804 IoT Wireless Frequency Bands

804.1 Introduction

This chapter explores the specific frequency bands used in IoT applications: the 2.4 GHz ISM band, 5 GHz Wi-Fi band, and sub-GHz bands. Understanding the characteristics, advantages, and limitations of each band is crucial for selecting the right wireless technology for your IoT deployment.

Learning Objectives

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

Understand the characteristics of the 2.4 GHz ISM band and its challenges
Compare 5 GHz vs 2.4 GHz trade-offs for range, bandwidth, and interference
Identify sub-GHz bands and their regional variations
Select appropriate frequency bands based on application requirements

804.2 Prerequisites

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

Electromagnetic Waves and the Spectrum: Understanding electromagnetic wave properties and the radio spectrum
Basic networking concepts: Familiarity with wireless communication principles

804.3 IoT Wireless Frequency Bands

⏱️ ~20 min | ⭐⭐ Intermediate | 📋 P08.C18.U04

804.3.1 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"
%%{init: {'theme': 'base', 'themeVariables': { 'primaryColor': '#2C3E50', 'primaryTextColor': '#2C3E50', 'primaryBorderColor': '#16A085', 'lineColor': '#16A085', 'secondaryColor': '#E67E22', 'tertiaryColor': '#ECF0F1'}}}%%
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 × 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 804.1: Diagram showing 2.4 GHz ISM band channel allocation with Wi-Fi, Zigbee, and Bluetooth

Alternative View: 2.4 GHz Interference Sources and Mitigation

This variant shows all the interference sources in the crowded 2.4 GHz band and how to mitigate them:

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#2C3E50', 'primaryTextColor': '#fff', 'primaryBorderColor': '#16A085', 'lineColor': '#E67E22', 'secondaryColor': '#16A085', 'tertiaryColor': '#7F8C8D', 'fontSize': '11px'}}}%%
graph TB
    subgraph SOURCES["Interference Sources at 2.4 GHz"]
        S1["Wi-Fi Networks<br/>(20-40 MHz channels)"]
        S2["Bluetooth/BLE<br/>(1 MHz hopping)"]
        S3["Zigbee/Thread<br/>(2 MHz channels)"]
        S4["Microwave Ovens<br/>(2.45 GHz broadband)"]
        S5["USB 3.0 Cables<br/>(EMI leakage)"]
        S6["Baby Monitors<br/>(analog/digital)"]
    end

    subgraph MITIGATE["Mitigation Strategies"]
        M1["Use Wi-Fi Ch 1/6/11<br/>(non-overlapping)"]
        M2["BLE Adaptive Hopping<br/>(avoids busy channels)"]
        M3["Zigbee Ch 25-26<br/>(above Wi-Fi Ch 11)"]
        M4["Physical distance<br/>from microwaves"]
        M5["Shield USB cables<br/>or use USB 2.0"]
        M6["Spectrum analyzer<br/>before deployment"]
    end

    S1 --> M1
    S2 --> M2
    S3 --> M3
    S4 --> M4
    S5 --> M5
    S6 --> M6

    style SOURCES fill:#E67E22,stroke:#2C3E50,color:#fff
    style MITIGATE fill:#16A085,stroke:#2C3E50,color:#fff

The 2.4 GHz band is extremely crowded. Best practices: survey the spectrum before deployment, use non-overlapping channels, and consider 5 GHz or sub-GHz alternatives when interference is severe.

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)

Show code

viewof kc_mwireless_3 = InlineKnowledgeCheck({
  id: "kc-mwireless-3",
  question: "Your Zigbee smart home network experiences intermittent disconnections. Wi-Fi channel scanner shows heavy Wi-Fi traffic on channels 1, 6, and 11. Which Zigbee channel(s) would minimize interference?",
  choices: [
    "Zigbee channel 11 (overlaps Wi-Fi channel 1)",
    "Zigbee channels 15, 20, 25, or 26 (between Wi-Fi channels)",
    "Zigbee channel 26 (highest frequency, most power)",
    "Use any channel and enable frequency hopping"
  ],
  correctIndex: 1,
  explanation: "Zigbee channels should be selected to avoid overlapping with Wi-Fi's three non-overlapping channels (1, 6, 11). Wi-Fi channels are 22 MHz wide, while Zigbee channels are only 2 MHz wide. Zigbee channels 15, 20, 25, and 26 fall between the Wi-Fi channels and experience minimal interference. Channel 26 is particularly popular as it sits above Wi-Fi channel 11. The diagram in the text shows these 'safe' channels positioned between the wide Wi-Fi channels, providing the best coexistence strategy."
})

Show code

viewof kc_mwireless_4 = InlineKnowledgeCheck({
  id: "kc-mwireless-4",
  question: "A factory deploys 50 Wi-Fi access points on 2.4 GHz. Despite using channels 1, 6, and 11, packet loss is high. A spectrum analyzer reveals broadband interference at 2.45 GHz every 2 minutes. What is the most likely cause?",
  choices: [
    "Bluetooth devices are using adaptive frequency hopping",
    "Industrial microwave ovens are heating materials",
    "USB 3.0 cables are leaking electromagnetic interference",
    "Neighboring Wi-Fi networks are overlapping"
  ],
  correctIndex: 1,
  explanation: "Microwave ovens operate at 2.45 GHz (center of the 2.4 GHz ISM band) and emit broadband interference when active. The 2-minute periodic pattern suggests scheduled industrial heating cycles. Microwave interference is particularly damaging because it's broadband (affects all 2.4 GHz channels simultaneously) and high-power (often exceeding Wi-Fi signals by 20+ dB). Bluetooth uses narrowband 1 MHz channels with rapid hopping, USB 3.0 causes continuous low-level interference, and overlapping Wi-Fi networks would show as discrete channel interference rather than broadband noise."
})

804.3.2 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"
%%{init: {'theme': 'base', 'themeVariables': { 'primaryColor': '#2C3E50', 'primaryTextColor': '#2C3E50', 'primaryBorderColor': '#16A085', 'lineColor': '#16A085', 'secondaryColor': '#E67E22', 'tertiaryColor': '#ECF0F1'}}}%%
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["✓ No DFS<br/>✓ Indoor use<br/>Lower power"]
    C --> C1["⚠ Radar detection<br/>⚠ Channel switching<br/>Higher power"]
    D --> D1["✓ No DFS<br/>✓ 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 804.2: 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) band…

804.3.3 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)

Show code

viewof kc_mwireless_5 = InlineKnowledgeCheck({
  id: "kc-mwireless-5",
  question: "A European company designs a LoRa-based agricultural sensor for 868 MHz with 25 mW transmit power and 100% duty cycle. When deployed in the US market at 915 MHz, what compliance issue will arise?",
  choices: [
    "915 MHz is not available in the US—must use 868 MHz",
    "25 mW power is too low—FCC allows up to 1W (1000 mW)",
    "1% duty cycle limit in Europe is not a problem in US, but frequency must change to 915 MHz",
    "Design already compliant—no changes needed"
  ],
  correctIndex: 2,
  explanation: "Europe's 868 MHz band has a 1% duty cycle restriction (transmit max 36 seconds per hour) under ETSI regulations, while the US 915 MHz band under FCC Part 15 has no duty cycle limit but requires frequency change. The European design's 100% duty cycle would violate ETSI rules but is perfectly legal in the US at 915 MHz. The 25 mW power is conservative (FCC allows up to 1W), so no power increase needed. This regional variation is why many IoT devices have separate hardware variants for EU (868 MHz) and US (915 MHz) markets."
})

Show code

viewof kc_mwireless_6 = InlineKnowledgeCheck({
  id: "kc-mwireless-6",
  question: "A smart city project needs 10 km rural range with 10-year battery life. Data payload: temperature reading every hour (20 bytes). Which frequency band and technology combination is most appropriate?",
  choices: [
    "5 GHz Wi-Fi with sleep mode between transmissions",
    "2.4 GHz Zigbee mesh network with multiple hops",
    "Sub-GHz LoRaWAN at 868/915 MHz with SF12 spreading factor",
    "Licensed cellular NB-IoT for guaranteed quality of service"
  ],
  correctIndex: 2,
  explanation: "Sub-GHz LoRaWAN perfectly matches these requirements: (1) 10+ km range with direct gateway connectivity (no multi-hop overhead), (2) Excellent path loss characteristics at 868/915 MHz (~9 dB better than 2.4 GHz), (3) Extremely low power consumption (10+ year battery life standard for hourly readings), (4) SF12 spreading factor provides maximum range at cost of lower data rate (acceptable for 20 bytes/hour). Wi-Fi 5 GHz has range <100m and high power consumption. 2.4 GHz Zigbee requires multi-hop infrastructure for 10 km (complex, expensive, higher power from forwarding). Cellular NB-IoT requires monthly operator fees and subscription management."
})

%% fig-cap: "Sub-GHz frequency bands for IoT by region"
%% fig-alt: "Regional sub-GHz ISM band allocation showing 433 MHz (global unlicensed), 868 MHz (Europe ETSI), 915 MHz (North America FCC), and 920-928 MHz (Asia-Pacific) with power limits and duty cycle restrictions, used by LoRa, Sigfox, NB-IoT, and Z-Wave protocols"
%%{init: {'theme': 'base', 'themeVariables': { 'primaryColor': '#2C3E50', 'primaryTextColor': '#2C3E50', 'primaryBorderColor': '#16A085', 'lineColor': '#16A085', 'secondaryColor': '#E67E22', 'tertiaryColor': '#ECF0F1'}}}%%
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 804.3: Regional sub-GHz ISM band allocation showing 433 MHz (global unlicensed), 868 MHz (Europe ETSI), 915 MHz (North America FCC), and 920-928 MHz (Asia…

804.4 Summary

This chapter explored the three main frequency bands for IoT:

2.4 GHz ISM Band: - Globally unlicensed, widespread device support - Heavily congested with Wi-Fi, Bluetooth, Zigbee, microwave ovens - Zigbee channels 15, 20, 25, 26 minimize Wi-Fi interference - Used by Wi-Fi, Bluetooth/BLE, Zigbee, Thread

5 GHz Band: - Higher bandwidth, less interference, 23+ non-overlapping channels - Shorter range, poor wall penetration, higher power consumption - DFS requirements in UNII-2/2e bands (radar detection) - Best for high-speed Wi-Fi in same-room applications

Sub-GHz Bands: - Excellent range (10+ km), superior building penetration - Lower power consumption, lower data rates - Regional variations: 433 MHz (global), 868 MHz (Europe), 915 MHz (US), 920-928 MHz (Asia) - Used by LoRa, Sigfox, Z-Wave, NB-IoT

Selection Criteria: - Long range + battery life → Sub-GHz - Balanced performance + ubiquity → 2.4 GHz - High bandwidth + short range → 5 GHz

804.5 What’s Next

Continue exploring wireless fundamentals with these chapters:

Spectrum Licensing and Propagation: Licensed vs unlicensed spectrum, regional regulations, and path loss
Design Considerations and Labs: Frequency selection frameworks and hands-on spectrum analysis
Knowledge Checks and Assessments: Test your understanding with scenario-based questions

804.6 References

Standards: - FCC Part 15: Radio Frequency Devices (US regulations) - ETSI EN 300 220: Short Range Devices (European regulations) - IEEE 802.15.4: Low-Rate Wireless Networks (Zigbee, Thread) - IEEE 802.11: Wireless LAN (Wi-Fi)