Transcript Bluetooth Techniques

Ch 7. Wireless Personal Area
Networks
Myungchul Kim
[email protected]
Wireless Personal Area Networks
• WPANs
• Bluetooth
• Home Networking
• UWB Overview
• Wireless Sensor Networks
WPANs
• Short range networks (< 10 meters)
• Used in homes, cars, small offices
• Can be interconnected to form large
networks
• IEEE 802.15 is the main standards
environment
• Many active areas of work: Bluetooth,
UWB, Wireless sensor networks, Zigbees
Bluetooth Wireless LANs
• Overview
• Applications and Examples
• Piconets and Scatternets
• Standards Overview
• Core standards
Bluetooth Overview
• Founders: Ericsson, IBM, Intel, Nokia, Toshiba; May 98
• Currently: Over 1000 companies
• Low-cost, short range radio link between mobile PCs,
phones and other portable devices
• 2.4 GHz ISM band (unlicensed): Short packets, fasthopping, and FEC limits impacts of interference
• Software for service and device discovery
• Typical application: cellular phone to PDA or earphone
• Supports open-ended list of applications
– Data, audio, graphics, video
• Many products from Nokia, Motorola, Apple, etc.
• Bluetooth.com and palowireless.com/bluetooth have great
deal of info
Bluetooth
PSTN
Access
Point
Wired
LAN
Cellular
Network
Bluetooth Piconet
(1 Mbps, 10 meters)
Bluetooth Application Areas
• Cable replacement
– Eliminates need for numerous cable
attachments for connection (e.g., RS232)
• Data and voice access points
– Real-time voice and data transmissions
• Ad hoc networking
– Device with Bluetooth radio can establish
connection with another when in range
Piconets and Scatternets
• Piconet
– Basic unit of Bluetooth networking
– Master and one to seven slave devices
– Master determines channel and phase
• Scatternet
– Device in one piconet may exist as master or slave in
another piconet
– Allows many devices to share same area
– Makes efficient use of bandwidth
Bluetooth Configurations
Master
A
B
E
D
Slave
Slave
Slave/Master
C
Slave
F
G
Slave
Slave
H
Slave
•2.4 GHZ ISM band supports around 80 physical channels with 1 MHz. bandwidth
•These 80 channels are managed through piconets and scatternets
•All radios in a scatternet share the same frequency hopping (FHSS)
Bluetooth Piconets
PC
Slave
PC
Master
PC Master
Piconet2
(Cubicle2)
Slave
printer
Ear
Phone
Slave
Cellular
Phone
Slave
Slave
/Master
PC
printer
Piconet1
(Cubicle 1)
PC
Slave
Slave
Piconet3
(Cubicle3)
Table 7-2: Bluetooth versus Wi-Fi
Bluetooth versus Wi-Fi
Factor
Wi-Fi
Bluetooth
Data Rate
11 Mbps
1 Mbps
100 meters
10 meters
Application focus
Cable replacement
Connection
to
corporate networks
Ease of use
Piconets good
small networks
Security
Short
distance,
multiple levels (link
level, app level)
WEP
Power
Very
low
power
(smaller devices such
as
consumer
electronics)
High power
Distance
(range)
Covered
for
Complex even for 2
devices
State Transitions in Bluetooth
Disconnected
State
Standby
Page
Inquire
Active
Connecting
State
Active State
Park,
Sniff,
Hold-
Low-Power
Typical Scenario:
States
1. Devices initially in standby mode
2. Issue an inquire (I am available, does someone need me)
3. Devices scan the inquire list and then page the ones they want to invite
4. Devices go into an active transfer mode (Piconet)
5. If too many in a piconet, go into park-sniff-hold mode
6. After transfer go into standby mode
Bluetooth Standards Documents
• Standards specifications
– Details of various layers of Bluetooth protocol
architecture (more than 1500 pages)
• Bluetooth is a layered protocol architecture
– Core protocols (5 layer) - required
– Cable replacement and telephony control protocols
– Adopted protocols (PPP, WAP,,) .
• Profile specifications
– Use of Bluetooth technology to support various
applications
Protocol Architecture
• Core protocols
 Radio layer - Bluetooth transceiver operating in the
2.4 GHz
 Baseband layer -Bluetooth Link Controller (LC) lowlevel link routines (complex).
 Link Manager Protocol (LMP) is used by the Link
Managers (on both side) for link
 Host Controller Interface (HCI) a command
interface to access to hardware status and control
registers.
 Logical Link Control and Adaptation Protocol
(L2CAP) supports higher level protocol multiplexing
 Service Discovery Protocol (SDP) applications to
discover which services are provided by a Bluetooth
device
Bluetooth Stack
vCard/vCal
OBEX
WAE
ATCommands
TCS
Bin
Legend
SDP
WAP
Core
Cable
replacemen
Telephony
control
TCP UDP
IP
Adopted
PPP
Audio
RFCOMM
Logical Link Control and Adaptation Protocol ( L2CAP)
Host Controller Interface
Link Management Protocol (LMP)
Baseband
Bluetooth Radio
Shaded areas (see legend) represent different families of Bluetooth Protocols
Protocol Architecture (cont.)
 Cable replacement protocol: provides emulation of
serial ports over the L2CAP protocol (e.g., emulates
EIA RS232 communications over the Bluerooth
baseband layer.
• Telephony control protocols: (TCS BIN) defines
the signalling and control sequences needed for
telephone conversations over Bluetooth.
• Adopted protocols: minimize new by Bluetooth:
 PPP: used to transport IP packets over point-to-point links
such as dial-up lines.
 TCP/UDP/IP. foundation protocols for the Internet
 OBEX: The object-exchange protocol developed for the
exchange of objects (similar to HTTP, vCard and vCalendar)
 WAE/WAP: The Wireless Application Protocol and Wireless
Application environment are included in Bluetooth.
Usage Models
 File transfer: to transfer files over Bluetooth. protocols
used can be SDP or OBEX.
 Internet bridge (Dial-Up networking): to wirelessly
connect a PC with a cordless modem or a cellular
phone uses PPP and AT protocols
 LAN access: connect a piconet device to access a
LAN. uses SDP and PPP-IP protocols.
 Synchronization: synchronize device-to-device PIM
(personal information management) information such
as calendars and phone books. The model uses OBEX
and IrMC (infrared mobile communications)
 Three-in-one phone: Telephone headsets and
handsets can be used in this model as audio input and
output devices. This model uses Audio, SDP, and AT
commands.
Usage Models
File Transfer Application
OBEX
RFCOMM
Modem Emulation or Driver Application
AT Commands
SDP
PPP
SDP
RFCOMM
L2CAP
L2CAP
a) File Transfer
LAN Access Application
IP
b) Dial-Up Networking
Synchronization Application
IrMC
SDP
PPP
RFCOMM
SDP
OBEX
RFCOMM
L2CAP
L2CAP
c) LAN Access
c) LAN Access
Radio Specification
• 2.4 GHZ ISM band that can support around 80 physical
channels with 1 MHz. bandwidth
• These 80 channels are managed through piconets and
scatternets.
• Several classes of transmitters
– Class 1: Outputs 100 mW for maximum range
• Power control mandatory
• Provides greatest distance
– Class 2: Outputs 2.4 mW at maximum
• Power control optional
– Class 3: Nominal output is 1 mW
• Lowest power
• Much less powerful than cellular phones (GSM
operates at 1 to 3 Watts)
Baseband Specification
• Very complicated
• Specifies
–
–
–
–
–
–
–
Frequency hopping
Physical Links
Bluetooth Packet Fields
Error correction
Logical Channels
Bluetooth Audio
Bluetooth Security
Baseband Specification
• Frequency Hopping in Bluetooth. FH occurs by
jumping from one channel to another (80). (all
devices on a piconet share same).
• Physical Links between Master and Slave.
 Synchronous connection oriented (SCO). point-to-point
connection of master and slave. Mainly for voice
 Asynchronous connectionless (ACL). Point-to-multipoint
link between master and all slaves is also supported.
 Bluetooth Packet Fields. Single slot & multiple slot
 consist of three fields:
 Access code – used for timing synchronization, offset
compensation, paging, and inquiry
 Header – used to identify packet type and carry protocol
control information
 Payload – contains user voice or data and payload header, if
present
Baseband Specification (cont.)
• Error Correction Schemes:. different types of error
correction codes that includes ARQ.
• Logical Channels and Channel Control: Bluetooth
defines five types of channels for different types of
payload such as Link control (LC), Link manager
(LM), User asynchronous (UA), User isochronous
(UI), and User synchronous (US).
• Bluetooth Audio. choice of two
– pulse code modulation (PCM)
– continuously
variable
modulation.(variable step)
slope
delta
(CVSD)
– The choice is made by link manager
• Bluetooth Link Security. includes Authentication,
Encryption (privacy) and Key management.
Link Management Protocol (LMP)
• LMP
manages the radio links between
Bluetooth masters and slaves.
• LMP specifies exchange of LMP PDUs
• PDUs supported by the LMP:
– General response
– Security Service
•
•
•
•
•
Authentication
Pairing: establish a key between authenticated pairs
Change link key
Change current link key
Encryption
L2CAP
• Provides a link-layer protocol between entities
with a number of services
• Similar to LLC
• Relies on lower layer for flow and error control
• Makes use of ACL links, does not support SCO
links
• Provides two alternative services to upper-layer
protocols
– Connection service
– Connection-mode service
Cordless Systems and
Wireless Local Loop
• Cordless networks
• Wireless MANs (Wireless Local
Loops)
Cordless Phone
Public
Switched
Telephone
Network
(PSTN)
Handset
Base Unit
• Basically a cellular phone with no location services
• Typical coverage is 100-300 meters
• User owns handset and base unit -- no initial need for standards
Cordless System Operating
Environments
• Residential – a single base station can
provide in-house voice and data support
• Office
– A single base station can support a small office
– Multiple base stations in a cellular
configuration can support a larger office
• Telepoint – a base station set up in a public
place, such as an airport
Time Division Duplex (TDD)
• Also known as time-compression multiplexing
• Data transmitted in one direction at a time, with
transmission between the two directions
– Simple TDD: Bit stream is divided into equal segments, compressed in
time to a higher transmission rate, and transmitted in bursts
– Wireless TDD typically used with TDMA
• A number of users receive forward channel signals in turn and then
transmit reverse channel signals in turn, all on same carrier frequency
• TDMA/TDD used more often :
• Improved ability to cope with fast fading (base station can detect
strongest signals and send at the same)
• Improved capacity allocation (can assign more slots to forward
channel for improved forward traffic)
TDD
Time
Base
Station
Handset
A1
B1
A1
B1
A2
B2
A2
•Base station sends data blocks A1, A2
•Handset sends data blocks B1, B2
B2
Cordless Standards
• DECT (Digital Enhanced Cordless Telecommunications)
developed in Europe
• PWT (Personal Wireless telecomm) developed in US
• DECT is most commonly used standard (mainly
• DECT Architecture (suited for voice)
– Physical layer – data transmitted in TDMA-TDD
frames over one of 10 RF carriers
– Medium access control (MAC) layer – selects
establishes/releases connections on physical channels;
supports three services:
• Broadcast
• Connection oriented
• Connectionless
– Data link control layer – provides for the reliable
transmission of messages using traditional data link
control procedures
Home R/F
Second Floor
Printer
Main PC
Laptop
Internet
Gateway
xDSL, cable,
ISDN, or other
Baby
Monitor
Wireless LAN2
(Master/slave)
TV
Phone
First Floor
Laptop
Wireless connection
= Wireless Adapter
Wireless connection
Home R/F Specification
150 feet,
10 Mbps
INTERNET
APPLICATIONS
TCP
VOICE
APPLICATIONS
UDP
DECT
IP
HomeRF MAC LAYER
HomeRF PHYSICAL LAYER
www.homerf.org
How SWAP (Shared Wireless Application
Protocol) Supports Voice and Data
802.11
Uses CSMA/CA
Good for data
DECT
Uses TDMA
Good for voice
SWAP Frame
SWAP Frame = CSMA/CA + TDMA
Good for voice and data
UWB -- Overview
• Ultra Wideband (UWB) is emerging as a new wireless
personal area network technology.
• Originally developed in the 1960s for the military.
• FCC approved the commercial implementation of UWB in
February 2002, within limits.
• UWB provides high data rates (around 50 Mbps) in very
short distances (10 meters).
• UWB is a radio system that uses narrow pulses (millions of
pulses per second) for communication and sensing by
using short-range radar.
• UWB radio sends data in millions of pulses across a wide
frequency band
• Legal in the US as long as it uses less power than normal
radio frequency leakage.
Wireless Sensor Networks
(Overview)
• WSNs typically consist of small, low-powered devices
(sensors)
• Sensors can be developed to measure temperature,
humidity, motion, color changes in a painting, or any other
measurable thing.
• Most WSNs consist of millions of tiny processors
communicating over slow wireless networks,
• WSNs may consist of devices with a wide range of
computation, communication, and sensing capabilities.
• The WSNs may use Bluetooth or IEEE 802.11 networks
• ZigBee IEEE 802.15.4
Sensor Node (Mote)
Sensor Node (Mote)
Sensor
Interface
Radio
CPU
Battery
Interface
WSN Hierarchy
WSN Design
Not Used
X
B
A
Y
WSN
C
D
E
Access
Point
General
Network
(Corporate
LAN,
Internet)
WSN Protocol Stack
HIGHER LAYERS (APPPLICATION, PRESENTATION, SESSION),
• Data Applications
• Voice applications
TRANSPORT LAYER
• End-to-End Message Delivery
• End-to-End Error Control
NETWORK LAYER
• Addressing
•Network Routing
DATA LINK LAYER
• Error Detection and Correction
• Contention Management (Multiple Access Control)
• Power Management
PHYSICAL LAYER
• Frequency Allocations
• Transmission and Propagation (Fading, Scattering, etc.)
• Signal Encoding (Modulation/Demodulation)
Summary
•WPANs
• Bluetooth
•Home Networking
•UWB Overview
•Wireless Sensor Networks