BLUETOOTH TM :A new radio interface providing ubiquitous connectivity Jaap C.Haartsen Ericssion Radio System B.V IEEE

Introduction A new universal radio interface that enable electronic devices to connect and communicate via short-range radio connections Operates in the unlicensed 2.45GHz frequency band and makes use of frequency hopping

Introduction Low-power,small-sized and low-cost radios that can be embedded in a wide range of future products The interface supports: Synchronous services — voice Asynchronous services — file transfer

History At the beginning of 1998, a group of five companies — Ericsson, Nokia, IBM, Toshiba, and Intel — founded a Special Interest Group At the end of 1999, the group was extended with Microsoft, Motorola, Lucent, and 3COM to further develop

General Purposes Bridging standards: a universal access mechanism Functional integration: a functional integration is obtained by connecting several devices wirelessly Universal interface: provide a universal interface and overcome incompatible connectors and protocols

The Bluetooth TM air interface Peer connectivity Unlicensed spectrum FSK transceivers Dynamic slot structure Packet transmission

Peer Connectivity Bluetooth TM is based on peer connectivity: any device must be able to connect to any other device Cellular phone and wireless LANs system is based on an infrastructure of interconnected stationary base stations

Unlicensed spectrum The ISM band ranging from 2400 MHz to MHz A major issue for Bluetooth TM is interference immunity Optimal interference immunity against jammers is obtained by frequency hopping

Unlicensed spectrum (cont.) Bluetooth TM is based on FH-CDMA using 79 carriers 1MHz spaces The nominal hopping rate is 1600 hops/s Each Bluetooth TM unit has its own pseudo-random hopping sequence

Hop selection mechanism

PSK transceivers The air interface uses a Gaussian- shaped (BT=0.5) FSK modulation with a symbol rate of 1 Ms/s Gives a – 20dB spectral bandwidth of 1 MHz FSK radios are simple, cheap, and robust

Dynamic slot structrue The Bluetooth TM air interface is based on time slots A time slot lasts 625 us In a point-to-point connection, one unit always starts to transmit in the even- numbered slots where the other unit transmit in the odd-numbered slots

Dynamic slot structrue (cont.) A circuit-switched connection is created by a SCO(Synchronous Connection- Oriented) link All slot not in use for SCO links can be used for packet-switched traffic through a ACL(Asynchronous Connection-Less) link

Dynamic slot allocation

Packet transmission The information stream is fragmented into packets Only one packet can be sent in each slot All packets have the same format: access code, packet header, user payload

Packet format

Packet transmission (cont.) Access code : the identity of the master Packet header : 3-bit slave address 2-bit ARQ control information 4-bit packet type code 8-bit header-error-check(HEC) code

The Bluetooth TM connectivity Pico- and scatternets Connection establishment Synchronization Security

Pico- and scatternets Two or more Bluetooth TM units sharing the same FH channel form a piconet A cluster of co-located, independent piconet is called a scatternet The number of units active in a piconet is limited to 8

Pico- and scatternets (cont.) The master-slave concept has been introduced One unit in the piconet is assigned to be the master The remaining units participating on the channel are slaves

Pico- and scatternets (cont.) The master-slave are only roles which exist during the presence of the piconet Using the 3-bit slave address in the header, the master can direct packets to the proper recipients

Connection establishment The pager :the unit who wants to make the connection The recipient :the unit in standby that must be susceptible to the pager The burden of solving the time- frequency uncertainty has been placed at the pager

Standby state A unit in standby resides in a low-power state Sleeps most of the time Wakes up at the fixed intervals to scan a single hop carrier for a short period of time

Page message Consists of a single 68-bit code A shortened version of the 72-bit access code used in front of the packet The code is derived from the identity of the recipient

Paging To page a unit, its identity must be known If a pager has no identity or wants to discover which units are in range, it can issue an inquiry message The inquiry procedure works similar as the page procedure

Synchronization In the Bluetooth TM system, each unit has a free-running native clock An accuracy of 20ppm when the unit is active and 250ppm when the unit is in a low-power mode

Synchronization (cont.) A Bluetooth TM unit have a list of unit addressed with corresponding native clocks The slave add an offset to their native clock in order to be hop synchronized to the master

Synchronization

Security Apply a conventional challenge- response scheme To prevent eavesdropping, payload information is encrypted Keys of 128 bits are pair-wise generated during an initialization phase

Conclusion Bluetooth TM is a young technology The applications seem to be unlimited and new scenarios are discussed every day Higher data rates are envisioned which will boost the current data rate by a factor 10 to 20