---
title: "CDMA characteristics, advantages and limitations"
subject: "Wireless Communication"
chapter: 7
key: "semester_7/wireless_communication:cdma-characteristics-limitations"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/cdma-characteristics-limitations
site: BCT Engineering
---

# CDMA characteristics, advantages and limitations

Wireless Communication · Chapter 7: Multiple Access in Wireless Communication

- Asked in: 2079 Bhadra, 2+6 marks
- Video: [Lec 6 | CDMA | Code Division Multiple Access | Wireless Communication | Vaishali Kikan](https://www.youtube.com/watch?v=Mg1NnzBB4Wo) — Dopamine
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/wireless_communication/cdma-characteristics-limitations
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-7

## Question

What do you understand by CDMA? Mention its characteristics, advantages and limitations.

## Short answer

CDMA is a spread-spectrum technique where all users share the same band simultaneously and are separated by unique codes. It gives universal frequency reuse, soft capacity, soft handoff, multipath diversity, and privacy, but suffers from the near-far problem requiring power control, self-jamming, complexity, cell breathing, and needs wide bandwidth.

## Answer

#### CDMA

**Code Division Multiple Access (CDMA)** is a spread-spectrum multiple access technique in which all users transmit **simultaneously on the same frequency band**, and each user is separated by a unique **spreading code** (PN or Walsh). The narrowband data is multiplied by a high-rate code, spreading it over a wide band; the receiver correlates with the same code to recover the user's data, while other users' signals remain spread and appear as low-level noise.

#### Characteristics

- All users share the full bandwidth at all times; no time or frequency division.
- Users separated by codes with low cross-correlation; message signal bandwidth ≪ transmitted bandwidth (processing gain G = W/R).
- **Interference-limited, soft capacity**: adding a user only raises the noise floor slightly.
- **Power control** is essential to overcome the near–far problem.
- Multipath is exploited using the **RAKE receiver**.
- **Soft handoff** between cells is possible.
- Frequency reuse factor of 1.
- Example: IS-95 (1.25 MHz, 1.2288 Mcps), WCDMA (5 MHz, 3.84 Mcps).

#### Advantages

1. Higher capacity than FDMA/TDMA, with soft (graceful) capacity limit.
2. Universal frequency reuse – no frequency planning.
3. Soft handoff reduces call drops.
4. Multipath diversity through RAKE receivers; resistance to fading.
5. Voice activity and sectorization directly raise capacity.
6. Inherent privacy and resistance to narrowband interference/jamming.
7. Lower average transmit power, longer battery life.

#### Limitations

1. **Near–far problem** – strong nearby signals mask weak distant ones; needs accurate, fast power control.
2. **Self-jamming / multiple access interference** – codes are not perfectly orthogonal (especially with asynchronous users and multipath), so each user adds interference.
3. Complex receivers: code acquisition, synchronisation, RAKE, power control.
4. **Cell breathing** – cell coverage shrinks as load increases.
5. Needs wide contiguous bandwidth.
6. Performance degrades as the number of users grows.

## Check yourself

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

1. How are users separated in CDMA?
   A. By unique spreading codes while sharing the same band at the same time
   B. By time slots
   C. By carrier frequencies
   D. By polarization
   Answer: A. All users transmit simultaneously and are recovered by code correlation. (Key point: CDMA definition)

2. What does soft capacity mean?
   A. No hard user limit; adding users slightly raises the noise floor
   B. Exactly 64 users
   C. Capacity unaffected by users
   D. Users are rejected at a fixed number
   Answer: A. CDMA is interference-limited, degrading gracefully. (Key point: Soft capacity)

3. What is the near-far problem?
   A. A strong nearby signal masks weak distant ones
   B. Distant users get more power
   C. Codes become orthogonal
   D. Cells grow
   Answer: A. It is solved by accurate, fast power control. (Key point: Near-far)

4. What is cell breathing?
   A. Coverage shrinks as load increases
   B. Coverage grows with load
   C. Cells change frequency
   D. Cells become hexagonal
   Answer: A. More users raise interference, which reduces effective cell radius. (Key point: Cell breathing)

## Related in Wireless Communication

- [CDMA vs LTE system architecture](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Acdma-vs-lte-architecture) — Wireless Communication, chapter 8
- [FHMA principle and near-far effect in CDMA](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afhma-near-far-cdma) — Wireless Communication, chapter 7

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