BLUETOOTHTM:A new radio interface providing

ubiquitous connectivity

Jaap C.HaartsenEricssion Radio System B.V.

2000 IEEE

Introduction

A new universal radio interface that enable electronic devices to connect and communicate via short-range radio connectionsOperates 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 productsThe 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 GroupAt the end of 1999, the group was extended with Microsoft, Motorola, Lucent, and 3COM to further develop

General Purposes

Bridging standards: a universal access mechanismFunctional integration: a functional integration is obtained by connecting several devices wirelesslyUniversal interface: provide a universal interface and overcome incompatible connectors and protocols

The BluetoothTM air interface

Peer connectivityUnlicensed spectrumFSK transceiversDynamic slot structurePacket transmission

Peer Connectivity

BluetoothTM is based on peer connectivity: any device must be able to connect to any other deviceCellular 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 2483.5 MHzA major issue for BluetoothTM is interference immunityOptimal interference immunity against jammers is obtained by frequency hopping

Unlicensed spectrum (cont.)

BluetoothTM is based on FH-CDMA using 79 carriers 1MHz spacesThe nominal hopping rate is 1600 hops/sEach BluetoothTM 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/sGives a –20dB spectral bandwidth of 1 MHzFSK radios are simple, cheap, and robust

Dynamic slot structrue

The BluetoothTM air interface is based on time slotsA time slot lasts 625 usIn 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) linkAll 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 packetsOnly one packet can be sent in each slotAll packets have the same format: access code, packet header, user payload

Packet format

Packet transmission (cont.)

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

The BluetoothTM connectivity

Pico- and scatternetsConnection establishmentSynchronizationSecurity

Pico- and scatternets

Two or more BluetoothTM units sharing the same FH channel form a piconetA cluster of co-located, independent piconet is called a scatternetThe number of units active in a piconet is limited to 8

Pico- and scatternets (cont.)

The master-slave concept has been introducedOne unit in the piconet is assigned to be the masterThe 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 piconetUsing 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 connectionThe recipient :the unit in standby that must be susceptible to the pagerThe burden of solving the time-frequency uncertainty has been placed at the pager

Standby state

A unit in standby resides in a low-power stateSleeps most of the timeWakes 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 codeA shortened version of the 72-bit access code used in front of the packetThe code is derived from the identity of the recipient

Paging

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

Synchronization

In the BluetoothTM system, each unit has a free-running native clockAn accuracy of 20ppm when the unit is active and 250ppm when the unit is in a low-power mode

Synchronization (cont.)

A BluetoothTM unit have a list of unit addressed with corresponding native clocksThe slave add an offset to their native clock in order to be hop synchronized to the master

Synchronization

Security

Apply a conventional challenge-response schemeTo prevent eavesdropping, payload information is encryptedKeys of 128 bits are pair-wise generated during an initialization phase

Conclusion

BluetoothTM is a young technologyThe applications seem to be unlimited and new scenarios are discussed every dayHigher data rates are envisioned which will boost the current data rate by a factor 10 to 20