What is Bluetooth Low Energy (BLE)?

Bluetooth Low Energy (or Bluetooth LE, Bluetooth Smart, or Bluetooth 4.0+) is the power- and application-friendly version of Bluetooth that was built for the Internet of Things (IoT) devices.

You might wonder:
• How it is possible that a BLE device could work for years on one coin cell battery?
• What is difference between BLE and Classic Bluetooth?
• Why has BLE tech grown in popularity?

How the Bluetooth Smart appeared

In 2001, Nokia found contemporary wireless technologies did not address many applications. The company began developing a wireless technology which would use less power. The results were published in 2004 in a paper called Low end extension for Bluetooth.
After 2 years, Nokia and partners began using the name Wibree. Wibree was presented as short-range, wireless technology that is 10 times more energy-efficient than Bluetooth.

In 2010 the Bluetooth Special Interest Group (SIG) announced the formal adoption of the Bluetooth Core Specification Version 4.0 with low energy technology.
The first smartphone to implement the 4.0 specification was the iPhone 4S, released in October 2011. A number of other manufacturers followed suit with Bluetooth Smart Ready (just another name for BLE) devices in 2012.

BLE vs BR/EDR vs Smart Ready: How are they different?

BLE has many names, including Bluetooth Smart and as similar term used: ‘Smart Ready’, where the device support both Classic (BR/EDR) Bluetooth and BLE.

The key differences between LE and BR/EDR is the channel numbers (40 as opposed to 79) and types of radio connections.
Bluetooth LE allows for short bursts of long-range radio connection that prolong battery life.
Classic Bluetooth (or Bluetooth BR/EDR) establishes a short-range, continuous wireless connection, which makes it ideal for use cases such as streaming audio.
Dual-Mode (or Smart Ready) chipsets are available to support single devices such as smartphones or tablets that need to connect to both BR/EDR devices (such as audio headsets) and LE devices (such as wearables or retail beacons). [*]

Differences between Classic, LE and Dual mode Bluetooth architectures [*]

Comparison size of Bluetooth LE and Classical modules. [*]

How BLE Works

There are a numbers of clear and detailed explanations of BLE fundamentals, including “Getting Started with Bluetooth Low Energy” by Kevin Townsend. But how do we answer the practical question: How could the BLE chip work for years without charging?

How is low power achieved?

The easiest way to avoid consuming precious battery power is to turn the radio off as often as possible and for as long as possible. The BLE chip is programmed for:
1. Fast connection (i.e. able to send data more quickly than classic Bluetooth)
2. Low standby time (i.e. lower duty cycle)

Faster Connections

In Bluetooth low energy technology devices are optimized for connections to scanning devices.
• Scanning device: The devices can connect and send and acknowledge data in 3 ms
• In classic Bluetooth technology a link level connection can take up to 100 ms
• In classic Bluetooth technology an L2CAP connection can take significantly longer

Lower standby time

• Bluetooth low energy technology uses only 3 advertising channels
• Classic Bluetooth technology uses 16 to 32 channels
• Radio frequency (RF) is on for 1.2 ms instead of 22.5 ms

Idle current is dominated by deep sleep current

• Sensor type of applications send data less often (0.5 s to 4 s intervals)
• RF current is negligible due to low duty cycles
• Protocols optimized for this communication model

How do devices find each other?

This process is termed ‘Device Discovery’ and is the responsibility of another part of the Bluetooth architecture called the Generic Access Profile (GAP).

Such devices are looking, or scanning, other devices, receiving and processing advertising packets and filtering them. The scanning period is tunable between 2.5 ms and 10.24 s.

At the same time, another device advertises, emitting small packets of data periodically, from 20 ms to 10.24 s. These packets contain information about the advertising device. It should be kept in mind that the power consumption in BLE advertising mode is higher than in connection mode.

The device which advertises is called a Bluetooth Peripheral whereas the one doing the scanning is a Bluetooth Central device.

One device can do scanning and advertising simultaneously. And one can be in a connection with a central or peripheral and can do advertising at the same time.

A single node can “talk” to several hundred nodes simultaneously as the theoretical limit is about 500 nodes, according to this post in Nordic Semiconductor. Nordic Semiconductor.

How the advertising packet and scan response packet is sent. [*]

Limitations of Bluetooth LE

BLE is used for applications that do not need to exchange large amounts of data. Its low-energy nature dictates the following key limitations.

BLE Data Throughput

The theoretical upper limit is 1 Mbps. In practice, a typical scenario assumes 5-10 Kb per second. But even transmitting at these relatively modest data rates, 10 KB/s will quickly drain any small coin cell battery. That means, BLE should not be used to transfer media data, for example.

BLE Operating Range

A typical operating range is between 2 to 5 meters, given a conscious effort to reduce the range and save battery life.
The best way to use BLE devices is to send short messages, like the examples in the image below.

Sending short messages and then returning to sleep is a key BLE feature. [*]

Security on BLE devices

Security on BLE devices is implemented using several levels. Key generation is implemented on the Host level, while the Controller level performs the encryption function.
The third security level supports the ability to send authenticated data over an unencrypted transport between two devices with CSR.
Also, BLE supports a feature that reduces the ability to track a LE device over a period of time by changing the Bluetooth device address on a frequent basis.
For information protection Bluetooth utilizes features against MITM, Passive Eavesdropping and Privacy/Identity Tracking.
Optionally, transferred data could be encrypted by AES-128 with a CCM encryption engine.

BLE technology applications

There are a huge numbers of ways BLE technology can be applied. The intention is IoT, as it says on the official site: “Bluetooth is evolving from a smartphone and personal area network solution to a scalable, low-power wireless networking technology.” (ABI Research). “This development will unlock growth in beacons, home automation, building automation, lighting, and other smart city applications over the next decade and beyond.”

Future posts will cover common and, especially, interesting cases for BLE technology.

The next generation of Bluetooth

At the 16 June SIG conference, the next generation of Bluetooth technology was announced: Bluetooth 5. It supports quadrupled range, doubled speed and increases data broadcasting capacity by 800%. Specification for Bluetooth version 5 available on official site.

Suggested note:
Bluetooth devices, by nature, are still finicky to work with and different chips naturally vary in their transfer speed or range. Add to that different firmware attributable to each individual manufacturer and not a single source, and the variation increases. Numbers in this article are general estimates based on what developers have seen in practice and shared on the web.