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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, fast-hopping, 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
Cellular Network
PSTN
AccessPoint
WiredLAN 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
A
F
B
HG
E CD
Master
Slave/Master
Slave Slave Slave
Slave Slave 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
Master
Slave Slave
Slave/Master
Slave Slave
Piconet1(Cubicle 1)
Piconet3(Cubicle3)
PC
CellularPhone
EarPhone
PC
PC
printer
MasterSlave
SlavePiconet2(Cubicle2)
PC
PC
printer
Bluetooth versus Wi-FiTable 7‑2: Bluetooth versus Wi-Fi
Factor Wi-Fi Bluetooth
Data Rate 11 Mbps 1 Mbps
Distance Covered (range)
100 meters 10 meters
Application focus Cable replacement Connection to corporate networks
Ease of use Piconets good for small networks
Complex even for 2 devices
Security Short distance, multiple levels (link level, app level)
WEP
Power Very low power (smaller devices such as consumer electronics)
High power
State Transitions in BluetoothStandby
Inquire Page
Active
Typical Scenario:1. Devices initially in standby mode2. Issue an inquire (I am available, does someone need me)3. Devices scan the inquire list and then page the ones they want to invite4. Devices go into an active transfer mode (Piconet) 5. If too many in a piconet, go into park-sniff-hold mode6. After transfer go into standby mode
Park, Sniff, Hold-
DisconnectedState
ConnectingState
Active State
Low-Power States
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) low-level 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
Bluetooth Radio
Baseband
Logical Link Control and Adaptation Protocol ( L2CAP)
Link Management Protocol (LMP)
RFCOMM Audio
SDPTCS Bin
AT-Commands
PPP
IP
TCP UDP
WAP
WAE
OBEX
vCard/vCal
Host Controller Interface
Shaded areas (see legend) represent different families of Bluetooth Protocols
Core
Cable replacement
Telephonycontrol
Adopted
Legend
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
L2CAP
File Transfer Application
SDPOBEX
RFCOMM
a) File Transfer
L2CAP
Modem Emulation or Driver Application
SDPAT Commands
RFCOMM
b) Dial-Up Networking
L2CAP
LAN Access Application
SDPPPP
RFCOMM
c) LAN Access
PPP
IP
L2CAP
Synchronization Application
SDPOBEX
RFCOMM
c) LAN Access
IrMC
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
• 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
• 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 slope delta (CVSD) modulation.(variable step)
– The choice is made by link manager
• Bluetooth Link Security. includes Authentication, Encryption (privacy) and Key management.
Baseband Specification (cont.)
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
Base UnitHandset
Public SwitchedTelephoneNetwork(PSTN)
• 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
A1 A2B1 B2
A1 A2B1 B2
BaseStation
Handset
•Base station sends data blocks A1, A2 •Handset sends data blocks B1, B2
Time
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
Wireless LAN2
(Master/slave)
First Floor
= Wireless AdapterWireless connection
Wireless connection
Second Floor
Printer
Baby Monitor
TV
Phone
Laptop
Laptop
xDSL, cable, ISDN, or other
Main PC
InternetGateway
Home R/F Specification
HomeRFHomeRF PHYSICAL LAYERPHYSICAL LAYER
IPIP
TCPTCP UDPUDP
INTERNETINTERNET
APPLICATIONSAPPLICATIONS
VOICEVOICE
APPLICAPPLIC--
ATIONSATIONS
HomeRFHomeRF MAC LAYERMAC LAYER
DECTDECT
150 feet, 10 Mbps
www.homerf.org
How SWAP (Shared Wireless Application
Protocol) Supports Voice and Data
SWAP Frame
DECTUses TDMAGood for voice
802.11Uses CSMA/CAGood for data
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)
CPUSensor
Interface
Radio
Interface
Sensor Node (Mote)
Battery
WSN Hierarchy
Network of Tiny Sensors
Network of Tiny Sensors
Network of Powerful Sensors
Powerfulserver
WSN Design
A
C
B
ED
Access Point
General Network(Corporate LAN, Internet)
X Y
Not Used
WSN
WSN Protocol Stack
PHYSICAL LAYER • Frequency Allocations• Transmission and Propagation (Fading, Scattering, etc.)• Signal Encoding (Modulation/Demodulation)
DATA LINK LAYER • Error Detection and Correction • Contention Management (Multiple Access Control) • Power Management
NETWORK LAYER • Addressing •Network Routing
TRANSPORT LAYER • End-to-End Message Delivery• End-to-End Error Control
HIGHER LAYERS (APPPLICATION, PRESENTATION, SESSION), • Data Applications• Voice applications
Summary
•WPANs• Bluetooth•Home Networking •UWB Overview•Wireless Sensor Networks
