Wired cables for peripherals (mouse, keyboard, headset) are inconvenient. Wi-Fi was designed for network connectivity, not device-to-device personal area networking. Bluetooth provides short-range, low-power, low-cost wireless connectivity between personal devices without the overhead of Wi-Fi or the complexity of network setup.
Bluetooth (IEEE 802.15.1) is a wireless personal area network (WPAN) standard for short-range device-to-device communication. It operates in the 2.4 GHz ISM band, uses FHSS to avoid interference with Wi-Fi and other devices, and is designed for low power consumption and simple pairing.
Physical and MAC Layer:
- Radio Layer: 2.4 GHz ISM band; FHSS with 1,600 hops/second across 79 channels
- Baseband Layer: Time slots of 625 µs; synchronous connections for voice, asynchronous for data
- LMP (Link Manager Protocol): Manages link setup, authentication, encryption
- L2CAP (Logical Link Control and Adaptation Protocol): Multiplexes multiple channels, handles QoS
- RFCOMM: Emulates serial port (RS-232) for legacy device support
- SDP (Service Discovery Protocol): Discovers services on paired devices
Architecture:
- Piconet: One master + up to 7 active slaves; all communication goes through master
- Scatternet: Multiple piconets interconnected through shared slaves
- Master/Slave roles: Determined at pairing; masters control frequency hopping
Versions:
- Bluetooth 1.0/1.0b: Initial; 723 kbps; many interoperability issues
- Bluetooth 2.0 + EDR: 3 Mbps; faster pairing
- Bluetooth 3.0 + HS: 24 Mbps; uses Wi-Fi for high-speed data transfer
- Bluetooth 4.0 + LE: Bluetooth Low Energy; 1 Mbps; years of battery life (IoT)
- Bluetooth 5.0: 2 Mbps + LE; improved range and broadcast (Beacons)
- Bluetooth 5.1: Direction finding (AoA/AoD) for indoor positioning
- Bluetooth 5.3+: LE Audio; Auracast; LC3 codec
- Master/slave architecture: master controls the piconet timing
- FHSS: 1,600 hops/second avoids narrowband interference; no co-channel interference
- Low power: designed for battery-powered devices (LE variants especially)
- Simple pairing: no network setup required; devices discover and pair
- Coexists with Wi-Fi in 2.4 GHz band without interference due to FHSS
- Range: ~10 m for standard, up to 200 m for extended range (Bluetooth 5.0+)
- Related: IEEE 802.11 — both operate in 2.4 GHz but coexist without interference
- Related: IEEE 802.15 — Bluetooth IS the 802.15.1 standard
- Related: Spread Spectrum — Bluetooth uses FHSS spread spectrum
- Related: Wi-Fi vs Bluetooth vs ZigBee — comparison of short-range wireless standards
- Related: FHSS — Bluetooth’s specific spread spectrum technique
- The 2.4 GHz ISM band is shared by Wi-Fi, Bluetooth, microwave ovens, cordless phones, and ZigBee — interference is managed by FHSS
- Range is limited (10 m) — not suitable for longer-range applications
- Security was weak in early versions (Bluetooth 1.0); PIN-based pairing was vulnerable
- BLE (Bluetooth Low Energy) is a different physical layer from classic Bluetooth