5G NSA Layering Design Guideline
Multilayer Strategy Selection-different factors
1.Functionality or Performance of existing network
The layering strategy maybe need to be aligned with the existing LTE network when 5G is introduced. For instance, in the early-stage coverage maybe more important than throughput. From commercial aspect the 5G symbol on the subscribers' UE maybe important.In other cases, the NR layer maybe used to offload congested LTE layers, thus pushing LTE users from a specific LTE layer to anchor layer (ENDC) or straight to NR (for SA). The choice or preference of LTE layer in certain clutter will also determine the choice of NR layer for the case of ENDC. For example, in rural area LTE 900 maybe preferred due to coverage, thus only NR layers that can be combined with LTE 900 will be selected for deployment or perhaps UEs from other LTE layers will be steered to LTE 900 (effectively ENDC with the NR layer)
2.Network behavior and End User experience to Mobility and Interworking.
Distribution of UE across the network during idle and connected mode may influence the decision on layering when NR layer is deployed. If the ENDC capable UE is camping more often in non ENDC layers, then certain layering features or parameters may need to be tuned to push the ENDC UEs to the correct LTE anchor layers.Type of services and with their target QoS requirements can be a factor in case of VoLTE. ENDC capable UE may need to be released to correct LTE layer for incoming/outgoing VoLTE calls.
3.New layer (carrier/band/micro & pico) is introduced in the network
If a new NR layer is obtained/ frequency re-farmed and added to an existing NSA or SA network, the strategy might change. For example, the new layer maybe a capacity layer thus the balancing weight might need to be tuned for the LTE anchors and NR handover features and parameters may need to be activated (i.e., inter frequency NR handovers).On the other hand, re-farming of existing LTE layer (worse if it is an anchor band) to NR may lead to redesign of the strategy and implementation.
4.New System (e.g., SA or FR2) is introduced in the network (assuming existing NSA, FR1 or wise-versa)
In this case Inter-frequency features and strategy will need to be implemented. How and when (thresholds) for the measurement triggering and handover triggering will need to be planned. Besides that, NSA-SA interworking strategy may also need in case of deployment of SA.In the future if NE-DC is to be deployed in the network alongside ENDC and SA, then the layering strategy will need to be re-planned
5.New Feature is introduced (e.g., Available after SW upgrade or activation) that require changes for the layering strategy (Layering or other features)
If new feature with more efficient load balancing, layer selection or ENDC combination selection is made available with new SW, then the layering strategy may need to be changed to accommodate or deploy the new features.
6.DSS and/or NR Carrier Aggregation
In networks that has DSS or CA enabled, the layering strategy may need be implemented in a such a way to optimize the UE experience and throughput. The introduction of FR1 NR FDD-TDD CA for instance prefers NR FDD cell as the PScell thus steering(SA) or addition of ENDC (NSA) must prefer the FDD layer for CA enabled UEs.
7.UE capabilities to support features/bands/frequencies/system increase in the network
If certain UE’s with specific band combination is made available (maybe it wasn’t available earlier), then the steering strategy to the desired LTE layer need to be planned. For instance, if in a network with two FR1 layer (60Mhz and 100 MHz) maybe in early days the number of UE’s supporting 60Mhz are less thus it may only have one anchor, later when more UEs are available the strategy might change to have more anchors. It may also be applicable for band combination support against the available MRDC bands
Below are some Important must design criteria heighlighted dark and supporting details/Feature
NSA ENDC ||Candidate LTE Anchor Criteria
1.Allowed 3GPP Band combinations
2.UE Capabilities
3.LTE Layer Bandwidth
4.LTE Layer Coverage
5.Operators Strategy
NSA ENDC ||LTE Layer Steering Configuration for ENDC
1.EN-DC capable UEs in idle mode camp on the LTE anchor layer
2.5G neighbours are defined for the BTSs in the LTE anchor layer
3.Set parameters such that 5G radio connections are added when there is sufficient 5G radio coverage and addition attempts are not made when the 5G radio coverage is insufficient
4.Make sure that LTE carrier aggregation works also for UEs with ongoing 5G connection
Non- Stand Alone ENDC ||LTE Layer Steering Configuration for ENDC||Idle Mode Steering Features
Must Feature
LTE487 Idle Mode Load Balancing
LTE1677 Idle Mode Mobility Balancing Extensions
LTE2166 Dedicated Idle Mode Mobility Priorities
LTE2050 Load Triggered Idle Mode Load Balancing
LTE2051 Measurement Based Idle Mode Load Balancing
LTE5501 EN-DC Aware Idle Mode Load Balancing
NSA ENDC ||LTE Layer Steering Configuration for ENDC||Connected Mode Steering Features
Must Feature
LTE5150 EN-DC capability based mobility trigger
CB006607 UE MR-DC Capabilities Based Handover (NSA)
CB007163 EN-DC Capability-based Handover to Preferred Layer
NSA ENDC ||NR Layering Configuration
Intra-Frequency
Must Feature
5GC000572 Intra-frequency Inter-DU en-gNB mobility (Cloud)
5GC001094 Intra-frequency Intra-DU en-gNB mobility
5GC000573 Intra-frequency Inter en-gNB mobility
SRAN19A LTE4530 Inter-SgNB Mobility for LTE-NR DC 3x
Inter-Frequency
Must Feature
5GC001095 Inter-Frequency mobility (NSA option 3X) without MeNB coordination
5GC002199 Inter-Frequency mobility (NSA option 3X) with MeNB coordination
LTE5227 SgNB initiated co-ordination of NR Measurements
Connected mode – Intra LTE
Must Feature
LTE4281 LTE connected mobility for LTE-NR DC option 3x
LTE5348 Inter-eNB handover for for LTE-NR DC option 3x
5GC000575 Intra-MeNB LTE handover without gNB change
5GC000574 Inter-MeNB LTE handover without gNB change
Non- Stand Alone ENDC ||Non-Collocated Anchors
It is important to add the non-collocated LTE cells as ENDC pair to the NR cells that overlaps. The steering features and connected mode features as described in earlier section of this document also need to be enabled and configured accordingly. The performance of ENDC and end user experience will improve when the non-collocated sites are defined and configured correctly.Drawbacks associated with configuring non-co-sited anchors in some situations. For instance, if 5G coverage overlap is smaller than the LTE coverage
NSA ENDC ||LTE Multiple Layers and NR one Layer
NSA ENDC ||LTE Multiple Layers and NR one Layer ||Single LTE Anchor
NSA ENDC ||LTE Multiple Layers and NR one Layer||Two or more LTE Anchors
NSA ENDC ||LTE Multiple Layers and NR one Layer ||All LTE Carriers as Anchors
NSA ENDC ||LTE Multiple Layers and NR one Layer ||Intra Frequency NR Hand Over
Must Feature
5GC000572 Intra-frequency Inter-DU en-gNB mobility
5GC001094 Intra-frequency Intra-DU en-gNB mobility
5GC000573 Intra-frequency Inter en-gNB mobility
In above features A3/A5 event is triggered based on SS-RSRP/SS-RSRQ measurements or combined decision depending on the configuration
NSA ENDC ||LTE Multiple Layers and NR Multiple Layers
In some scenarios, the NR will be deployed with more than one frequency/band. In such cases the preference of NR+LTE band combination may depend on the UE capability, coverage and capacity. Enabling additional B1-NR measurements consideration into EN-DC aware idle mode load balancing account will be useful in this scenario
NSA ENDC ||LTE Multiple Layers and NR Multiple Layers||B1-NR measurements Prioritizations
SRAN20A CR-31168 NR band priority with 2 B1
LTE5226 Increased number of NR carriers
LTE4193 Dynamic Trigger for LTE-NR DC Option 3X
CR-32377 NR band priority with 3 B1
LTE4259 Increased Carrier Monitoring in Connected
CB006067 Configurable number of NR carriers for en-gNB measurements
CB007873 Inter-band DL CA FDD - TDD FR1 NSA (Option 3x)
NSA ENDC ||LTE Multiple Layers and NR Multiple Layers||FR1 Layers Only
LTE4193 Dynamic Trigger for LTE-NR DC Option 3
LTE5003 Data buffer trigger for EN-DC
NSA ENDC ||LTE Multiple Layers and NR Multiple Layers||FR1&FR2 Layers
In this scenario, the prioritization can be applied based on the operator’s strategy. For instance, in good coverage (when both FR1 and FR2 is available) prefer FR2 and in poor coverage prefer FR1.
LTE4259 Increased Carrier Monitoring in Connected Mode
\NSA ENDC ||LTE Multiple Layers and NR Multiple Layers||Inter Frequency NR Hand Over
5GC001095 Inter-Frequency mobility (NSA option 3X) without MeNB coordination
LTE5227 SgNB initiated co-ordination of NR Measurements
NSA ENDC ||Counter and KPIs for NSA ENDC Layering
Average number of UEs capable for EN-DC
Share of 4G RRC connections done with EN-DC capable EU
UE EN-DC capability utilization ratio
E-UTRAN Initial E-RAB Setup Attempts for MCG bearer with NR PDCP
Maximum number of UEs capable for EN-DC
Maximum number of LTE-NR DC UEs with a configured SCG split bearer at the PCell
Average number of LTE-NR DC UEs with a configured SCG split bearer at the Pcell
5G NSA Average number of NSA users
Number of preparations attempts for SgNB Addition
Number of RRC Reconfiguration attempts due to Intra-MeNB HO
Number of successful RRC Reconfiguration due to Intra-MeNB HO
Number of failed RRC Reconfiguration due to Intra-MeNB HO
Number of successful Intra-MeNB HO without PS-Cell Change
Number of successful Intra-MeNB HO with PS-Cell Change
Number of RRC Reconfiguration attempts due to Intra-MeNB HO
Number of successful RRC Reconfiguration due to Inter-MeNB HO
Number of failed RRC Reconfiguration due to Inter-MeNB HO
Number of successful Inter-MeNB HO without PS-Cell Change
Number of successful Inter-MeNB HO with PS-Cell Change
E-UTRAN Total Inter-Frequency EN-DC capability based Handover Success Ratio
E-UTRAN Inter-eNB X2 HO with EN-DC keeping total success ratio
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