---
title: "Co-channel and adjacent channel interference"
subject: "Wireless Communication"
chapter: 2
key: "semester_7/wireless_communication:cochannel-adjacent-interference-terms"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/cochannel-adjacent-interference-terms
site: BCT Engineering
---

# Co-channel and adjacent channel interference

Wireless Communication · Chapter 2: Cellular Mobile Communication Concepts

- Asked in: 2080 Chaitra, 2.5+2.5 marks
- Video: [Wireless Technology | Tutorial #15 | Co-Channel Interference (CCI)](https://www.youtube.com/watch?v=LDlGN5iXOL8) — RANJI RAJ
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/wireless_communication/cochannel-adjacent-interference-terms
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-2

## Question

Explain the following terminologies: (i) Co-channel interference (ii) Adjacent channel interference.

## Short answer

Co‑channel interference is caused by cells using the same frequencies, reduced by greater reuse distance Q = √(3N). Adjacent channel interference is from adjacent frequencies leaking due to imperfect filters and near‑far effect, mitigated by better filtering and channel assignment.

## Answer

#### Co-channel interference (CCI)
- Interference between signals from **cells that use the same set of frequencies** (co-channel cells) under frequency reuse.
- Cannot be removed by increasing transmitter power, because the interfering signal grows equally. It is reduced only by **physically separating co-channel cells** by a minimum distance D, i.e. a larger reuse ratio Q = D/R = √(3N), or by sectoring.
- Measured by S/I = (√(3N))ⁿ / i₀ for the first tier of i₀ interferers. AMPS needs S/I ≥ 18 dB, which gives N = 7 with n = 4.

#### Adjacent channel interference (ACI)
- Interference from signals at **frequencies adjacent (next) to the wanted signal**, caused by imperfect receiver filters letting nearby frequencies leak into the passband.
- Becomes serious through the **near–far effect**: a nearby transmitter on an adjacent channel overpowers a weak, distant wanted signal.
- Reduced by careful **filtering** and **channel assignment** – not assigning adjacent channels in the same cell, keeping a large frequency separation between channels in a cell (e.g. channels 1, 22, 43, … in AMPS), and power control.

| Point | Co-channel | Adjacent channel |
|---|---|---|
| Source | Same frequency in other cells | Neighbouring frequency |
| Cause | Frequency reuse | Imperfect filtering, near–far effect |
| Remedy | Larger D/R, sectoring | Better filters, channel separation, power control |
| Depends on | Cluster size N | Filter selectivity, channel plan |

## Check yourself

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

1. Co-channel interference arises between:
   A. Adjacent frequencies in the same cell
   B. Cells that use the same set of frequencies
   C. Mobiles and satellites
   D. Base stations and the MSC
   Answer: B. It is caused by frequency reuse. (Key point: CCI meaning)

2. The effective way to reduce CCI is:
   A. Increase power
   B. Use cheaper filters
   C. Assign adjacent channels in the same cell
   D. Increase separation D (larger D/R) or use sectoring
   Answer: D. Power increase does not help since the interference increases equally. (Key point: CCI cure)

3. ACI is caused by:
   A. Imperfect receiver filters letting nearby frequencies leak into the passband
   B. Reuse of identical frequencies
   C. Cluster size being too large
   D. Handoff failures
   Answer: A. Signals at neighbouring frequencies leak through. (Key point: ACI cause)

4. Which measure reduces ACI?
   A. Using adjacent channels in the same cell
   B. Reducing D/R
   C. Large frequency separation between channels in a cell and good filtering
   D. Increasing cluster size only
   Answer: C. Channel assignment, filtering and power control address ACI. (Key point: ACI cure)

## Related in Wireless Communication

- [CCI vs ACI and co-channel reuse ratio proof](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Acci-aci-prove-reuse-ratio) — Wireless Communication, chapter 2
- [Derivation of co-channel reuse ratio](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aderive-cochannel-reuse-ratio) — Wireless Communication, chapter 2
- [Numerical: co-channel distance for 7-cell reuse](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Acochannel-distance-seven-cell) — Wireless Communication, chapter 2
- [Frequency reuse and co-channel reuse ratio](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afrequency-reuse-cochannel-reuse-ratio) — Wireless Communication, chapter 2

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