From Experimental Robotics
Bluetooth was originally designed to provide power-efficient, low-cost short range radio communications, and has matured into a global technology specification for wireless communication between portalble devices, desktop machines and peripherals.
The Bluetooth radio is built into a small microchip and operates in the 2.4GHz Band, a globally available frequency band ensuring communication compatibility worldwide.
Bluetooth uses Frequency Hop Spread Spectrum (FHSS)to avoid any interference. A Bluetooth channel is divided into time slots each 625 micro second in length. The devices hop through these timeslots making 1600 hops per second. This trades bandwidth efficiency for reliability, integrity and security.
Bluetooth supports two kinds of links: Asynchronous Connectionless (ACL) links for data transmission and Synchronous Connection oriented (SCO) links for audio/voice transmission. The gross Bluetooth data rate is 1 Mbps while the maximum effective rate on an asymmetric ACL link is 721 Kbps in either direction and 57.6 Kbps in the return direction. A symmetric ACL link allows data rates of 432.6 Kbps. Bluetooth also supports up to three 64Kbps SCO channels per device. These channels are guaranteed bandwidth for transmission.
Bluetooth communication occurs between a master radio and a slave radio. Bluetooth radios are symmetric in that the same device may operate as a master and also the slave. Each radio has a 48-bit unique device address (BD_ADDR) that is fixed.
The Radio layer defines the requirements for a Bluetooth transceiver operating in the 2.4 GHz ISM band.
The Baseband layer describes the specification of the Bluetooth Link Controller (LC) which carries out the baseband protocols and other low-level link routines.
The Link Manager Protocol (LMP) is used by the Link Managers (on either side) for link set-up and control.
The Host Controller Interface (HCI) provides a command interface to the Baseband Link Controller and Link Manager, and access to hardware status and control registers.
Logical Link Control and Adaptation Protocol (L2CAP) supports higher level protocol multiplexing, packet segmentation and reassembly, and the conveying of quality of service information.
The Radio Frenquency Communication protocol (RFCOMM) provides emulation of serial ports over the L2CAP protocol. The protocol is based on the ETSI standard TS 07.10.
The Service Discovery Protocol (SDP) provides a means for applications to discover which services are provided by or available through a Bluetooth device. It also allows applications to determine the characteristics of those available services.
PPP/OBEX/AT/TCP/IP are adopted to allow older applications to work with Bluetooth wireless technology.
The BlueSMiRF is a 'black box' wireless serial link operating in the 2.4GHz unlicensed band. The link can handle full-duplex data rates from 9600bps all the way up to 115200bps with a range of 200-300ft. The BlueSMiRF firmware buffers incoming and outgoing data, and has full error checking and guarantees packet delivery. With a built in antenna and real-time, on-the-fly configuration the BlueSMiRF was designed to be a powerful and simple to use wireless link.
TX-O :Transmit from the BlueSMiRF-Serial Output. Normally connected to the RX Pin on any microcontroller or equivalent UART.
RX-I :Receive into the BlueSMiRF-Serial Input. Normally connected to the TX Pin on any microcontroller or equivalent UART.
CTS-I :Clear-To-Send into the BlueSMiRF. Used for hardware flow control. Connect to RTS if not used.
RTS-O :Ready-To-Send from the BlueSMiRF. Used for hardware flow control.Connect to CTS if not used.
Future of Bluetooth
Bluetooth technology already plays a part in the rising Voice over IP (VOIP) scene, with Bluetooth headsets being used as wireless extensions to the PC audio system. As VOIP becomes more popular, and more suitable for general home or office users than wired phone lines, Bluetooth may be used in Cordless handsets, with a base station connected to the Internet link.
In March 2006, the Bluetooth Special Interest Group (SIG) announced its intent to work with UWB manufacturers to develop a next-generation Bluetooth technology using UWB technology and delivering UWB speeds. This will enable Bluetooth technology to be used to deliver high speed network data exchange rates required for wireless VOIP, music and video applications.
Some useful links: