Handover Summary for 2G, 3G, LTE, 5G & 6G

[kumarashu81]

The process of transferring an ongoing call, data session, or n/w connection from one cell or radio frequency to another. This occurs when a mobile device moves out of the coverage area of one cell or when network conditions change

1. Handover in 2G (GSM): when a mobile device moves from one GSM cell (base station) to another. It’s typically between two cells operating on the same frequency or adjacent ones.

   • Types:
     • Intra-Cell Handover: Within the same base station, changing channels or time slots
     • Inter-Cell Handover: Between two different base stations
     • Inter-Frequency Handover: Between two cells operating on different frequencies.
     • Hard Handover: The connection to the old cell is broken before establishing the new one (break-before-make)

2. Handover in 3G (UMTS) : its Introduced the concept of “soft handover,” where a device can connect to multiple base stations simultaneously.

   • Types:
     • Soft Handover: The mobile device maintains connections with more than one cell during the handover (make-before-break).
     • Softer Handover: When a device connects to two sectors of the same cell.
     • Hard Handover: Like in 2G, but less frequent due to the soft handover approach.

3. Handover in 4G/LTE: Its use hard handover, similar to GSM but with faster and more efficient transitions due to its all-IP network design. LTE doesn’t have soft handover, as the system is optimized to handle handovers without requiring multiple connections.

   • Types:

     • Intra-LTE Handover: Between LTE cells operating on the same or different frequencies.
     • Inter-RAT Handover: Between LTE and 3G/2G networks.
     • X2-Based Handover: Handover between eNodeBs (LTE base stations) that have a direct interface.
     • S1-Based Handover: Handover involving the core network (MME and SGW), typically when the eNodeBs don’t have a direct connection.

   • When: LTE handovers are triggered when the signal quality drops below a certain threshold, and the device connects to the strongest neighboring cell.

4. Handover in 5G (NR): Introduces more advanced handover mechanisms, supporting ultra-reliable low-latency communication (URLLC), massive machine-type communication (mMTC), and enhanced mobile broadband (eMBB). 5G handovers are seamless and aim to maintain service quality across diverse use cases.

   • Types:

     • Intra-NR Handover: Within the 5G network.
     • Inter-NR Handover: Between different frequency bands within 5G.
     • Inter-RAT Handover: Between 5G and 4G or even 3G/2G, ensuring backward compatibility.
     • Dual Connectivity: In 5G, dual connectivity allows a device to be connected to both LTE and 5G at the same time, providing a smoother transition.

   • When: 5G handovers can be triggered by user movement, load balancing (optimizing network resources), or switching between different frequency bands (e.g., between sub-6 GHz and mmWave).

5. Expected Features of Handover in 6G:

   • AI-Driven Handover Decisions
   • Multi-Layer Handover
   • Handover at Terahertz Frequencies
   • Edge-Enabled Handover

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