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Bluetooth low energy and short range wireless communications

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article image Small, power-efficient devices such as wearable athletic and medical sensors are typically based on a single-mode Bluetooth LE system

In use for over ten years, the Bluetooth wireless data protocol now comes with the new low energy standard giving designers another option for wireless connectivity between devices with extremely low power consumption. 

LX Group examines the Bluetooth LE (low energy) in this article, and discusses its benefits with implementation examples.

Aimed at novel applications of short-range wireless communication in connected Internet-of-Things devices for medical, fitness, sports, security and home entertainment applications, Bluetooth LE was merged into the main Bluetooth specification as part of the Bluetooth Core Specification v4.0 in 2010.

Also known as ‘Bluetooth Smart’, Bluetooth LE enables new applications of Bluetooth networking in small, power-efficient Internet-of-Things devices that can operate for months or even years on tiny coin cell batteries or other small-scale energy sources. Bluetooth LE devices offer ultra-low power consumption, particularly in idle or sleep modes, multi-vendor interoperability and low cost, whilst maintaining radio link range that is sufficiently long enough for the intended applications.

The Bluetooth LE protocol is not backwards-compatible with the ‘classic Bluetooth’; however, the Bluetooth 4.0 specification does allow for dual-mode Bluetooth implementations where the device can communicate using both classic Bluetooth and Bluetooth LE. While Bluetooth Low Energy uses a simpler modulation system than classic Bluetooth, it employs the same 2.4 GHz ISM band, allowing dual-mode devices to share a common antenna and RF electronics for both Classic and Bluetooth LE communication.

Small, power-efficient devices such as wearable athletic and medical sensors are typically based on a single-mode Bluetooth LE system in order to minimise power consumption, size and cost. Dual-mode Bluetooth is typically implemented in devices such as notebooks and smart phones, allowing communication with both Bluetooth LE and classic Bluetooth devices. When operated in Bluetooth LE mode, the Bluetooth LE stack is used while the RF hardware and antenna is usually the same set of hardware as used for classic Bluetooth operation.

The power consumption of devices using Bluetooth LE for Bluetooth communication is a fraction of that of classic Bluetooth devices. Given that devices can operate for a year or more on a single coin cell, the low power consumption aspect potentially makes Bluetooth LE very attractive for Internet-of-Things networks, telemetry and data logging from environmental sensor networks, for example.

Since many modern consumer devices such as mobile phones and notebooks have built-in Bluetooth LE support, data can be delivered directly to the user’s fingertips from the Bluetooth sensor network with no need for an intermediary gateway or router, which would be otherwise required for an Internet-of-Things network employing technologies such as 802.15.4 ZigBee. This direct interoperability with a large installed base of smart phones, tablets and notebooks could potentially be a very significant attraction of Bluetooth LE networks in wireless sensor network and Internet-of-Things applications.

An active Bluetooth radio has a peak current consumption of about 10 milliamps, reduced to about 10 nanoamps (ideally) in sleep mode. In a Bluetooth LE system, the objective is to operate the radio with a very low duty cycle of about 0.1-0.5%, resulting in average current consumption of 10 microamps. At an average current consumption of 20 microamps, such a system could be operated off a typical CR2032 lithium coin cell (with a charge capacity of 230 milliamp-hours) for 1.3 years without battery replacement.

The lower power consumption of Bluetooth LE is not achieved by the nature of the radio transceiver itself, but by the design of the Bluetooth LE stack to allow low duty cycles for the radio and optimisation for transmission in small bursts.

The Bluetooth specifications define many different profiles for Bluetooth LE devices, particularly for how a device works in particular families of applications. Manufacturers are expected to implement the appropriate profiles for their device in order to ensure compatibility between different devices from different vendors. 

Bluetooth LE profiles in use include Health Thermometer Profile for medical temperature measurement devices; Glucose Monitor Profile for medical blood glucose measurement and logging; Proximity Profile, which allows one device to detect whether another device is within proximity, using RF signal strength to provide a rough range estimate; Running Speed and Cadence profile, for monitoring and logging athletic performance; Heart Rate Profile for heart-rate measurement in medical and athletic applications; and Phone Alert Status Profile, which allows a client device to receive notifications from a smart phone. 

The Bluetooth LE shows a lot of promise, and with a minimal chip set cost gives the designer another cost-effective wireless protocol. Clients seeking a reliable implementation can partner with LX Group, which is equipped to create or tailor just about anything from a wireless temperature sensor to a complete Internet-enabled system within the required time-frame and budget.  

An award-winning electronics design company based in Sydney, Australia, LX Group specialises in embedded systems design and wireless technologies.

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