When devices whisper to each other – Part 3: Bluetooth Low Energy

In the last post of this series, we learned about Bluetooth Classic, the traditional Bluetooth that has been around for more than two decades. Today, we look at a variation of Bluetooth that was introduced half a decade ago in order to support really small devices running all day: Bluetooth Low Energy.

What is Bluetooth Low Energy?

Bluetooth Low Energy or BLE is a communication protocol using the same hardware and frequency as traditional Bluetooth, but with several variations that make it draw extremely low power from the device that supports it. The idea is to make Bluetooth run on really tiny devices that need to run all day several years in a row.

What is the purpose of Bluetooth Low Energy?

The purpose of BLE is to support devices so small that they can only hold a ‘button’ battery, or the battery that power our wristwatches. Using a standard-sized Lithium ion battery capable of delivering 2500 mA – 4000 mA of current, like the ones used in smartphones, would be unviable for devices that size. If wristwatches were to use batteries so big, then they’d look like calculators tied to our wrists 🙂

Is BLE compatible with Classic?

Let’s take the vague question and turn it into two questions.

Can the same device support BLE and Classic?

Yes, and also at the same time. The microchip, radio transmitter and receiver used in Classic and BLE are the same. The difference is only in the way that power is managed. We’ll talk about the differences in another section.

Can a Classic device and BLE device talk to each other?

A device using Classic cannot talk to a device using BLE. The signal modulation of the two methods is different and one cannot understand the other. Using BLE to communicate with a Classic device is like whispering to a hearing impaired person.

What is different between the two?

Bluetooth LE operates at a significantly lower power than Classic. Power consumption is only 5% of that of Classic. As a result, the current flowing is in the order of microamperes rather than milliamperes.

So what is the result? The achievable data rate is quite low. Where Classic can achieve data rates of 2 – 3 Mbps, LE’s data rate is less than 100 Kbps, making it impractical for continuous data transfer such as music streaming.

Then what can we use it for? To stay powered and transmit bursts of data from time to time. Where can one use that form of communication? Think fitness bands, temperature sensors, thermometres, etc. Every so often, the device can transmit a short burst of information to a master device in the same room, e.g. a smartphone, laptop, a desktop computer or a central console.

Thus the purpose of LE has been established. With the clear, the creators of LE went another step further to optimise power. Unless there is something to transfer, an LE device spends most of its time with its transmitter in sleep mode, at which point it is drawing negligible power just to stay powered on. This is what makes it possible to make the device really tiny and to operate it with a coin-sized battery.

Profiles in Bluetooth Low Energy

We saw the type of profiles (e.g. headset, remote control, etc) for Classic Bluetooth. Let’s now look at the profiles created specifically designed for Low Energy.

Blood pressure / Thermometre / Glucose profiles: These are obviously profiles for medical devices, measuring the blood pressure, body temperature and sugar levels for hypertension, fever and diabetic patients respectively. Devices with these profiles transmit their assigned measurements at periodic intervals. The transmission from the patient is continuously sent to and monitored by doctors and health care professionals.

Cycling speed / cadence / power / Heart rate / Location and navigation / Running speed / cadence / body weight profiles: These are used during in-place and moving workouts and fitness-based activities. These are mostly used by fitness wearable devices such as bands, straps, earrings, pendants and smart cloth fabric. The data is usually sent to the user’s personal smart phone and from there to the cloud.

Environment Sensing profile: is a profile that measures a group of environmental factors, such as temperature, humidity, suspended particulate matter (SPM for air quality), oxygen concentration and CO2 concentration. This usually measures weather and pollution patterns in cities.

Human Interface Device (HID): Similar to the HID profile of Bluetooth Classic, but much more low powered. Humans cannot send data to a computer at a rate faster than a few bytes per second. E.g. the best they can do is to type on a keyboard, move and click a mouse or touch on a touch-screen. None of this is capable of sending data at several Megabits per second, so it makes sense to convert HID devices to low power. Using LE allows for the manufacture of devices that are really tiny, e.g. a remote control that is smaller than the palm of your hand. By reducing the battery size, a mouse or keyboard can be made feather light.

Proximity sensing profile / beacon: This is one of the most popular uses of LE. A transmitting device is placed at specific locations and it sends small data packets called beacons at frequent intervals. These beacons are simply URLs identifying the transmitting device. Each device sends a unique URL. A receiving device catches the URL and from that URL identifies the device.

But how is that useful? The beacons can be used to notify that a receiver has reached a certain destination. Imagine that you have placed beacons inside a tourist city’s major landmarks. The transmitters send out beacons to the tourist’s smartphone indicating that he/she has reached a certain landmark. Beacons are also used by tracked packages in a shipping service. The beacons let various stations along the way know that they have reached a particular facility, e.g. a sorting facility, head office, dispatch facility, etc.

Conclusion

As you can see, Bluetooth LE shares the name ‘Bluetooth’ with its Classic counterpart and even mostly functions the same. But the purpose is different and the way it consumes power is significantly different. Most devices use both versions of Bluetooth within the same chip to provide both functionalities. This is why with your single smartphone, you are able to play music over a headset, but at the same time, pick up workout information from your fitness band.

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2 thoughts on “When devices whisper to each other – Part 3: Bluetooth Low Energy”

  1. Hey, i just want to tell you that it is a very informative article that helped me to enhance my knowledge but i have only one confusion which is about HID. can you please elaborate this article kindly.

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