Bluetooth Protocol in detail

Bluetooth Protocol is a wireless technology standard for connecting fixed or mobile devices using short radio link. It aims at providing wireless communication along with small size, minimal power consumption and low price.

Bluetooth is a short range communication that is simple, secure and available everywhere. Billions of devices ranging from mobile phones and computers to medical devices and home entertainment products are enabled with Bluetooth devices.

Bluetooth protocol is a standardized protocol for sending and receiving data via a 2.4GHz wireless link. It’s a secure protocol, and it’s perfect for short-range, low-power, low-cost, wireless transmissions between electronic devices.

Working Principle of Bluetooth

The Bluetooth protocol operates at 2.4GHz in the same unlicensed ISM frequency band where RF protocols like ZigBee and WiFi also exist. There is a standardized set of rules and specifications that differentiates it from other protocols. If you have a few hours to kill and want to learn every nook and cranny of Bluetooth, check out the published specifications, otherwise here’s a quick overview of what makes Bluetooth special.

The radio-wave connection between two devices is used to send and receive data between two Bluetooth devices. The data send and received at a time is equal to 720 Kilo bytes per second. There are 79 frequency channels of a frequency 2.45 Giga Hertz through which the devices send and receive data to each other. When two devices are trying to be paired, they are actually searching for a common frequency through which they can send and receive data. When such a frequency is discovered, the devices are “found”. The connecting of two devices does not hamper the connecting of two other devices because they usually use different channels of frequency and hence do not overlap. In simple terms, this is the principle behind Bluetooth technology.

Versions of Bluetooth

Bluetooth v1.2

The v1.x releases laid the groundwork for the protocols and specifications future versions would build upon. Bluetooth v1.2 was the latest and most stable 1.x version.

These modules are rather limited compared to later versions. They support data rates of up to 1 Mbps (more like 0.7 Mbps in practice) and 10 meter maximum range.

Bluetooth v2.1 + EDR

The 2.x versions of Bluetooth introduced enhanced data rate (EDR), which increased the data rate potential up to 3 Mbps (closer to 2.1 Mbps in practice). Bluetooth v2.1, released in 2007, introduced secure simple pairing (SSP), which overhauled the pairing process.

Bluetooth v2.1 modules are still very common. For low-speed microcontrollers, where 2 Mbps is still fast, v2.1 gives them just about everything they could need.

Bluetooth v3.0 + HS

Bluetooth v3.0’s optimum speed is 24 Mbps. That speed can be a little deceiving though, because the data is actually transmitted over a WiFi (802.11) connection. Bluetooth is only used to establish and manage a connection.

It can be tricky to nail down the maximum data rate of a v3.0 device. Some devices can be “Bluetooth v3.0+HS”, and others might be labeled “Bluetooth v3.0”. Only those devices with the “+HS” suffix are capable of routing data through WiFi and achieving that 24 Mbps speed. “Bluetooth v3.0” devices are still limited to a maximum of 3 Mbps, but they do support other features introduced by the 3.0 standard like better power control and a streaming mode.

Bluetooth v4.0 and Bluetooth Low Energy

Bluetooth 4.0 split the Bluetooth specification into three categories: classic, high-speed, and low-energy. Classic and high speed call back to Bluetooth versions v2.1+EDR and v3.0+HS respectively. The real standout of Bluetooth v4.0 is Bluetooth low energy (BLE).

BLE is a massive overhaul of the Bluetooth specifications, aimed at very low power applications. It sacrifices range (50m instead of 100m) and data throughput (0.27 Mbps instead of 0.7-2.1 Mbps) for a significant savings in power consumption. BLE is aimed at peripheral devices which operate on batteries, and don’t require high data rates, or constant data transmission.

Bluetooth networks

Bluetooth network consists of many bluetooth users. There are two types of network topologies in bluetooth i.e. Piconet and scatternet. Piconet is formed by one master and one slave as well as one master and multiple slaves. There will be maximum 7 active slaves in the piconet. Hence there will be about 8 maximum devices communicating in a small network referred as piconet. Slaves can only transmit when they have been requested by the master bluetooth device. There will be about 255 slaves in parking state. Active slaves are polled by the master for transmission. Each station will get 8 bit parked address. Total 255 parked slaves are possible in one piconet. The parked station can join in just 2ms. All the other stations can join in more time. About 10 such piconets exist in the bluetooth radio coverage area.

Combinations of multiple piconets is known as scatternet. A device can participate in multiple piconets. It will timeshare and need to be synchronized with the master of current piconet.

It supports data rate based on different versions from 720 kbps to about 24 Mbps. It will have distance coverage to about 1 to 100 meters based on power class supported on bluetooth devices.

Power Classes

The transmit power, and therefore range, of a Bluetooth module is defined by its power class. There are three defined classes of power:

Class NumberMax Output Power (dBm)Max Output Power (mW)Max Range
Class 120 dBm100 mW100 m
Class 24 dBm2.5 mW10 m
Class 30 dBm1 mW10 cm

Some modules are only able to operate in one power class, while others can vary their transmit power.

Bluetooth profiles:

  • Advanced Audio Distribution Profile (A2DP)
  • Audio/Video Remote Control Profile (AVRCP)
  • Basic Imaging Profile (BIP)
  • Basic Printing Profile (BPP)
  • Common ISDN Access Profile (CIP)
  • Cordless Telephony Profile (CTP)
  • Dial-Up Network Profile (DUN)
  • Fax Profile (FAX)
  • General Audio/Video Distribution Profile (GAVDP)
  • Generic Object Exchange Profile (GOEP)
  • Hands-Free Profile (HFP)
  • Hard Copy Cable Replacement Profile (HCRP)
  • Headset Profile (HSP)
  • Human Interface Device Profile (HID)
  • Intercom Profile (ICP)
  • Object Push Profile (OPP)
  • Personal Area Networking Profile (PAN)
  • Service Discovery Application Profile (SDAP)
  • Service Port Profile (SPP)
  • Synchronization Profile (SYNC)
  • Video Distribution Profile (VDP)

Bluetooth protocol has over twenty different profiles that cover a host of different types of Bluetooth enabled devices from mobile phones to printers, headset, microphones, laptops, vehicles and with Bluetooth now being used for IoT / M2M applications, it also covers the variety of devices likely to be encountered in these scenarios as well.

Bluetooth connection process

Inquiry — If two Bluetooth devices know absolutely nothing about each other, one must run an inquiry to try to discover the other. One device sends out the inquiry request, and any device listening for such a request will respond with its address, and possibly its name and other information.

  1. Paging — Paging is the process of forming a connection between two Bluetooth devices. Before this connection can be initiated, each device needs to know the address of the other (found in the inquiry process).
  2. Connection — After a device has completed the paging process, it enters the connection state. While connected, a device can either be actively participating or it can be put into a low power sleep mode.
  3. Mode of operation:
    • Active Mode — This is the regular connected mode, where the device is actively transmitting or receiving data.
    • Sniff Mode — This is a power-saving mode, where the device is less active. It’ll sleep and only listen for transmissions at a set interval (e.g. every 100ms).
    • Hold Mode — Hold mode is a temporary, power-saving mode where a device sleeps for a defined period and then returns back to active mode when that interval has passed. The master can command a slave device to hold.
    • Park Mode — Park is the deepest of sleep modes. A master can command a slave to “park”, and that slave will become inactive until the master tells it to wake back up.

There are different types of Bluetooth Modules Available in market, below link gives detail information for Bluetooth modules which useful for developing any project using Bluetooth protocol :

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