DCCA Features and Enhancements in 5G New Radio

In another new whitepaper on 5G-Advanced, Nokia has detailed DCCA (DC + CA) features and enhancements from Rel-15 until Rel-18. The following is an extract from the paper:

Mobility is one of the essential components of 5G-Advanced. 3GPP has already defined a set of functionalities and features that will be a part of the 5G-Advanced Release 18 package. These functionalities can be grouped into four areas: providing new levels of experience, network extension into new areas, mobile network expansion beyond connectivity, and providing operational support excellence. Mobility enhancements in Release 18 will be an important part of the ‘Experience enhancements” block of features, with the goal of reducing interruption time and improving mobility robustness.

Fig. 2 shows a high-level schematic of mobility and dual connectivity (DC)/Carrier Aggregation (CA) related mechanisms that are introduced in the different 5G legacy releases towards 5G-Advanced in Release 18. Innovations such as Conditional Handover (CHO) and dual active protocol stack (DAPS) are introduced in Release 16. More efficient operation of carrier aggregation (CA), dual connectivity (DC), and the combination of those denoted as DCCA, as well as Multi-Radio Access Technology DC (MR-DC) are introduced through Releases 16 and 17.

For harvesting the full benefits of CA/DC techniques, it is important to have an agile framework where secondary cell(s) are timely identified and configured to the UE when needed. This is of importance for non-standalone (NSA) deployments where a carrier on NR should be quickly configured and activated to take advantage of 5G. Similarly, it is of importance for standalone (SA) cases where e.g. a UE with its Primary Cell (PCell) on NR Frequency Range 1 (FR1) wants to take additional carriers, either on FR1 and/or FR2 bands, into use. Thus, there is a need to support cases where the aggregated carriers are either from the same or difference sites. The management of such additional carriers for a UE shall be highly agile in line with the user traffic and QoS demands; quickly enabling usage of additional carriers when needed and again quickly released when no longer demanded to avoid unnecessary processing at the UE and to reduce its energy consumption. This is of particular importance for users with time-varying traffic demands (aka burst traffic conditions).

In the following, we describe how such carrier management is gradually improved by introducing enhancements for cell identification, RRM measurements and reduced reporting delays from UEs. As well as innovations related to Conditional PSCell Addition and Change (CPAC) and deactivation of secondary cell groups are outlined.

The paper goes on to discuss the following scenarios in detail for DCCA enhancements:

• Early measurement reporting
• Secondary cell (SCell) activation time improvements
• Direct SCell activation
• Temporary RS (TRS)-based SCell Activation
• Conditional Secondary Node (SN) addition and change for fast access
• Activation of secondary cell group

The table below summarizes the DCCA features in 5G NR

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• The 3G4G Blog: ATIS Webinar on '5G Standards Development Update in 3GPP Release 17 and 18'
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TSDSI's Low Mobility Large Cell (LMLC) Requirements in 5G

Back in November 2020, ITU completed the evaluation for global affirmation of IMT-2020 technologies. Three new technologies were successfully evaluated by ITU and were found to conform with the International Mobile Telecommunications 2020 (IMT-2020) vision and stringent performance requirements. The technologies are: 3GPP 5G-SRIT and 3GPP 5G-RIT submitted by the Third Generation Partnership Project (3GPP), and 5Gi submitted by Telecommunications Standards Development Society India (TSDSI). 

I have explained in earlier videos that 5G-SRIT  and 5G-RIT corresponds to Non-Standalone and Standalone respectively. 5Gi on the other hand is an updated version of 5G-RIT designed mainly to improve rural coverage. 

ITU completes evaluation for global affirmation of IMT-2020 technologies - https://t.co/dmALByqXh1 - So the 2 3GPP (@3GPPLive) 5G technologies 5G-SRIT and 3GPP 5G-RIT, and 5Gi submitted by TSDSI (@TSDSI_India) conform with IMT-2020 vision and stringent performance requirement. https://t.co/lFhfugcLux

— Zahid Ghadialy (@zahidtg) November 27, 2020

TSDSI announced this as follows:

TSDSI’s 5G Radio Interface Technology named as “5Gi” has cleared the rigorous processes of  International Telecommunication Union (ITU) and has been approved by the SG5 of ITU as a part of Draft Recommendation M.[IMT-2020.SPECS] in its meeting held on 23rd November 2020.

5Gi, the first  ever Mobile Radio Interface Technology contribution from India to become part of ITU-R’s  IMT recommendation, went through a rigorous evaluation process of the ITU-R working groups over the past 3 years before getting the approval.

This standard is a major breakthrough for bridging the rural-urban digital divide in 5G deployment due to enhanced coverage. It enables connecting majority of India’s villages through towers located at gram panchayats in a cost effective manner. It has found support from several countries as it addresses their regional needs from a 5G standpoint.

The standard will now be circulated by ITU to member states for adoption and approval. Specifications are expected to be published by ITU in early February 2021.

TSDSI thanks its members, the Department of Telecommunications, Govt. of India and its partners for their support over the last four years in helping get this standard reach the final stage in ITU.

In a keynote address presented to the 2020 IEEE 5G World Forum plenary session, Radha Krishna Ganti from TSDSI discusses rural connectivity challenges in India, Low Mobility Large Cell requirements, benefits of implementing LMLC for rural coverage, and internet ecosystem updates. His talk is embedded as follows:

TSDSI explains their 5Gi technology as follows:

TSDSI standard fulfils the requirements of affordable connectivity in rural, remote and sparsely populated areas. Enhanced cell coverage enabled by this standard, will be of great value in countries and regions that rely heavily on mobile technologies for connectivity but cannot afford dense deployment of base stations due to lack of deep fibre penetration,  poor economics and challenges of geographical terrain. The International Telecommunication Union (ITU), a UN body that is setting requirements for IMT 2020 (aka 5G), had earlier adopted the Low-Mobility-Large-Cell (LMLC) use case proposed by TSDSI as a mandatory 5G requirement in 2017. This test case addresses the problem of rural coverage by mandating large cell sizes in a rural terrain and scattered areas in developing as well as developed countries. Several countries supported this as they saw a similar need in their jurisdictions as well. TSDSI successfully introduced an indigenously developed 5G candidate Radio Interface Technology, compatible with 3GPP Technology, at the International Telecommunications Union (ITU) in 2019 for IMT 2020 ratification. The RIT incorporates India-specific technology enhancements that can enable larger coverage for meeting the LMLC requirements. It exploits a new transmit waveform that increases cell range developed by research institutions in India (IIT Hyderabad, CEWiT and IIT Madras) and supported by several Indian companies. It enables low-cost rural coverage and has additional features which enable higher spectrum efficiency and improved latency.

While technically this sounds interesting and as discussed in the talk, would make sense due to a large market like India, there are other solutions that are already possible that probably may make this redundant.

As someone who worked with the rural communities to bring coverage in hard to reach areas, small cells and In-band backhaul was one such solution to improve coverage in not-spot areas. Examples of that here and here. Relays are other option that don't cost much but can bring coverage quickly, at a much lower price.

Typically, in practice, the cells easily reach 10km radius. In theory this distance can be as much as 100km. Last year, Australian operator Telstra and vendor Ericsson announced that they have successfully managed to increase the range of an LTE cell from 100 km to 200 km. So, we can already have large cells with existing 4G/5G cells. 

Facebook connectivity is working on SuperCell concept, a Wide-Area Coverage Solution for Increasing Mobile Connectivity in Rural Communities. Details here. NGMN published a paper on Extreme Long Range Communications for Deep Rural Coverage. Details here.

Finally, we also have 5G Integrated Access and Backhaul (IAB) that can be used for backhauling and solving backhaul issues. They will end up playing a role in rural areas as well as dense urban areas eventually.

Let me know what you think.

Related Posts:

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UE Radio Capability Signaling Optimization (RACS) in Rel. 16

The data volume of UE Radio Capability Information defined in 3GPP 38.306 is already high and will further increase starting with Rel. 16 due to additional supported bands and other features.

Due to this 3GPP has standardized in Release 16 what is called UE Radio Capability Signaling Optimization (RACS) for both, E-UTRAN/EPS and NG RAN/NGC networks. 

Release 16 RACS does not apply to NB-IoT.

The first key element of this feature set is the introduction of a new UE Radio Capability ID that is structured as defined in 3GPP 23.003 and shown in figure 1 below:

Figure 1: UE Radio Capability ID according to 3GPP 23.003

The components of this new ID are:

•    TF - Type Field (TF): identifies the type of UE radio capability ID.

            Type = 0 -> manufacturer-assigned UE radio capability ID
            Type = 1 -> network-assigned UE radio capability ID

•  The Vendor ID is an identifier of UE manufacturer and only present if TF = 0. The vendor IDs are provided by Internet Assigned Numbers Authority (IANA). The complete list of assigned numbers is publicly available here: https://www.iana.org/assignments/enterprise-numbers/enterprise-numbers

•  The Version ID configured by the UE Capability Management Function (UCMF) that is part of the EPS/5GC. The Version ID value makes it possible to detect whether a UE Radio Capability ID is current or outdated.

·      The Radio Configuration Identifier (RCI) identifies the UE radio configuration.

The PLMN-assigned UE Radio Capability ID is assigned to the UE using the Non-Access Stratum UE Configuration Update Command or Registration Accept message (figure 2).

Figure 2: PLMN-assigned UE Radio Capability Update according to 3GPP 23.743

The new UCMF (UE radio Capability Management Function) stores All UE Radio Capability ID mappings in a PLMN and is responsible for assigning every PLMN-assigned UE Radio Capability ID.

Due to introduction of the UMCM in the core networks the new Nucmf service-based interface is defined for the 5GC and new S17 reference point is defined for the EPS as shown in figure 3.

Figure 3: Network Architecture with UCMF according to 3GPP 21.916

Each UE Radio Capability ID stored in the UCMF can be associated to one or both UE radio capabilities formats specified in 3GPP TS 36.331 [LTE RRC] and 3GPP TS 38.331 [NR RRC]. The AMF must only be able ot handle the NR RRC format while the MME uses the LTE RRC format. Which format is required by the UCMF is configurable.

If at any time the AMF/MME has neither a valid UE Radio Capability ID nor any stored UE radio capabilities for the UE, the AMF/MME may trigger the RAN to provide the UE Radio Capability information and subsequently request the UCMF to allocate a UE Radio Capability ID.

In NG RAN the UE Capability Request can be requested by the AMF as a flag in any NGAP Downlink NAS Transport message or by sending a NGAP UE Radio Capability Check Request (for checking compatibility of IMS voice capabilities). This triggers a NR RRC UE Capability Transfer procedure and subsequently NGAP UE Radio Capability Info Indication or NGAP UE Radio Capability Check Response (for IMS voice support parameters).

Using the NGAP UE Capability ID Mapping procedure the NG RAN node is able to request the most recent UE Capability ID mapping information from the core network functions AMF/UCMF. The same functionality is implemented in S1AP for signaling between eNB and MME/UCMF.

If the volume of the LTE/NR RRC UE Capability to be sent by the UE is larger than the maximum supported size of a PDCP SDU (specified in 3GPP 38.323) then the UE Capability Info can be transported in LTE/NR RRC using a chain of UL Dedicated Message Segment messages.

Figure 4: RRC UL Dedicated Segment Message transporting UE Radio Capability Information according to 3GPP 36.331 and 38.331

Each of these message will have a dedicated segment number and the last one has the rrc-MessageSegmentType =  “lastSegment”, which triggers reassembly of the orignal UE Capabability information in the receiving entity.