Mobile Systems ITU

Mobile Systems

Bluetooth

Ver. 1.1

Mobile Systems ITU

What is Buetooth ?

In Feb. 1998 five major telecom and PC companies formeda special interest group (SIG)• Ericsson• Nokia• IBM• Toshiba• Intel • 3Com, Lucent, Microsoft, Motorola (joined in Dec. 1999).

To create a standard radio interface to establish ”local connectivity between electronic devices”.

Mobile Systems ITU

What is Bluetooth?

Mobile Systems ITU

What is Bluetooth?

• The system must operate globally.• The system must support peer connectivity, thus

- No wired infrastructure to provide for call set-up, and networking => ad hoc network.

• The connection must support voice and data for multi-media applications.

• The radio transiver must be small and operate at low power, and fit into f.inst. mobile phones, headsets, PDA.

Mobile Systems ITU

The Communication Channel (I)

The Bluetooth uses • A Frequency Hopping /time division duplex scheme.• FH/TDD scheme.

The channel is devided into consequtive time slots, where• each slot takes 625 µsec.• A different hop channel for each slot, which gives• 1600 hops/sec.One packet is transmitted for each slot.Alternate between transmitting and receiving.

Mobile Systems ITU

The Communication Channel (II)

625 µsec.

f(k)

f(k+1)

f(k+2)

time

time

Mobile Systems ITU

The Communication Channel (III)

72 54 0-2745

A Bluetooth packet:

Acces code Packet Header Payload

3 4 1 1 1 8

bits

bits

M_addr Type Flow ARQN SEQN HEC

Packet Header: 54 bits (18 bits replicated 3 times).

Mobile Systems ITU

The Communication Channel (IV)

3 4 1 1 1 8 bits

M_addr Type Flow ARQN SEQN HEC

Packet Header: 54 bits (18 bits replicated 3 times).

M_addr: Address assigned by a Master to a Slave. 0 is broadcast to all slaves.

Type: SCO: Synchronous connection-oriented link (f.inst. Speech). ACL: Asynchronous connectionless link.

Flow: Flag asserted by a device, if its receive buffer is full, and it is not able to receive any more data.

Mobile Systems ITU

The Communication Channel (V)

3 4 1 1 1 8 bits

M_addr Type Flow ARQN SEQN HEC (header error check)

Packet Header: 54 bits (18 bits replicated 3 times).

ARQN: Automatic Retransmission Query Asserted if the previous reception was sucessfull from CRC check.

SEQN: Negated whenever a new packet is sent. Keep value if packet is resend. If ARQN is lost because of error in the returned header, the packet will be sent again. Ignore packets with identical SEQN.

Mobile Systems ITU

The Communication Channel (VI)

Received packet CRC check

Transmitted package

Retransmision

New Transmision

ACK/NAKACK/NAK

Mobile Systems ITU

Physical Link Definition (I)

Two types of links to support multimedia applications:• synchronous connection-oriented (SCO) link,• asynchronous connectionless (ACL) link.

SCO links are symmetrical point-to-point connections foraudio and voice.• Reserve two consecutive slots (forward and return) with a fixed period (constant sampling period).

ACL supports symmetrical or asymm. packet switched,point-to-multipoint, for bursty data transmission.The master use polling to control the ACL.

Mobile Systems ITU

Physical Link Definition (II)

The ACL (Asynchronous Connectionless Link) is constantlypresent between the master and slave.

The ACL link have both control and data transfer.

The SCL (Synchronous Connection-oriented Link) can be setup and released dependent of needs.

A Paging process: Initiate a connection by sending the device the Bluetooth address in an ID packet (access codeonly).

Mobile Systems ITU

A Piconet with 1 Master and 2 Slaves

Master

Slave 1

Slave 2

SCO

ACL

SCO

SCO period

ACL

625 x 2 sec.

Mobile Systems ITU

Ad Hoc Connectivity (I)

Inquiry Page Connection

Typical 5.12 sec. 0.64 sec. 0.1 – 300 minutesMax. 10.24 sec. 7.68 sec.

Inquiring: done by executing an inquiry procedure to • discover other Bluetooth devices,• to know the identity of the recipient (new device).

Mobile Systems ITU

Ad Hoc Connectivity (II)

The inquiring unit transmits:

• an inquiry access code on the • inquiry wake-up channels according to • an inquiry sequence,

which are common to all Bluetooth devices.

When a recipient receives the inquiry access code it• returns a packet containing its identity and clock.

Following that, the inquiring unit can start the paging process.

Mobile Systems ITU

Ad Hoc Connectivity (III)

• Standby mode:- Do not transmit, but listen to hop channels with low duty cycle.- Interval between wake-up events is up till 3.84 sec.- The unit listens for about 11 msec. on a single hop channel.

• Start to make a connection:- Broadcast page or inquiry messages.

• The pager must know the standby units identity- for generation of access code,- to select hop channels,- to predict where the device is in the hop sequence.

Mobile Systems ITU

Piconets (I)

• Two or more Bluetooth units, sharing a frequency hop- ping (FH) channel form a Piconet.• One of the units is master; all other are slaves. • Only one master at time:

- The master identity and clock, specify channel parameters, f.inst.

hop sequence and the access code preceeding all packets.

S

M

S

Mobile Systems ITU

Piconet (II)

• The master unit controls all traffic on channel.

- Allocate slots for SCO (Synchronous Connection Oriented) links.- Use polling for ACL (Asynchronous Connectionless) links. If no information from master to slave use a POLL Packet, with acces code and header only.- Polling avoids collision, thus saving bandwidth.- Slaves can be polled, according to the demand.- Master can dynamically ajust the scheduling algorithm.

Mobile Systems ITU

Scatternet (I)

In Piconet the users share1 Mbit/sec.

The spectral bandwidth is79 MHz in total (ISM band).

Better BW utilization throughcreation of several Piconets,each having different hoppingsequences.

Scatternet: Collection of Pico-nets joined by common members.

Mobile Systems ITU

Scatternet (II)

MM/SS

SS

S

S

Piconet 1

Piconet 2

One device is slave in one piconet and master in another.

The device that links thescatternet, must maintaintwo different hopping se-quences!

This is done by time sharing,and leads to reduction ofdatarate, compared to onenet.

Mobile Systems ITU

Scatternet (III)

MS

S

Piconet 1

One device is slave in two piconets.

S M

S

S

S

Piconet 2It is not possible tohave a device whichis a master on twodifferent piconets:

A piconet is definedby the clock andBluetooth device adr.of the master.

All devices with samemaster are on the same piconet.

Mobile Systems ITU

Scatternet (IV)

Master 1

Slave 1/Master 2

Slave 2

Empty time slots, becauseof change of synchronization.Reduce throughput by 1/2 to1/3.

Expensive to exchange data between piconets.

Mobile Systems ITU

Scatternet (V)

Why not unite the timing, such that the whole scatternet is synchronized?

M

S S M/S

S M/S

M

S M/S

S SSynchronize?

This timing propagation, is not directly supported in Bluetooth.

Mobile Systems ITU

Scatternet (VI)

Estimate scatternet efficiency:

1791 )1( NTH

TH is the normalized throughput per piconet, assuming N piconets co-located.

Mobile Systems ITU

Power Management (I)

Designed for universal interface to portable, battery driven equipment => reduce the power consumption.

• The hopping mechanism remains synchronized even if no packets are exchanged for some 100 msec.• The reciever decides quickly if a package is recieved by

- comparing the recieved signal with the access code by using- correlation.- If no package is reived the device go to sleep.

Mobile Systems ITU

Power Management (II)

If the proper access code is received then

• continue to read the packet header and• check the slave address in the header.

- If address is ok then read the payload, otherwise- stop working with this package.

Microlevel power saving.

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Power management (III)

Power saving at the macro level.

A master can put a slave into HOLD mode:

• During the HOLD period no communication is possible.• When HOLD period expires, the slave returns to the channel instantaneously (it remains synchronized).

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Power management (IV)

Power saving at the macro level.

A master can put a slave into PARK mode:

• The slave enters a low-duty cycle mode where it perio-dically listen to the master.

• The slave remains synchronized in the piconet, but can only continue communicating when being UNPARKED.• The master supports the PARK mode by transmitting a beacon signal at regular intervals.

Mobile Systems ITU

Power management (V)

Power saving at the macro level.

A master can put a slave into SNIFF mode:

• The slave enters a low-duty cycle mode where it perio-dically listen to the master.

• The slave remains synchronized in the piconet.• The SNIFF mode is used for low bandwidth applications.

Mobile Systems ITU

Power management (VI)

Power saving at the macro level.

When a unit is in standby mode:

• it only wakes up in 11 msec. on a single frequency, (use f.inst. the inquiry channel).

The burden of finding a unit in standby mode is placed onthe pager (f.inst. a ticket automaton, laptop or a mobilephone).

Mobile Systems ITU

The Audio Channel (I)

Comparison of Audio Data rates:• Audio CD: Stereo 16 bit @ 44.1 kHz 1411.2 kbit/sec.

• MP3-encoded Audio: Stereo near CD qty. 128 kbit/sec.

• POTS telephone: mono 8 bit @ 11.025 kHz 88 kbit/sec.

• Bluetooth SCO channel: mono 8 bit 8 kHz 64 kBit/sec.

Mobile Systems ITU

Audio Channel (II)

Bit Error Rates (BER) and the quality of audio:

Audio data is retransmitted.

• An BER of 0.1% does not significantly degrade the quality of the speech.• An BER of 1% is quite noticable.• An BER > 5% causes the output to become unintelligible.

Mobile Systems ITU

Quality of Service (I)

The Bluetooth Spec. provides Quality of Service (QoS) configuration:

• The type of QoS:- Does the link guarantee the settings, or- is it best effort, or- no QoS service at all.

• Token rate: the rate data may be sent on the link.

• Token rate bucket size: How much storage for buffer.

Mobile Systems ITU

Quality of Service (II)

The Bluetooth Spec. Provides Quality of Service (QoS) configuration:

• Peak bandwidth: The max. Rate of back to back packets.

• Latency: Delay in the transmission.

• Delay variation: The spread between the maximum and minimum delay over a link.

Mobile Systems ITU

References (I)

1 Bob O’Hara, Al Petrick, ”The IEEE 802.11 Handbook” IEEE Press, 1999. Reading material: p. 1 - 69, p. 88 (from Power management) - 98 (not including Combining Management Tools).

2 Jennifer Bray, Charles F. Sturman, ”Bluetooth”, Prentice-Hall 2001. Supplementary literature.

Mobile Systems ITU

References (II)

3 IEEE Std. 802.11/1997 ”Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications”. IEEE Standards Board, June 26, 1997.

Download: www.dtv.dk -> Search literature -> Search of other literature at DTV -> IEEE/IEE Electronic Library -> Standards -> 802.11 GO

Mobile Systems ITU

References (III)

4 Brian P. Crow, Indra Widjaja, Jeong Geun Kim, Prescott T. Sakai ”IEEE 802.11 Wireless Local Area Networks” IEEE Communications Magazine, September 1997, pp. 116-126. Reading material: p. 116, p. 117, p. 118 excluding the Physical Layer. P. 119, p. 120, p. 121.

5 Jaap C. Haartsen, Sven Mattisson ”Bluetooth - A New Low-Power Radio Interface Providing Short-Range Connectivity”. IEEE Proceedings of the IEEE, Vol. 88, No. 10, October 2000. Reading material: p. 1651- 1657 not including V. Implementation Considerations.