You've heard of Bluetooth, but do you know about Bluetooth modules? Take a look at this introduction to the basics of Bluetooth

With the continuous development of Bluetooth technology in recent years, in the case of power consumption continues to reduce, the transmission rate of Bluetooth has also been improved, so that the application of Bluetooth more widely. But if you want to design a perfect Bluetooth system, you must fully grasp the technicalbluetooth lte module knowledge of Bluetooth, such as: RF design, protocol stack, system integration and Bluetooth module selection and other aspects of expertise. This article will introduce the Bluetooth module basics.

A, data transmission

Bluetooth module can transmit data through serial port (SPI, IIC) and MCU control device.

Bluetooth module can be the host and slave. The host is able to search for other Bluetooth modules and actively establish a connection, the slave can not actively establish a connection, can only wait for others to connect themselves.

Second, low power consumption

Bluetooth Low Energy (Bluetooth Low Energy), referred to as BLE, Bluetooth low energy wireless technology uses many intelligent means to minimize power consumption.

Bluetooth low energy architecture has two chip composition: single-mode chip and dual-mode chip. The Bluetooth single-mode device is a new chip in the Bluetooth specification that only supports Bluetooth Low Energy technology - part of a technology specifically optimized for ULP operation. Bluetooth single-mode chips can communicate with other single-mode chips and dual-mode chips, when the latter need to use the Bluetooth low energy technology part of their own architecture to send and receive data. Dual-mode chips can also communicate with standard Bluetooth technology and other dual-mode chips that use the traditional Bluetooth architecture.

Note: According to the application can be divided into data Bluetooth module and voice Bluetooth module, the former to complete the wireless data transmission, the latter to complete the wireless data transmission of voice and stereo audio.

Third, the composition of the Bluetooth protocol

The protocols in the Bluetooth protocol system are divided into four layers according to the concern of SIG.

1, core protocols: BaseBand, LMP, L2CAP, SDP.

2, cable replacement protocol: RFCOMM.

3, telephone transmission control protocols: TCS-Binary, AT command set.

4, optional protocols: PPP, UDP/TCP/IP, OBEX, WAP, vCard, vCal, IrMC, WAE.

In addition to the above protocol layers, the specification defines the Host Controller Interface (HCI), which provides command interfaces to the baseband controller, connection manager, hardware status and control registers. As seen in the above diagram, HCI is located in the lower layer of L2CAP, but HCI can also be located in the upper layer of L2CAP.

The Bluetooth core protocol consists of a Bluetooth-specific protocol developed by the SIG. The vast majority of Bluetooth devices require the core protocol (plus the wireless part), while the other protocols depend on the needs of the application. In short, cable replacement protocols, telephone control protocols and adopted protocols form the application-oriented protocols based on the core protocol.

Fourth, the basic architecture of Bluetooth

1, the underlying hardware module

(1) radio frequency module (Radio): Bluetooth the lowest layer, with microstrip antenna, responsible for data reception and transmission.

(2) baseband module (BaseBand): wireless media access conventions. Provide synchronous connection-oriented physical link (SCO) and asynchronous connectionless physical link (ACL), responsible for frequency hopping and Bluetooth data and information frame transmission, and provide different levels of error correction (FEC and CTC).

(3) Link control module (LC): encoding and decoding of Bluetooth packets.

(4) Link management module (LM): responsible for creating, modifying and publishing logical links, updating physical link parameters between devices, and performing link security and control.

(5) Host Controller Interface (HCI): is the software and hardware interface part, consisting of baseband controller, connection manager, control and event registers, etc.; the software interface provides unified commands for the lower hardware and interprets the transfer of messages and data between the upper and lower layers. The hardware interface contains UART, SPI and USB, etc.

2、Intermediate protocol layer

(1) Logical Link Control and Adaptation Protocol (L2CAP): the basis of the Bluetooth protocol stack, but also the basis of other protocol implementations. Provides connection-oriented and connectionless data encapsulation services to the upper layer; employs multiplexing technology, segmentation and reorganization technology, and group extraction technology to perform protocol multiplexing, segmentation and reorganization, authentication quality of service, group management, and other behaviors.

(2) Audio Video Distribution Transport Protocol (AVDTP) and Audio Video Control Transport Protocol (AVCTP): both are mainly used as protocols for Audio/Video transmission in Bluetooth devices; the former is used to describe the transmission and the latter is used to control the format and mechanism of signal exchange.

(3) Service Discovery Protocol (SDP): Bluetooth technology framework is crucial layer, all application model basis. Dynamic query device information and service types, to establish a corresponding service communication channel, to provide the upper layer to discover the available service types and attributes protocol information.

(4) serial port emulation protocol (RFCOMM): the implementation of the emulation of 9-pin RS232 serial port function, to achieve serial communication between devices.

(5) Binary Telephone Control Protocol (TCS): based on the ITU-T Q.931 proposal to use a bit-oriented protocol, which defines the control signaling (Call Control Signalling) used to establish voice and data calls between Bluetooth devices, and is responsible for handling the mobile management process for groups of Bluetooth devices.

3、Bluetooth Profile

Bluetooth Profile is a wireless interface specification for data communication between Bluetooth devices. Currently there are four categories, thirteen protocol rules, manufacturers can customize the specification. A few of the most common Profile files.

(1) Generic Access Profile (GAP): the basis for all other profiles, defines a common method for establishing baseband links between Bluetooth devices, and allows developers to define new profiles based on the GAP. Contains all the functions implemented by Bluetooth devices, common steps for discovering and connecting devices, basic user interface and other common operations.

(2) Service Discovery Application Profile (SDAP): Describes how the application discovers remote device services using SDPs that can be connected to SDPs that send/receive service queries to/from other Bluetooth devices.

(3) Serial Port Profile (SPP): Defines how to set up a virtual serial port and how to connect two Bluetooth devices based on the ETSI TS 07.10 specification. Speed up to 128kb/s.

(4) General Object Exchange Profile (GOEP): can transfer any object (such as pictures, documents, etc.) from one device to another.

V. Bluetooth protocol stack levels

1, the physical layer (PHY): RF transmission.

2, link layer (LL): control the RF state, including waiting, advertising, scanning, initialization, connection.

3, host control interface layer (HCI): host and controller communication interface.

4, logical link control and adaptation protocol layer (L2CAP): provide data encapsulation services to allow logical point-to-point communication.

5、Security management layer (SM): encryption and decryption, providing services for secure connections and data exchange.

6, Attribute Protocol Layer (ATT): allows a device (server) to present specific data (attributes) to another device (client).

7、Generic Attribute Profile Layer (GATT): defines the service framework for using ATT. All data communication between two devices that establish a connection is handled through the GATT subroutine.

8, common access profile layer (GAP): provides common functions for all Bluetooth devices, such as transmission mode and access procedures, protocols and application descriptions. the GAP service contains device discovery, connection mode, security, authentication, federation model and service discovery.

Six, Bluetooth transmission process

1, master-slave establishment process

2、Master-slave communication transmission module

There are Master Transmission Protocol Module (MTTM) and Slave Transmission Protocol Module (STTM).

The MTTM can work in the Transparent Transmission Mode (TTM) and Command Mode (CM), and works as follows: the user connects the slave device through the AT command control module. After the link is successfully established, MTTM automatically finds the pass-through channel of the slave device, and if the slave device belongs to STTM, MTTM enters TTM by default, otherwise it enters CM.

The purpose of the pass-through mode is to realize the pass-through or direct-drive control function, the host CPU can communicate with STTM in both directions through the universal serial module, MTTM forwards the data to STTM directly, and then outputs from STTM serial port to the slave CPU. the reverse can also be done.