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

# Handoff margin

Wireless Communication · Chapter 2: Cellular Mobile Communication Concepts

- Asked in: 2075 Bhadra, 3 marks
- Video: [What is a Handover Hysteresis Margin in Cellular Communications?](https://www.youtube.com/watch?v=_Ty8RhjRlMw) — Iain Explains Signals, Systems, and Digital Comms
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/wireless_communication/handoff-margin
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-2

## Question

Define handoff margin with appropriate figure.

## Short answer

Handoff margin is Δ = Pr,handoff − Pr,minimum usable. Too large a margin causes unnecessary handoffs; too small a margin risks dropped calls. Typical margins are 6–12 dB for 1G and 0–6 dB for 2G with mobile-assisted handoff.

## Answer

**Handoff margin** Δ is the difference between the signal level at which a handoff is initiated and the minimum usable signal level for acceptable voice quality:
```text
Δ = Pr,handoff − Pr,minimum usable
```

```text
 Received
 power (dBm)  BS1                     BS2
    │ \                               /
 Pr,handoff ─ ─\─ ─ ─ ─ ─ ─ ─ ─ ─ ─ /─ ─
    │  ↑ Δ       \                /
 Pr,min ─ ─ ─ ─ ─ ─\─ ─ ─ ─ ─ ─ /─ ─ ─ ─
    │                \         /
    └──────────────────────────────── distance
     BS1         handoff region    BS2
```
- Typical minimum usable level: −90 to −100 dBm.
- If Δ is **too large**, unnecessary handoffs occur, loading the MSC.
- If Δ is **too small**, there may not be enough time to complete the handoff before the signal falls below Pr,min, and the call drops.
- Δ depends on handoff processing time: 1G systems needed about 6–12 dB; 2G systems with mobile-assisted handoff need only about 0–6 dB.

## Check yourself

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

1. Handoff margin is:
   A. Pr,min - Pr,handoff
   B. Pr,handoff - Pr,min usable
   C. The distance between base stations
   D. The cell radius
   Answer: B. It is the gap between the handoff trigger level and the minimum usable level. (Key point: Definition)

2. A margin that is too large causes:
   A. Dropped calls
   B. Lower interference
   C. Fewer handoffs
   D. Unnecessary handoffs and MSC load
   Answer: D. Handoffs start too early. (Key point: Margin too large)

3. A margin that is too small causes:
   A. Dropped calls, since there is not enough time to complete the handoff
   B. Unnecessary handoffs
   C. Higher capacity
   D. Longer calls
   Answer: A. The signal can fall below Pr,min first. (Key point: Margin too small)

## Related in Wireless Communication

- [2G vs 3G, prioritized handoff, cell dragging](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3A2g-vs-3g-prioritized-handoff) — Wireless Communication, chapter 1