e001X10.pdf

Presently, data transfers between the PC and printers, scanners, fax machines and

modems, as well as communication between a laptop and a cellular phone, still

require inconvenient cable interconnections and the time-consuming installation

of drivers. Wouldn’t it be nice if all your data-processing devices could indepen-

dently converse with each other, with no need for cables or driver installation? This

is now possible, thanks to Bluetooth, a short-range radio system that renders

cables redundant and which should allow new applications to be developed.

By G. Kleine

Bluetooth

2.4-GHz data radio instead of computer cables

geted unit price, given large-scale

mass production (more than one million

pieces), is less than five dollars.

Frequencies

Nokia Mobile Phones, Ericsson

Mobile Communications, IBM, Intel and

Toshiba recognized the potential of this

technology and founded the Bluetooth

Special Interest Group (BSIG) [1,2] in May

of 1998. Its objective is to define a uni-

versal standard for radio data communi-

cation between data-processing equip-

ment. In the beginning, the main area of

interest was data transfers between cel-

lular phones and peripheral equipment,

in order to eliminate annoying and incon-

venient cables. Later, the area of interest

was extended to include other applica-

tions, ranging from wireless connections

between PCs and laptops and their

peripheral equipment to the ad-hoc con-

figuration of wireless networks.

Presently, more

than 1100 firms are members of the

Bluetooth Special Interest Group (BSIG)

(see the box ‘King Bluetooth and his

friends’). They include not only all lead-

ing computer and communications

technology firms, but also automobile

and aeroplane manufacturers and

representatives of the entertainment

industry. The BSIG presented the provi-

sional version of the Bluetooth 1.0 spec-

ification in the autumn of 1999. It has

been made publicly available on the

Internet [2] , in order to promote the

establishment of the Bluetooth system.

This extensive specification fills more

than 1500 pages. The primary objec-

tive of the Bluetooth project is the

development of extremely inexpensive,

compact modules that can be built

into a variety of equipment. The tar-

When the BSIG was looking for licence-

exempt frequency bands that are avail-

able worldwide, it came across the

Industrial, Scientific and Medical (ISM)

bands. These frequency bands may

be used without any licence or fee for

industrial, scientific and medical

equipment with a limited radiated

power. In addition to the available

ISM bands listed in Table 1 , there are

other ISM bands at 5.8 GHz,

24.25 GHz and 122.5 GHz, but

these cannot be utilized at a rea-

sonable cost at the present time.

Since the possibility of interfer-

ence from other unlicensed users

of the ISM bands must always be taken

into account, and given that Bluetooth

should have a data transfer rate of

around 1 Mb/s, the only suitable choice

is the 2.4-GHz ISM band (2400 to

2483 MHz). This band is 83 MHz wide

and thus provides enough room to

avoid interfering signals coming from

equipment that uses a particular fre-

quency, such as a microwave oven.

This frequency band is available world-

wide, although its extent is somewhat

reduced in Japan (2471 to 2497 MHz),

France and Spain.

In order to avoid problems with antici-

pated interference signals, most of

which have fixed frequencies, Bluetooth

makes use of spread-spectrum tech-

niques. This means that the frequency

is changed rapidly (up to 1600 times

per second) in a pseudo-random man-

ner, with the result that enough interfer-

10 - 1/2000 Elektor Electronics EXTRA —————————————— PC T OPICS

ence-free frequencies are available to

allow the desired data transfer rate to

be achieved, even with error protection

(see Figure 1 ). This process is called

Frequency-Hopping Spread Spectrum

(FHSS). Bluetooth uses 79 frequencies in

the range between 2.402 and

2.480 GHz, with a separation of 1 MHz.

Due to the previously-mentioned reduc-

tion of the available frequency band,

only 23 hop frequencies are used in

France, Spain and Japan.

Piconet A

Piconet B

Collision (Slot unavailable)

2.480 GHz

Piconets and scatter nets

A pair of devices equipped with Blue-

tooth modules can autonomously

establish contact with each other, using

the frequency-hopping technique. In

order to prevent mutual interference

with other Bluetooth equipment in the

same vicinity that might use the same

frequencies, the frequency sequence is

determined by the address and clock

rate of the device that initiates the con-

nection. This device thus becomes the

master device in this radio group, while

all other participants are designated as

slaves and must synchronize themselves

to the master device.

Up to eight Bluetooth radios can use a

single channel. Such a group forms a

network that is called a piconet (see

Figure 2 ). In this context, the term

channel means that all members of the

piconet employ the same hopping

sequence, which means that they use

the same series of frequencies. Since

each Bluetooth device is assigned a

unique 48-bit address by a central reg-

istration agency, it is not possible for two

separate channels to have the same

hopping sequence.

By independently setting up additional

piconets in the same vicinity, it is possi-

ble to use more than eight Bluetooth

devices in one location, such as an

office, with high data transfer rates and

without interference.

A slave transmit/receive device operat-

ing in a particular piconet is addressed

by the master device in one time slot of

a time-division multiplexed (TDM) pro-

tocol and may respond in the subse-

quent time slot. The slave is free to par-

ticipate in another piconet in the

remaining time slots. In order to do so,

it sets its receiver to the frequency to

which the other piconet has just

hopped and synchronizes itself to the

master device of that piconet. Multiple

radio networks that are interconnected

in this manner are referred to in Blue-

tooth terminology as scatter nets (see

Figure 2). TDM collisions are avoided by

the fact that the slave devices syn-

chronize themselves to the clock rate of

2.402 GHz

625

992041 - 11

Figure 1. Frequency hopping (simplified representation)

Bandwidth Shared with / Notes

26.957 MHz - 27.283 MHz 0.326 MHz CB, cordless phones, ...

40.660 MHz - 40.700 MHz 0.040 MHz small bandwidth

433.050 MHz - 434.790 MHz 1.74 MHz Amateur radio

868 MHz - 870 MHz 2.00 MHz little used, small bandwidth

2.400 GHz - 2.483 GHz 83.00 MHz Microwave ovens, door openers

1 Note: additional ISM Bands may be allocated around 5.8 GHz, 24.250 GHz and 122.5 GHz

Slave

Piconet A

Slave

Master

Piconet B

Slave

A3&B1

Slave

Master

Slave

B4&C1

Slave

Piconet C

992041 - 12

Figure 2. Piconets and scatter nets

PC T OPICS ————————————— Elektor Electronics EXTRA

11 - 1/2000

Table 1. Some ISM frequency bands (not available in all countries)

Frequency range 1

Access

Code

Packet

Header

Payload

packet to be requested. The header of

every packet is always protected using

FEC, so that even if FEC is switched off,

re-transmission can always be insti-

gated via ARQ if interference occurs.

a) Packet format

72 bit

54 bit

0 ... 2745 bit

SCO and ACL

f i

f i +1

f i +2

f i +3

f i +4

f i +5

The Bluetooth Baseband Protocol

defines two types of data transfers:

point-to-point and single-point to multi-

ple-point.

Point-to-point transfers are referred to

as Synchronous Connection Oriented

(SCO). They are primarily intended to

be used for voice data transmission.

The link is thus symmetrical, which

means that the data rate is the same in

each direction. In practice, a full-

duplex link is implemented by utilizing

alternating time slots, with the data for

one direction contained in one slot and

the data for the other direction con-

tained in the following slot. In contrast

to data transfers, which are not time-

critical, it is naturally not possible to use

the ARQ technique for speech trans-

missions if interference occurs on cer-

tain frequencies. Instead, the Continu-

ous Variable-Slope Delta (CVSD)

method is used for voice encoding,

since it exhibits good bit-error behav-

iour and produces only a slight

increase in the background noise level

in case of errors. The sampling rate for

voice data transfers is 64 kb/s, the

same as for ISDN.

Single-point to multiple-point transfers

are asynchronous and connection-

independent; they are based on data

packets. Such links are referred to as

Asynchronous Connectionless (ACL) in

Bluetooth terminology. This type of trans-

fer is used by a master device to com-

municate with several slave devices at

the same time. In addition to being

used for sending messages to all slave

devices, this type of transfer is also used

for sending data packets to a particu-

lar slave device. In order to increase

the data transfer rate, a packet may

use not only one 625-µs time slot, but

also three or even five slots, as shown in

Figure 3 . To make this possible, fre-

quency-hopping is suspended and the

frequency at the start of the packet

transfer (f i ) is maintained for the dura-

tion of the three or five slot intervals. This

allows the ‘holes’ between successive

slots, which are otherwise reserved for

frequency hopping, to be used for the

data transfer. In order to maintain over-

all synchronization, frequency hopping

resumes on completion of the transfer

with the frequency that would normally

be used for the fourth slot (f i+4 ) or the

fifth slot (f i+5 ), as appropriate.

b) Multi-Slot

packets

AH P

625

f i

f i +3

f i +4

f i +5

AH P

3x 625 µ

f i

f i +5

AH P

5x 625 µ

992041 - 13

Figure 3. Packet format and multi-slot packets

the master.

As we have seen, up to eight devices

are allowed in a single Bluetooth

piconet. The higher-level scatter net

can contain up to ten piconets, so that

it is possible to configure systems con-

taining up to 80 Bluetooth devices

within a 10-metre radius. Even when a

single device is a member of all ten

piconets, the data transfer rate in any

piconet is reduced by no more than

around ten percent.

transmitted power, at 1 mW (0 dBm)

nominal, allows for an effective range

of at least ten metres under normal

conditions. In certain special cases, the

generation of higher field strengths (up

to 100 mW transmitted power, or

+20 dBm) is permitted with spread-

spectrum transmissions, which enables

effective ranges of up to 100 metres to

be attained. The Bluetooth radio mod-

ule can adapt its transmitted power to

the transmission environment, within

certain limits.

Error protection in the Bluetooth system

is also adaptive, which means that error

protection is dispensed with in favour of

a higher data transfer rate if there is a

very high-quality radio link. Two-stage

Forward Error Correction (FEC) is only

activated if interference occurs in the

radio link. This naturally reduces the

data transfer rate. In addition, the Auto-

matic Retransmission Query (ARQ) tech-

nique is used, except for voice chan-

nels. ARQ allows re-transmission of a

Modulation

and error protection

Gaussian Frequency-Shift Keying (GFSK)

modulation is employed for the fre-

quency-hopping narrow-band carrier

of each channel. With a frequency

deviation of around 150 kHz, the 3-dB

carrier bandwidth is 220 kHz. This fairly

simple modulation scheme was chosen

in order to keep the cost of the trans-

ceiver chips as low as possible. The

Table 2. ACL link data rates

FEC

Slots

Data rate, symmetrical

Data rate, asymmetrical

none

2 x 172.8 kBit/s

172.8 kBit/s + 172.8 kBit/s

none

2 x 384.0 kBit/s

576.0 kBit/s + 86.4 kBit/s

none

2 x 432.6 kBit/s

721.0 kBit/s + 57.6 kBit/s

yes

2 x 108.8 kBit/s

108.8 kBit/s + 108.8 kBit/s

yes

2 x 256.0 kBit/s

384.0 kBit/s + 54.4 kBit/s

yes

2 x 286.7 kBit/s

477.8 kBit/s + 36.3 kBit/s

12 - 1/2000 Elektor Electronics EXTRA —————————————— PC T OPICS

Data transfers from a slave device to a

master, or from one slave to another

slave via the master, require the per-

mission of the master. For ACL links, the

symmetry of the data rates in the two

directions is controlled by the master.

With asymmetric links, the data rate in

one direction can be as high as

721 kb/s, in which case the rate in the

other direction is only 57.6 kb/s. Both of

these values are based on five-slot

transfers without forward error correc-

tion (FEC). If FEC and the previously-

mentioned ARQ procedure are

employed, the data rate naturally

drops. A 2/3-rate FEC is used. With a

symmetrical link and no error protec-

tion, the maximum data rate is

432.6 kb/s in each direction. Table 2

lists additional data rates for ACL links.

With both types of links, ACL and SCO,

there are 16 different types of packets

that can be used for data transfers.

Some of these are reserved for control

functions. Every packet has a 72-bit

identification field (Access Code),

which is derived from the 48-bit master

address and which is protected by FEC.

Following this comes a 54-bit header

field, which is also protected by 1/3-

rate FEC. After this, in a normal packet,

come up to 2745 bits of payload data

(see Figure 3 ). Three-slot and five-slot

packets can transfer correspondingly

more payload data.

Bluetooth transfers can also be

encrypted, using a 128-bit key for

authentification. The user can deter-

mine whether he or she wants to use

encryption in one direction or in both

directions. This setting is saved. This

allows the user to exactly specify the

equipment with which a cellular phone

(for example) is allowed to communi-

cate. For example, you could allow

your phone to access your own note-

book, while denying any access to

your colleagues.

With Bluetooth, it is possible to have

either one asynchronous ACL channel

or up to three simultaneous, synchro-

nous SCO channels plus one asynchro-

nous data channel with a parallel 64-

kb/s speech channel.

Status:

Standby

Not connected

Inquiry

Page

Connecting

Unknown Address

Known Address

Transmit

Data

Connected

Active

Park

Hold

Low

Power

Sniff

Releases

Mac Address

Keeps

Mac Address

992041 - 14

Figure 4. Bluetooth module state diagram

A Bluetooth module that is not yet con-

nected transmits a call via the wake-up

carriers, which is answered by any

other nearby Bluetooth radio(s). After an

introductory handshake, the two

devices set up a piconet, in which the

device that first issued the call takes on

the role of master. Based on its address,

it establishes the hopping sequence for

this piconet. The slave device, and any

other devices that later join this

piconet, synchronize themselves to the

clock rate of the master device.

Figure 4 shows the state diagram of a

Bluetooth module. Starting from the

Standby mode, it moves to the Inquiry

state on detecting a second device. In

this state, it transmits a general call fol-

lowed by an address request. Once the

address of the other device has been

determined, or if this was already known

in the Standby mode, the module trans-

fers to the Page mode. After a typical

delay of 0.6 second, the connection

becomes active (Connected state).

Data transmission can now take place

(in the Transmit Data state). After a suc-

cessful data transmission, the Bluetooth

module can either return to the Standby

mode or enter one of three low-power

(energy-saving) modes.

The first low-power mode is the Hold

mode, in which the device remains an

active member of the piconet. When an

internal timer in the slave device times

out, the slave briefly makes itself known

to the master before restarting the timer.

If necessary, the slave can leave the

Hold mode immediately in order to trans-

fer data. The master can force a slave

into the Hold mode, but a slave can also

voluntarily enter the Hold mode.

In the second low-power mode, the

Sniff mode, the slave is programmed to

periodically ‘listen’ to the piconet to

determine whether there is a data

transfer waiting for it.

The third low-power mode is the Park

mode. In this mode, the slave drops out

of the piconet and makes its Media

Access Control (MAC) address free

(each member of a piconet has a MAC

address, with a value of 0 to 7). After

this, it remains passive, and its only

activity is to maintain synchronization

with its piconet master at relatively long

time intervals.

Interesting Bluetooth

applications

In the first instance, Bluetooth should

eliminate cables for connections

between laptop or desktop computers

and printers, scanners and fixed Local

Area Networks (LANs). With it, even (wire-

less) keyboards, mice and joysticks or

trackballs need not necessarily have a

line-of-sight path to the computer.

Other imaginable applications relate to

laptop computers and cellular phones.

For example, if you write your e-mail

messages in the aeroplane using your

laptop, you would no longer have to

worry about how to send them. As soon

as you leave the aeroplane and switch

Piconet states

Bluetooth modules that are not members

of any piconet operate in the Standby

mode, in which they search for possible

transfers in their immediate environment

every 1.28 seconds. They do this by test-

ing 32 of the possible 79 frequencies,

which are designated as wake-up car-

riers. In France, Spain and Japan there

are 16 wake-up carriers among the total

of 23 possible frequencies.

PC T OPICS ————————————— Elektor Electronics EXTRA

13 - 1/2000

Loop

Filter

Balun

2.4-GHz

Antenna

tronics, there are suggestions for using

Bluetooth as the basis for wireless con-

nections to (for example) a video cam-

era or a still camera. The camera could

pass the image via a cellular phone to

the mains network, or save it on a lap-

top, all via a wireless link. It would be

possible to send still pictures as sponta-

neous ‘electronic postcards’ via Blue-

tooth to your cellular phone and thereby

to their ultimate destinations. Remote

control of television sets and stereo

installations could also be implemented

using Bluetooth, which would eliminate

the annoying need to search for a line-

of-sight path to the equipment.

VCO

Tank

RF IC

Antenna

Filter

Control & Data

Balun

Bluetooth Radio ASIC

992041 - 15

Figure 5. Block diagram of a Bluetooth radio module

on your cellular phone again, the lap-

top could make a Bluetooth connec-

tion and send the e-mail. The use of a

Bluetooth radio module inside the aero-

plane should also be allowed, due to

its low transmitted power level (100 mW

maximum).

In the future, you could also dispense

with cables when using a cellular

phone with a hands-free installation.

You could leave your cellular phone

switched on in your pocket and enjoy

a wireless link to the headset of the

hands-free unit. The use of a hands-free

unit makes an important contribution to

safety for commercial vehicles as well.

Finally, you could equip your laptop

with speakers and a microphone. The

speech signal could be passed on to

the cellular phone in your briefcase via

a wireless Bluetooth link. This would

make it possible to transfer speech,

data and graphics using only one

device, the laptop computer.

One very practical suggestion is to use

Bluetooth for automatic file synchro-

nization between a laptop computer, a

desktop computer and a Personal Dig-

ital Assistant (PDA). Whenever these

devices are located in the same vicin-

ity, they could independently

exchange e-mail messages, appoint-

ments and addresses, in order to bring

each other up to date. It would even

be possible for a field-service techni-

cian (for example) to use a Bluetooth

cellular phone to automatically update

or modify his appointments calendar,

based on information from the main

office. In future conferences and meet-

ings, the participants could bring along

their laptops with Bluetooth interfaces

and set up a spontaneous network. This

would allow the exchange of graphics,

texts and data, or the wireless remote

control of a projector.

Wireless Internet access using Bluetooth

should allow for more freedom of

movement. Internet pages could reach

your laptop via wireless links from a cel-

lular phone, locally-installed modem or

your firm’s LAN. A Bluetooth cellular

phone could automatically switch from

GSM to DECT operation, both at home

and in the office, as soon as it makes

contact with a local cordless-phone

base station. This would allow you to

simply use the same unit for all your

phone conversations.

From the world of entertainment elec-

The first Bluetooth

components

Ericsson has developed a Bluetooth

Development Kit in cooperation with

Symbionics. It includes extensive docu-

mentation and design-support soft-

ware. The baseband processor is pro-

vided by VLSI, and comes from the

VWS26000 Bluetooth family [6] . The

radio module (see Figure 5 ), which is a

hybrid, is an Ericsson product (PBA 313)

[4] . You can also obtain a Bluetooth

Developer’s Kit from Philips Semicon-

ductors. The baseband portion is once

again a VLSI ASIC, and the radio mod-

ule contains the UAA-3558 Bluetooth

transceiver. This kit contains two identi-

cal Bluetooth daughterboards that can

be used to set up an initial radio link.

Figure 6 shows the typical structure of

a Bluetooth module. The firm Cam-

bridge Silicon Radio [7] is working on

single-chip Bluetooth components with

integrated radio modules. The

Bluecore™01, Bluecore™02 and

Bluecore™03 ASICs are intended to

incrementally incorporate additional

Bluetooth functions. The size of a com-

plete module should ultimately shrink to

that of a postage stamp. Finally, numer-

ous semiconductor manufacturers,

such as Temic, Philips and Motorola,

offer 2.4-GHz transceiver ICs especially

for use in Bluetooth radio modules. All

Bluetooth modules must pass a BSIG

certification procedure in order to

ensure compatibility.

2.4-GHz

Antenna

CPU

Baseband

Radio

Competition for Bluetooth

Link

Manager

Link

Controller

RF Section

There is also competition for Bluetooth

as a short-range radio networking tech-

nology. For some time now, it has been

possible to transfer data between a PC

and its peripheral equipment using an

infrared-light interface that complies

with the Infrared Data Association (IrDA)

protocol. However, infrared links

absolutely require free line-of sight

992041 - 16

Figure 6. Block diagram of a Bluetooth module

14 - 1/2000 Elektor Electronics EXTRA —————————————— PC T OPICS

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