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How does Bluetooth Low Energy (BLE) Work?

Ever Wondered how smart devices discover one another, query for services, and exchange information? Yes, it’s cool and just as helpful that your fitness tracker can share information about how you successfully ran in the morning with your smartphone. So, we ask, what is the underlying technology that makes any of this possible? Bluetooth Low Energy takes the spot.

Bluetooth Low Energy

What is Bluetooth Low Energy?

BLE (aka Bluetooth Smart) is a wireless means of data transfer specially designed for low cost, low bandwidth, and low power applications/devices. The keyword is low. It is a variant of the Bluetooth communication protocol introduced in June 2010 in the Bluetooth 4.0 Core Specification by the Bluetooth SIG (Special Interest Group). This standard is optimized to provide the lowest power consumption compared to other wireless communication technologies. Thus, it has opened many doorways of opportunity for product designers on a low-cost budget and a tight energy budget where battery life is a higher priority than high data transfer speeds.

It is safe to say that almost all smartphones today are BLE enabled. The pages of history write the iPhone 4s from Apple as the first BLE enabled smartphone. Immediately after Bluetooth LE got the Apple stamp, other smartphone vendors started to join in. This offered peripheral vendors a unique opportunity to create innovative devices that can talk with mobile phones through BLE. Today we have wireless headphones, smartwatches, fitness trackers, and beacons that can exchange information with smartphones or preferably be controlled with the mobile apps on the phone.

Bluetooth LE and IoT

Another applicability of Bluetooth LE is in the IoT community. For a novice, the Internet of Things is purely about linking devices over the internet so that anyone, anywhere, can interact and control them. It is a community/internetwork of heterogeneous physical devices that detect, collect, process, and exchange data. BLE makes sharing data amongst IoT devices not to be too much of a burden on their energy tanks; otherwise, no device would want to participate in the IoT network. Think of it like this, devices use their energy to share data, so if data sharing costs them a lot of energy, they will not do it because it would be “too expensive.” Thanks to BLE, data sharing is affordable; IoT devices that run on coin cell batteries can operate for months, even years, without depleting their batteries.

Types of BLE Communication: Connection-Oriented and Broadcasting

A BLE device can act as either a central (client) device or a peripheral (server) device in a connection-oriented communication form. A central device is responsible for scanning for connectable devices and initiating requests for connection and data exchange. On the other hand, a peripheral device can receive commands and requests from the central device. Communication between the two occurs in 4 steps: advertise, initiate, connect and exchange.

BLE Advertise, Initiate, Connect, Exchange

Advertise, Initiate, Connect, Exchange

A peripheral device that wants to communicate transmits advertising packets in a set of intervals so that central devices can find them. Meanwhile, the central device is repeatedly listening/ scanning for connectable advertising packets, and when it spots one, it sends a request to the peripheral to establish a connection. After a connection is established, the two devices can exchange information in both directions.

Bluetooth Low Energy, like Classic Bluetooth, uses the 2.4 GHz ISM (Industrial, Service, Medical) spectrum for operation. The spectrum ranges from 2402 MHz to 2480 MHz. BLE divides it into 40 1 MHz channels separated by 2MHz. The channels are numbered from 0 to 39, and channels 37, 38, and 39 are used solely for sending advertising packets. The remaining channels are used for data transmission after a connection has been established. Although 37, 38, and 39 consecutively follow each other on the number system, they are spread out on the BLE spectrum and are separated by a couple of channels. This is an act of caution taken so that when one of the advertising channels is blocked or facing an interruption, the others will likely not be affected.

The second type of BLE communication is known as Broadcasting or Bluecasting. It is connectionless and unidirectional. Here, a BLE device sends data out one-way to anyone or anything that is observing and capable of receiving the broadcasted data. It provides no security for the transmitted data and is thus not suitable for sharing sensitive information. However, it can be used in applications like file-sharing of public data files in the office.

Limitations of BLE

BLE is a great technology, but it is not a one-size-fits-all. There other applications where Wi-Fi and other technologies are more suitable. Limitations of BLE include:

  • Operating Range– BLE is used for short-range communication, typically between 2-5 meters.
  • Interference– It works on the same bandwidth of 2.4 GHz as Wi-Fi and Classic Bluetooth to experience RF interference from classic Bluetooth and Wi-Fi signals.
  • Low data rates/ throughput – Bluetooth LE offers a low- power consumption at the cost of high data rates. Like any other RF technology, BLE devices have a radio transmitter to convert data to RF waves for transmission. When the radio is on, energy is consumed, and when it is off, the power is saved. BLE is then designed to turn on the RF radio as few times as possible. It does this by dividing a connection into spaced intervals and only turning on the radio during the connection interval to transmit low amounts of data in the form of short bursts. At the end of the connection interval, the radio is turned off, and it will be turned on at the beginning of the following interval. There is no continual transmission of data, so data rates suffer.

Summary

This section gives an overview of the Bluetooth Low Energy Technology. BLE is a version of Bluetooth that transmits data using the least amount of energy. It is not better than the previous version of Bluetooth- Classic Bluetooth. The two differ in design goals, so it is unfair to compare two players who are not necessarily optimized for the same application. BLE is optimized for IoT. It is more than evident that the rapid growth of IoT caused many industries to modify themselves to accommodate it. Bluetooth SIG added BLE into their Bluetooth version 4.0 to be relevant for IoT- the game-changer.

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