---
title: "Proper and improper handoff"
subject: "Wireless Communication"
chapter: 2
key: "semester_7/wireless_communication:proper-improper-handoff"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/proper-improper-handoff
site: BCT Engineering
---

# Proper and improper handoff

Wireless Communication · Chapter 2: Cellular Mobile Communication Concepts

- Asked in: 2081 Baisakh, 1+3 marks
- Video: [What is handoff? Handoff Strategies](https://www.youtube.com/watch?v=ktnBPBOZY4E) — ECIT Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/wireless_communication/proper-improper-handoff
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-2

## Question

What is Hand-off? Explain proper and improper HO with necessary drawing.

## 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.

## Answer

**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
```text
 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
```text
 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 |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is handoff?
   A. Switching a mobile off and on again when signal is weak
   B. Transfer of an ongoing call from one base station or channel to another without interruption
   C. Allocating a new channel to a new call
   D. Increasing the power of the serving base station
   Answer: B. Handoff keeps the call alive as the mobile leaves the serving cell. (Key point: Definition of handoff)

2. The handoff margin is:
   A. Delta = Pr,min - Pr,handoff
   B. Delta = Pr,handoff + Pr,min
   C. The distance between two base stations
   D. Delta = Pr,handoff - Pr,min
   Answer: D. The handoff threshold is set above the minimum usable signal by the margin Delta. (Key point: Handoff margin)

3. In an improper handoff, what happens?
   A. The signal falls below Pr,min before the handoff is completed and the call is dropped
   B. The handoff completes at point C and the call continues
   C. The mobile is handed to a base station with a stronger signal
   D. The call is blocked at set-up
   Answer: A. If the transfer is not finished in time, the call drops at Pr,min. (Key point: Improper handoff)

4. Which is a cause of improper handoff?
   A. A margin that is large enough
   B. A free channel in the target cell
   C. Too small a margin, slow MSC processing or no free channel in the new cell
   D. Fast MSC processing
   Answer: C. These factors prevent the handoff finishing before Pr,min is reached. (Key point: Causes of improper handoff)

## Related in Wireless Communication

- [Proper vs improper handoff; cellular concept N = 7](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Ahandoff-situation-cellular-n7) — Wireless Communication, chapter 2
- [Hand off and its strategy in GSM](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Ahandoff-strategy-gsm) — Wireless Communication, chapter 2