Definition
BLE (Bluetooth Low Energy) is the low-energy mode of Bluetooth 4.0 and above, suitable for smart locks, asset tags, wearable devices, etc. BLE 5.1 supports AoA (Angle of Arrival) positioning and can achieve indoor meter-level RTLS.
Technical Features
BLE operates in the 2.4GHz ISM band and uses frequency hopping spread spectrum (FHSS) technology to resist interference, with a typical transmission power of 0–10dBm and a reception sensitivity of approximately -93dBm (BLE 4.2) to -97dBm (BLE 5.0). Connection establishment time is short (around 3ms), supporting multiple master-slave connections, with single connection intervals configurable from 7.5ms to 4s. BLE 5.0 introduces a 2Mbps physical layer as an optional mode, theoretically doubling throughput; the new Coded PHY (125kbps/500kbps) can significantly extend transmission range. BLE 5.1 introduces AoA (Angle of Arrival) and AoD (Angle of Departure), which, combined with multi-antenna arrays, enable centimeter-level indoor positioning, widely used in scenarios such as asset tracking, personnel positioning, and navigation guidance.
Use Cases
BLE is widely used in the Internet of Things: smart locks pair with mobile apps via BLE to enable near-field unlocking and temporary key issuance; asset tags (Beacons) periodically broadcast UUIDs, with gateways or mobile phones enabling indoor positioning and trajectory analysis; wearable devices (bands, watches) report heart rate, steps, and other data with low power consumption; medical devices (glucose meters, blood pressure monitors) upload measurement results to mobile phones or the cloud via BLE; industrial sensors can use BLE gateways to aggregate data, reducing wiring costs. Compared with Zigbee, BLE has a mature ecosystem and native mobile support, making it more suitable for consumer-level and lightweight industrial applications.
Protocol architecture and GATT
The BLE protocol stack from top to bottom includes the application layer, GAP (Generic Access Profile), GATT (Generic Attribute Profile), L2CAP, HCI, Link Layer, and Physical Layer. GATT defines a hierarchy of services, characteristics, and descriptors. Devices expose readable and writable attributes through a GATT server, and clients discover and access them through UUIDs. Common standard services include Battery Service, Device Information Service, Heart Rate Service, etc. Manufacturers can define private services and characteristics to implement custom data interaction. Connection parameters (connection interval, slave latency, supervision timeout) need to balance power consumption and real-time performance according to the application scenario.
Power Consumption and Battery Life
The typical average current of BLE in a connected state can be as low as a few microamps to tens of microamps (depending on advertising/connection intervals), allowing button cell batteries to last for months or even years. The main factors affecting power consumption include: the shorter the advertising or connection interval, the higher the power consumption; the amount of data per connection event; whether deep sleep is enabled (such as slave latency negotiated in connection parameters). During development, battery life can be optimized by increasing connection intervals, reducing the data volume per connection event, and reasonably using slave latency. Beacon-type devices usually operate in pure advertising mode without connections, resulting in extremely low power consumption.