The principle of car bluetooth technology

The principle of bluetooth technology and its application in the field of automobile

Bluetooth is a wireless communication technology that supports short-distance communication of devices (usually within 10 meters). Data communication between many devices such as peripherals. Bluetooth can effectively simplify the communication between mobile communication terminal equipment and between equipment and the Internet, so that data transmission becomes more rapid and efficient.

With the development of science and technology, Bluetooth technology is playing an increasingly important role. Bluetooth technology is closely related to people's lives, and people's demand and dependence on Bluetooth are increasing day by day. This paper analyzes the principle of bluetooth technology, and discusses the application of bluetooth technology in the field of automobiles.

1.The principle of Bluetooth technology

1.1 Bluetooth protocol stack

Figure 1 shows a schematic diagram of the bluetooth protocol stack architecture. The goal of the Bluetooth protocol is to allow applications that follow the specification to interoperate. To achieve interoperability, applications on communicating devices must run on the same protocol stack. So far, the Bluetooth protocol has 1.0, 1.1, 1.2, 2.0, 2.1, 3.1, 4.0, 4.1 and other versions. With the evolution of the protocol and the development of technology, the data rate is gradually increased. The 1.0 version of Bluetooth is the basic bit rate (BR, Basic Rate), the maximum physical layer data rate is 1Mbps; the 2.0 version is the enhanced bit rate (EDR, Enhanced Data Rate), and its physical layer data transmission rate is increased to 2Mbps or 3Mbps; the 3.0 version The introduction of alternative radio frequency technology (AMP, Alternative MAC PHY), using IEEE 802.11 to achieve a physical layer data rate up to several 100Mbps. Version 4.0 introduced Bluetooth Low Energy (BLE, Bluetooth LowEnergy). From the perspective of protocol support, Bluetooth devices can be basically divided into three categories: classic devices, dual-mode devices (supporting both classic Bluetooth and BLE), and single-mode devices (only supporting BLE). Single-mode devices are called Bluetooth Smart, and dual-mode devices are called Bluetooth SmartReady. It should be noted that single-mode devices can only communicate with dual-mode devices, not classic Bluetooth.

Figure 1 Schematic diagram of the bluetooth protocol stack architecture

(1) The radio frequency (RF, Radio Frequency) layer defines the frequency band and channel arrangement, the requirements that transmitters and receivers working in this frequency band should meet, etc., and realizes the filtering and transmission of data streams.

The baseband (BB, Baseband) layer protocol provides two physical links: a connection-oriented synchronous mode (SCO, Sychronous Connection-Oriented) and a connectionless asynchronous mode (ACL, Asychronous Connection-Less).

Link Management Protocol (LMP, Link Manager Protocol) is responsible for link establishment, control and link security. LMP performs identity authentication and encryption through connection initiation, exchange, and verification, and determines the size of baseband data packets through negotiation; LMP controls the energy-saving mode and work cycle of wireless devices.

The host control interface (HCI, Host Controller Interface) is the interface between the underlying hardware and the upper layer protocol, providing instructions for accessing hardware functions such as baseband, link controller, link manager, and status registers.

(2) Logical Link Control and Adaptation Protocol (L2CAP, LogicalLink Control and Adaptation Protocol) belongs to the data link layer. L2CAP provides connection-oriented and connectionless data services for upper-layer protocols. Segmentation and reorganization and delivery of quality of service. L2CAP allows high-level protocols to send and receive data packets in 64K bytes, and L2CAP only supports ACL. The priority of sending LMP messages is higher than that of user information, so the messages sent by LMP will not be delayed due to L2CAP communication. LMP is mainly used to control data transmission, while L2CAP provides packet transmission and control to the upper layer.

(3) The Bluetooth Telephone Control Protocol (TCS-BIN) defines call control signaling for establishing voice and data calls between Bluetooth devices, and handles the mobility management process of TCS devices. AT-commands defines a set of commands for controlling mobile phones and modems in multi-user mode.

(4) AVCTP (Audio/Video Control Transport Protocol) describes the exchange message transmission mechanism of A/V equipment. AVDTP (Audio/Video Distribution Transport Protocol) defines the negotiation, establishment and transmission mechanism of A/V streams.

(5) Service Discovery Protocol (SDP, Service Discovery Protocol) is a protocol based on the client/server structure, and the client application discovers the existing server and its attributes through SDP. SDP only provides mechanisms for discovering services, but not methods for consuming those services. Almost all Bluetooth devices support the SDP protocol, except for the Bluetooth devices that only do Client.

(6) Cable emulation protocol The RFCOMM protocol is a serial port emulation protocol based on the technical standard (ETSI) 07.10 of the European Telecommunications Standards Institute. The RFCOMM protocol provides emulation of the RS-232 serial port on L2CAP.

(7) Attribute protocol (ATT, Attribute protocol) was introduced for BLE in version 4.0, which allows devices to show device capabilities to other devices in the form of "attributes".

(8) Bluetooth Network Encapsulation Protocol (BNEP, Bluetooth Network Encapsulation Protocol) directly bears IPv4/IPv6 through L2CAP.

(9) OBEX defines data objects and communication protocols for exchanging these objects, and OBEX is also used for IrDA simulation. In Bluetooth protocol version 1.0, OBEX is carried by RECOMM, while in BR/EDR, OBEX is based on TCP/IP carried by BNEP.

1.2 Bluetooth application scenarios and profiles

As shown in Figure 1, according to the purpose of the protocol and its association with the Bluetooth Special Interest Group (SIG), Bluetooth protocols can be classified into the following categories:

(1) Bluetooth Core Protocols (Bluetooth Core Protocols), including RF, BB, LMP, L2CAP, SDP, and AUDIO; (2) Adaptation protocols, including RFCOMM, ATT, and BNEP; (3) Telephony Control Protocols , including TCS Binary and AT-commands; (4) A/V control protocols, including AVCTP and AVDTP; (5) Reference protocols (Adopted Protocols), including PPP, UDP/TCP/IP, OBEX, WAP/WAE, vCard/ vCal and IrDA. For specific Bluetooth application scenarios (Bluetooth Usage Models), in order to maintain compatibility and interoperability between Bluetooth devices more easily, the Bluetooth specification introduces Profile.

Profile defines the protocol covered by an application scenario and the features necessary to support Bluetooth device communication. The most basic profiles are general access applications (GAP, Generic Access Profile) and general attribute applications (GATT, Generic Attribute Profile). GAP carries traditional BR /EDR, while GATT carries BLE. Figure 2 illustrates the hierarchical relationship between the Bluetooth protocol and Profile.

Figure 2 Bluetooth Profile and protocol hierarchy relationship

In addition to GAP, commonly used profiles include SDAP (Service Discovery Application Profile), SPP (Serial Port Profile), and GOEP (Generic Object Exchange Profile). The Profile list adopted by the Bluetooth SIG can be found on the Bluetooth development portal (http://developer.bluetooth.org). The Hands-Free Application Protocol Framework HFP mentioned below is one of them.

1.3 Typical Bluetooth system framework

A typical Bluetooth system includes a wireless unit, link controller, link management and interface, software protocol, and host terminal.

As shown in Figure 3, the host terminal is responsible for functional modules and Bluetooth communication control, and other modules implement Bluetooth communication.

In practical applications, the chip basic circuit set that integrates several Bluetooth functions is usually called a Bluetooth module, and subsequent development is carried out on the basis of the Bluetooth module, which greatly simplifies the development of Bluetooth applications.

The world's major chip manufacturers are actively investing in the research and development and testing of Bluetooth modules, and have launched Bluetooth modules covering different protocol stack levels. For example, CSR in the UK owns or once owned three kinds of Bluetooth modules, HCI ROM, HCI RFCOMM ROM and Full embedded solution.

(1) HCI ROM only covers the protocol layer below HCI. The hardware HCI interface usually uses UART/USB/SDIO, while the L2CAP protocol layer in Figure 1 needs software implementation and runs on an external processor.

(2) The difference between HCI RFCOMM ROM and HCI ROM is that it integrates RFCOMM and L2CAP into the chip, which can reduce the code amount of the host processor, but the data throughput rate will be affected.

(3) Full embedded solution covers all protocol layers of Bluetooth, and the most popular one is this Bluetooth module.

2.The application of Bluetooth technology in the automotive field

With the maturity and development of bluetooth technology, bluetooth technology has been used more and more widely, and the automotive field is one of the most active fields. According to the statistics of ABI Research, it is estimated that by 2017, there will be 60 million cars equipped with Bluetooth technology. Compared with 2013, the market growth rate has increased by 47%.

2.1 Car hands-free system

Car hands-free system is a typical application of Bluetooth technology in the automotive field. The system uses the mobile phone as the gateway, and the mobile phone supporting the Bluetooth function can be placed anywhere within 10 meters of the vehicle-mounted hands-free system. call.

The Hand Free Profile (HFP) specifies the minimum set of functions required for a mobile phone to interact with a hands-free device (vehicle or headset) via Bluetooth. The protocol stack of the Hand Free Profile is shown in Figure 4. HFP defines two roles: voice gateway (AG, AudioGateway) and hands-free unit (HF, Hand-free). Among them, the voice gateway provides audio input and output and its control, and the typical voice gateway is a Bluetooth mobile phone; the hands-free unit provides remote control function, and can use the vehicle-mounted hands-free equipment.

2.2 Vehicle detection system based on Bluetooth OBD

The on-board diagnostic system (OBD, On-Board Diagnostics) can monitor the working conditions of the engine electronic control system and other functional modules of the vehicle in real time during the running of the vehicle. Stored on memory within the system as diagnostic trouble codes. With the improvement of various sensors and electronization of vehicles, OBD has added various monitoring functions.

As the communication interface of the on-board monitoring system, the OBD interface can provide data such as fuel consumption records, battery voltage, air-fuel ratio, throttle opening, and the number of knocks, in addition to reading fault codes for vehicle repair. The data can be read out through a dedicated data cable and then displayed on the matching display screen. The more convenient way is to add a Bluetooth OBD interface adapter and a smart phone software. At present, many kinds of Bluetooth OBD modules are launched on the market, and the data read by the OBD interface are transmitted to the smart phone through Bluetooth, and then presented to the user through the software of the mobile phone.

2.3 Bluetooth Rearview Mirror

Bluetooth rearview mirror is to add Bluetooth technology to the rearview mirror of the car, so that the rearview mirror can increase the hands-free call function. quality.

Summarize

In addition to the automotive field, the typical application fields of Bluetooth technology include wireless office, information appliances, medical equipment, school education and factory automatic control. It can be predicted that with the advancement of technology and the reduction of production costs, the application field of Bluetooth technology will expand, which will further change people's life and work methods, and significantly improve the quality of life and work.

The above is the principle of Bluetooth technology and its application in the automotive field introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. If you have Bluetooth product design and development needs, you can trust us. We have rich experience in custom development of smart electronic products. We can evaluate the development cycle and IC price as soon as possible, and can also calculate the PCBA quotation. We are a number of chip agents at home and abroad, including MCU, voice IC, BLE Bluetooth IC, dual-mode Bluetooth module, and wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth development, wifi technology, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.