For beginners! Explaining how BLE communication works: from connection to data transmission and reception

overview
Bluetooth Low Energy (BLE) is an essential communications technology for modern IoT devices and wearable technology. BLE provides stable connections while saving power, and is used in a variety of applications, from smartphones to smart home devices. However, for engineers learning about its communication mechanisms for the first time, it can seem somewhat complicated. This article provides an easy-to-understand explanation of the basic BLE communication process, helping even beginners to gain a confident understanding of BLE technology. We will introduce the process from advertising to data transmission and reception.

Introduction: BLE Channel Concepts

The concept of a "channel" is very important in BLE communication. Simply put, a channel is like a "pathway" for sending and receiving data.
BLE communicates using the 2.4GHz frequency band. This frequency band is divided into a total of 40 channels, each with a bandwidth of 2MHz. Data is sent and received through these channels.

There are two main types of channels:

Advertising Channels: Three channels (37, 38, 39) are used as advertising channels.
These are used by devices to announce their presence and establish new connections.
Data Channels: The remaining 37 channels are data channels.
These are used for actual data communication, for example when sending data from sensors.
BLE communicates by switching channels to avoid interference with other devices and exchange data efficiently.

Frequency Hopping

BLE uses frequency hopping to improve communication reliability and avoid interference. This technology switches the frequency used for data transmission and reception in a set pattern. BLE uses 40 channels within the 2.4GHz ISM band and rapidly switches between these channels to minimize interference from other wireless devices. Frequency hopping makes BLE communication stable and efficient, ensuring reliable data transmission and reception.

BLE communication establishment process: from advertising to connection

The first step in BLE communication is for devices to recognize each other's existence and establish a connection. This process consists of three steps: advertising, scanning, and connection request, and they play an important role in ensuring smooth initial interactions between devices. By understanding these steps, you can learn the basic mechanisms of how BLE devices start communication.

BLE communication establishment process: Image diagram

Advertising

The first step for a BLE (Bluetooth Low Energy) device to start communication is advertising. This is a way for a device to let others know of its presence by periodically broadcasting on three channels (37/38/39). Advertising packets contain information about the device name and the services it provides, making it easy for other devices to find devices that can be connected to. Advertising is done periodically to indicate that the device is available for connection.

scan

Scanning is the process by which BLE devices find other devices. The central device listens to surrounding advertising packets and identifies connectable devices. This step is an important way for a device to learn what services it offers. By scanning, the device can create a list of potential connections and select the best one.

Connection Request

After scanning to find the device you want to connect to, the next step is to send a connection request. This is the process in which the central device requests a connection to a specific peripheral device. If the connection request is accepted, communication is established between the two devices. This step allows data to be sent and received between the devices.

Pairing BLE devices: Preparing to send and receive data

After the connection is established, the next step is to prepare for secure communication and data exchange between the devices. At this stage, trust between the devices is established through the processes of pairing, service discovery, and characteristic acquisition, and preparations are made for specific data exchange. This lays a solid foundation for BLE communication, ensuring smooth data transmission and reception.

* Service discovery: Find out what data and functions peripheral devices provide
* Acquire characteristics: Check the specific data read and write details within the service

Pairing

After a communication partner has been found and a connection established, the next step is pairing. Pairing is a process that allows devices to communicate securely, and involves exchanging encryption keys. This prevents data eavesdropping and tampering, ensuring secure communication. Once pairing is completed, subsequent connections will be smoother.

How to send and receive BLE data: using read, write, and notification

Once communication is ready, data transmission and reception begins. At this stage, the actual data exchange between devices occurs through data reading, writing, notification and indication, and frequency hopping. By understanding these processes, you can understand how BLE devices exchange information and achieve real-time data updates.

BLE data transmission and reception method: Image diagram

Reading Data

Data reading is the process by which a central device obtains information from a peripheral device. The central sends a read request and the peripheral returns the requested data. This allows you to obtain the information you need in real time. Data reading is used to obtain sensor information or check the status of a device.

Writing data

Writing data is the process by which a Central device sends information to a Peripheral device. By sending a write request, you can change settings or update data in the Peripheral device, allowing you to control the device's behavior or adjust its settings.

Summary

We hope that this column will help you understand how BLE communication works and put it to use in your actual development. BLE is used in a variety of IoT devices because it enables low-power and flexible communication. We hope you will get to know BLE and explore new technologies.