• Bluetooth (English: Bluetooth), a wireless communication technology standard that enables fixed and mobile devices to exchange data over short distances to form a personal local area network (PAN)

  • It uses short-wave high-frequency (UHF) radio waves to communicate over the ISM band of 2.4 to 2.485 GHz

  • The technology was developed by telecoms firm Ericsson in 1994

  • It was originally designed to create a wireless communications alternative to RS-232 data lines. It can link multiple devices and overcome synchronization issues.

  • The Bluetooth standards are maintained by the Bluetooth Technology Alliance (SIG), which has more than 30,000 members in telecommunications, computing, networking and consumer electronics

Bluetooth working mode

Bluetooth technology is divided into two types: base rate/Enhanced data rate (BR/EDR) and low power consumption (LE).

BR/EDR creates one-to-one device communication based on point-to-point network topology. LE uses a variety of network topologies such as point-to-point (one-to-one), broadcast (one-to-many), and grid (many-to-many)

Bluetooth applications

Bluetooth technology has been used in more than 30,000 bluetooth alliance members in 8.2 billion products

Bluetooth specifications and features

The first version of bluetooth was released in 1998, with a maximum transmission speed of 723.1k/s and a distance of 10 meters. The latest version is bluetooth 5.2, released in 2020, with a maximum transmission speed of 48M/s and a distance of 300 meters

  • One of the most important is bluetooth 4th generation

On July 7, 2010, Bluetooth 4.0 was released. The most important feature of Bluetooth 4.0 is power saving. Bluetooth 4.0 is the only comprehensive protocol specification since the birth of Bluetooth

  • Bluetooth 4.0 is the only comprehensive protocol specification for Bluetooth, which is different from the current mainstream Bluetooth H2. x+EDR and the unpopular Bluetooth H3.0 +HS.
  • Three modes, low power Bluetooth, traditional Bluetooth and high speed Bluetooth, are also proposed.
  • Among them: high-speed Bluetooth mainly focuses on data exchange and transmission; Traditional Bluetooth focuses on information communication and device connection. Low-power Bluetooth, as its name suggests, is designed to connect devices that don’t need much bandwidth. Its predecessor is The Wibree technology developed by NOKIA. It was originally developed as an extremely low-power mobile wireless communication technology for mobile devices. After being adopted and normalized by the SIG, it was renamed Bluetooth Low Energy (later referred to as Bluetooth Low Power). The three specifications can also be combined to allow for a wider range of application modes, and Bluetooth 4.0 increases Bluetooth transmission distances beyond 100 meters (in low-power modes).
  • Single mode and Dual mode.
  • Single mode can only communicate with BT4.0 and cannot be backward compatible (cannot communicate with 3.0/2.1/2.0); Dual mode is backward compatible with BT4.0 and 3.0/2.1/2.0
  • Ultra-low peak, average and standby mode power consumption, enhanced coverage, the maximum range can exceed 100 meters.
  • Speed: support ultra-short data packets at 1Mbps data transmission rate, at least 8 eight-bit, up to 27. All connections use ultra-low cycle to sniff subrating added to Bluetooth 2.1.
  • Frequency hopping: Uses adaptive frequency hopping common to all Versions of the Bluetooth specification to minimize crosstalk with other 2.4 GHz ISM band wireless technologies.
  • Master control: Can sleep longer and only wake up when action needs to be performed.
  • Latency: As little as 3 milliseconds to complete connection setup and start data transfer.
  • Robustness: All data packets are checked with 24-bit CRC to ensure maximum interference resistance.
  • Security: Data packets are encrypted and authenticated using the AES-128 CCM encryption algorithm.
  • Topology: 32-bit addressing is used for each reception of each packet, theoretically connecting billions of devices; Optimized for one-to-one connections and supports one-to-many connections in star topology; With fast connections and disconnections, data can be moved within a mesh topology without maintaining a complex mesh network.

At the end of 2013, the Bluetooth Technology Alliance introduced the Bluetooth 4.1 specification with the intent that Bluetooth Smart technology would eventually become a central driver of the development of the Internet of Things.

  • This version is bluetooth 4.0 software update. Terminals running Bluetooth 4.0 devices can obtain this version through software update.
  • For developers, the update is an important step forward in the history of Bluetooth technology. The update provides greater flexibility and control, enabling developers to create more innovative products that catalyze the growth of the Internet of Things (IOT).
  • Supports multiple device connections.
  • Smart Connection: added support for setting the connection frequency between devices. The manufacturer can set the device setting connection so that the device can control the device power more intelligently.

In December 2014, the Bluetooth Technology Alliance launched the Bluetooth 4.2 specification.

Summary: The low power transmission distance is 30 meters, the speed is about 1M/s, the application throughput is 0.2m/s, the delay is less than 6ms in the non-connected state, the total time of sending data is 3ms, the power consumption is 1/100 of the traditional Bluetooth, in some cases

The fifth generation Bluetooth supports indoor positioning and navigation functions. Combined with wifi, it can achieve positioning accuracy of less than 1 meter, allowing the acceptance of Beacon data without pairing (such as advertising, Beacon, location information, transmission rate increased by 8 times), and the optimization of the bottom layer of the Internet of Things

  • Bluetooth 5.0 was released in June 2016. The effective transmission distance will be four times that of the 4.2le version, and the transmission speed will be twice that of the 4.2le version (the speed limit is 24Mbps). Bluetooth 5.0 also supports indoor location navigation (combined with WiFi for indoor location accuracy of less than 1 meter), allows no pairing to receive Beacon data (such as advertising, Beacon, location information, transmission rate increased by 8 times), and many underlying optimizations for the Internet of Things.

In January 2019, the Bluetooth Technology Alliance launched the Bluetooth 5.1 specification.

In January 2020, the Bluetooth Technology Alliance launched the Bluetooth 5.2 specification.

The main disadvantages of Bluetooth are interference and security

  • Bluetooth has long been criticized for interference with radio waves at 2.4GHz, especially with wireless lans. When interference occurs, the interference is resolved by re-sending packets.

  • On the JAVA and Symbian60 platforms, using bluetooth hacker or bluetooth spy software, a partner can control a bluetooth-enabled phone by agreeing to pair up. This kind of software can realize the function has: check the other party’s mobile phone in the phone book, SMS, electricity, serial number; Change the scene mode and interface language of the other party’s mobile phone, open the Built-in JAVA software of the other party’s mobile phone, control the multimedia player of the other party’s mobile phone, and make calls and send messages remotely.

Three ways to implement bluetooth architecture

Android phones, for example, contain a lot of SoC (System on a Chip), an integrated circuit that integrates a computer or other electronic System into a single Chip. Monolithic systems can process digital signals, analog signals, mixed signals and even higher frequency signals. Monolithic systems are often used in embedded systems), each SoC has its own separate function

The application of mobile phone is allowed in the AP chip. Generally, Android or ios developers only need to deal with the AP chip. The display, 4G, WiFi and Bluetooth all have their own special SoC

  • AP is your SoC processor, mobile phone running system running app
  • The mobile phone
    • software
      • The operating system
      • hardware
        • External:
          • Screen, case, etc
        • Internal: motherboard
          • Power management
          • AP=Application Processor= Application Processor= Main CPU= Main control chip =SoC: used to run (e.g. in mobile phones)
Architecture 1: Host + Controller dual-chip architecture
  • The Bluetooth specification defines a set of standards that allow mobile phone manufacturers, such as Apple, to replace an old AP with a new one without any changes to the Bluetooth module. Similarly, replacing the old Bluetooth module with a new one does not require any changes on the AP terminal.
  • This standard divides the Bluetooth protocol stack into two parts: host and Controller. Host runs on AP, controller runs on Bluetooth module, and they communicate with each other through HCI protocol. Moreover, host contains the parts of the protocol stack, and controller contains the parts of the protocol stack. The HCI protocol for communication between the two is defined in detail in the Bluetooth core specification, so I call it a dual-chip standard solution. Users are free to substitute Host or Controller schemes as long as they follow this standard.
  • Of course, this solution can be applied to any device besides mobile phones. AP chip manufacturers generally directly adopt Bluez and other open source protocol stacks to implement Host function, while The Controller part is mostly implemented by Bluetooth manufacturers themselves.
  • The popular Zephyr open-source Bluetooth stack also supports this architecture. Zephyr was originally launched by Wind River Systems in November 2015 as a “Rocket core” for (IoT) devices.
Architecture 2: Single chip overall solution
  • Mobile phone peripheral Bluetooth device is another very important application of Bluetooth. Usually, mobile phone peripheral devices have relatively simple functions, but are very sensitive to cost. Therefore, it is very wise to use a chip to realize the whole Bluetooth protocol stack, that is, all the functions of bluetooth protocol stack are put on a chip
  • In other words, both host and controller are on the same chip, and since both host and controller are on the same chip, there is no need for a physical HCI to exist. Hosts and controllers interact directly with each other through apis.
Architecture 3: Custom dual chip architecture, generally bluetooth devices

Some Bluetooth devices have strong functions, which require a very powerful MCU as the main application, while bluetooth SoC is only a part of the whole system. In this case, most of the bluetooth protocol stack functions or the whole Bluetooth protocol stack functions are run in the Bluetooth SoC, while Bluetooth applications are run in the main MCU. The communication protocol between the master MCU and the Bluetooth SoC is defined by the vendor, so it is called a custom dual chip architecture solution.

  • This scenario is also so common that it can be said that any architecture other than architecture 1 and 2 can be called Architecture 3. There is a very special case in architecture 3, that is, the HCI interface is used to communicate between the master MCU and the Bluetooth SoC. Since the HCI here is only used for physical communication, and the communication subjects are not hosts and controllers, and the communication packet application data does not follow the Bluetooth core specifications, it cannot be considered as the first architecture

  • How does the Bluetooth protocol stack module work

  • bluetooth