RF Systems 3.0: Understanding Bluetooth (Classic BT & BLE) from PHY to MAC Layer (A Complete Guide)

This is a beginner to advanced guide on understanding the Bluetooth tech stack for Classic BT and Bluetooth Low Energy and LE Audio.

The Curious Case of the Two Bluetooths

In 1998, five companies, Ericsson, Nokia, IBM, Toshiba, and Intel, formed the Bluetooth Special Interest Group (SIG) to kill the RS-232 serial cable. They succeeded wildly. By 2005, Bluetooth was in every phone, headset, and laptop.

But by 2006, engineers hit a wall: the protocol that replaced serial cables was terrible at running on coin-cell batteries.

So the SIG did something radical. Instead of patching the old protocol, they designed a completely new radio, one that shared the brand, the 2.4 GHz band, and nothing else of importance. In 2010, Bluetooth 4.0 shipped with Bluetooth Low Energy (BLE) alongside Classic Bluetooth (BR/EDR). They’ve coexisted under one name ever since, confusing developers for over a decade.

Here, we uncover what actually differs at the two layers that matter most for anyone building wireless systems: the PHY (how bits become radio waves) and the MAC (how devices share the air).

The 2.4 GHz Neighbourhood

Both Bluetooth live at 2400–2483.5 MHz, the globally unlicensed ISM band. So do Wi-Fi, Zigbee, microwave ovens, and baby monitors. This is the technical equivalent of a crowded farmer’s market on a Saturday, everyone’s shouting, and your job is to be heard without deafening anyone else.

How each protocol handles this crowd reveals its design philosophy.

Let’s find out!