4G Layer Priority Configuration for Anchoring Strategy in 5G NSA

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Hello 5G experts,

For the anchoring strategy in 5G NSA (EN-DC), is it recommended to configure different priorities for each LTE layer, or should all 4G layers use the same priority?

I’m interested in understanding best practices from real network deployments, especially regarding how LTE layer priority impacts NR anchoring and overall NSA performance.

4G Layer Priority Configuration for Anchoring Strategy in 5G NSA
4G Layer Priority Configuration for Anchoring Strategy in 5G NSA1024×1024 176 KB

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For anchoring in 5G Non-Standalone (NSA), the recommendation is generally to configure different priorities for your 4G (LTE) layers rather than the same priority.

In an NSA environment (specifically EN-DC), the LTE network acts as the “Master Node” or anchor. How you set these priorities determines which LTE cell the phone “camps” on before it even attempts to add a 5G connection.

  1. Why Different Priorities?
    The goal of an anchoring strategy is to ensure that 5G-capable devices stay on LTE bands that are physically co-located with or have the best compatibility with your 5G (NR) cells.
  • Steering to Capacity: You typically want to give the highest priority to the LTE band that has the best throughput or the one that is physically “inter-worked” with 5G. For example, if your 5G is on n78 (3.5 GHz), you might prioritize an LTE band like B3 (1800 MHz) or B1 (2100 MHz) as the anchor.
  • Avoiding “Blind” Anchoring: If all 4G layers have the same priority, the device will simply camp on the strongest signal (based on RSRP). If that “strongest” cell doesn’t have a 5G neighbor configured or isn’t capable of Dual Connectivity (EN-DC), the user will never see the 5G icon, even if they are standing right under a 5G tower.
  1. The “Anchor Layer” Concept
    Most operators designate a specific LTE band as the Primary Anchor Layer.
  • High Priority: Assigned to the “Best” Anchor (e.g., LTE B3).
  • Medium Priority: Assigned to other LTE bands that also support 5G anchoring.
  • Low Priority: Assigned to coverage-only bands (like B20/800MHz or B28/700MHz) that might not be configured for 5G dual connectivity.
  1. Risks of Same Priority
    If you set the same priority for all LTE layers:
  • Ping-Ponging: The UE may frequently jump between 4G cells based on minor signal fluctuations, which can trigger constant “SCG (Secondary Cell Group) Addition/Release” signaling, draining the battery and increasing network overhead.
  • Sub-optimal 5G Availability: You lose the ability to “push” 5G devices toward the frequency where 5G is actually deployed.

Summary of Recommendations

Feature Recommended Configuration Reason
Priority Level Different (Hierarchical) Steers 5G UEs to the most capable “anchor” band.
Idle Mode Use SIB5 / RRC Release Ensures the phone is already on the right anchor when it wakes up.
Connected Mode Frequency-based handover Moves active 5G users back to the anchor if they drift to a non-anchor 4G cell.
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Same priority will increase time to show 5G on the UE.

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The recommendation for an anchoring strategy in 5G NSA (EN-DC) is to configure different priorities for each LTE layer rather than using the same priority for all and incurring a myriad of problems.

Recommendation: Use Different Priorities (Priority Carrier Configuration)

It is recommended to implement a Priority Carrier Configuration where LTE layers are prioritized according to their capacity and the number of NR bands they support (by UEs commercially available in Market).

  • Why different priorities? LTE layers use the same priority (Equal Priority Configuration) –> UEs camping based on best signal strength (a low-band coverage layer or lower pathloss) –> under-utilized LTE high-band capacity cells (even with higher bandwidth) → a lot of signalling in idle and dedicated mode for LTE+NR combination/capacity balancing issues → unsatisfied users and churn.

  • The “Autonomous Push”: Assigning a higher priority (e.g., Priority 7) to high-cap and/or high-band lte carrier (one which most UEs also support with NR band) ensures that 5G-capable UEs “autonomously” move to this layer as soon as they enter usable coverage. This relieves the network from the signaling overhead of frequently moving across layers.

Factors to Consider:

LTE priority settings directly influence EN-DC availability and the speed at which a UE can access 5G resources.

  1. Steering 5G UEs to Suitable Anchors (5G_Idle_Go): Best practices involve using Capability-Aware Idle Mode Control (CAIMC) to modify priorities specifically for 5G UEs at the time of RRC Connection Release via Idle Mode Mobility Control Information (IMMCI).

  2. UE Capability-Based Ranking: In deployments with multiple NR bands, the strategy is used to assign the highest priority to LTE frequencies that support the maximum number of NR band combinations for a specific UE.

  3. Performance vs. Load: While pushing UEs to a high-capacity anchor is preferred for peak rates, it can lead to overloading. Best practices include Load-Aware Prioritization, where the eNodeB reduces the priority of an EN-DC anchor frequency in the IMMCI if that frequency’s Subscription Ratio exceeds a high-load threshold.

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Please could explain why it will increase the time