---
title: "Frequency reuse and channel assignment strategies"
subject: "Wireless Communication"
chapter: 2
key: "semester_7/wireless_communication:frequency-reuse-channel-assignment"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/frequency-reuse-channel-assignment
site: BCT Engineering
---

# Frequency reuse and channel assignment strategies

Wireless Communication · Chapter 2: Cellular Mobile Communication Concepts

- Asked in: 2082 Baisakh, 2+4 marks
- Video: [Channel Assignment - Cellular Concept - Wireless Mobile Communication](https://www.youtube.com/watch?v=j9uKSOTgukQ) — 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/frequency-reuse-channel-assignment
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-2

## Question

What do you mean by frequency reuse? Explain various channel assignment strategies used in mobile communication.

## Short answer

Frequency reuse uses the same channels in cells far enough apart to keep co-channel interference acceptable, increasing capacity without extra spectrum. Channel assignment strategies are fixed (with borrowing), dynamic, and hybrid.

## Answer

#### Frequency reuse
**Frequency reuse** is the use of the same radio channels in different cells that are far enough apart that their co-channel interference stays within limits. The total channels S are divided among N cells of a cluster, and the cluster is repeated M times over the service area, so capacity C = M × S grows with the number of clusters without extra spectrum.

```text
        ___
    ___/ 2 \___
   / 7 \___/ 3 \      One N = 7 cluster: each cell
   \___/ 1 \___/      uses a different channel set.
   / 6 \___/ 4 \      The cluster is repeated, so the
   \___/ 5 \___/      next cell "1" is D = 4.58R away.
       \___/
```

#### Channel assignment strategies
1. **Fixed channel assignment (FCA)**
   - Each cell is given a fixed set of channels in advance.
   - A call is blocked if all channels of that cell are busy.
   - **Borrowing strategy:** a cell may borrow a channel from a neighbouring cell if none of its own is free; the MSC ensures the borrowed channel does not cause interference.
   - Simple and needs little control, but cannot adapt to changing traffic.

2. **Dynamic channel assignment (DCA)**
   - Channels are not permanently assigned; on each call request the MSC allocates a channel from the common pool using an algorithm that considers future blocking, reuse distance, channel usage and cost.
   - Uses channels efficiently and lowers blocking, but needs real-time data collection and heavy MSC computation.

3. **Hybrid channel assignment** – some channels fixed in each cell, the rest in a common pool assigned dynamically.

| Point | Fixed | Dynamic |
|---|---|---|
| Allocation | Pre-planned | On demand |
| Blocking at high load | Higher | Lower |
| Control complexity | Low | High |
| Adapts to traffic | No (only borrowing) | Yes |

## Check yourself

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

1. What is frequency reuse in a cellular system?
   A. Using every channel in every adjacent cell at the same time
   B. Using the same channels in different cells that are far enough apart for co-channel interference to stay within limits
   C. Using one channel for several calls in the same cell
   D. Increasing transmitter power so the same channel covers a larger area
   Answer: B. Frequency reuse repeats the same channels in distant cells, so capacity grows with the number of clusters without extra spectrum. (Key point: Meaning of frequency reuse)

2. If S channels are split among N cells of a cluster and the cluster is repeated M times, the system capacity is:
   A. C = S / N
   B. C = N x S
   C. C = M / S
   D. C = M x S
   Answer: D. Each cluster uses all S channels and there are M clusters, so C = M x S. (Key point: Capacity with clusters)

3. In fixed channel assignment (FCA), what happens when all channels of a cell are busy?
   A. The new call is blocked, unless a channel can be borrowed from a neighbouring cell
   B. A channel is always allocated from a common pool by the MSC
   C. The call is queued forever until a channel frees
   D. The cell automatically increases its transmit power to get more channels
   Answer: A. FCA gives each cell a pre-set channel group, so a call is blocked when they are used up; borrowing is the only flexibility. (Key point: Fixed channel assignment)

4. Which statement correctly describes dynamic channel assignment (DCA)?
   A. Channels are permanently pre-assigned to cells, giving low control complexity
   B. It needs no real-time data and has the simplest control
   C. Channels are allocated from a common pool on each call request, giving lower blocking but needing heavy MSC computation
   D. It gives higher blocking than FCA at high load
   Answer: C. DCA allocates channels on demand using real-time information, which lowers blocking but raises MSC complexity. (Key point: Dynamic channel assignment)

## Related in Wireless Communication

- [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
- [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
- [Parameters of mobile multipath channel](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Amobile-multipath-channel-parameters) — Wireless Communication, chapter 3
- [3G versus 4G mobile communication](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3A3g-vs-4g) — Wireless Communication, chapter 1, asked 6×

## Related in other subjects

- [Static channel assignment and CSMA/CD](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Astatic-channel-csmacd) — Computer Networks and Security, chapter 3
- [Channel in communication system and its classification](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Achannel-classification) — Communication Systems, chapter 1
- [Advantages of digital communication; source and channel encoders](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adigital-advantages-source-channel-encoders) — Communication Systems, chapter 1
- [In-channel multi-frequency signaling design](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Ainchannel-mf-design) — Telecommunications, chapter 5