The Bluetooth Low Energy (BLE) specification was introduced in Bluetooth version 4.0. Prior versions of Bluetooth are also referred to as Bluetooth Classis. Bluetooth Classic and BLE are not compatible. Therefore, a device can either support Bluetooth Classic, BLE or both. A single-mode device that only implements BLE cannot communicate with a device that only implements Bluetooth Classic.
So what are the differences and similarities between the two?
As the name indicates, it mainly has to do with power consumption. Bluetooth was originally designed for continuous, streaming data applications. You can exchange a lot of data at close range. People can receive data and talk at the same time, and exchange multimedia data between devices.
With BLE’s low power consumption, applications can run on a small battery for 5 - 10 years. BLE was designed for applications that do not need to exchange a large amount of data, and therefore, can run on battery power for years at a cheaper cost. This is important for applications that only need to exchange small amounts of data periodically, which makes it ideal for supporting IoT applications.
Both Bluetooth Classic and BLE operate in the 2.4 GHz ISM band. Unlike Bluetooth Classic, BLE remains in sleep mode most of the time except for when a connection is initiated - this is how power consumption is kept to a minimum. Power consumption is also kept low because the actual connection time for BLE is only a few milliseconds, unlike Bluetooth Classic that takes about 100 milliseconds. The maximum, or peak, power consumption is only 15 mA, and the average power consumption is only about 1 µA.
BLE Protocol Stack
The Controller is usually implemented as a System-on-Chip (SOC) with an integrated radio. The Host runs on an application processor and includes upper layer functionality. Communications between the Controller and Host is standardized as the Host Controller Interface (HCI). Non-core profiles (application layer functionality not defined by the Bluetooth specification) is on top of the Host.
The Physical Layer
BLE defines 40 radio frequency (RF) channels with 2 MHz spacing. The data rate is 1 Mbps. The bit error rate (BER) is 10-3. The physical channels use GFSK modulation. There are two types of channel:- Advertising channels are used for device discovery, connection establishment and broadcast transmission. Three channels are defined as advertising channels and are assigned center frequencies that minimizes overlapping with IEEE 802.15.4 channels 1, 6 and 11.
- Data channels are used for bidirectional communication between connected devices.
An adaptive frequency hopping mechanism is used to overcome interference and wireless propagation issues, such as fading. It selects on of the 37 available data channels for communication for a given time interval.
