---
title: "Multiple access; FDMA vs CDMA"
subject: "Wireless Communication"
chapter: 7
key: "semester_7/wireless_communication:multiple-access-fdma-vs-cdma"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/multiple-access-fdma-vs-cdma
site: BCT Engineering
---

# Multiple access; FDMA vs CDMA

Wireless Communication · Chapter 7: Multiple Access in Wireless Communication

- Asked in: 2070 Magh, 2+4 marks
- Video: [Comparison of FDMA, TDMA and CDMA - Multiple Access - FDMA vs TDMA vs CDMA](https://www.youtube.com/watch?v=anxrpFA3d5I) — Padmasri Naban
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/wireless_communication/multiple-access-fdma-vs-cdma
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-7

## Question

What is multiple access technique? Compare FDMA with CDMA.

## Short answer

Multiple access enables simultaneous sharing of spectrum among users. FDMA assigns narrow frequency bands per user, demands frequency planning, and has hard capacity. CDMA spreads all users over a wide band with unique codes, providing universal frequency reuse, soft capacity, soft handoff, and inherent security, but requires strict power control.

## Answer

#### Multiple access technique
Multiple access is the technique by which **many users share a common, limited radio spectrum at the same time** without causing serious interference to each other. The shared resource is divided in frequency (FDMA), time (TDMA), code (CDMA) or space (SDMA). Narrowband systems (FDMA, TDMA) give each user a small part of the spectrum; wideband systems (CDMA) let every user occupy the whole band. Each is combined with FDD or TDD duplexing.

#### FDMA vs CDMA

| Point | FDMA | CDMA |
|---|---|---|
| Principle | Each user gets its own frequency band | All users share the band, separated by codes |
| Bandwidth | Narrow per user (30 kHz AMPS) | Wide (1.25 MHz IS-95) |
| Time usage | Continuous on its channel | Continuous, same time as others |
| Frequency reuse | Cluster N = 4–12; planning needed | N = 1; no planning |
| Capacity limit | Hard (fixed channels) | Soft (interference limited) |
| Handoff | Hard handoff | Soft handoff |
| Power control | Not critical | Essential (near-far effect) |
| Multipath | Causes fading | Used by RAKE receiver |
| Guard needs | Guard bands, sharp filters | No guard bands between users |
| Security | Low | High (PN codes) |
| Example | AMPS, NMT | IS-95, WCDMA |

## Check yourself

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

1. Typical bandwidth per user?
   A. FDMA wide 1.25 MHz; CDMA narrow 30 kHz
   B. FDMA narrow (30 kHz AMPS); CDMA wide (1.25 MHz IS-95)
   C. Both 200 kHz
   D. Both 30 kHz
   Answer: B. FDMA gives narrow channels; CDMA users occupy the whole wide band. (Key point: Bandwidth comparison)

2. How does the capacity limit differ?
   A. Both hard
   B. FDMA soft, CDMA hard
   C. FDMA hard (fixed channels), CDMA soft (interference-limited)
   D. Both soft
   Answer: C. Fixed channels cap FDMA; CDMA capacity degrades gradually with interference. (Key point: Capacity limit)

3. Which row is correct?
   A. FDMA soft handoff; CDMA hard handoff
   B. FDMA hard handoff, power control not critical; CDMA soft handoff, power control essential
   C. Both hard
   D. Both need power control equally
   Answer: B. CDMA uses soft handoff and needs power control due to near-far. (Key point: Handoff and power control)

4. Which needs guard bands and sharp filters?
   A. FDMA
   B. CDMA
   C. Both neither
   D. SDMA only
   Answer: A. FDMA channels need guard bands; CDMA has none between users. (Key point: Guard needs)

## Related in Wireless Communication

- [Spread spectrum multiple access; FDMA vs CDMA](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aspread-spectrum-ma-fdma-cdma) — Wireless Communication, chapter 7
- [CDMA vs TDMA; FHSS multiple access](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Acdma-advantages-fhss-types) — Wireless Communication, chapter 7
- [Advantages and disadvantages of FDMA, TDMA, CDMA](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afdma-tdma-cdma-pros-cons) — Wireless Communication, chapter 7
- [Multiple access and near-far effect mitigation](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Amultiple-access-near-far) — Wireless Communication, chapter 7
- [Multiple access, TCDMA and TDFH](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Atcdma-tdfh) — Wireless Communication, chapter 7
- [Frequency hopped multiple access (FHMA)](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afhma-operation) — Wireless Communication, chapter 7, asked 5×

## Related in other subjects

- [Multiplexing vs multiple access](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Amux-vs-multiple-access) — Data Communication, chapter 6
- [Multiple tube fermentation (MPN) technique](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Amtf-mpn-procedure) — Water Supply Engineering, chapter 4, asked 5×
- [Multiple access protocols](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Amultiple-access-protocols) — Computer Networks and Security, chapter 3, asked 2×
- [Multiple access in IEEE 802.5](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aieee-802-5-access) — Computer Networks and Security, chapter 3