12.3 Technology Overview

Bluetooth is a wireless technology operating in the unlicensed 2.4-GHz ISM (industrial/scientific/medical) spectrum capable of providing radio connectivity up to 10 m between Bluetooth-capable devices. It offers frequency hopping to reduce interference and fading. A shaped, binary FM modulation is applied to minimize the transceiver complexity. A slotted channel is applied with a nominal slot length of 625 m s. For full duplex communication, a time division multiplexing (TDM) scheme is used. On each channel, information is exchanged through packets that are transmitted on a different hop frequency.

Bluetooth offers two different link types. The synchronous connection oriented (SCO) link type provides a circuit-switched connection, mainly intended for audio connections between two Bluetooth devices at a data rate of 64 kbps in the full-duplex mode. The asynchronous connectionless (ACL) link provides packet-switched communications at a maximum data rate of 432 Kbps in symmetric or 721 Kpbs in asymmetric modes.

Link-level security mechanisms, which include device-level authentication and ciphering, is specified for the Bluetooth. Robustness in the link level is guaranteed by the use of error correction control mechanisms.

The Bluetooth system mainly consists of a radio unit, a link control unit, and a support unit for link management and host terminal interface functions (Figure 12-2). A more in-depth protocol stack is discussed in the following sections.

Figure 12-2. Bluetooth system functional blocks.