The Bluetooth Evolution

Wireless Solutions Part 2

Over a millennium ago, King Harald Gormsson was famous for two things; uniting Denmark and Norway in 958, and for his dead tooth, which was a dark grey-blue in colour. Fast-forward to 1996, when three industry leaders – Intel, Ericsson and Nokia – met to plan standardisation of a new short-range radio technology. During the meeting, Jim Kardash from Intel suggested Bluetooth as a temporary code name. He was later quoted as saying “King Harald Bluetooth…was famous for uniting Scandinavia just as we intended to unite the PC and cellular industries with a short-range wireless link.”

As we now know, the temporary name became permanent, with Bluetooth and its variants becoming synonymous with short-range wireless technology today; integrated into more than 8.2 billion products produced by over 30,000 Bluetooth SIG members. It is a low-power wireless connectivity technology used to stream audio, transfer data and broadcast information between devices. Bluetooth’s two flavours are Basic Rate/Enhanced Data Rate (BR/EDR) and Low Energy (LE).

Current Bluetooth hierarchy

After development through many revisions, Bluetooth has evolved into two flavours - Basic Rate/Enhanced Data Rate (BR/EDR) and Low Energy (LE).

Bluetooth BR/EDR allows continuous wireless connection and uses a point to point (P2P) network topology in establishing one-to-one (1:1) device communications. BR/EDR audio streaming is widely used in wireless speakers, headsets and hands-free in-car systems.

Bluetooth Low Energy (LE) enables short-burst wireless connections and uses multiple network topologies, including point-to-point (P2P), broadcast and mesh.

P2P is used to create one-to-one (1:1) device communications. It is ideal for data transfers and well suited for connected device products such as fitness trackers and health monitors. Broadcast is a network topology that establishes one-to-many (1:m) device communications. It optimises localised information sharing, making it ideal for beacon solutions such as point-of-interest (PoI) information and item- and way-finding services.

Mesh is a network topology for many-to-many (m:m) device communications. Bluetooth LE Mesh creates large-scale device networks tailor-made for building automation, sensor network, asset tracking and any solution where multiple devices need to reliably and securely communicate with one another.

Of these two standards, LE is particularly important to manufacturers and integrators wishing to build and use Bluetooth-enabled IoT sensors, because of its low-energy capabilities – a critical requirement for sensor nodes relying on battery power and/or energy harvesting.

Bluetooth evolution

Bluetooth has evolved through 1.0, 1.2, 2.0, 2.1, 3.0, 4.0, 4.1 and 4.2, and is currently at 5.

A document, Bluetooth Report , describes how the Bluetooth Special Interest Group (SIG) has managed the evolution of these steps. It notes how version 2 abolishes radio frequency interference using frequency hopping, and provides security against snooping and tracking.

Bluetooth 2.0 also improved on 1.2 with both higher connection speed and lower power consumption. Version 2.1, released in 2007, provided more data transmission security, further reduction in power consumption and an improved pairing system which did not require any PIN. In 2009, Bluetooth 3.0 introduced Wi-Fi connection capability, allowing faster data transmission. Then, the appearance of 4.0 served as a game-changer for Bluetooth, as it launched the concept of Low Energy and associated functionality. These features meant that Bluetooth LE, unlike previous Bluetooth revisions, could be designed into many types of IoT sensors, including remote devices relying on coin cells or energy-harvesting. These possibilities are described in the ‘Bluetooth 4.0 LE platform’ section below.

The Bluetooth 4.0 LE platform

Bluetooth 4.0, also called Bluetooth Smart, solves two key Bluetooth challenges ; not only the battery drain issue mentioned above, but also the constant pairing and re-pairing of connected devices. The new generation of Bluetooth tech places less emphasis on maintaining a constant stream of information. Instead, it focuses on sending smaller bits of data when needed and then puts the connection to sleep during periods of non-use.

Additionally, Bluetooth 4.0 allows device manufacturers to replace proprietary sensor technology with Bluetooth. This means that, for example, a pedometer or blood glucose monitor that could previously only talk to a specific wrist device or control unit, if enhanced with Bluetooth 4.0, could speak to any Bluetooth phone or computer device without an intermediary.

When two 4.0 devices are paired, they waste less battery power because the connection is dormant unless critical data is being shared. With the previous generation of Bluetooth, it was best to shut down your hardware when it was not in use. The Bluetooth Special Interest Group estimates between 1 and 2 years of battery power in some devices with Bluetooth 4.0.

Bluetooth Smart encompasses both Bluetooth Smart Ready and Bluetooth Smart devices. Bluetooth Smart Ready applies to smartphones, notebooks and PCs that can receive signals from Bluetooth sensors, and process the data internally or forward over a WiFi or Ethernet link, across the Internet and on to a cloud computing resource. Bluetooth Smart devices are the sensors or actuators collecting or receiving data in the field. They can remain asleep for extended periods while remaining paired to a Smart Ready device – then wake up instantly and start transmitting data if a monitored variable changes significantly.

Smart Ready phones and PCs are backward-compatible with previous-generation Bluetooth peripherals, but Smart peripherals only work with a Smart Ready partner.

Fig.1: Bluetooth Smart logo – Image via Wikimedia Commons

Designing for BLE

Silicon Labs has written a detailed White Paper: ‘Designing for Bluetooth Low Energy’ . After presenting some of the Paper’s highlights below, we will look at further evolutionary improvements to the BLE 4.0 platform – versions 4.1, 4.2 and 5.0.

Summary of BLE advantages

As well as being ultra-low power, BLE offers the following advantages:

Low cost
Reliable and robust with Adaptive Frequency Hopping (AFH), retransmissions and Cyclic Redundancy Checks (CRCs)
Secure: Pairing, bonding, privacy, Man in the Middle protection, AES-128 encryption
Supports rapid development:

Standardised profiles to cover key uses (Heart rate, proximity, glucose etc)
Profiles can be developed as applications, supporting fast deployment
Vendor-specific profiles obviate the need to wait for Bluetooth SIG to standardise profiles or for operating system developers to integrate them

Widely-deployable; supported by major platforms including iOS, Android 4.3, Windows 8 and 10, OSX and Linux

Overview of Bluetooth Low Energy Architecture

Fig.2: Bluetooth Low Energy architecture – Image via Silicon Labs

The components are:

Physical layer: controls radio transmission/receiving.
Link Layer: defines packet structure, includes the state machine and radio control, and provides link layer-level encryption.

These two layers are often grouped into a controller, with the remaining layers grouped into a host. A host-to-controller interface (HCI) standardizes communication between the controller and the host.

Overview of host layer components

L2CAP (Logical Link Control and Adaption Protocol) acts as a protocol multiplexer and handles segmentation and reassembly of packets. It also provides logical channels, which are multiplexed over one or more logical links. Typically, application developers do not need to worry about the details of interacting with the L2CAP layer, as interaction is handled by the Bluetooth stack.

ATT (Attribute Protocol) provides a means to transmit data between Bluetooth devices.

GATT (Generic Attribute Profile) is used to group individual attributes into logical services, for example, the Heart Rate Service, which exposes the operation of a heart rate sensor. In addition to the actual data the GATT also provides information about the attributes i.e. how they can be accessed and what security level is needed.

GAP (Generic Access Protocol) allows BLE devices to advertise themselves or other devices, make device discovery, open and manage connections and broadcast data,

SM (Security Manager) provides a means to bond devices, encrypt and decrypt data and enable device privacy.

The physical and link layers

The physical layer operates in the 2.4 GHz ISM (Industrial Scientific and Medical) band, which is licence-free in most countries. The BLE specification defines 40 RF channels with 2 MHz channel spacing. Three of the 40 channels are advertising channels (shown in green), used for device discovery, connection establishment, and broadcast. The advertising channel frequencies are selected to minimize interference from IEEE 802.11 channels 1, 6 and 11, which are commonly used in several countries.

Fig.3: Bluetooth low energy channels and frequencies – Image via Silicon Labs

The Bluetooth link layer provides the first level of control and data structure over the raw radio operations and bit stream transmission and reception:

Bluetooth low energy state machine and state transitions
Data and advertisement packet formats
Link Layer operations
Connections, packet timings, retransmissions
Link layer level security

Application developers do not need to understand these in detail, but some essential concepts affect the application design, development, and end device operation. These are summarised below.

The basic link layer operations are:

Advertising
Scanning
Connection establishment

Advertisement is a fundamental operation in which devices broadcast their presence, allowing other devices to detect this and establish connections, and optionally broadcast data like a list of supported services, or the device name and TX power level. This activity is complemented by scanning, where a scanner listens for incoming advertisements to discover, discover and connect, or simply receive the data broadcast by the advertising devices. Both passive (cycling through each advertising channel and listening) and active (listening and responding with a request for further information) scanning modes are supported.

Connection establishment allows application data to be transmitted in a reliable and robust manner, as Bluetooth low energy connections use CRCs, acknowledgements, and retransmissions of lost data to ensure correct data delivery. Additionally, the Bluetooth low energy connections use Adaptive Frequency Hopping (AFH) to detect and adapt to the surrounding RF conditions and provide a reliable physical layer. Connections also support encryption and decryption of data to ensure its confidentiality.

Profiles

Profiles are definitions of possible applications and specify general behaviours that Bluetooth enabled devices use to communicate with other Bluetooth devices. Profiles build on the Bluetooth standard to more clearly define what kind of data a Bluetooth module is transmitting. The device’s application determines which profiles it must support, from hands-free capabilities to heart rate sensors to alerts and more.

A Bluetooth profile is really an interface specification. It defines the data which a device has, what another device can do with that data over a Bluetooth connection and how the device with the profile should respond when a connected device acts upon its data in some way.

For Bluetooth LE, developers can use a comprehensive set of adopted profiles, or they can use the Generic Attribute Profile (GATT) to create new profiles. This flexibility helps support innovative new applications that maintain interoperability with other Bluetooth devices.

The Bluetooth site gives access to more detailed information on a wide range of profiles.

Evolutionary enhancements to LE 4.0

Silicon Labs has written a post describing the evolutionary advances from Bluetooth 4.0 – through 4.1 and 4.2 to 5. Below are the highlights of this post.

Bluetooth 4.1 brought three major advances over 4.0:

No overlap or interference with 4G
Better device power management by pairing that allows automatic powering up and down
Devices can act as both hubs and endpoints simultaneously so peripherals can communicate independently

Bluetooth 4.2 was introduced in 2014 for next-generation IoT devices. It also offered:

Improved Internet connectivity and security
Packet capacity up almost 10x that of 4.1
Data range increased by 2.5 times
These last two improvements will make device-to-device communications as well as connections over the Internet more efficient, and allow more frequent firmware updates and faster uploads of sensor data logs to a smartphone, the cloud or some intermediate location on an ISP provider's servers or routers.

Bluetooth 5.0 provides higher throughput and lower latency, longer range broader and more flexible Internet Protocol access and mesh routing capability. Specifically, it offers:

Up to 2x the bandwidth of Bluetooth 4.2

Bandwidth increased to 2 Mbps
Rapid and reliable over-the-air firmware updates and fast upload of days’ worth of collected data from a sensor when a mobile device is turned on

Up to 4x the range of Bluetooth 4.2

Achieve up to 4x longer range for similar power requirements by decreasing bandwidth – theoretically up to 300 metres , or more in some circumstances
Can achieve coverage of an entire home, building or locality
Allows designers a flexible trade-off of range, speed and power requirement

Up to 8x the broadcasting message capacity of 4.2, with support for larger data packets, and ability to offload advertising data from the three traditional advertising channels to up to 37 broadcasting channels. With less broadcast time required for completion of tasks, richer connectionless beacon-based Bluetooth solutions with new threshold features such as asset tracking become possible.
Detect and prevent interference between 2.4 GHz ISM band and neighbouring LTE band
Mesh networking: a feature of particular significance for IoT applications. In a mesh network, all devices can communicate with each other rather than being tied to a central hub. This makes the size and area covered by the network almost unlimited. Applications such as a factory production floor with hundreds of sensors can accordingly be accommodated.

Bluetooth evaluation and development products

Farnell offers a broad range of Bluetooth development kits and modules from many different semiconductor manufacturers. They represent a wide variance in computing, communications and I/O capabilities, but all are intended to help developers integrate Bluetooth into their products more easily. Here are some examples:

Development example #1: Bluetooth LE Evaluation module for developers

TI offers a CC2541 evaluation module kit that can be used as a reference board for prototyping. It is based on the CC2541 system on chip (SoC) solution that allows robust network nodes to be built with low total bill of material costs. It includes an RF transceiver, enhanced 8051 MCU, programmable flash memory, 8 KB RAM and other supporting features and peripherals. It is highly suited to systems where ultra-low power consumption is a priority.

The kit comprises two CC2541 evaluation modules; one is pre-configured as a central device, the other as a peripheral. It is designed as an add-on to the CC2540 development kit, which provides a complete hardware performance test platform and generic software development environment for single-mode Bluetooth low energy applications.

Development example #2: Bluetooth Low Energy module with integrated chip antenna

The Silicon Labs BLE112-A-V1 is a Bluetooth smart module with integrated chip antenna and software version 1.0 targeting low power sensors and accessories. It integrates all features required for a Bluetooth smart application, including Bluetooth radio, software stack and GATT based profiles. The BLE112 single-mode Bluetooth smart module can also host end user applications, which means no external microcontroller is required in size- or price-constrained devices.

It has flexible hardware interfaces to different peripherals and sensors and can be powered directly from a standard 3V coin cell battery or a pair of AAA batteries. In the lowest power sleep mode, it consumes just 500 nA and will wake up within a few hundred microseconds.

Applications include wireless, communications & networking, sensing & instrumentation, consumer electronics, medical and security.

Fig.4: Silicon Labs Bluetooth low energy module with integrated chip antenna

Development example #3: Setting up haptic feedback with BLE and iOS

There are many devices that can benefit from haptic (vibration) feedback. Examples include watches, fitness trackers, wearables, portable medical equipment, HMIs and others. The vibration is usually achieved with either an Eccentric Rotating Mass (ERM) motor or Linear Resonant Actuator (LRA).

Farnell offers a reference design that allows prototyping of such applications. The board features an ERM and LRA Haptic Driver with an integrated pre-licensed effect library from Immersion. It can be programmed and controlled to create effects and notifications using an included iOS app via a SimpleLink Bluetooth Low Energy (BLE) CC2541 wireless MCU.

The app’s other features include an ability to send direct I2C commands, and setting up the board to respond to a GPIO trigger.

Development example #4: Evaluation module for sensing, navigation, position, 3-axis accelerometer/magnetometer/gyroscope

The FRDM-FXS-MULT2-B is a Freedom Expansion Board enabling sensor fusion using the MMA8652FC 3-axis accelerometer, FXLS8471Q 3-axis accelerometer, MAG3110 3-axis magnetometer, FXAS21002C 3-axis gyroscope, MPL3115A2 pressure sensor and FXOS8700CQ 3-axis accelerometer, plus a 3-axis magnetometer and the MMA9553L sensing platform. The board offers 12-axis sensing, wireless communication via Bluetooth and the compatible Android™ app, the sensor fusion toolbox. The board is also supported by the intelligent sensing framework (ISF).

Target applications include Industrial and Test & Measurement.

Fig.5: NXP Bluetooth 12-axis sensing evaluation board

Note for system integrators: In selecting devices like the CC2541, it’s useful to look for an I2C interface, as this will ease integration into larger systems - most CPUs have I2C pins. The alternative is to use a USB port, which consumes extra space and cost.

Conclusion

Since its inception in 1996, Bluetooth has found its way into many billions of products worldwide – its ubiquity is reflected in the fact that it’s a household name. It was the appearance of Bluetooth 4.0, also known as Bluetooth Low Energy, in June 2010 that made the technology an attractive solution for a new area of products and applications; particularly IoT sensors with severely restricted power budgets.

As Bluetooth has evolved further to 5.0, the Low Energy offering has been enhanced in many ways, including improved data capacity, wider bandwidth, longer transmission range, reduced interference with other wireless services, better Internet security and connectivity, and mesh networking.

In this article, we have looked at Bluetooth from a developer’s perspective. We have seen how the technology has evolved, and reviewed the essential building blocks of Bluetooth Low Energy. Then, we have given some practical examples of Bluetooth development kits and modules, showing how developers can accelerate their learning and reduce their time to market as they build BLE into their own products.