Chapter 5. The Physical Layer

You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat.

—Albert Einstein

5.1. Background

Two or more Bluetooth low energy devices use radio waves to send and receive information among them. Radio has been around for many years, starting with very simple spark-gap transmitters, evolving through amplitude modulation and frequency modulation, and recently, to phase-shift keying and other more complex modulation schemes.

The sections that follow provide an introduction to how radios work, ...

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