---
title: "Noise vs interference and their limitations"
subject: "Communication Systems"
chapter: 1
key: "semester_6/communication_systems:noise-interference-limitations"
source: https://www.bctengineer.com/q/semester_6/communication_systems/noise-interference-limitations
site: BCT Engineering
---

# Noise vs interference and their limitations

Communication Systems · Chapter 1: Introduction

- Asked in: 2070 Bhadra (CS I), 3+3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/communication_systems/noise-interference-limitations
- Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-1

## Question

Differentiate between noise and interference. What are the limitations posed by them in communication system?

## Short answer

Noise is random, always present, and cannot be fully removed; interference is deterministic from other sources, often eliminable. Noise limits SNR, channel capacity, range, and receiver sensitivity. Interference causes crosstalk, reduces spectrum reuse, and demands better selectivity and filtering.

## Answer

#### Noise vs interference
**Noise** is any random, unwanted electrical disturbance from natural or device sources. **Interference** is contamination by an unwanted signal from another man-made source, often of similar nature to the wanted signal.

| Point | Noise | Interference |
|---|---|---|
| Nature | Random, statistical | Usually deterministic, structured |
| Source | Thermal agitation, shot effect, atmosphere, cosmic | Other transmitters, machines, power lines, crosstalk |
| Spectrum | Broad, often white | At specific frequencies of the interferer |
| Predictability | Cannot be predicted exactly | Can often be identified and located |
| Removal | Cannot be removed fully; only reduced | Can often be eliminated by filtering, shielding, planning |
| Example | Hiss in a receiver, snow on TV | Adjacent channel station, ignition noise, hum |

#### Limitations posed by noise
1. **Limits SNR and quality:** analog output becomes noisy; digital links suffer bit errors.
2. **Limits channel capacity:** by Shannon, $C=B\log_2(1+S/N)$; lower SNR means lower maximum data rate.
3. **Limits range:** the signal weakens with distance while noise stays, so repeaters are needed.
4. **Sets receiver sensitivity:** the minimum detectable signal is fixed by the noise floor ($kTB$ and noise figure).
5. **Forces more power or bandwidth:** higher transmitter power, low-noise amplifiers or wideband modulation (FM, spread spectrum) are needed.

#### Limitations posed by interference
1. **Crosstalk and unwanted programmes** in the receiver, reducing intelligibility.
2. **Limits spectrum reuse:** stations need guard bands and geographic separation, reducing the number of channels.
3. **Image and adjacent-channel problems** require better selectivity, raising receiver cost.
4. **Jamming** can block a link completely in strong interference.
5. **Requires shielding, filtering and regulation**, adding design cost.

## Check yourself

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

1. Which is true?
   A. Noise can be eliminated completely, interference cannot
   B. Neither can be reduced
   C. Noise can only be reduced, while interference can often be eliminated by filtering or shielding
   D. Both are removed by amplification
   Answer: C. Noise is random and cannot be fully removed. (Key point: Removal)

2. How does noise limit data rate?
   A. Capacity C=B log2(1+S/N) falls with lower SNR
   B. It increases B
   C. It has no effect
   D. Capacity depends only on power
   Answer: A. Shannon capacity depends on SNR. (Key point: Capacity)

3. What sets the minimum detectable signal?
   A. Antenna colour
   B. The noise floor (kTB and noise figure)
   C. Carrier phase
   D. The modulation index only
   Answer: B. Sensitivity is limited by the noise floor. (Key point: Receiver sensitivity)

4. What does interference limit?
   A. Thermal noise level
   B. Shannon's constant
   C. Antenna length
   D. Frequency reuse, needing guard bands and geographic separation
   Answer: D. Interference forces guard bands, reducing number of channels. (Key point: Spectrum reuse)

## Related in Communication Systems

- [Noise vs interference vs distortion](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-interference-distortion) — Communication Systems, chapter 1
- [Noise vs interference; minimizing effects; need for modulation](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-interference-minimize-modulation-need) — Communication Systems, chapter 1
- [Distortion vs noise vs interference](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adistortion-noise-interference-diff) — Communication Systems, chapter 1
- [Reasons for modulation; noise vs distortion vs interference](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Amodulation-reasons-noise-distortion-compare) — Communication Systems, chapter 1
- [External vs internal noise; interference sources; need for modulation](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aexternal-internal-noise-interference-needs) — Communication Systems, chapter 1
- [Distortion, noise, interference; four types of noise](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adistortion-noise-interference-four-noise) — Communication Systems, chapter 1

## Related in other subjects

- [Short note: Interference in mobile communication](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Ainterference-mobile-communication) — Wireless Communication, chapter 2
- [Limitations of single bus system](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Asingle-bus-limit) — Computer Organization and Architecture, chapter 1, asked 2×
- [Block diagram of digital communication system](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Ablock-diagram-digital-comm) — Data Communication, chapter 1, asked 8×
- [Communication system and block diagram](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Acomm-system-block-diagram) — Basic Electronics Engineering, chapter 5, asked 7×