- 2073 Magh · 5 marks
Short note: Handover
Short answer
Handover transfers an ongoing call to another channel or base station without interruption when signal falls. It uses a handoff margin to balance unnecessary handoffs and dropped calls. Types include hard (break-before-make), soft (make-before-break), and mobile-assisted. Guard channels and queuing prioritise handoffs to prevent dropped calls.
Write a short note on handover.
Handover (handoff) is the process of transferring an ongoing call or data session from one channel or base station to another without interruption, when the mobile moves into another cell or the signal quality falls.
Process
- The serving base station monitors signal strength. When it falls to the handoff threshold Pr,handoff, the MSC looks for a better neighbouring cell and a free channel.
- The call must be transferred before the signal falls to the minimum usable level Pr,min. The difference Δ = Pr,handoff − Pr,min is the handoff margin; too large Δ causes unnecessary handoffs, too small Δ causes dropped calls.
- In 1G, base stations measured the mobile's signal; in 2G (GSM) the mobile measures neighbours and reports them (mobile-assisted handoff, MAHO).
Power BS1 BS2
│ \ /
│ \ Pr,handoff /
│ \ Δ /
│.......\ Pr,min /........
└──────────────────────── distance
Types
- Hard handover (break before make) – GSM, LTE.
- Soft handover (make before break) – CDMA, WCDMA; connected to several base stations at once.
- Intra-cell, inter-cell, inter-MSC (intersystem) handover.
Prioritising handover: guard channels reserved for handoffs and queuing of handoff requests, because dropping a call is worse than blocking a new one.
Practical issues: umbrella cells for high-speed users, cell dragging, and dwell time variation due to fading.
✓ Answer checked by Claude Opus 5.5 (high effort)