813  IoT Frequency Bands and Licensing

813.1 Introduction

⏱️ ~8 min | ⭐⭐ Intermediate | πŸ“‹ P08.C16B.U01

Building on the electromagnetic fundamentals from the previous chapter, this chapter explores the specific frequency bands used for IoT communication and the regulatory frameworks that govern their use. Understanding these bands and their trade-offs is essential for selecting the right wireless technology for your application.

NoteLearning Objectives

By the end of this chapter, you will be able to:

  • Compare 2.4 GHz, 5 GHz, and sub‑GHz bands for range, penetration, interference, and data rate trade-offs
  • Explain channel allocation and interference in the 2.4 GHz ISM band
  • Distinguish licensed vs unlicensed spectrum and common regulatory constraints
  • Identify regional spectrum variations and compliance requirements (FCC, ETSI, etc.)
  • Apply ISM band regulations including power limits and duty cycle restrictions

813.2 Prerequisites

Before diving into this chapter, you should be familiar with:

Series Navigation: - Previous: Electromagnetic Waves and Spectrum Basics - Next: Cellular Spectrum for IoT - Next: Propagation and Design

Specific Technologies: - Wi-Fi Fundamentals - 2.4 GHz and 5 GHz details - Bluetooth Overview - 2.4 GHz frequency hopping - LoRaWAN Overview - Sub-GHz LPWAN - LPWAN Fundamentals - Sub-GHz technology comparison

813.3 IoT Wireless Frequency Bands

⏱️ ~20 min | ⭐⭐ Intermediate | πŸ“‹ P08.C16B.U02

813.3.1 The 2.4 GHz ISM Band

The 2.4 GHz band (2.400 - 2.483 GHz) is the most commonly used frequency range for local and personal area IoT networks. It’s part of the Industrial, Scientific, and Medical (ISM) radio bands, which are unlicensed and available worldwide.

Advantages: - Globally unlicensed (no licensing fees) - Widespread device support - Mature technology ecosystem - Good balance of range and bandwidth

Challenges: - Heavy congestion (Wi-Fi, Bluetooth, Zigbee, microwave ovens) - Interference from multiple sources - Limited number of non-overlapping channels

%% fig-cap: "2.4 GHz ISM band channel allocation and overlap"
%% fig-alt: "Diagram showing 2.4 GHz ISM band from 2400-2483 MHz with Wi-Fi channels 1, 6, 11 (22 MHz wide each) and Zigbee channels (2 MHz wide) overlaid, illustrating channel overlap and interference zones, plus non-overlapping Zigbee channels 15, 20, 25, 26 between Wi-Fi channels"
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graph TB
    A["2.4 GHz ISM Band<br/>2400 - 2483 MHz"] --> B["Wi-Fi Channels<br/>22 MHz wide<br/>Ch 1, 6, 11 non-overlapping"]
    A --> C["Zigbee/802.15.4<br/>2 MHz wide<br/>Channels 11-26"]
    A --> D["Bluetooth<br/>79 channels<br/>Freq hopping"]

    B --> B1["Channel 1: 2401-2423 MHz<br/>Channel 6: 2426-2448 MHz<br/>Channel 11: 2451-2473 MHz"]
    C --> C1["Safe Channels:<br/>Ch 15, 20, 25, 26<br/>Between Wi-Fi channels"]
    D --> D1["Adaptive Hopping<br/>Avoids busy channels<br/>79 Γ— 1 MHz hops"]

    style A fill:#2C3E50,stroke:#16A085,stroke-width:3px,color:#fff
    style B fill:#E67E22,stroke:#16A085,stroke-width:2px
    style C fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style D fill:#E67E22,stroke:#16A085,stroke-width:2px

Figure 813.1: How wide Wi-Fi channels can overlap multiple Zigbee channels in the 2.4 GHz ISM band (and which Zigbee channels tend to be safer).

Common IoT protocols using 2.4 GHz: - Wi-Fi (IEEE 802.11 b/g/n) - Bluetooth and Bluetooth Low Energy (BLE) - Zigbee (IEEE 802.15.4) - Thread (IPv6-based mesh)

813.3.2 The 5 GHz Band

The 5 GHz band (primarily 5.150 - 5.875 GHz) offers higher bandwidth and less congestion than 2.4 GHz. It’s used mainly for Wi-Fi (IEEE 802.11a/n/ac/ax) and provides:

Advantages: - Higher data rates (more bandwidth available) - Less interference from non-Wi-Fi devices - More non-overlapping channels (23+ in most regions)

Limitations: - Shorter range than 2.4 GHz - Reduced penetration through walls and obstacles - Higher power consumption - Not supported by all IoT devices

%% fig-cap: "5 GHz band characteristics and channel allocation"
%% fig-alt: "5 GHz Wi-Fi band allocation showing UNII-1 (5150-5250 MHz), UNII-2 (5250-5350 MHz), UNII-2 Extended (5470-5725 MHz), and UNII-3 (5725-5875 MHz) bands with 20/40/80/160 MHz channel widths, DFS requirements, and 23+ non-overlapping channels"
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graph TB
    A["5 GHz Wi-Fi Band<br/>5150 - 5875 MHz"] --> B["UNII-1<br/>5150-5250 MHz<br/>4 channels indoor"]
    A --> C["UNII-2/2e<br/>5250-5725 MHz<br/>DFS required"]
    A --> D["UNII-3<br/>5725-5875 MHz<br/>7 channels outdoor"]

    B --> B1["βœ“ No DFS<br/>βœ“ Indoor use<br/>Lower power"]
    C --> C1["⚠ Radar detection<br/>⚠ Channel switching<br/>Higher power"]
    D --> D1["βœ“ No DFS<br/>βœ“ Outdoor use<br/>Highest power"]

    A --> E["Channel Widths:<br/>20/40/80/160 MHz<br/>23+ non-overlapping"]

    style A fill:#2C3E50,stroke:#16A085,stroke-width:3px,color:#fff
    style B fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style C fill:#E67E22,stroke:#16A085,stroke-width:2px
    style D fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style E fill:#E67E22,stroke:#16A085,stroke-width:2px

Figure 813.2: 5 GHz Wi-Fi channel groups (UNII-1/2/2e/3) and typical DFS considerations (region-dependent).

813.3.3 Sub-GHz Bands

Sub-GHz frequencies (below 1 GHz) are increasingly popular for IoT applications requiring long range and low power consumption. Common bands include:

  • 868 MHz (Europe): LoRa, Sigfox, Z-Wave
  • 915 MHz (North America): LoRa, Sigfox, Z-Wave
  • 433 MHz (Worldwide): Simple remote controls, sensors

Characteristics: - Excellent range (kilometers in open areas) - Superior building penetration - Lower power consumption - Lower data rates - Regional frequency variations (licensing requirements vary)

%% fig-cap: "Sub-GHz frequency bands for IoT by region"
%% fig-alt: "Regional sub-GHz ISM band allocation showing 433 MHz (region-dependent), 868 MHz (Europe ETSI), 915 MHz (North America FCC), and 920-928 MHz (Asia-Pacific) with power limits and duty cycle restrictions, used by LoRaWAN, Sigfox, Z-Wave, and other sub-GHz ISM devices"
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graph TB
    A["Sub-GHz IoT Bands"] --> B["433 MHz<br/>Global ISM<br/>10 mW typical"]
    A --> C["868 MHz<br/>Europe ETSI<br/>25 mW, 1% duty"]
    A --> D["915 MHz<br/>US/Americas FCC<br/>1W, no duty limit"]
    A --> E["920-928 MHz<br/>Asia-Pacific<br/>Varies by country"]

    B --> B1["Simple remotes<br/>Garage doors<br/>Sensors"]
    C --> C1["LoRa EU<br/>Sigfox EU<br/>Z-Wave EU"]
    D --> D1["LoRa US<br/>Sigfox US<br/>Z-Wave US"]
    E --> E1["LoRa Asia<br/>Regional variants"]

    style A fill:#2C3E50,stroke:#16A085,stroke-width:3px,color:#fff
    style B fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style C fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style D fill:#E67E22,stroke:#16A085,stroke-width:2px
    style E fill:#E67E22,stroke:#16A085,stroke-width:2px

Figure 813.3: Common sub‑GHz ISM allocations by region (e.g., EU868, US915, AS923) and why multi-region devices need configurable bands.

813.4 Spectrum Licensing

⏱️ ~12 min | ⭐⭐ Intermediate | πŸ“‹ P08.C16B.U03

TipMinimum Viable Understanding: ISM Band Regulations

Core Concept: ISM (Industrial, Scientific, Medical) bands are unlicensed frequency allocations where anyone can transmit without a license, but must follow strict rules on transmit power (EIRP), duty cycle, and channel access methods set by regional regulators (FCC in US, ETSI in Europe, etc.).

Why It Matters: Violating ISM regulations can result in product recalls, fines, and legal liability. The rules differ significantly by region: EU868 limits devices to 14 dBm EIRP with 1% duty cycle (36 seconds per hour), while US915 allows 30 dBm with no duty cycle limit but requires frequency hopping. A device certified for US deployment will be illegal in Europe, and vice versa.

Key Takeaway: Before any IoT product deployment, identify your target regions and verify compliance with local regulations. For global products, design firmware that supports region-specific configurations (frequency, power, duty cycle). Use pre-certified radio modules (FCC/CE/IC marked) to simplify compliance testing, but remember that the final product still requires certification in most jurisdictions.

813.4.1 Licensed vs Unlicensed Spectrum

Radio frequency spectrum is a finite resource regulated by governmental bodies. Understanding the distinction between licensed and unlicensed spectrum is crucial for IoT deployment.

%% fig-cap: "Licensed vs unlicensed spectrum characteristics and trade-offs"
%% fig-alt: "Comparison diagram showing licensed spectrum (exclusive use, requires fees, protected from interference, used by cellular operators for 4G/5G) versus unlicensed ISM bands (free to use, shared spectrum, subject to power limits, used by Wi-Fi/Bluetooth/LoRa) with respective advantages and limitations"
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graph LR
    A["RF Spectrum<br/>Allocation"] --> B["Licensed Spectrum<br/>Cellular Operators"]
    A --> C["Unlicensed ISM<br/>Anyone can use"]

    B --> B1["βœ“ Exclusive rights<br/>βœ“ No interference<br/>βœ“ Guaranteed QoS<br/>βœ— Expensive fees"]
    C --> C1["βœ“ Free to use<br/>βœ“ Global standards<br/>βœ— Shared/crowded<br/>βœ— Interference risk"]

    B --> B2["4G LTE<br/>5G NR<br/>NB-IoT (licensed)"]
    C --> C2["Wi-Fi<br/>Bluetooth<br/>LoRa, Zigbee"]

    B1 --> D["Regulatory<br/>Approval<br/>Required"]
    C1 --> E["Follow<br/>Power/Duty<br/>Limits"]

    style A fill:#2C3E50,stroke:#16A085,stroke-width:3px,color:#fff
    style B fill:#E67E22,stroke:#16A085,stroke-width:2px
    style C fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff
    style D fill:#E67E22,stroke:#16A085,stroke-width:2px
    style E fill:#16A085,stroke:#2C3E50,stroke-width:2px,color:#fff

Figure 813.4: Trade-offs between licensed spectrum (managed interference/QoS) and unlicensed ISM bands (shared access, higher interference risk).

Licensed Spectrum: - Requires regulatory approval and fees - Exclusive use rights (cellular operators) - Protected from interference - Examples: 4G LTE (700-2600 MHz), 5G (3.5 GHz, mmWave)

Unlicensed Spectrum (ISM Bands): - Free to use (within regulatory limits) - Shared among many users and devices - Subject to power and duty cycle restrictions - Examples: 2.4 GHz, 5 GHz, 868/915 MHz

813.4.2 Regional Variations

Different countries allocate spectrum differently. IoT devices must comply with regional regulations:

Region Sub‑GHz (common ISM) 2.4 GHz ISM 5 GHz Wi‑Fi Notes
Europe EU868 (863–870 MHz) 2.400–2.4835 GHz Region-specific (5 GHz sub‑bands; DFS/power vary) ETSI regulations
North America US915 (902–928 MHz) 2.400–2.4835 GHz Region-specific (5 GHz sub‑bands; DFS/power vary) FCC Part 15
Asia-Pacific Varies (e.g., AS923 / 920–928 MHz) 2.400–2.4835 GHz Varies by country Always check local rules
Global (short range) 315/433 MHz (region-dependent) Universal Varies by country Common for simple remotes; verify allocations
WarningTradeoff: Sub-GHz (868/915 MHz) vs 2.4 GHz Band

Option A (Sub-GHz): Range 2-15 km outdoor, +157 dB link budget (LoRa SF12), excellent wall penetration (-3 dB per concrete wall), bandwidth 0.3-50 kbps, 10+ year battery life on 2xAA cells. Path loss at 1 km: ~92 dB.

Option B (2.4 GHz): Range 50-300m indoor/outdoor, +100 dB link budget (BLE), moderate penetration (-6 dB per concrete wall), bandwidth 250 kbps-2 Mbps, 1-5 year battery life. Path loss at 100m: ~80 dB.

Decision Factors: Choose Sub-GHz for rural deployments, outdoor sensors, smart agriculture, or utility metering where range exceeds 500m. Choose 2.4 GHz for smart home, building automation, wearables, or any application requiring >100 kbps throughput or existing Wi-Fi/BLE ecosystem integration.

813.5 Summary

This chapter covered IoT frequency bands and spectrum licensing:

  • 2.4 GHz ISM band is globally available but congested; Wi-Fi channels 1, 6, 11 are non-overlapping; Zigbee channels 15, 20, 25, 26 avoid Wi-Fi interference
  • 5 GHz band offers more bandwidth and less congestion but shorter range and requires DFS in some sub-bands
  • Sub-GHz bands (433, 868, 915 MHz) provide excellent range and penetration but vary by region
  • Licensed spectrum provides guaranteed QoS but requires fees; unlicensed ISM bands are free but shared
  • Regional regulations differ significantly; devices must comply with local power limits, duty cycles, and certification requirements

813.6 What’s Next

Continue with the next chapters in this series:

813.7 Knowledge Check

  1. In the 2.4 GHz ISM band, which Zigbee channel is typically chosen to sit between Wi-Fi channels 1 and 6 to reduce overlap?

Wi-Fi channel 1 occupies roughly 2401–2423 MHz and channel 6 occupies roughly 2426–2448 MHz; Zigbee channel 15 (centered at 2425 MHz) falls in the gap between them and is commonly used as a β€œsafer” choice.

  1. Which statement best captures the trade-off between licensed and unlicensed spectrum for IoT?

Licensed spectrum is managed (often by carriers), which can improve reliability and reduce interference, but it comes with costs and regulatory/operational constraints; unlicensed is free but shared.

  1. What is the main reason sub-GHz bands (868/915 MHz) achieve longer range than 2.4 GHz?

Free-space path loss increases with frequency (20Β·log₁₀(f) term in FSPL). Lower frequencies also diffract around obstacles better and penetrate building materials more effectively.

Scenario: A 15-floor commercial building uses Wi-Fi for laptops/phones (channels 1, 6, 11) and Zigbee for 500 lighting sensors, thermostats, and door locks. Network ops reports: Zigbee sensors on floors 8-12 experience 20-40% packet loss during peak Wi-Fi usage (9-11am, 1-3pm). Wi-Fi operates at +20 dBm, Zigbee at 0 dBm (typical). Building has 3 Wi-Fi access points per floor using channels 1, 6, and 11.

Think about: 1. Why does a 22 MHz-wide Wi-Fi channel (e.g., channel 1 at 2.401-2.423 GHz) overlap multiple 2 MHz-wide Zigbee channels? 2. How does the 20 dB power difference (+20 dBm Wi-Fi vs 0 dBm Zigbee) affect interference visibility? 3. Which Zigbee channels (11-26) fall into the β€œgaps” between Wi-Fi channels 1, 6, and 11?

Key Insight: Careful channel planning eliminates interference without changing hardware:

The 2.4 GHz ISM Band Overlap:

Wi-Fi Channels (22 MHz wide):
Ch 1:  2401-2423 MHz  β–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆ
Ch 6:  2426-2448 MHz            β–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆ
Ch 11: 2451-2473 MHz                      β–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆβ–ˆ

Zigbee Channels (2 MHz wide):
Ch 11: 2405 MHz  β–ˆβ–ˆ
Ch 12: 2410 MHz    β–ˆβ–ˆ
Ch 13: 2415 MHz      β–ˆβ–ˆ
Ch 14: 2420 MHz        β–ˆβ–ˆ
Ch 15: 2425 MHz          β–ˆβ–ˆ  ← Between Wi-Fi 1 & 6
Ch 16: 2430 MHz            β–ˆβ–ˆ
...
Ch 20: 2450 MHz                        β–ˆβ–ˆ  ← Between Wi-Fi 6 & 11
...
Ch 25: 2475 MHz                                    β–ˆβ–ˆ  ← Above Wi-Fi 11
Ch 26: 2480 MHz                                      β–ˆβ–ˆ  ← Above Wi-Fi 11

Safe Zigbee Channels (non-overlapping with Wi-Fi 1, 6, 11): - Channel 15 (2425 MHz): Gap between Wi-Fi 1 and 6 - Channel 20 (2450 MHz): Gap between Wi-Fi 6 and 11 - Channel 25 (2475 MHz): Above Wi-Fi 11 - Channel 26 (2480 MHz): Above Wi-Fi 11

Verify Your Understanding: - If you wanted to add Bluetooth devices on the same network, which Zigbee channels would you choose to minimize interference with both Wi-Fi and Bluetooth? - How would you use a spectrum analyzer to verify channel selection in a live deployment?