75  Wireless Signal Propagation Fundamentals

75.1 Overview

This comprehensive guide to wireless signal propagation for IoT has been organized into four focused chapters for better learning. Each chapter builds on the previous one, taking you from basic concepts to hands-on practice.

NoteKey Takeaway

In one sentence: Radio signal strength decreases with distance and frequency, and a link budget calculation tells you whether your wireless system will work before you deploy it.

Remember this rule: Every 3 dB of antenna gain doubles your effective range (or lets you halve transmit power), and lower frequencies (sub-GHz) travel farther and penetrate walls better than higher frequencies (2.4/5 GHz) at the cost of data rate.

75.2 Chapter Guide

75.2.1 1. Radio Wave Basics for IoT

Start here to understand the fundamental physics of wireless communication.

Read: Radio Wave Basics for IoT

Topics covered:

  • The electromagnetic spectrum and frequency-wavelength relationship
  • IoT frequency bands (Sub-GHz, 2.4 GHz, 5 GHz, mmWave)
  • Trade-offs between frequency bands (range vs data rate)
  • Why lower frequencies penetrate walls better

Estimated reading time: 15 minutes

75.2.2 2. Path Loss and Link Budgets

Learn to calculate whether your wireless link will work before deployment.

Read: Path Loss and Link Budgets

Topics covered:

  • Free Space Path Loss (FSPL) formula and calculations
  • Real-world path loss models (indoor, outdoor, urban)
  • Complete link budget equation and worked examples
  • Signal strength measurements (dBm, RSSI, SNR)
  • Link margin requirements for reliable systems

Estimated reading time: 20 minutes

75.2.3 3. Fading, Multipath, and RF Interference

Understand why signals vary unpredictably and how to design for it.

Read: Fading, Multipath, and RF Interference

Topics covered:

  • Multipath propagation and how it causes fading
  • Types of fading (slow/shadow, fast/multipath, frequency-selective)
  • Fading margin selection for different environments
  • RF interference sources and mitigation strategies
  • Channel planning and frequency hopping
  • Site survey checklist for deployments

Estimated reading time: 25 minutes

75.2.4 4. Practical Considerations and Lab

Apply your knowledge with hands-on experiments and engineering trade-offs.

Read: Practical Considerations and Lab

Topics covered:

  • Indoor vs outdoor deployment challenges
  • Antenna selection guide (chip, dipole, Yagi, parabolic)
  • Engineering trade-offs (frequency band, power, margin, antennas)
  • Knowledge check with 8 questions
  • Hands-on Wokwi Lab: ESP32 RSSI measurement and packet transmission simulation
  • Challenge exercises for deeper understanding

Estimated reading time: 45-60 minutes (including lab)

75.3 Learning Path

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flowchart LR
    A["1. Radio Wave<br/>Basics"] --> B["2. Path Loss &<br/>Link Budgets"]
    B --> C["3. Fading &<br/>Interference"]
    C --> D["4. Practical<br/>Lab"]

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Recommended approach:

  1. New to wireless? Start with Chapter 1 and work through sequentially
  2. Need link budget help? Jump to Chapter 2 for formulas and examples
  3. Troubleshooting connectivity? Chapter 3 covers interference and fading
  4. Ready to experiment? Chapter 4 has the hands-on lab

75.4 Prerequisites

Before diving into these chapters, you should be comfortable with:

75.5 What You’ll Be Able to Do

After completing all four chapters, you will be able to:

  • Explain how radio waves propagate through different environments
  • Calculate free-space path loss and link budgets for IoT deployments
  • Interpret signal strength measurements (dBm, RSSI) and their meaning
  • Compare frequency bands and their trade-offs for IoT applications
  • Identify the factors that affect wireless range in real-world scenarios
  • Select appropriate wireless technologies based on propagation requirements
  • Design systems with appropriate fading margins for reliability
  • Troubleshoot RF interference issues in IoT deployments