The Bluetooth
Low Energy (LE) radio is specifically designed for ultra-low power operation,
offering a versatile platform for developers. Operating across 40 channels
within the 2.4GHz unlicensed ISM frequency band, Bluetooth LE empowers
developers to tailor their products to meet the unique connectivity demands of
their target markets.
It supports a
wide range of communication topologies, spanning from point-to-point and
broadcast to the latest addition of mesh networking, enabling Bluetooth to
underpin the creation of robust, large-scale device networks. Initially
renowned for its device-to-device communication capabilities, Bluetooth LE has
now become a prominent player in the world of device positioning technology,
catering to the growing demand for high-precision indoor location services. It
boasts features that allow one device to determine the presence, distance, and
direction of another.
Bluetooth
operates within the 2.4GHz ISM band, specifically between 2.402 and 2.480 GHz,
with a slight extension from 2.400 to 2.4835 GHz, inclusive of 2 MHz guard
bands at the lower end and 3.5 MHz guard bands at the upper end. This frequency
range falls within the globally unlicensed but regulated industrial,
scientific, and medical (ISM) 2.4 GHz short-range radio frequency band.
Bluetooth's radio technology employs a technique known as frequency-hopping
spread spectrum, wherein transmitted data is segmented into packets and each
packet is transmitted using a hopping mechanism.
Here's a breakdown of Bluetooth Low Energy's key
specifications:
·
Frequency Band: Bluetooth LE operates
within the 2.4GHz ISM Band (2.402 – 2.480 GHz Utilized).
· Channels: It utilizes 40 channels, with
2 MHz spacing, including 3 advertising channels and 37 data channels.
·
Channel Usage: Bluetooth LE employs
Frequency-Hopping Spread Spectrum (FHSS).
·
Modulation: The modulation technique
used is GFSK.
·
Data Rate: Bluetooth LE offers different
data rates, including LE 2M PHY (2 Mb/s), LE 1M PHY (1 Mb/s), LE Coded PHY
(S=2, 500 Kb/s), and LE Coded PHY (S=8, 125 Kb/s).
·
Transmission Power: The maximum
transmission power is 100 mW (+20 dBm).
·
Receiver Sensitivity: Receiver
sensitivity varies depending on the PHY, ranging from ≤-70 dBm to ≤-82 dBm.
·
Communication Topologies: Bluetooth LE
supports various communication topologies, including point-to-point, broadcast,
and mesh networking.
The 40 RF
channels in Bluetooth LE are categorized into three advertising channels
(channel indices: 37, 38, 39) and thirty-seven data channels (channel indices:
0 to 36). The separation of advertising channels across the 2.4 GHz spectrum is
intentional to prevent interference from other devices operating in the same
spectrum, such as WLAN. Advertising channels are primarily used for
transmitting advertising packets, scan request/response packets, and connection
indication packets, while data channels serve as the main conduit for data
exchange.
There are two types of link layer channels in
Bluetooth LE:
·
Advertising Channel Usage: These
channels are utilized for device discovery, connection establishment, and
broadcast transmissions.
·
Data Channel Usage: Data channels
facilitate bidirectional communication between connected devices, with adaptive
frequency hopping employed for subsequent connection events.
In essence,
Bluetooth LE operates within the license-free 2.4 GHz ISM band, employing 40
communication channels, including 3 advertising channels and 37 connection
channels. These channels are strategically used in different BLE communication
modes, offering both connection-less and connection-oriented capabilities. The
connection-less mode leverages the three advertising channels to broadcast
advertising packets, which are instrumental in setting up the
connection-oriented mode. During connection-oriented mode, one BLE device
assumes the role of the master, while the other becomes the slave, enabling
bidirectional data transfers to take place.
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