---
title: "FDMA with example"
subject: "Data Communication"
chapter: 6
key: "semester_5/data_communication:fdma-describe"
source: https://www.bctengineer.com/q/semester_5/data_communication/fdma-describe
site: BCT Engineering
---

# FDMA with example

Data Communication · Chapter 6: Multiplexing and Spreading

- Asked in: 2070 Chaitra, 5 marks
- Video: [FDMA : Frequency Division Multiple Access (Mobile Communication /Computing) (HINDI)](https://www.youtube.com/watch?v=6xA1l_c8RLk) — 5 Minutes Engineering
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/data_communication/fdma-describe
- Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-6

## Question

Describe FDMA with example.

## Short answer

FDMA splits the total bandwidth into non-overlapping frequency channels with guard bands. Each user is assigned one channel and transmits continuously, so no time synchronization is needed. An example is the first-generation AMPS cellular system, which used30 kHz channels in the824-894 MHz band.

## Answer

**Frequency Division Multiple Access (FDMA)** is a channel access method in which the available bandwidth is divided into non-overlapping frequency bands, and each station (user) is given one band for its whole communication. All stations can transmit at the same time, each on its own band.

#### Features
- The bandwidth is split into N channels with guard bands between them.
- Each user has a dedicated channel; band-pass filters separate the users.
- Transmission is continuous, so no slot synchronisation is needed.
- Channels are allocated on demand (at call set-up) and freed when the call ends.
- It is simple, but it wastes bandwidth when a user is idle, and the guard bands waste spectrum.

```text
 Freq
  f4 |==== User 4 ====|
  f3 |==== User 3 ====|
  f2 |==== User 2 ====|
  f1 |==== User 1 ====|
     +------------------> time
 (guard bands between bands)
```

#### Example
The first-generation cellular system **AMPS** uses 30 kHz channels in the 824–894 MHz band: one channel for the uplink (mobile to base) and one for the downlink, which gives FDD. AM/FM radio stations working in different frequency bands are another example.

Difference from FDM: FDM multiplexes several signals at one place, whereas FDMA gives access to stations located in different places.

## Check yourself

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

1. How does FDMA share the bandwidth?
   A. Each station gets a time slot
   B. Each station uses its own code
   C. The band is divided into non-overlapping frequency bands, one per user
   D. All stations share one band randomly
   Answer: C. FDMA gives each user a dedicated frequency band for the whole communication. (Key point: Principle)

2. Which is a feature of FDMA?
   A. Needs strict slot synchronisation
   B. Continuous transmission with band-pass filters separating users
   C. Uses chip codes
   D. Does not use guard bands
   Answer: B. Transmission is continuous so no slot sync is needed; filters separate users. (Key point: Features)

3. What is a drawback of FDMA?
   A. Wasted bandwidth when a user is idle and in guard bands
   B. Needs accurate time slots
   C. Cannot be allocated on demand
   D. Needs PN codes
   Answer: A. Idle users waste their band and guard bands waste spectrum. (Key point: Drawback)

4. Which is an FDMA example?
   A. GSM time slots
   B. AMPS with 30 kHz channels
   C. CDMA2000
   D. Ethernet CSMA
   Answer: B. First-generation AMPS used 30 kHz channels. (Key point: Example)