If you’ve been following the rollout of 5G technology, you may already be familiar with terms like 5G NSA (Non-Standalone) and SA (Standalone). In the context of 5G NSA, if you’ve explored the topic further, you may also have come across the term EN-DC (E-UTRA-NR Dual Connectivity), which refers to a specific type of dual connectivity where your phone connects to both 4G (via LTE) and 5G (via NR) networks simultaneously.
As someone with a general understanding of physics, you might wonder: If 5G often operates at higher frequencies compared to 4G (e.g., mmWave or mid-band), and a phone connects to both technologies at the same time, how does this affect coverage, given that higher frequencies typically have shorter ranges due to propagation challenges?
Let’s explore this question in more detail, but first, let’s briefly break down how EN-DC works.
What is EN-DC?
EN-DC stands for E-UTRA-NR Dual Connectivity, where E-UTRA refers to 4G LTE (Evolved Universal Terrestrial Radio Access) and NR refers to 5G New Radio. It allows a device to maintain simultaneous connections to both 4G and 5G networks, combining the coverage advantages of 4G with the speed and capacity improvements of 5G.
The Coverage Puzzle with Co-located 4G and 5G
Many mobile operators are deploying 5G using their existing 4G infrastructure, often installing 5G equipment right alongside 4G base stations in a setup called co-location. In mobile networks, co-location simply means two or more cells (regardless of technology) share the same physical site infrastructure.
This leads to an important question: Since 4G typically operates at lower frequencies (700MHz-2.6GHz) with better propagation characteristics, while 5G often uses higher frequencies (3.5GHz-28GHz+) with shorter range, wouldn’t this create coverage gaps in EN-DC deployments?
How EN-DC Network Architecture Works
EN-DC is about dual-connectivity so it establishes two connections for your mobile phone using two co-ordinated base stations:
- Master Node (MN): The 4G LTE base station (eNode B or eNB) that manages control signals as well as wide coverage. Since in 5G NSA, a 4G LTE core network (EPC) is used, meaning all the intelligent work needs to be done via EPC, this control stays with 4G LTE base station.
- Secondary Node (SN): The 5G base station (gNode B or gNB) that adds high-speed capacity. 5G base station here provides a bigger data pipe to increase bandwidth.
These two base stations connect using a special interface called X2 which is a standard LTE-NR communication link. EN-DC does not require these nodes to be physically co-located. While co-location is common to leverage existing infrastructure, the specification itself doesn’t mandate it.
Managing the Coverage Differences
EN-DC’s architecture specifically addresses the coverage mismatch between 4G and 5G through three key mechanisms:
- 4G as the Anchor Layer:
First, the 4G network serves as the reliable anchor layer, maintaining constant control signaling and core network connectivity. And how is it reliable? Because 4G LTE base station (eNB) has a longer range compared to it’s 5G counterpart (gNB) due to lower frequency. This ensures your device stays online even when 5G signals become unavailable. - 5G for Enhanced Capacity:
Second, the 5G connection operates as a capacity layer that activates only when you’re within its coverage area meaning where 4G eNB and 5G gNB ranges overlap. So 5G here seamlessly complements the 4G connection rather than replacing it, giving you faster speeds where available while maintaining the stability of the 4G foundation. - Intelligent Fallback:
Finally, the system features intelligent fallback. When you move beyond 5G coverage, your device automatically transitions back to 4G without any noticeable interruption – no dropped calls or broken connections. This handoff happens so smoothly that users won’t even notice the change.
The result is the best of both worlds: the broad reliability of 4G coverage combined with 5G’s enhanced speeds wherever they’re available, all delivered through a single, unified connection.
What Dual Connectivity Coverage Really Looks Like
EN-DC creates a smart coverage system that automatically adapts to your location:
In areas with both strong 4G and 5G signals (Optimal Performance Zone), you get maximum performance through dual connectivity. Where only 4G reaches (Basic Connectivity Zone), you maintain uninterrupted basic service.
Your data flows through three optimized paths:
- MCG Bearers (Master Cell Group bearers): Primarily using the 4G link for reliable connectivity
- SCG Bearers (Secondary Cell Group bearers): Primarily using the 5G link for maximum speed
- Split Bearers: Dynamically distributing traffic across both 4G and 5G for optimal throughput
This means you get:
- Seamless transitions between coverage areas
- Peak speeds where 5G is available, with reliable 4G everywhere else
- Automatic fallback that keeps you connected even when 5G signals weaken
The Smart Design Behind EN-DC
EN-DC represents a pragmatic evolution in network deployment, designed to:
• Reliability: Leverage existing 4G LTE infrastructure for ubiquitous coverage
• High-Speed: Strategically augment capacity with 5G NR where available
• Fallback: Maintain uninterrupted service continuity during transitions
This architecture provides operators with a migration path that:
- Preserves coverage guarantees through mature LTE networks
- Enables targeted 5G performance enhancements
- Ensures backward compatibility during the transition period
The result is a commercially viable approach to 5G introduction that balances:
✓ Coverage reliability (via 4G anchor)
✓ Performance gains (via 5G when available)
✓ Service continuity (through seamless interworking)
Conclusion: A Smarter Layered Network, Not a Coverage Gap
The differing propagation characteristics of 4G and 5G in EN-DC deployments don’t create coverage gaps – they establish intelligent performance tiers. Your device dynamically selects the optimal connection:
• Maximum Performance: Dual connectivity where 5G is available
• Reliable Connectivity: Reliable 4G fallback everywhere else
As 5G infrastructure expands, the high-performance zones will grow organically. Meanwhile, the robust 4G foundation ensures uninterrupted service – truly delivering the best of both network generations.
