kelvin hilton [email protected] personal area networks

Kelvin [email protected]

Personal Area Networks

mailto:[email protected]

15/07/2003 Copyright: All rights reserved. Not to be reproduced without consent. 2kch/soc/sdmc/01 page

ObjectivesUnderstanding:

The motivation behind BluetoothPiconets & ScatternetsHow Bluetooth devices communicateThe Bluetooth Packet structure/payloadApplications of Bluetooth


Introducing the Vision

It seems that ever since we invented wired networks we have been dreaming of a world without them!Two main philosophies

Remove the wire but retain the concepts, network principles, protocols, etc (WLAN)Start with no legacy/pre-conceptions

“ ...technology [enabling] low-cost radios that can be embedded in existing…devices [leading] toward ubiquitous connectivity and truly connecting everything to everything. ”

J.C.Haartsen. 2000 (Bluetooth pioneer)


Background1994 Ericsson were looking at ways of connecting headsets to handsets without wires (a multi-communicator link)1998 together with IBM, Intel, Nokia & Toshiba formed a Special Industry Group (SIG)They called the new technology they were proposing Bluetooth after Danish King Harald Gormsen epithet was Blåtand (Bluetooth!) who is credited with uniting Scandinavia in the 10th Century


BackgroundGoals of specification

Low powerLow cost < $5 US for the chipReplacing the umbilical connection

Proposed usingShort-range radio technologyAd hoc piconetworkingDynamic device discoveryUnlicensed frequencySupport data and voice

Specification eventually became 802.15HP tried same thing with Ir but failed!


Background1998 May – Bluetooth SIG announced1999 July – version 1.0A released1999 Dec – version 1.0B released2001 Mar – version 1.1 released2001 First commercial devices launched2004 Version 2.0 adds enhanced data rates up to 2.1 Mbps2007 Version 2.1 adds enhanced power management and NFC

1999 Ericsson erected monument to Harald Gormsen depicting a man holding a laptop & a cellular phone!


BackgroundScenarios

Connecting Peripherals – wired world, connector variations (LAN, Serial, USB, etc)Ad hoc networks - anyone, anywhere, conferences, tradeshows, lectures even!Network Access Points – automatic up/downloads from servers as you enter buildings, get off planes, etc all trafficked via a handset or PDA


Bluetooth ArchitectureThe basic concept of a Bluetooth “network” is the piconet

A collection of devices connected in an Ad Hoc fashionNo central server instead uses the concept of Master/SlaveRange of reception

Three classes of device were specified with 100m (100mW). 10m (2.5mW), 1m (1mW) range

A unit can exist within a piconet as 1 of 4 nodes

MasterSlaveParkedStandby


Piconet

Sb

S

P

SS

M

Sb StandbyP ParkedM MasterS Slave


Overview of Master/Slave Relationship

Only 1 unit can be a Master within a piconetMaster initiates the exchange of dataSlave can only respond to the Master, cannot initiate communicationSlave to slave communication is not possibleEach Master can connect to 7 simultaneous Slaves or 255 Parked nodesMaster assigns a 3bit Active Member Address (AM_ADDR) to each slave participating in the piconetMaster assigns an 8bit Parked Member Address to none participating but registered nodes (PM_ADDR)


Overview of Master/Slave Relationship

A parked node has agreed with the Master to park (low power state), can only be activated by MasterA Standby node is physically located within the range of the Master but is not associated with any piconetAn active node may be a in more than one piconet (called a Bridge Slave or Bridge Node)Collection of interconnected piconets are called a ScatternetA Master can only be a Master of one piconet


Scatternet

Sb

S

P

S

MS

SS

M


Traditional Ad Hoc Networks

d

d

d

d

d

d

d

d

No overlap


Bluetooth Scatter Ad Hoc Networks

Allow overlap

d

d

dd

d

d

d

d

d

d


Selecting the FrequencyTo provide a truly ubiquitous experience the SIG had to select a frequency that was available worldwideTo achieve low cost must be an unlicensed frequencyAround the world frequency allocation is licensed/controlled by governmentsThere is some coordination via the ITUSIG selected the Industrial, Scientific, Medical (ISM) band


ISMOriginally reserved for the “professions” now open worldwide for commercial useCentred around 2.4 GHzIn US range is 2400 to 2483.5 MHz regulated by FCCSame in Europe (excepting France & Spain) regulated by ETSIJapan 2400 MHz to 2500 MHzRegulations differ regarding the use of the frequency (spread of signal, power of transmission)SIG selected the lowest common denominator


Accessing the FrequencyISM at 2.4 GHz provides about 80 MHz of bandwidthBluetooth designers defined 79 carrier channels with 1 MHz spacingISM band only supports a gross bit rate of 1Mb/s per channel (channel = 1 MHz)Therefore, theoretical limit across the spectrum of 79 Mb/sBluetooth uses as a base the Code Division Multiple Access scheme (CDMA)


Frequency Division

= 2400 MHzff+ 1 f+ 2

……..

f + 79


Accessing the FrequencyDedicating a piconet to one channel would limit the maximum number of simultaneous piconets available to 79Using only 1 channel per communication would not be very secure (or efficient)!Therefore, the specification of the ISM states that users must hop (called Frequency Hopping, FH*) between different channels within the frequency bounds (called spread spectrum)However, fixed hopping sequence is also a security risk, therefore Bluetooth designers use a pseudorandom hopping sequence

* Therefore, the actual access scheme used by Bluetooth is called (FH)-CDMA


Accessing the FrequencyThe sequence of hops is defined by the Master nodeEach Bluetooth device has a 28bit native clock that ticks once every 312.5 s (mircoseconds)Each Bluetooth device has a unique 48bit IEEE MAC address (called the Bluetooth device address BD_ADDR)Slave uses the BD_ADDR of Master to identify the hopping sequence and offsets its native clock to synchronise with the MasterBluetooth radios complete 1600 hops/s


Accessing the FrequencyHow long we stay on a given frequency channel is called the dwell timeWhen using time to divide up each channel each unit of time is called a slot Bluetooth uses the minimum dwell time required to transmit (Tx) one packetThis is 625 s (mircoseconds)Master transmits on even slots and slaves transmit on odd slots (classic Time Division Multiplexing, TDM) 50/50 split of slotsFurther, to ensure full-duplex communication Bluetooth uses Time Division Duplexing (TDD) such that unit alternates between send & receive


Accessing the Frequency

Time (t)

t

Master

Slave

f n

Packet

Tx

Packet

Tx

Packet

Tx

625s Single Slot

f fn + FH1 n + FH2


Collision PreventionTo prevent two or more Slaves transmitting at a time Master applies polling, the Master decides which slave can transmit in which slotOnly the slave addressed in the previous Master slot transmission can transmit in the succeeding Slave slotIf data is received incorrectly it is resent in the next appropriate slot


Polling

t

tf n

Tx

addr

esse

d to

B

f f

n +

FH

1

n +

FH

2

Master

Slave A

tSlave BB a

llow

ed t

o Tx

Tx

addr

esse

d to

A

A a

llow

ed t

o Tx

fn

+ F

H3


ModulationBluetooth uses Gaussian-shaped Frequency Shift Keying (GFSK)

Version 2.0 use Phase Shift Keying (PSK)

Basically binary 1 is sent as a positive nominal modulation and 0’s are sent as negative nominal modulations


Bluetooth PacketsOnly 1 packet per slotBluetooth specifies 15 types of packets

4 control packetsID packets used for reconnection, signalling, etcNULL packets for flow control or Automatic Repeat Requests (ARQ)FHS packets used to exchange real-time clock and identity information for hop synchronisationPOLL packets used by Master to force a Slave response

Remaining are used to define payload packets


Bluetooth Packets625 bits per packet theoretical

Have to allow a settling time for radio circuits to stabilise after a hop & decode/encode the packet, ranges from 200 – 260 s, faster the settling time the more electrical/processor power required

All packets have same general formatAccess codeHeaderData

Access Code

72 bits

Header

54 bits

Payload

0 - 2745 bits

The is a payload size is theoretical


Access Code

Used for synchronizationOffset compensationIdentificationSignallingThree types (Sync words)

Channel Access Code (CAC)Device Access Code (DAC)Inquiry Access Code (IAC)

Basically used to uniquely identify the piconetOnly if the Access Code corresponds to the Master Access Code will the packet be accepted by the receiving node

Access Code

72 bits

Header

54 bits

Payload

0 - 2745 bits


Access Code

Access Code

72 bits

Header

54 bits

Payload

0 - 2745 bits

preamble

4

Sync Word

64

trailer

4


Header

3bits AM_ADDR (zeroed address used for broadcast) hence maximum of 7 slaves 4bit packet type code1bit Flow flag used by slave to alert when its data buffer is full1bit Acknowledge/ Negative Acknowledge for ARQ (ACK/NACK)1bit Sequence flag used for retransmission8bit header error check code (HEC) used as a Cyclic Redundancy Check (CRC) for the headerBluetooth uses 1/3 Forward Error Correction (FEC) on the header (3 x Tx)

Access Code

72 bits

Header

54 bits

Payload

0 - 2745 bits


Header

Access Code

72 bits

Header

54 bits

Payload

0 - 2745 bits

AM_ADDR

3

Type

4

F A S

1 1 1

HEC

8


Real-Time PayloadReal-time (including voice) uses Synchronous Connection Oriented Links* (SCO)

Point-to-PointCircuit-switched – 64kbps (uplink/downlink) using reserved Pulse Code Modulation (PCM) channelsUp to three voice channels can be active in a piconet (maybe to 1, 2 or three slaves)

High Voice (HV) 1 – 1/3 FECHV2 – 2/3 FECHV3 – no FEC

Only uses one slot packets* Links are the name for the logical channel between two communicating entities


Real-Time Payload

Access Code

72 bits

Header

54 bits

Payload

240 bits

10 bytes

20 bytes

30 bytes

HV1

HV2

HV3

366 bits

1/3 FEC (1 full-duplex voice channel active at a time)

2/3 FEC (2 full-duplex voice channel active at a time)

no FEC (3 full-duplex voice channel active at a time)

relia

bilit

y

best

worst


Real-Time Round-Trip Delay

HV1

Tx Tx TxRx Rx Rx

1.25ms

HV2

HV3

1 Channel Reserved

2.5ms

Two Channels Reserved

3.75ms

Two Channels Reserved


Data PayloadPackets can be one, three or five slotsMultislot packets are transmitted on a single carrier hop

The hop channel which is used for the first hop remains in use for the remaining packets (no hop after 1st packet sent)Hopping resumes on the next channel that would have been valid if single hops had been used

eg If 3 slot packet used then next hop will be f + FH3

Odd number ensures master-slave sequence duplex maintained


Multislot Transmission

One Slot Tx

Three Slot Tx

Five Slot Tx

Tx Tx TxRx Rx Rx

fn fn + FH1fn + FH2

fn + FH3fn + FH4

fn + FH5

Tx Rx Tx Rx

RxTx


Data PayloadData uses Asynchronous Connectionless (ACL) links

Includes 16bit CRCVariable data payload

Data Medium (DM) uses 2/3 FECDM1 – uses 1 slotDM3 – uses 3 slotsDM5 – uses 5 slots

Data High (DH) no FECDH1 – uses 1 slotDH3 – uses 3 slotsDH5 – uses 5 slots

Best effort delivery, FEC optionalOnly one link can exist between a Master & a Slave, Master can link to 7 slavesBroadcasting is possible


One Slot ACL Packet Format

Access Code

72 bits

Header

54 bits

Payload

0 - 240 bits

Header Data CRC

16bits8bits 216bits

Logical Channel Flow Field Unused

3bits 1bit 4bits


One Slot ACL Packet Payload

Access Code

72 bits

Header

54 bits

Payload

0 - 240 bits

Header Data CRC

16bits8bits 216bits

DM1 (2/3 FEC) Data

136bits

Data

216bits

DH1 no FEC


One Slot ACL Data RateDM1

Tx(136 bits x 800 hops/s) / 1000 = 108.8 kbps

Rx(136 bits x 800 hops/s) / 1000 = 108.8 kbps

DH1Tx

(216 bits x 800 hops/s) / 1000 = 172.8 kbps



Three Slot ACL Packet Format

Settling period reduced allowing larger first packetAsymmetric Tx = 3 Slots Rx = 1 Slot

Access Code

72 bits

Header

54 bits

Data

0 - 1500 bits

Header

16bits

CRC

16bits


Three Slot ACL Data RateDM3

Tx(968 bits x 400 hops/s) / 1000 = 387.2 kbps


DH3Tx

(1464 bits x 400 hops/s) / 1000 = 585.6 kbps



Five Slot ACL Packet Format

Asymmetric Tx = 5 Slots Rx = 1 Slot

Access Code

72 bits

Header

54 bits

Data

0 - 2745 bits

Header

16bits

CRC

16bits


Five Slot ACL Data RateDM5

Tx(1792 bits x (1600/6 hops/s)) / 1000 = 477.8 kbps

Rx(136 bits x (1600/6 hops/s)) / 1000 = 36.3 kbps

DH5Tx

(2712 bits x (1600/6 hops/s)) / 1000 = 723.2 kbps

Rx(216 bits x (1600/6 hops/s)) / 1000 = 57.6 kbps


Bluetooth Packet Miscellaneous

Therefore we get maximum throughput of 723.2 from 1Mbps availableCan mix SCO & ACL traffic on the same piconet


Overview of Device Discovery

Device n

Idle Idle

InquiryWake-up

Broadcast ID & Clock Data

FHS with ID & Clock DataInquiry Response

IdleID & DAC Packet

Wake-up

Ack PageID & DAC Packet

Device A now Master

Page

FHS for Piconet

Device n now SlaveConfirm with ID & DAC Packet

Connection Connection

Device A


IssuesBluetooth is a shared medium, starts with theoretical 1Mbps for each device that joins the bit rate diminishesBluetooth and WLAN are competitors sharing the same frequency leads to interferenceDesigned by committee (hence the profile proliferation)

Questions ?

kelvin hilton [email protected] personal area networks

Documents

bluetooth network

kchsocsdmc01 pageintroducing

bltand bluetooth

bluetooth pioneercopyright

mbps2007 version

bluetooth sig announced1999

network principles

wired networks