Bluetooth 9

8/13/2019 Bluetooth 9

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Bluetooth

An overview


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Introduction


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What is Bluetooth

Bluetoothis a universalradio interface in the 2.4 GHzfrequency band that enables electronic devices to connectand communicate wirelesslyvia short-range (10-100 m),

ad-hocnetworks.Key Features:

Peak data rate : 1 Mbps

Low power : peak tx power


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Bluetooth History

Invented in 1994 by L. M. Ericsson, Sweden

Named after Harald Blaatand Bluetooth, king

of Denmark 940-981 A.D.Bluetooth SIG founded by Ericsson, IBM, Intel,

Nokia and Toshiba in Feb 1998

More than 1900 members today

Bluetooth version 1.0 and 1.1 have been released


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Motivation for Bluetooth

Cordless

headset

Cell

phone

mouse

Started as a Cable

replacement

technology

Ubiquitous Computing

environment of intelligent

networked devices

Mobile access to

LANs/Internet

Home Networking

Automatic

Synchronization of data

Voice applications -

hands-free headset


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System Challenges

Work across a diverse set of deviceswith varying

computing power and memory

Dynamic environment- the number, location and variety

of devices changing - connection establishment, routing

and service discovery protocols have to take this into

consideration

Unconsciousconnection establishment

Size of the implementation should be small. The power

consumption should not be more than a fraction of the host

device .


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System Architecture

RFBaseband

Link ManagerAudio

L2CAP

Data

RFCOMMSDP

IP

Applications

Bluetooth Protocol Stack

The Radio, Baseband and Link

Manager are on firmware. The

higher layers could be in soft-

ware. The interface is thenthrough the Host Controller

(firmware and driver)

The HCI interfaces defined for

Bluetooth are UART, RS232 andUSB.


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Bluetooth Air Interface

Piconet channel definition

Physical link definition

Packet definition


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Choices made

ISM Band

Global Availability License Free

2,400-2,483.5 MHz in

Europe and US

2,471-2,497 MHz in Japan

Frequency Hopping

Interference from baby

monitors, garage dooropeners, cordless phones

and microwave ovens.

Spread-Spectrum for

interference suppression

FH supports low power,

low cost radio

implementations


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Frequency Hopping

1Mhz

83.5 Mhz

791

Divide Frequency band into 1 MHz hop channels

Radio hops from one channel to another in a pseudo

-random manner as dictated by a hop sequence

The instantaneous (hop) bandwidth remains small

Narrow band interference rejection


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Piconets, Masters and Slaves

m sIn principle each unit is a peer with the

same hardware capabilities

Two or more Bluetooth units that share

a channel form a piconetOne of the participating units is becomes

the master (by defn the unit that

establishes the piconet).

Participants may change roles if a slave

unit wants to take over as master

Only one masterin a piconet.

Upto 7 slaves


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Piconet Channel

The piconet channel is represented by a pseudo-random

hopping sequence(through 79/23 RF frequencies)

The hopping sequence is unique for the piconet and is

determined by the device address of the masterof the

piconet. The phase is determined by the master clock.

Channel is divided into time slots - 625 microsecs each .

Each slot corresponds to a different hop frequency.

Time Division Duplex- master and slave alternately

transmit/listen.

Packet start aligned with slot start


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Piconet Channel

m

s1

625 sec

f1 f2 f3 f4


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Physical Link

Synchronous Connection Oriented (SC0) Link:- symmetric point-to-point link between m and s- reserved 2 consecutive slots at regular intervals

- master can support upto 3 simultaneous SCO links- mainly for audio/voice- never retransmitted

Asynchronous Connection-less (ACL) Link:

- symmetric/asymmetric- point-to-multipoint between master and all slaves- on a per-slot basis (polling scheme for control)- only one ACL link per piconet- packets retransmitted (ARQ)


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Packets

All data on the piconet channel is conveyed in packets

13 packet types are defined for the Baseband layer- Controlpackets (ID, NULL, FHS, POLL)

- Voicepackets (SCO)- Datapackets (ACL)

Multi-slot packets (1/3/5) : To support high data rates.Packets always sent on a single-hop carrierthat for thefirst slot. After multi-slot packet revert to original hopsequence.

Packet format - (68/72 bits) Access Code, (54 bits) Header,(0-2745 bits) Payload.


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Packet Format

Access

codeHeader Payload

Voice

1/3/5 slot packets

Unprotected/ 2/3 FECARQ scheme retran-

smit lost data pkts

Single-slot packets

64 kbps

Unprotected/ 1/3 or

2/3 FEC

Never retransmitted

Robust CVSD encoding

used

72 bits 54 bits 0 - 2745 bits

data

header CRC

SCO ACL


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Data Rates on ACL

TYPE SYMMETRI

C (Kbps)

ASYMMETR

IC (Kbps)

DM1 (2/3 FEC) 108.8 108.8 108.8

DH1(unprotected)

172.8 172.8 172.8

DM3 256.0 384.0 54.4

DH3 384.0 576.0 86.4

DM5 286.7 477.8 36.3

DH5 432.6 721.0 57.6.


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Access Code

Access code is used for timing synchronization, inquiryand paging. There are 3 types of access codes

Channel Access Code(CAC) : Used to identify a uniquepiconet. Derived from the device address of the master ofthe piconet. All normal (non inquiry and paging) packetson the piconet will use the CAC.

Device Access Code(DAC) : Used for paging procedure(initial synchronization). Derived from the device addressof the slave.

Inquiry Access Code: Used for inquiry procedure (to getdevice addresses). 2 types : Generic and Device IACs


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Header

Addressing (3) : Max 7 slaves per piconet

Packet type (4) : 13 packet types (some unused)

Flow control (1) 1-bit ARQ (1) : Broadcast packets are not Acked

Sequencing (1) : for filtering retransmitted packets

HEC (8) : Verify Header Integrity

Total = 18 bits

Encode with 1/3 FEC to get 54 bits


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Error Correction/Flow Control

Error Correction

- 1/3 FEC

- 2/3 FEC

- ARQ (Retransmit till Ack is received/ timeout)

Flow Control

- FIFO queues at TX and RX

- If RX queue is full the flow control bit is set in the

header of the next packet sent.- The TX freezes its FIFO queue till the bit is reset.


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NETWORKING

Connection Establishment

Piconet Communication

Scatternet Communication


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Connection Establishment

Two step process : Inquiryto get device addr

Pagingfor Synchronization

Inquiry: Uses the Inquiry hop sequence and the

IAC (DIAC or GIAC)

Paging: Uses the Paging hop sequence and the DACof the device to be paged


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Connection Establishment - Paging

Master Slave

Page Page Scan

Master Page

Response

Slave Page

Response

Connected Connected

Page pkt

ID pkt

FHS pkt

ID pkt

POLL

NULL

Uses FHS to get

CAC and clk infoAssigns active

addr


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Connection Establishment times

ConnectedPagingInquiry

Typical

Max

5.12 s

15.36 s

0.64 s

7.38 s


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Connection Modes

Active Mode: Device actively participates on the piconetchannel

Power Saving modes

Sniff Mode: Slave device listens to the piconet at areduced rate . Least power efficient.

Hold Mode: The ACL link to the slave is put on hold.SCO links are still supported. Frees capacity for inquiry,

paging, participation in another piconet.

Park Mode: The slave gives up its active memberaddress. But remains synchronized (beacon channel).Listens to broadcasts. Most power efficient.


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Intra-piconet communication

The master controls all traffic on the piconet

SCO link - reservation

The master allocates capacity for SCO links by reserving slots

in pairs.

ACL linkpolling scheme

The slave transmits in the slave-to-master slot only when it hasbeen addressed by its MAC address in the previous master-to-

slave slot. Therefore no collisions.


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Device Addressing

Bluetooth Device Address(BD_ADDR)

unique 48 bit address

Active Member Address(AM_ADDR)

- 3 bit address to identify activeslave in a piconet

- MAC address of Bluetooth device

- all 0 is broadcast address

Parked Member Address(PM_ADDR)

- 8 bit parkedslave address


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Why Scatternets

A group of overlapping piconets is called a

scatternet

Users in a piconet share a 1 Mbps channelindividualthroughput decreases drastically as more units are added

The aggregate and individual throughput of users in a

scatternet is much greater than when each user participates on

the same piconet

Collisions do occur when 2 piconets use the same 1 MHz hop

channel simultaneously. As the number of piconets increases,

the performance degrades gracefully


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Inter-piconet communication

A unit may particpate in more

than one piconet on a TDM basis.

To participate on a piconet it

needs the masters identity and theclock offset.

While leaving the piconet it

informs the master

The master can also multiplex as

slave on another piconet. But all

traffic in its piconet will suspended

in its absence.


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System Architecture

RFBaseband

Link ManagerAudio

L2CAP

Data

RFCOMM

SDPIP

Applications

Bluetooth Protocol Stack

The Radio, Baseband and Link

Manager are on firmware. The

higher layers could be in soft-

ware. The interface is thenthrough the Host Controller

(firmware and driver)

The HCI interfaces defined for

Bluetooth are UART, RS232 andUSB.


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Link Manager

LMP (Link Manager Protocol) basically consists of a

number of PDUs sent in the baseband payload.

LMP packets can be recognised by the L_CH field in the

baseband header.

Link Manager handles

- Piconet management (attach/detach slaves, master-

slave switch)

- Link Configuration (low power modes, QoS, packettype selection)

- Security


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L2CAP

Logical link and adaptation protocol

Only ACL links

Concept of L2CAP channels and Channel idsanalogous tosockets in TCP/IP

Functions

Protocol multiplexing

Segmentation and reassembly

QoS specifications

Signalling channel for connection request, config etc


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Higher layers

SDP

Service Discovery Protocolruns on a client server model. Each

device runs only one SDP server and one client may be run foreach application.

RFCOMMTransport protocol providing serial data transfer


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References


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References

Jaap Haarsten, BluetoothThe universal radiointerface for ad-hoc wireless connectivity,Ericsson Review, no. 3, 1998.

www.ericsson.se/review Palowireless

www.palowireless.com/infotooth/tutorial

Aman Kansal, Connection Establishment inBluetooth

The official bluetooth site - www.bluetooth.com

http://opensource.nus.edu.sg/projects/bluetooth/
http://www.ericsson.se/reviewhttp://www.palowireless.com/infotooth/tutorialhttp://www.bluetooth.com/http://opensource.nus.edu.sg/projects/bluetooth/http://opensource.nus.edu.sg/projects/bluetooth/http://www.bluetooth.com/http://www.palowireless.com/infotooth/tutorialhttp://www.ericsson.se/review

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Bluetooth 9

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