- 2081 Baisakh · 1+3 marks
Proper and improper handoff
Short answer
Handoff is the transfer of an ongoing call between base stations without interruption. Proper handoff completes before signal drops below minimum usable level; improper handoff occurs when the handoff margin is too small or processing is too slow, causing the call to be dropped.
What is Hand-off? Explain proper and improper HO with necessary drawing.
Handoff (handover) is the transfer of an ongoing call from one base station (or channel) to another without interrupting it, when the mobile moves out of the coverage of the serving cell.
A handoff is started when the received signal falls to a handoff threshold Pr,handoff, which is set above the minimum usable signal Pr,min. The difference is the handoff margin Δ = Pr,handoff − Pr,min.
(a) Improper handoff
Signal BS1 BS2
│ \ /
│ \_ Pr,handoff (A) /
│ \ /
│ ........\ Pr,min (B) ... /..
│ call dropped here
└──────────────────────────────── distance
The signal at point A reaches the handoff threshold, but the handoff is not completed before the signal falls below Pr,min at B (because of a too-small Δ, slow processing at the MSC, or no free channel in BS2). The call is dropped.
(b) Proper handoff
Signal BS1 BS2
│ \ /
│ \_ Pr,handoff (A) ______/
│ \ ____/ handoff to BS2 (C)
│ ........\ Pr,min ..........
└──────────────────────────────── distance
At A the handoff threshold is reached, the MSC finds a channel in BS2 and the call is transferred at C, before the signal from BS1 drops below Pr,min. The call continues without interruption.
| Point | Proper | Improper |
|---|---|---|
| Timing | Completed before Pr,min | Not completed in time |
| Result | Call continues | Call dropped |
| Cause | Correct Δ, fast processing | Δ too small, delay, no free channel |
✓ Answer checked by Claude Opus 5.5 (high effort)
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