---
title: "Short note: WiFi"
subject: "Wireless Communication"
chapter: 8
key: "semester_7/wireless_communication:wifi-short-note"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/wifi-short-note
site: BCT Engineering
---

# Short note: WiFi

Wireless Communication · Chapter 8: Wireless Systems and Standards

- Asked in: 2076 Bhadra, 5 marks
- Video: [IEEE 802.11 Wireless Fidelity (Wi-Fi)](https://www.youtube.com/watch?v=t3FVP5wuG4g) — Neso Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/wireless_communication/wifi-short-note
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-8

## Question

Write a short note on WiFi.

## Short answer

Wi-Fi is IEEE 802.11 WLAN technology in unlicensed ISM bands. Versions range from 802.11b at 11 Mbps to 802.11ax at about 9.6 Gbps, using OFDM, MIMO and OFDMA. MAC uses CSMA/CA with RTS/CTS and ACKs; security is WPA2/WPA3.

## Answer

**Wi-Fi** is the trade name (Wi-Fi Alliance) for wireless local area networks based on the **IEEE 802.11** standards. It connects laptops, phones and other devices to each other and to the Internet over short range (about 30–100 m) using unlicensed ISM bands.

**Versions**
| Standard | Year | Band | Max rate | PHY |
|---|---|---|---|---|
| 802.11b | 1999 | 2.4 GHz | 11 Mbps | DSSS/CCK |
| 802.11a | 1999 | 5 GHz | 54 Mbps | OFDM |
| 802.11g | 2003 | 2.4 GHz | 54 Mbps | OFDM |
| 802.11n (Wi-Fi 4) | 2009 | 2.4/5 GHz | 600 Mbps | OFDM + MIMO |
| 802.11ac (Wi-Fi 5) | 2013 | 5 GHz | ~6.9 Gbps | MU-MIMO, 256-QAM |
| 802.11ax (Wi-Fi 6) | 2019 | 2.4/5/6 GHz | ~9.6 Gbps | OFDMA |

**Architecture**
```text
 [STA]~~\
 [STA]~~~[Access Point]---Ethernet---Internet
 [STA]~~/     (BSS)
 Ad hoc: [STA]~~~[STA] (IBSS, no AP)
```
- **Infrastructure mode**: stations connect through an access point (AP); several APs linked by a distribution system form an ESS.
- **Ad hoc mode**: stations talk directly.

**MAC**: CSMA/CA (carrier sense multiple access with collision avoidance) with optional RTS/CTS to solve the hidden-terminal problem; acknowledgements for each frame.

**Security**: WEP (weak, obsolete) → WPA → WPA2 (AES-CCMP) → WPA3.

**Advantages**: no cabling, mobility, cheap, high data rates. **Limitations**: short range, interference in the crowded 2.4 GHz band, shared capacity, security concerns.

**Applications**: home and office networks, public hotspots, campus networks, offloading mobile data, IoT devices.

## Check yourself

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

1. Wi-Fi is based on which standard?
   A. IEEE 802.11
   B. IEEE 802.16
   C. IEEE 802.15.1
   D. IEEE 802.3
   Answer: A. Wi-Fi is the Wi-Fi Alliance name for 802.11 WLANs. (Key point: Standard)

2. Which MAC method does Wi-Fi use, and why not collision detection?
   A. CSMA/CA with ACKs, optional RTS/CTS for the hidden-terminal problem
   B. CSMA/CD like Ethernet
   C. TDMA with fixed slots
   D. Pure ALOHA
   Answer: A. Wireless stations cannot reliably detect collisions while transmitting, so collisions are avoided. (Key point: MAC method)

3. What forms an ESS?
   A. Two stations in ad hoc mode
   B. Several APs linked by a distribution system
   C. One AP with no stations
   D. A single IBSS
   Answer: B. A BSS is one AP and its stations; linked BSSs form an ESS. (Key point: Infrastructure mode)

4. Which PHY technique is introduced by 802.11ax (Wi-Fi 6)?
   A. DSSS/CCK
   B. MU-MIMO only on 5 GHz
   C. FHSS
   D. OFDMA
   Answer: D. 802.11ax added OFDMA; 802.11b used DSSS/CCK. (Key point: Wi-Fi 6)