Soft vs. Softer Handover in Wireless Communication

This article explains the difference between soft handover and softer handover, concepts used in wireless communication systems, specifically when the Radio Resource Control (RRC) layer is in the CELL_DCH state. Both soft and softer handovers involve maintaining multiple active radio links.

With multiple radio links active, adding and removing them becomes much easier, leading to several advantages:

• Antenna Diversity: Alternate radio links can leverage antenna diversity techniques (refer to our diversity page for more details).
• Reduced Call Drop Rate: Maintaining multiple connections greatly reduces the likelihood of dropped calls.
• Seamless Handovers: Provides a smoother handover experience with minimal interruption to voice or data flow.

Soft Handover

A soft handover occurs when a mobile device (User Equipment or UE) switches between two sectors within the same cell of a NodeB (base station). Imagine the NodeB as a pie, and the sectors as slices of that pie. The UE is moving from one slice to another, still served by the same “pie”.

Softer Handover

A softer handover, on the other hand, happens when the mobile device switches between two different cells, each belonging to a different NodeB. Think of it as moving from one “pie” to another.

Softer handovers are further categorized into two types:

• Intra RNC Handover: This occurs when the two different NodeBs are controlled by the same Radio Network Controller (RNC).
• Inter RNC Handover: This occurs when the two different NodeBs are controlled by different Radio Network Controllers (RNCs).

Reference: 3GPP TS 25.331