By: Allen Cabreros, Advanced Engineer Future Electronics
Bluetooth Smart wireless technology is the new ultra-power efficient, app-friendly version of Bluetooth transforming the low power wireless industry. This technology is rapidly opening new opportunities and applications in industry verticals from consumer electronics, medical devices and home automation to retail and wearables. We, at Future Connectivity Solutions (FCS) group, are dedicated to providing Bluetooth Smart solutions to meet the rapid growth and demand in the low power wireless market. FCS is partners with STMicroeletronics, Dialog Semiconductor, Murata, Panasonic, Cypress Semiconductor and Microchip Technology to provide the latest and fastest time to market solutions. Bluetooth Smart is also an important technology in driving the Internet of Things (IoT), which has a strong focus from Future Electronics and the listed partners.
While the power efficiency of Bluetooth Smart devices from various suppliers makes it perfect for devices needing to run off tiny batteries for long periods, one of the big drivers of the technology behind Bluetooth Smart is its ability to work with a wide variety of applications on smartphones or tablets that consumers already own. The developer friendly Bluetooth Smart architecture is now supported by all major operating systems natively. This makes it easy for developers to create apps that link with everyday objects like heart rate monitors, toothbrushes, and even shoes. With Bluetooth Smart, developers are only limited by their imaginations. In a 2013 market research from ABI, the world market forecast is showing that total shipments of Bluetooth Smart and Bluetooth Smart Ready devices will double Bluetooth “Classic” shipments in 2014.
What Applications are Fit for Bluetooth Smart?
Bluetooth Smart is meant for low bandwidth and low latency data that is sent infrequently. If you ask what the maximum throughput of Bluetooth Smart is for your application, then it might not be the right technology. Bluetooth Smart is great for state types of data. State data is where ANT/ANT+ and ZigBee play well with in regard to command and control (on/off), monitoring low resolution sensors, and status indication. Pedometers, heart rate monitors, thermometers, positioning data, and proximity are all great low bandwidth, low latency types of applications. Bluetooth Classic has been used for data “cable replacement” technology.
Bluetooth Smart vs. Bluetooth Classic
In order to achieve the ultra low power consumption, changes were made to the existing Bluetooth baseband, link management layer and upper data management layers (L2CAP). The changes to achieve the ultra-low power consumption, was in the radio duty-cycle, link management and link establishment. GFSK modulation is still the same with Bluetooth Classic, the application throughput is reduced to a theoretical throughput of ~0.27Mb/s from 0.7Mb–2.1Mb/s.
The new link management layer reduces radio duty cycle and adds new mechanisms to keep power consumption low but still add robustness and low latency to the link. As an example, Bluetooth Smart, does not need to send an acknowledgement packet right away (or not acknowledge at all) and the device can go into low power mode for X amount of time and then later wake to send an ACK packet. The result allows the Bluetooth Smart device to receive or even send data without burning precious battery life on acknowledgements.
Channel spacing, modulation index, max output power, and packet types are other items that have changed to with Bluetooth Smart. This means Bluetooth Classic is not compatible with Bluetooth Smart. Only Bluetooth Smart and Bluetooth Smart Ready devices can communicate with each other. Bluetooth Smart Ready devices support both Bluetooth Classic and Bluetooth Smart, making them a dual mode device.
New Roles and Data Modes
Bluetooth Smart also defines new roles and device types. This is similar to the master and slave roles in Bluetooth Classic. There are central and peripheral device role types within Bluetooth Smart. Roles are defined in profiles and how services can be provided between Bluetooth Smart and Bluetooth Smart Ready devices. However, any device can be either role and switch between them.
A central device’s role performs the function of discovering, connecting and accessing the available services from the peripheral device. smartphones, tablets, PCs are typically the central device as they have displays and user interfaces to discover, connect, and view data and services from peripheral devices.
A peripheral device role performs functions such as advertisements, being discoverable and connectable to central devices, and providing services. Typical peripheral devices today are keyfobs, fitbits, watches, temperature sensors, mice or keyboard. Peripheral devices are typically Bluetooth Smart only devices and would be battery-powered.
One of the big advantages of Bluetooth Smart is the ability to advertize and broadcast data without the need of establishing a complete connection. Establishing a complete connection would require a higher radio duty cycle and consume more power. Some applications and data can use this advertisement mode to save power and do not require a bidirectional full duplex RF link. One example is a temperature sensor where temperature can be broadcasted periodically. A central device would not need to create a full connection to the peripheral device to obtain this small amount of temperature data.
In advertisement mode, only 3 channels are used to broadcast the data. The 3 channels are dedicated for advertising, scanning and connecting of Bluetooth Smart device. There are 37 other channels than can then be used for connection oriented data channels. This is a total of 40 channels with 2MHz of spacing. Bluetooth Classic uses 80 channels 1MHz spacing. The 3 advertising channels are strategically placed at 2402MHz, 2426MHz and 2480MHz to avoid the 3 non-overlapping WiFi channels of channel 1, channel 6 and channel 11. In an active connection there are still 9 channels that do not overlap with these WiFi channels. The 3 advertisement channels are also used to discover and create active connections between devices. After discovery and connection requests, the devices then start a frequency hopping spread spectrum (FHSS) scheme on the other 37 channels.
New Data Structure – ATT and GATT
Bluetooth Smart is more of a “wire replacement” technology. However, the information is exchanged using a client-server model. It uses a service-based architecture based on the ATTribute protocol (ATT). All communication in Bluetooth Smart takes place over the Generic ATTribute profile (GATT). An application or another profile uses the GATT profile so a client and server can interact in a structured way. The server contains a number of attributes, and the GATT profile defines how to use the ATT protocol to discover, read, write and obtain data. The services are used as defined in the profile specifications and GATT enables you to expose these services and characteristics within the specified profiles.
Currently there are 18 GATT based profiles with defined attributes that are reserved. These attributes have universally unique identifiers (UUID). There are 16-bit, 32-bit and 128-bit UUIDs that can be used. The 16-bit and 32-bit are reserved for current and future Bluetooth Smart applications and profiles. However, the 128-bit UUIDs can be used for proprietary use for custom profiles and applications for vendor specific data.
Bluetooth Smart Revision 4.1 Additions
In December of 2013, the Bluetooth Special Interest Group ratified the 4.1 core specification that added optional features to Bluetooth Smart. Revision 4.1 extends functionality that is already provided in revision 4.0 of the specification. All of the new 4.1 functions are optional and it does not change or add mandatory items to revision 4.0. This means 4.1 and 4.0 devices are compatible. Previously qualified Bluetooth Smart 4.0 solutions do not need to re-qualify, but for 4.1 certification, the solutions will have to retest again.
Revision 4.1 changes:
1. Added coexistence signaling between Bluetooth Smart and cellular technologies such as LTE
• New cellular technology can often operate at 2.300GHz to 2.400GHz in the same band as Bluetooth Smart
2. Improved link supervision timeout handling
• The added feature in 4.1 will allow the devices to negotiate time intervals to reconnect to each other again in the case of a link loss. This will save precious battery life as the devices can go into sleep mode between the time intervals.
3. Dedicated L2CAP oriented channels
• The ability to have a direct connection to the L2CAP layer and channels will provide a direct data pipe stream in the same manner as Bluetooth Classic
4. Dual mode topology and link layer topology software features
• These features allow a Bluetooth Smart device to become both a central and peripheral device simultaneously and can be very useful to send information between two peripherals in an ecosystem. For example, a Bluetooth Smart watch can retrieve information from a heart rate monitor as a central device but still be a peripheral device to a smartphone. Previously the data would have to be relayed through the smartphone as a central device between the watch and heart rate monitor.
Changes to Bluetooth Qualification Listing
On February 1st, 2014, an additional means of funding the Bluetooth SIG’s activities was implemented to meet the demands placed on the alliance with the growth in Bluetooth products coming to the market.
These changes don’t alter any qualification process, and Bluetooth interoperability testing will continue to support designs past and present. The change addresses the mechanism by which products are qualified and listed. Historically, customers were allowed to reference pre-qualified components and subsystems for such modules and list their products at no charge.
Members implementing Bluetooth wireless technology into a product must complete a Declaration of Compliance (DoC) and a listing for the qualified design they built, changed, used or branded. The DoC and listing are followed by a fee for the process.
The fee ranges from $2K to $8K per EPL depending on the status of the lister with the Bluetooth SIG, associate member or adopter, size and revenue of the lister.
The fees are not associated with Future Electronics or partners. This charge is directly implemented by the Bluetooth SIG and is separate from the certification and testing costs. Although pre-certified Bluetooth and Bluetooth Smart solutions are available from Future Connectivity Solutions and our partners, the EPL fees still apply.
We, at FCS, are committed to providing the best and most efficient Bluetooth Smart solutions to our customers. Systems on Chip (SoC) and module solutions are available from FCS. These solutions are provided with ready-to-go Bluetooth Smart protocol stacks that are pre-certified with easy profile and application development environments. Sizes are as small as 2.5 x 2.5mm SoC to 17 x 19mm fully certified modules. In regards to lower, solutions with 4mA peak with >600nA sleep modes are available.
Modules and SoCs with integrated slow clocks, buck/boost, BALUN, antenna, with Bluetooth and FCC, IC, CE certification are available now. Roadmap products will integrate more features such as cap-touch IO, integrated accelerometer and MEMS sensors, M0+ apps processors and energy harvesting capabilities. Each solution will have a best fit in different types of Bluetooth Smart devices. FCS has solutions for Bluetooth Smart and Bluetooth Smart Ready applications.