If the SUPI authorization is revoked, then also the Network Slice-Specific authorization is revoked.

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5GC location Services

5GC location Services

  November 16, 2020    tls123

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Enhancement to the 5GC Location Services

The Location Services, specified in TS 23.273, include aspects of both regulatory and commercial nature.

The architecture and signalling procedures in NG-RAN are defined in TS 38.305.

Following aspects have been specified for 5G Location Services:

-    Service based 5G location architecture, including roaming and non-roaming, Function description of per Network Functions, etc.

-    General Concepts, e.g. Type of Location Requests, LCS Quality of services;

-    High Level Features, e.g. LMF selection, UE LCS privacy handling;

-    Location Service Procedures, which includes

-     5GC-MT-LR Procedure

-     5GC-MO-LR Procedure

-     Deferred 5GC-MT-LR Procedure for Periodic, Triggered and UE Available Location Events

-     LMF Change Procedure

-     Unified Location Service Exposure Procedure

-     Low Power Periodic and Triggered 5GC-MT-LR Procedure

-     Bulk Operation of LCS Service Request Targeting to Multiple UEs

-     Procedures to Support Non-3GPP Access

-     Procedures dedicated to Support Regulatory services

-     UE Assisted and UE Based Positioning Procedure

-     Network Assisted Positioning Procedure

-     Obtaining Non-UE Associated Network Assistance Data

-     UE Location Privacy Setting Procedure

-     Procedures with interaction between 5GC and EPC

-     Support of Concurrent Location Request;

-    Network Function Services, e.g. LMF services, GMLC services.

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LTE in high speed

LTE in high speed

  November 15, 2020    tls123

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 In Rel-13 and 14, the mobility and throughput performance were enhanced to cover high speeds (up to 350 km/h) by specifying the requirements for UE RRM, UE demodulation and base station demodulation, considering the two types of operator’s practical deployments shown in Figures 1 and 2. Figure 1 shows the case where no specific installation is deployed to handle high-speed trains, i.e. UEs in the train use the "standard" LTE eNBs. Alternatively, figure 2 shows the case where Single Frequency Network (SFN) are deployed. SFNs use so-called "Remote Radio Heads" (RRH), which are dedicated antennas deployed along the train track. In this case, the baseband unit (BBU) is connected to the RRH, e.g. using fiber.

Fig.1: Non-Single Frequency Network (SFN) high speed scenario

 

Fig2: SFN high speed scenario

These Rel-13 and 14 enhancements were conducted both for non-SFN and for SFN, but only for LTE single carrier, i.e. not covering Carrier Aggregation (CA).

Rel-16 improves the mobility and throughput performance, now considering CA and speeds up to 500 km/h. To this aim, it enhances RRM, UE demodulation and base station demodulation: it specifies enhanced RRM core requirements and corresponding RRC signals in respectively TS 36.133 and TS 36.331.

 

RRM requirements enhancements:

In Release 14 cases (limited to 350 km/h and single carrier), the latency requirements under DRX configuration up to 1.28s DRX cycle were enhanced by reducing the cell identification delay in connected mode and cell reselection delay in idle mode [1].

In Rel-16, considering Carrier Aggregation and speeds up to 500km/h, the following enhanced requirements were introduced to achieve good mobility performance and less paging outage:

1.    Enhanced RRM requirements for active SCells (for 350km/h velocity): The same requirements specified in Rel-14 high speed WI are applied to active SCells.

2. Enhanced RRM requirements for deactivated SCells (for 350km/h velocity): The cell identification delay and measurement period are reduced.

3.  Enhanced RRM requirements in DRX in connected mode (for 500km/h velocity):  The cell identification delay and measurement period on 1.28s DRX cycle are further reduced from those in Rel-14 high speed WI.

4.      Enhanced RRM requirements in idle mode (for 500km/h velocity): The cell detection delay is further reduced from those in Rel-14 high speed WI.

5.    Enhanced UL timing adjustment requirements in connected mode (for 500km/h velocity): The larger maximum autonomous time adjustment step is applied when the downlink bandwidth is wider than 10MHz.

 

Demodulation enhancements

6.      For UE and base station demodulation enhancements: In Release 14, UE and base station demodulation requirements were enhanced, for both cases of operator’s practical deployments shown in figures 1 and 2.

In Release 16, regarding the CA case in SFN (figure 2), the requirements specified in Rel-14 are expanded to Dual Connectivity's Secondary Cells (SCells) as defined in TS 36.331. Regarding further high speed up to 500 km/h, additional requirements are introduced to ensure the PDSCH/PUSCH/PRACH demodulation performance with larger Doppler shift.

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ATSSS support in 5g

ATSSS support in 5g

  November 15, 2020    tls123

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Coexistence with Non-3GPP systems: ATSSS

The ATSSS feature enables a multi-access PDU Connectivity Service, which can exchange PDUs between the UE and a data network by simultaneously using one 3GPP access network and one non-3GPP access network and two independent N3/N9 tunnels between the PSA and RAN/AN. The multi-access PDU Connectivity Service is realized by establishing a Multi-Access PDU (MA PDU) Session, i.e. a PDU Session that may have user-plane resources on two access networks, as shown on the figure below, extracted from TR 23.793. 

MA PDU session

These following procedures are defined in the context of this Feature:

-   Access Traffic Steering: it selects an access network for a new data flow and transfers the traffic of this data flow over the selected access network. Access traffic steering is applicable between one 3GPP access and one non-3GPP access.

-  Access Traffic Switching: it moves all traffic of an ongoing data flow from one access network to another access network in a way that maintains the continuity of the data flow. Access traffic switching is applicable between one 3GPP access and one non-3GPP access.

-   Access Traffic Splitting: it splits the traffic of a data flow across multiple access networks. When traffic splitting is applied to a data flow, some traffic of the data flow is transferred via one access and some other traffic of the same data flow is transferred via another access. Access traffic splitting is applicable between one 3GPP access and one non-3GPP access.

Key concepts of ATSSS supported in Release 16 include the following:

-   Multi-access PDU Session is a PDU Session that provides a PDU connectivity service, which can use one access network at a time, or simultaneously one 3GPP access network and one non-3GPP access network and two independent N3/N9 tunnels between the PSA and RAN/AN.

-    After the establishment of a MA PDU Session:

-    When there are user-plane resources on both access networks:

-    The UE applies network-provided policy (i.e. ATSSS rules derived by UE’s serving SMF based on ATSSS policy from serving PCF) and considers local conditions (such as network interface availability, signal loss conditions, user preferences, etc.) for deciding how to distribute the uplink traffic across the two access networks.

-    Similarly, the UPF anchor of the MA PDU Session applies network-provided policy (i.e. N4 rules derived by UE’s serving SMF based on ATSSS policy from serving PCF) and the feedback information received from the UE via the user-plane (such as access network Unavailability or Availability), the UPF then decides how to distribute the downlink traffic across the two N3/N9 tunnels and two access networks.

-    When there are user-plane resources on only one access network, the UE applies the ATSSS rules and considers local conditions for triggering the establishment or activation of the user plane resources over another access.

-  The type of a MA PDU Session may be one of the following types: i.e. IPv4, IPv6, IPv4v6, and Ethernet. The Unstructured type is not supported in Release 16.

-  The ATSSS feature can be supported over 3GPP and non-3GPP accesses, including untrusted and trusted non-3GPP access networks, wireline 5G access networks, etc., as long as a MA PDU Session can be established over the given type of access network

-     Two ATSSS steering functionalities are supported:

-     MPTCP functionality, for TCP traffic, with MPTCP proxy in UPF, by using the MPTCP protocol over the 3GPP and/or the non-3GPP user plane; and

-     ATSSS-LL functionality for all types of traffic, including TCP traffic, UDP traffic, Ethernet traffic, etc. ATSSS-LL functionality is mandatory for MA PDU Session of type Ethernet.

The following presents the example of the ATSSS traffic steering functionality within the UE.

Steering functionalities in an example UE model

-  The Performance Measurement Function (PMF) is supported by UPF and is specific for ATSSS-LL functionality, if enabled.  In Release 16, PMF supports two types of measurements between UE and UPF to assist access selection and they are:

-     UE and UPF make RTT measurements per access when the "Smallest Delay" steering mode is used; and

-     UE reports access availability/unavailability to UPF

The following presents the protocol stacks of the PMF for the user plane measurements over 3GPP and non-3GPP accesses respectively.

 

UE/UPF measurements related protocol stack for 3GPP access and for an MA PDU Session with type IP

In the case of an MA PDU Session with type Ethernet, the protocol stack over 3GPP access is that same as the one in the above figure, but the PMF protocol operates on top of Ethernet, instead of UDP/IP.

 

UE/UPF measurements related protocol stack for non-3GPP access and for an MA PDU Session with type IP

In the case of an MA PDU Session with type Ethernet, the protocol stack over non-3GPP access is that same as the one in the above figure, but the PMF protocol operates on top of Ethernet, instead of UDP/IP.

-   An ATSSS-capable UE may decide to request a MA PDU Session based on the provisioned URSP rules. In particular, the UE should request a MA PDU Session when the UE applies a URSP rule, which triggers the UE to establish a new PDU Session and the Access Type Preference component of the URSP rule indicates "Multi-Access".

-  The 5G QoS model for the Single-Access PDU Session is also applied to the MA PDU Session, i.e. the QoS Flow is the finest granularity of QoS differentiation in the MA PDU Session. One difference compared to the Single-Access PDU Session is that in a MA PDU Session there can be separate user-plane tunnels between the AN and the PSA, each one associated with a different access. The SMF shall provide the same QFI in 3GPP and non-3GPP accesses so that the same QoS is supported in both accesses. Non GBR QoS Flow can be distributed over 3GPP access and non 3GPP access, but GBR QoS Flow is transferred over single access.

- ATSSS is currently not supported when moving to EPC from 5GC, except for the specific case with wireline access integrated to EPC/5GC with 5G-RG; ATSSS with one User Plane leg in E-UTRA/EPC and one User Plane leg in wireline/5GC is supported.

Coexistence with Non-3GPP systems: Wireless and Wireline Convergence Enhancement

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Wireless and Wireline Convergence Enhancement

Wireless and Wireline Convergence Enhancement

  November 15, 2020    tls123

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Support of wireline access network

Support of Trusted Access network

Radio aspects 

Charging aspects

Coexistence with Non-3GPP systems: ATSSS

Support of wireline access network

The architecture for non-roaming is shown in figure 1, where the Wireline Access Gateway Function (W-AGF) is the access node performing the termination of N2 and N3 reference point, termination of access network interface Y4 and all access network specify functionalities, the relay of N1 to/from the UE., QoS enforcement, etc. The customer device, the UE, is replaced by the Residential Gateway which is augmented to support the 5G functionalities required to connect to 5G systems, such as NAS, URSP, PDU session, etc, called 5G-RG. The specification in TS 23.316 defines the modification to system architecture, procedure and flows, Policy and Charging Control for the 5G System in TS 23.501, TS 23.502 and TS 23.503.

The 5G-RG can also be connected via 3GPP Access basically by means of supporting the specification defined for UE. This scenario is called Fixed Wireless Access (FWA). Furthermore the 5G-RG may simultaneously connect to 3GPP Access and to wireline access by using the Single Access PDU session or supporting ATSSS feature. This scenario is called Hybrid scenario, using a terminology common on wireline access network. The ATSSS is supported as specified in TS 23.501, 23.502 and TS 23.503 where UE is replaced by 5G-RG and the Non-3GPP access is specifically referred to wireline access. In this latter case, TS 23.316 has also specified the support of interworking with EPC via 3GPP Access via a MA PDU session with a PDN Connection as user-plane resource associated with a MA PDU Session.

The support of legacy Residential Gateway not supporting 5G capability (FN-RG) is supported via W-AGF terminating the N1 NAS on behalf of UE and acting as a UE in respect the 5G core. 

In the case of Wireline Access Network defined in Broadband Forum the W-AGF functionalities is specified in BBF TR-470, BBF TR-456 and BBF TR-457, the 5G-RG is defined in BBF TR-124issue6 [8]. In the case of Wireline Access network defined in Cablelabs the W-AGF and 5G-RG functionalities are defined in CableLabs WR-TR-5WWC-ARCH.

Main impacts on the system by the WWC for wireline support are the following:

-    W-AGF: the access network function which performs the termination of N2 and N3 reference point, termination of access network interface Y4 and all access network specify functionalities, the relay of N1 to/from the UE. QoS enforcement, etc. When the W-AGF facing the FN-RG the W-AGF is supporting the termination of N1 NAS and performs the interworking between 5GC and the legacy wireline access network.

-    5G-RG: end user device replacing the UE which supports 5G capabilities (NAS protocol and procedure, USRP, IMSI, ATSSS) and extension of wireline access layer specific functionalities defined by Broadband forum and CableLabs. The 5G-RG may also support UE capability when connects via 3GPP Access.

-    FN-RG: end user device replacing the UE which does not support 5G capabilities.

-    Global Line Identifier (GLI): in case of wireline access based on BBF specifications this parameter uniquely identifies the line at which the 5G-RG in connected to within an operator domain.

-    Global Cable identifier (GCI): in case of wireline access based on CableLabs specification this parameter uniquely identifies the line at which the 5G-RG in connected to within an operator domain.

-    SUPI for FN-RG based on GCI and GLI.

-    All procedures defined in TS 23.502 have been modified to introduce the new network elements. The procedures are focused mainly on the part of specification that required improvements and to point out the access network interaction involving the W-AGF, 5G-RG and FN-RG to allow the Broadband Forum and CableLabs to develop the specifications under their responsibility.

-    IPTV support: The specification TS 23.316 in clauses 4.9.1 and 7.7.1 defines the support of IPTV via the support of multicast over unicast PDU session by using IGMP/MLD message send by STB via 5G-RG on PDU session and managed by UPF for adding the requiring 5G-RG to a multicast group and replicating the traffic received on N6 interface to the PDU session. The SMF is improved to control the support of IPTV by the UPF acting as PSA using PDR, FAR, QER, URR. This includes control of which IGMP and MLD requests the UPF is to accept or to deny.

-    QoS: the QoS model for wireline network is based on a subscription maximum aggregate bitrate including both GBR and Non-GBR traffic, hence the new parameter RG Total Maximum Bit Rate (RG-TMBR) has been defined. The RG-TMBR limits the aggregate bit rate that can be expected to be provided across all GBR and Non-GBR QoS Flows of a RG. The RG-TMBR is a parameter provided to the W-AGF by the AMF based on the value of the Subscribed RG-TMBR retrieved from UDM. The QoS control on wireline access network (i.e scheduling, rate limiting and traffic class management) is based on the line characteristic included in user subscription, for example different priority of service, different traffic class support by line of the single user, etc, for such reason the new parameter RG Level Wireline Access Characteristics (RG-LWAC) has been introduced. The format and content of RG LWAC is specified by BBF and it is transparently provided by UDM to AMF which may provide to the W-AGF at the time of the RG registration

-    mobility restriction based on GLI and GCI

-    support of BBF interaction with the Access Configuration System (ACS) to support the provisioning of configuration and remote management of 5G-RG as described in BBF TR-069 [12] or in BBF TR-369.

 Non- roaming architecture for 5G Core Network for 5G-RG with Wireline 5G Access network and NG RAN

Non- roaming architecture for 5G Core Network for FN-RG with Wireline 5G Access network and NG RAN

Support of Trusted Access network

The support of Trusted Network addresses the scenario where the Non-3GPP access network has a tighter relationship with 5GC in respect the untrusted scenario. However how the network is considered Trusted or Untrusted is not in the scope of this WID. The architecture for non-roaming is shown in figure 3, where the Trusted Non-3GPP Access Network (TNAN) is the access node performing the termination of N2 and N3 reference point, termination of access network interface, relay of N1 to/from the UE. From 3GPP point of view the TNAN network is composed by the TNGF and the Trusted Non-3GPP Access Point (TNAP) which are interconnected via the reference point Ta. However the detailed definition of TNAN and of Ta is beyond the WID scope. The reference point between the UE and the TNG, the NWt, is specified leveraging the IKEv2 defined for Untrusted. The main difference in contrast to Untrusted is in registration procedure, where it is assumed that EAP-5G can be carried between UE and TNAP directly on access layers, such on IEEE 802.11x and between TNAP and TNGF via Ta and not as part of IKEv2 establishment.  From other the point of view of other procedures, such as session management, the same procedure specified for Untrusted Non-3GPP access network can be used with basically the TNGF replacing the N3IWF, and modification that IKEv2 Child SA establishment is requested by TNGF and not by UE side.

Within the context of Trusted Non-3GP network, also the scenario of devices not supporting NAS connected via WLAN is specified. The role of TNGF is replaced the Trusted WLAN Interworking Function (TWIF) with the main difference that TWIF terminates the N1 NAS interface and it play the role of UE in respect the 5GC.

The specification is addressed in TS 23.501, TS 23.502 and TS 23.503

Non-roaming architecture for 5G Core Network with trusted non-3GPP access

Radio aspects 

The objective includes:

•  The description and enhancement of NG protocols to support the interface between the Trusted Non-3GPP Access Network and the 5GC;

•   The description and enhancement of NG protocols to support the interface between the Wireline 5G Access Network and the 5GC.

- from TS 29.413 and TS 38.413.

General radio aspects

-    Introduce the Trusted Non-3GPP Gateway Function (TNGF), Trusted WLAN Interworking Function (TWIF) to support the Trusted Non-3GPP Access, and Wireline Access Gateway Function (W-AGF) to support Wireline Access in TS 29.413 and TS 38.413.

-    Add the Global TNGF ID in the applicable NGAP messages between the TNGF and the AMF; add the Global TWIF ID in the applicable NGAP messages between the TWIF and the AMF; add the Global W-AGF ID in the applicable NGAP messages between the W-AGF and the AMF.

-    Add the selected PLMN Identity for trusted non-3GPP access and wireline access in Initial UE Message for Key derivation.

-    Add procedural texts that the Security Key IE may include KTNGF, or KTWIF, or KWAGF in TS 29.413.

 

Supporting the Trusted Non-3GPP Access with the 5GC – specific aspects

-    Add TNGF Identity Information, TWIF Identity Information in the UPLINK NAS TRANSPORT message containing a list of identifiers of NG-U terminations at TNGF/TWIF for UPF selection.

-    Add TNGF related and TWIF related User Location Information in the User Location Information IE.

 

Supporting the Wireline Access connectivity with the 5GC – specific aspects

-    Add W-AGF Identity Information in the UPLINK NAS TRANSPORT message containing a list of identifiers of NG-U terminations at W-AGF for UPF selection.

-    Add W-AGF related User Location Information in the User Location Information IE.

-    Add procedural texts to clarify the UE-AMBR is not used for wireline access in TS 29.413.

-    Add RG Level Wireline Access Characteristics in INITIAL CONTEXT SETUP REQUEST messages stored in the UE context by the W-AGF, indicating the wireline access technology specific QoS information corresponding to a specific wireline access subscription.

-    Add the Authenticated Indication in INITIAL UE MESSAGE to indicate that the FN-RG has been authenticated by the wireline 5G access network.

Charging aspects

The Wireless and Wireline Convergence for 5G system architecture (5WWC)is specified in TS 23.501, TS 23.502, TS 23.503 and TS 23.316. The enhancement to charging aspect for 5WWC is considered as part of this series specifications for this 5WWC.

Following charging scenarios are included in charging aspect of 5WWC as following:

-    UE Connects to 5G Core via Trusted Non-3GPP access

-    5G-RG connects to 5G Core via NR-RAN and via W-5GAN

-    FN-RG connects via W-5GAN.

The specifications related to 5WWC charging include TS 32.255, TS 32.291 and TS 32.298. The subscriber’s identifiers and PEI in 5G-RG and FN RG scenarios specified in TS 23.501 and TS 23.361 are used in charging information. The procedures and related triggers in 5WWC charging scenarios are also specified in charging aspect for 5WWC. The related changes to OpenAPI are specified in TS 32.291.

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5G V2X with NR sidelink

5G V2X with NR sidelink

  November 15, 2020    tls123

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Physical layer structure

Resource allocation

Sidelink HARQ feedback, sidelink CSI and PC5-RRC for unicast and groupcast

Cross-RAT and in-device coexistence between LTE V2X and NR V2X sidelinks

Physical layer structure

Sidelink bandwidth part (BWP) is defined to support the flexible numerologies in operating on various spectrum band such as the intelligent transport system (ITS) dedicated band and the licensed band of frequency range 1 (FR1) and FR2. For sidelink synchronization, GNSS, gNB/eNB and the NR sidelink UE can be used as a synchronization reference source of a UE.

The NR V2X sidelink uses the following physical channels and signals:

-    Physical sidelink broadcast channel (PSBCH) and its de-modulation reference signal (DMRS)

-    Physical sidelink control channel (PSCCH) and its DMRS

-    Physical sidelink shared channel (PSSCH) and its DMRS

-    Physical sidelink feedback channel (PSFCH)

-    Sidelink primary and secondary synchronization signals (S-PSS and S-SSS)

-    Phase-tracking reference signal (PT-RS) in FR2

-    Channel state information reference signal (CSI-RS)

Sidelink control information (SCI) in NR V2X is transmitted in two stages. The first-stage SCI is carried on PSCCH and contains information to enable sensing operations, as well as information about the resource allocation of the PSSCH. PSSCH transmits the second-stage SCI and the sidelink shared channel (SL-SCH) transport channel. The second-stage SCI carries information needed to identify and decode the associated SL-SCH, as well as control for hybrid automatic repeat request (HARQ) procedures, and triggers for channel state information (CSI) feedback, etc. SL-SCH carries the transport block (TB) of data for transmission over SL.

PSCCH and PSSCH are multiplexed in time and frequency within a slot for short latency and high reliability. DRMS is frequency multiplexed with PSCCH or PSSCH in the corresponding DMRS symbols. PSFCH, which is used for sidelink HARQ feedback for unicast and groupcast, is transmitted at the end of a slot, which is preceded by an additional guard symbol and an automatic gain control (AGC) symbol. Two multiplexing examples are shown in Figure 1(a) and 1(b).

Resource allocation

There are two resource allocation modes: mode 1 and mode 2. Mode 1 for resource allocation by gNB and Mode 2 for UE autonomous resource selection are very similar to Mode 3 and Mode 4 in LTE sidelink respectively. For mode 1, gNB schedules to UE the dynamic grant resources by downlink control information (DCI), or the configured grant resource type 1 and type 2 by radio resource control (RRC) signalling and DCI respectively.

In Mode 2, the sensing operation to determine transmission resources by UE comprises 1) sensing within a sensing window, 2) exclusion of the resources reserved by other UEs, and 3) select the final resources within a selection window. In Mode 2, shortly before transmitting in a reserved resource, a sensing UE re-evaluates the set of resources to check whether its intended transmission is still suitable, considering a possible aperiodic transmission after the resource reservation. If the reserved resources would not be part of the set for selection at this time, then new resources are selected from the updated resource selection window. In addition to the re-evaluation, pre-emption is also introduced such that a UE selects new resources even after it announces the resource reservation when it observes resource collision with a higher priority transmission from another UE.

Sidelink HARQ feedback, sidelink CSI and PC5-RRC for unicast and groupcast

NR sidelink supports sidelink HARQ-ACK for sidelink unicast and groupcast services for improved reliability. Two sidelink HARQ feedback operations are defined, HARQ-ACK with ACK and NACK, and HARQ-ACK with NACK only. When ACK/NACK operation is used, the sidelink HARQ-ACK procedure is similar to that of Uu for non-codeblock group feedback, i.e. the HARQ-ACKis transmitted based on the success or failure of the whole transport block. NACK-only operation is defined for groupcast to allow a a larger number of Rx UEs to share a single PSFCH resource by sending feedback only when a Rx UE receives SCI but fails to decode the transport block. The transmission of NACK-only feedback can be restricted to UEs within given a radius, and any UE beyond it does not provide any HARQ-ACK. This minimum range requirement of a service is provided together with the associated QoS parameters from service layers. For mode 1, sidelink HARQ-ACK information is reported to gNB to indicate whether additional retransmission resources are required or not.

In sidelink unicast transmission, Tx UE can configure aperiodic sidelink CSI reporting from the Rx UE to get information it can use for sidelink link adaptation and rank adaptation. CQI and RI are reported via MAC layer signalling, in a PSSCH transmission for this purpose. In addition, radio link monitoring is adopted to manage a sidelink connection.

To support exchange of the AS layer configuration and UE capability information between UEs, PC5-RRC is defined for unicast sidelink communication. The AS protocol stacks of the control plane for RRC is depicted in Figure 2.

Cross-RAT and in-device coexistence between LTE V2X and NR V2X sidelinks

Depending on the NR V2X and LTE V2X deployment, it is envisaged that an optional UE design can be supported where a device has both an LTE-V2X RAT and an NR-V2X RAT which are able to inter-communicate. 5G V2X defines two Cross-RAT operations. LTE Uu can control NR resource allocation mode 1 by providing configured grant Type 1 configurations via LTE RRC signalling, and resource allocation mode 2 by LTE Uu RRC providing the semi-static configurations relevant to resource pools, sensing, etc. NR Uu can control LTE resource allocation mode 3 by transmitting an NR DCI which contains the information needed to dynamically control the LTE sidelink, and resource allocation mode 4 by NR Uu RRC providing the necessary semi-static configurations within which the LTE-V2X RAT autonomously selects resources for sidelink transmission.

It is envisaged that there will exist devices that support both LTE-V2X and NR-V2X, and which will be operating in both systems concurrently. If the two RATs are widely spaced in frequency, e.g. being in different bands, then there need be no particular issues to consider since it is assumed that a separate RF chain will be provided for each band. If, however, a sufficiently close frequency spacing is deployed, then it is desirable to enable a single RF chain to be used in the implementation. In this case, the simultaneous transmission on both RATs is prevented by the UE's single power budget, and one RAT cannot be received/transmitted while the other RAT is doing the opposite. In this case, one of the RATs may be dropped at times when both occur simultaneously, but that in some cases where the priority of the V2X service on both RATs is known, the higher priority one is automatically selected.

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Architecture enhancements for 3GPP support of advanced V2X services

Architecture enhancements for 3GPP support of advanced V2X services

  November 15, 2020    tls123

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Architecture enhancements to the 5G System are specified in TS 23.287 in order to facilitate vehicular communications for Vehicle-to-Everything (V2X) services, over the following reference points, based on service requirements defined in TS 22.185 and TS 22.186:

- PC5 reference point: NR PC5 RAT, LTE PC5 RAT.

- Uu reference point: NR, E-UTRA.

Interworking between EPS V2X and 5GS V2X is also specified.

The following architectural reference models are specified:

-  5G System architectures for V2X communication over PC5 and Uu reference points

-  5G System architecture for AF-based service parameter provisioning for V2X communications

-  Architecture reference model for interworking with EPS V2X

The various parameters for V2X communications over PC5 and Uu reference points are specified and these parameters may be made available to the UE in following ways:

-  pre-configured in the ME; or

-  configured in the UICC; or

-  preconfigured in the ME and configured in the UICC; or

-  provided/updated by the V2X Application Server via PCF and/or V1 reference point; or

-  provided/updated by the PCF to the UE.

In addition to PCF initiated Policy Provisioning procedure, the UE may perform UE triggered Policy Provisioning procedure to the PCF when the UE determines the V2X Policy/Parameter is invalid (e.g. Policy/Parameter is outdated, missing or invalid).

Regarding V2X communication over PC5 reference point, two types of PC5 reference points exist: the LTE based PC5 reference point as defined in TS 23.285, and the NR based PC5 reference point as defined in TS 23.287. A UE may use either type of PC5 or both for V2X communication depending on the services the UE supports. The V2X communication over PC5 reference point supports roaming and inter-PLMN operations. V2X communication over PC5 reference point is supported when UE is "served by NR or E-UTRA" or when the UE is "not served by NR or E-UTRA".

V2X communication over NR based PC5 reference point supports broadcast mode, groupcast mode and unicast mode. For unicast mode, Layer-2 link establishment, Link identifier update, Layer-2 link release, Layer-2 link modification and Layer-2 link maintenance procedures are specified. Per-Flow PC5 QoS Model is introduced for V2X communication over NR based PC5 reference point.

Architecture enhancements for EPS to support V2X communication over NR PC5 reference point are specified in TS 23.285 [4].

For V2X communication over Uu reference point, only unicast is supported. Latency reduction for V2X message transfer via unicast may be achieved by using various mechanisms, including via e.g., edge computing defined in TS 23.501.

Notification on QoS Sustainability Analytics to the V2X Application Server is specified so that the V2X Application Server may request notifications on QoS Sustainability Analytics for an indicated geographic area and time interval in order to adjust the application behaviour in advance with potential QoS change.

To support V2X applications that can operate with different configurations (e.g. different bitrates or delay requirements), the V2X Application Server, acting as the Application Function, can provide, in addition to the requested level of service requirements, Alternative Service Requirements to the 5G System. This enables the 5G System to act on the Alternative Service Requirements and apply them for the extended NG-RAN notification (i.e. Alternative QoS Profiles are provided from SMF to NG-RAN), as described in TS 23.501 and TS 23.503.

In order to facilitate deployment of dedicated network slice for use of, for example, automotive industry and to facilitate roaming support, a new standardized Slice/Service Type (SST) value dedicated for V2X services, i.e. 4 is defined in TS 23.501.

Security aspects of 3GPP support for advanced V2X services are specified in TS 33.536.

 TS 24.587 and TS 24.588 are new specifications for V2X .

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CLI handling and RIM for NR

CLI handling and RIM for NR

  November 07, 2020    Mr. Standards

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 Rel-14 NR study showed that duplexing flexibility with cross-link interference mitigation shows better user throughput compared to static UL/DL operation or dynamic UL/DL operation without interference mitigation in indoor hotspot (4GHz and 30GHz) and urban macro scenarios (4GHz and 2GHz). Furthermore, semi-static and/or dynamic DL/UL resource assignments should also consider coexistence issues particularly among different operators where tight coordination are challenged. For efficient coexistence, not only coexistence requirements need to be understood but also advanced mechanisms to mitigate interference such as TRP-to-TRP measurement and adaptation based on measurements should be considered. The Rel-16 Work Item Cross Link Interference (CLI) handling to support flexible resource adaptation for unpaired NR cells achieves the following objectives:

•              CLI measurements and reporting at a UE (i.e., CLI-RSSI and SRS-RSRP), and network coordination mechanism(s) (i.e., exchange of intended DL/UL configuration) are developed.

•              Perform coexistence study to identify conditions of coexistence among different operators in adjacent channels is accomplished.

In NR deployment on lower TDD frequency, the impact of the troposphere bending will continue existing if no special mechanisms are introduced. In the RIM SI, the frameworks for mechanisms for gNBs to start and terminate the transmission/detection of reference signal(s), the functionalities and requirements of the corresponding RS(s) as well as the design of the RS(s), and the backhaul-based coordination mechanisms among gNBs have been studied. It is recommended to specify RIM RS(s) to support identifying remote interference related information, it is also recommended to specify the inter-set RIM backhaul signalling via the core network for backhaul-based solution. The Rel-16 Work Item Remote Interference Management (RIM) to deal with mitigation of the remote interference caused by gNBs achieves the following objectives:

• RIM RS resource and configurations, and the inter-set RIM backhaul signalling via the core network to convey the messages of “RIM-RS detected” and “RIM-RS disappeared are developed.

• Corresponding OAM functions to support RIM operation is identified.

 

CLI handling

Once different TDD UL/DL configurations are applied among neighboring cells, UL transmission from a UE in a cell causes interference to DL reception of some other UEs in the rest of the neighboring cells. The interference is referred as inter-cell UE-to-UE cross link interference (CLI). To mitigate an inter-cell UE-to-UE CLI, gNBs can exchange and coordinate the intended TDD UL/DL configuration over Xn and F1 interfaces. Taking into account the exchanged information, a gNB may decide the transmission and reception pattern in order to avoid CLI to neighboring cell or from neighboring cell.

For CLI handling, two types of CLI measurements and reporting (i.e., CLI-Received Signal Strength Indicator (RSSI) measurement and SRS-Reference Signal Received Power (RSRP) measurement) are specified. For CLI-RSSI measurement, the victim UE measures the total received power over configured CLI-RSSI measurement resource. For SRS-RSRP measurement, the victim UE measures the RSRP over configured SRS resource(s) which is/are transmitted from one or multiple aggressor UE(s). Then, Layer 3 filtering can be applied to the measurement result for both CLI-RSSI measurement and SRS-RSRP measurement. For measurement result reporting for both CLI-RSSI measurement and SRS-RSRP measurement, event triggered and periodic reporting are supported. Furthermore, CLI measurement and reporting can be configured for NR cells in multi-carrier option.

Semi-static and/or dynamic DL/UL resource assignment causes interferers between networks on adjacent channels. It has been tasked to investigate the adjacent channel co-existence effects arising when CLI, or more generically dynamic TDD is operated in an aggressor network. The technical report captures a description of the adjacent channel interference effects that arise with dynamic TDD as well as a simulation investigation of adjacent channel interference in a number of different deployment scenarios.

RIM

Due to the atmospheric ducting phenomenon, the DL signals of an aggressor cell in unpaired spectrum can interfere with the UL signals of a victim cell in the same unpaired spectrum bandwidth that is far away from the aggressor cell. Such interference is termed as remote interference. A remote interference scenario may involve a number of victim and aggressor cells, where the gNBs may execute Remote Interference Management (RIM) coordination on behalf of their respective cells.

To mitigate remote interference, RIM frameworks for coordination between victim and aggressor gNBs are specified. The coordination communication in RIM frameworks can be wireless- or backhaul-based. In both frameworks, all gNBs in a victim set can simultaneously transmit an identical RIM reference signal carrying the victim set ID over the air.

In the wireless framework, RIM-RS (RIM reference signal) type 1 and RIM-RS type 2 are specified. Upon reception of the RIM reference signal (RIM-RS type 1) from the victim set, aggressor gNBs undertake RIM measurement, and may send back a RIM reference signal (RIM-RS type 2) carrying the aggressor set ID if configured, and may undertake interference mitigation actions. The RIM reference signal (RIM-RS type 2) sent by the aggressor is able to facilitate estimation whether the atmospheric ducting phenomenon between victim and aggressor sets exists.

In the RIM backhaul framework, upon reception of the RIM reference signal (RIM-RS type 1) from the victim set, aggressor gNBs undertake RIM measurement, establish backhaul coordination towards the victim gNB set. The backhaul messages which carry the detection or disappearance indication are aggregated at gNB-CU via F1 interface and sent from individual aggressor gNBs to individual victim gNBs via NG interface, where the signalling is transparent to the core network.

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