1 Bluetooth low energy technology overview
Bluetooth low energy was introduced back in 2011as the hallmark feature of Bluetooth v4.0. Bluetooth low energy is ideal for applications requiring episodic or periodic transfer of small amounts of data. Therefore, Bluetooth low energy is especially well suited for sensors, actuators and other small devices that require extremely low power consumption. Works well with high numbers of communication nodes with limited latency requirements
- Very low power consumption
- Robustness equal to Classic Bluetooth
- Short wake‑up and connection times
- Good smartphone and tablet suppor
Figure 1: In the 2.4 GHz band, Bluetooth low energy uses 40 frequency channels instead of the 79 channels used in Classic Bluetooth
Many features of Classic Bluetooth are inherited in Bluetooth low energy, including Adaptive Frequency Hopping (AFH). These inherited features make Bluetooth low energy easy to set up and makes it robust and reliable in
tough environments. To support simpler and cheaper radio chipsets, Bluetooth low energy uses 40 2 MHz wide channels while Classic Bluetooth uses 79 1 MHz channels.
1.3 Difference between dual - mode Bluetooth (Bluetooth Smart Ready) and single‑mode Bluetooth low energy (Bluetooth Smart)
Figure 2 shows examples of Bluetooth modules (u‑blox) and end products that are either single‑mode Bluetooth low energy solutions or dual‑mode solutions. In this example, Bluetooth Smart Ready (dual‑mode) devices include the dual‑mode Bluetooth module OBS421 and smart phones. Bluetooth Smart (single‑mode) devices include the Bluetooth low energy module OLS425 and temperature sensors.
Figure 2: Single‑mode and dual‑mode module and product examples.
Single‑mode devices are stand‑alone Bluetooth low energy devices (also known as "Bluetooth Smart” devices) that are optimized for small battery‑operated devices with low cost and low power consumption in focus. Typical
single‑mode devices are, for example, sensors (heart rate sensor, temperature sensors, etc.) or other types of battery‑operated accessories.
Dual‑mode devices (also known as “Bluetooth Smart Ready” devices) use both Bluetooth low energy and Classic Bluetooth. Typical dual‑mode devices are mobile phones, tablets, computers or –in this context– a gateway device.
1.4 Client and Server concept in Bluetooth low energy
Figure 3: The Client / Server concept.
Bluetooth low energy uses a Client / Server model. A Client (that "wants data") connects and accesses one or several Servers (that "has data”). The Client typically operates in the Central role and the Server operates in the Peripheral role. Typically, a sensor or an accessory is the Server / Peripheral and a computer, phone, or tablet is the Client / Central device. In the gateway context, the gateway typically takes on the, Client / Central role.
1.5 "Advertising" is how devices are found in Bluetooth low energy
Since the devices are in sleep‑mode until an advertisement is initiated, the advertising feature enables Bluetooth low energy to keep the power consumption to a minimum.
Figure 4: The advertising feature of Bluetooth low energy.
The slave device (now having the Broadcaster role) is "advertising" when he wants to connect. The Client is scanning for new devices (acting in the Observer role). When the Observer finds a device it wants to connect to, it initiates a connection. The advertisement may contain broadcasted data.
1.6 Bluetooth low energy connections
Figure 5: Connected Device.
When connected, the Client / Central controls the communication by sending data and "polling" the Server / Perphral for data at regular intervals (called connection intervals). The selected interval is application dependent and can be speifically set.
1.7 Bluetooth low energy software stack
Figure 6: The Bluetooth low energy software stack
- L2CAP (Logical Link Control and Adaptation Protocol). This is a stack layer responsible for multiplexing data between various higher layer protocols as well as segmentation and reassembly of data packets.
- GAP (Generic Access Protocol) . This profile defines the generic procedures related to device discovery and link management when connecting to Bluetooth devices.
- GATT (Generic Attribute Protocol). Provides profile and service discovery for Bluetooth low energy. The described procedures show how to use the ATT (Attribute Protocol) for service discovery as well as how to read and write attributes (data). Services and profiles are developed on top of GATT.
- 6LoWPAN (IPv6 over Low power Wireless Personal Area Networks). An alternative to GATT is to use TCP/IP based communication with 6LoWPAN. 6LoWPAN technology can be used to compress the IP messages sent over Bluetooth low energy to save on size requirements and power consumption.
2 Internet of Things (IoT) overview
With yearly shipments of more than 10 billion microcontrollers that all can exchange information locally or through the Internet, a huge variety of so called “intelligent devices” are enabled. These devices include motion
sensors, pool pumps, gas/electric meters, street lights, and many other types of devices. A ll these devices can be accessed over the Internet thanks to the rapid increase in infrastructure coverage and Internet access. This
evolution is often called the Internet of Things (IoT). Other names include Internet of Everything (IoE), Web of Things, Embedded Web and Industrie 4.0. The goal is to establish an Internet connection for the small "things"
you carry with you or use in a factory, hospital, in a city or in a home. Companies such as Ericsson and Cisco have visions of more than 50 billion connected devices within the next 10 years.
Figure 7: Internet of Things (IoT).
A key requirement in the IoT vision is an easy‑to‑deploy and cost‑efficient low power wireless solution. Connecting all small devices and sensors directly to the fixed or cellular networks would be too costly. An easy‑to‑deploy,
cost‑efficient, and low power solution is a key requirement in IoT. Radio technologies such as Bluetooth, Bluetooth low energy, 802.15.4 / Zigbee or similar may be used to connect widely distributed small devices. The sensor
s are connected to a gateway that in turn is connected to Internet services (see figure 7 above). The gateways can be powerful–typically Linux‑based–systems with high computing capacity. The gateways can also be RTOS platform‑based when there is a need for small, cost‑efficient but still powerful wireless gateways.
3 Use cases for Bluetooth low energy in IoT
Below follows several examples of IoT use cases using Bluetooth low energy. All of the use cases assume the use of a gateway connected to the Internet using TCP/IP related protocols.
3.1 GATT‑based device and service / profile‑aware gateway