Transcript Chapter 14 Wireless LANs and PANs Copyright © 2003, Dr. Dharma P.

Chapter 14
Wireless LANs and PANs
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
IEEE 802.11
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It is the standard for wireless LANs.
It specifies MAC procedures and operate in 2.4
GHz range with data rate of 1Mbps or optionally
2Mbps.
User demand for higher bit rates and international
availability of 2.4 GHz band has resulted in
development of a high speed standard in the same
carrier frequency range.
This standard called 802.11b, specifies a PHY
layer providing a basic data rate of 11 Mbps and a
fall-back rate of 5.5 Mbps.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
IEEE 802.11
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The IEEE 802.11 and 802.11b standards can be
used to provide communication between a number
of PSs (Peer Stations) as an ad hoc network using
peer to peer mode(Fig 14.1)
As a client server wireless configuration (Fig 14.2)
Complicated distributed network (Fig 14.3)
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Server with
wireless card
Laptop with
wireless card
Figure 14.1 Peer-to-peer wireless mode
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Wired
Network
Wireless LAN access point
Wireless card
Figure 14.2 Client/Server wireless configuration
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Wireless Distributed Network
Wired network
Station
Access
point
Access
point
Distributed
system
Station
Access
point
Station
Station
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
IEEE 802.11
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The keys behind all the above networks are the
wireless cards and wireless LAN access points.
In an ad hoc network mode, there is no central
controller, the wireless access cards use CSMA/CA
protocol to resolve shared access.
In client server model, many PC’s or laptops
physically close to each other (20-500m) can be
linked to a central hub (access point).
This access point acts as a bridge between the wireless
and wired network.
A large area can be covered by installing several
access points in the building.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Scope of Various WLAN and WPAN Standards
Power consumption
Complexity
802.11a
HiperLAN
802.11g*
802.11b
802.11
WLAN
802.15.I
Bluetooth
* Standard in progress
802.15.4
WPAN
Data rate
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Ricochet
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A mobile data access service that is always on,
provides high speed, secure mobile access to the
desktop from outside the office.
It allows to link to the internet or the corporate
network without needing phone lines or cable
connections.
The Ricochet service is provided by Metricom.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Ricochet
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The Ricochet service is a wide area wireless system using
spread spectrum packet switching data.
The network operates within 902-928 MHz portion of RF
spectrum.
The Ricochet wireless Micro Cellular Data Network
(MCDN), consists of shoebox sized radio receivers, called
Micro cell radios (Fig 14.5)
Micro cells are typically mounted to street poles.
Micro cells require a small power from the street lights.
Each Micro cell radio employs 162 frequency hopping
channels.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Ricochet Mobile Communication Network
Microcell radios on
street lights, utility poles
Network interconnection facility
Gateway
Wireless access point
Name server
Modem radio
Router
Computer device
Gateway to Internet, Intranets,
LANS, Compuserve, AOL and
other on-line services
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
The Ricochet Wireless Modem
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It weighs 13 ounces.
Has the general dimensions of a small paperback
book, plugs directly into a desktop.
When a Ricochet modem is configured to operate
in bridge mode, it translates signals from other
Ricochet modems into signals that a wired modem
can receive.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Services Provided by Ricochet
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Provides immediate, dependable and secure
connections without the cost and
complexities of land based phone lines.
Sending E-mails, access to documents in
home networks.
Many real estate agents use this to search
for property listings while on road.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Key Features of Ricochet Modem
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V.34, 28,800 bps access.
Good Availability
Unlimited access.
Flexible pricing.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
HomeRF
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Two kind of networks: HomeRF (for home), Hiper
LAN (for business workspace).
43 million US homes now contain more than one PC.
A home network typically consists of one high speed
internet access port providing data to multiple
networked nodes.
Home networking allows all computers in a home to
simultaneously utilize the same high speed ISP
(Internet Service Provider) account.
Home networking allows two options: wired solution
and wireless solution.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
HomeRF (cont’d)
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Wired Solutions such as Ethernet, phone
line offers a fast reliable secure connections,
but the cost of wiring and installation is
high.
Wireless networks such as PC-Centric Data
offer more mobility to the users of the
network.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Advantages of Wireless HomeRF
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Mobility
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Flexibility: Simultaneous internet access while sharing
a single internet connection with other PCs.
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Simple: Installation time is small.
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Economical: Less than $100 for each networked PC.
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Secure
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Based on industry Standards: Enables interoperability
between many different manufacturers.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
HomeRF Technology
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In HomeRF all the devices can share the same
connections for voice and data.
Provides the foundation for a broad range of
interoperable consumer devices.
A specification for wireless communications in the
home called Shared Wireless Access Protocol
(SWAP) has been developed.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Figure 14.6 Architecture of HomeRF system
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Structure of MAC Frame HomeRF
Forward (downlink) slots
Voice slot transmission
D4
U4
D3
D2
U3
D1
U2
Control point beacon (CPB)
CFP1
Service slot
H
D4
B D3
o
U3
U4
U1 p
Reverse (uplink) slots
Retransmission node
Connection period
CSMA/CA access
mechanism
CFP2
D4
Superframe
20 ms
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
D3
U4
D2
U3
D1
U2
H D3
B
o
U3
U1 p
Connection node #1
Home RF Network
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A network consists of Resource providers, which
are gateways to different resources like cordless
phones, printers, fileservers and TV.
The goal of Home RF is to integrate all of them in
to a single Network suitable for all applications
and also remove all wires and utilize RF links in
the network.
This will support the mobility of devices.
With Home RF, cordless phone can connect to
PSTN ordinarily, but can also connect through a
PC for enhanced services.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Hiper LAN
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It stands for High Performance LAN.
It can support Multimedia data and asynchronous data
effectively at high rates (23.5 Mbps).
It is specifically designed to support as hoc computing
for multimedia systems, where there is no requirement
to deploy centralized infrastructure.
It employs 5.15 GHz and 17.1 GHz frequency bands,
with a coverage of 50m and mobility < 10 m/s.
It supports Packet oriented structure, which can be
used for networks with or without centralized control
(base station-mobile station and ad hoc).
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
HiperLAN contd..
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It supports 25 audio connections at 32 Kbps with a
max latency of 10 msec.
It supports 1 video connection of 2 Mbps with 100
msec latency and data rate of 13.4 Mbps.
HiperLAN/1 is designed to support ad hoc
computing for multimedia systems.
HiperLAN/1 MAC is compatible with standard
MAC service interface.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Hiper LAN goals
The goals of Hiper LAN are:
 QoS
 Strong Security
 Handover when moving between local area and
wide areas
 Increased throughput
 Ease of use, deployment
 Affordability
 Scalability
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Features of Hiper LAN/2
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High speed transmission (54 Mbps).
It uses modularization method called OFDM to
transmit analog signals.
The connection oriented approach makes support
for QoS easy.
It supports automatic frequency allocation,
eliminating the need for manual frequency
planning as in cellular networks.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Figure 14.8 A simple HiperLAN system
Fixed Network
AP
AP
AP
AP
MS
MS
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Hiper LAN/2
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The protocol architecture allows for interoperation with virtually
any type of network.
A mobile terminal may at any time request the access point and
enter a low power state for a sleep period.
At the end of this negotiated sleep period the mobile terminal
searches for any wake up signal.
In the absence of any wake up signal it again reverts back to its
low power state for sleep period.
The control is centralized to the AP (access point) which informs
the mobile terminal to transmit their data.
The air interface is based on TDD (time division duplex) and
dynamic TDMA.
Selective Repeat (SR) ARQ is an error control mechanism used to
increase reliability over the radio link.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Applications
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Hiper LAN/2 networks can be deployed at “hot
spot” areas such as airports and hotels, as an easy
way of offering remote access and internet
services to people.
It can also be used as an alternative access
technology to 3G networks.
It can be used in home environment to create a
wireless infrastructure for home devices such as
PCs, cameras, printers etc.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Bluetooth
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It is named after the King of Denmark that unified
different factions in Christianity through the country.
It is a short range RF communication.
Low cost, low power, radio based wireless link
eliminates the need for short cable.
Bluetooth radio technology built into both the cellular
telephone and the laptop would replace the cable used
today to connect a laptop to cellular phone.
Printers, desktops can all be wireless.
It also provides a universal bridge to existing data
networks (Fig 14.11).
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Figure 14.9 Use of Bluetooth to connect notebook
Bluetooth
Cellular
Link
Base Station
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Figure 14.10 Bluetooth connecting printers, PDA’s, desktops, fax
machines, keyboards, joysticks and virtually any other digital device
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Figure 14.11 Bluetooth providing a universal bridge to
existing data networks
Fixed Line
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Figure 14.12 Bluetooth: A mechanism to form ad hoc networks of
connected devices away from fixed network infrastructures
Bluetooth
Personal Ad
hoc Network
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Bluetooth
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The ultimate goal is to make small products
(PC/Laptops) have only one wire attached to
power cord.
In case of PDA, the power cord is also eliminated.
A simple application of Bluetooth is updating the
phone directory of the PC from a mobile
telephone.
A typical Bluetooth has a range of 10 m.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Features
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Fast frequency hopping to reduce interference.
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Adaptive output power to minimize interference.
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Short data packets to maximize capacity.
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Fast acks allowing for low coding overhead for links.
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Flexible packet types that support a wide application range.
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CVSD (Continuous Variable Slope Delta Modulation)
voice coding that can withstand high bit error rates.
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Transmission/reception interface tailored to minimize
power consumption
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Architecture of Bluetooth System and Scatternet
S2,3
Piconet 2
S3,1
S2,2
S3,2
M2
S2,1
S3,3
M3
S2,4 /S3,4
Piconet 3
S1,2 /S2,5
M1
M4
S1,1
S1,5
S 1,3 /S 4,4
Piconet 4
S1,4
Piconet 1
S4,1
S4,3
S4,2
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Bluetooth Technological Characteristics
Frequency band
2.4 GHz (unlicensed ISM band)
Technology
Spread spectrum
Transmission method
Hybrid direct sequence and frequency hopping
Transmission power
1 milli-watt (0 dBm)
Range
10 meters (40 feet)
Number of devices
8 per piconet, 10 piconets per coverage area
Data speed
Asymmetric link: 721+57.6 kbps
Symmetric link: 432.6 kbps
Maximum voice channels
3 per piconet
Maximum data channels
7 perpiconet
Security
Link layer w/s fast frequency hopping (1600 /sec)
Power consumption
30 μA sleep, 60 μA hold, 300 μA standby, 800 μA max transmit
Module size
3 square cm (0.5 square inches)
Price
Expected to fall to $5 in the next few years
C/I co-channel
11 dB (0.1% BER)
C/I 1 MHz
-8 dB (0.1% BER)
C/I 2 MHz
-40 dB (0.1% BER)
Channel switching time
220 μs
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Architecture
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Bluetooth radio typically hops faster and
uses shorter packets as compared to other
systems operating in the same frequency
band.
Use of FEC (Forward Error Correction)
limits the impact of random noise.
As the interference increases, the
performance decreases.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Architecture (cont’d)
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Bluetooth devices can interact with other Bluetooth devices.
One of the devices acts as a master and others as slaves.
This network is called “Piconet”.
A single channel is shared among all devices in Piconet.
There can be up to seven active slaves in the Piconet.
Each of the active slaves has an assigned 3 bit Active Member
address.
A lot of other slaves can remain synchronized to the Master
through remaining inactive slaves, referred to as parked nodes.
A parked device remains synchronized to the master clock and
can become active and start communicating in the Piconet
anytime.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Architecture (cont’d)
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If Piconets are close to each other, they have overlapping
areas.
The scenario where the nodes of two or more Piconets
mingle is called Scatternet.
Before any connections in the Piconet are created all
devices are in STDBY mode.
In this mode an unconnected unit periodically “listens” for
message every 1.28 seconds.
Each times a device wakes up, it tunes on the set of 32 hop
frequencies defined for that unit.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Bluetooth Core Protocol
Upper Layer
SDP
L2CAPE
LMP
Audio
Baseband
Low Radio Layer
SDP – Service Discovery Protocol
L2CAP – Logical Link Control and Adaptation Layer Protocol
LMP – Link Manager Protocol
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Bluetooth Core
Protocol
Protocols
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SDP: Provides a mean for applications to discover
which services are provided by or available
through a Bluetooth device.
L2CAP: Supports higher level protocol
multiplexing, packet segmentation and reassembly
and conveying of QoS information.
LMP: Used by Link managers for link set up and
control.
Baseband: Enables the physical RF link between
Bluetooth units forming a Piconet.
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Comparison between Different Architecture (1/2)
IEEE 802.11
Ricochet
HomeRF
HiperLAN
Bluetooth
Operational
spectrum
2.400-2.4835~5.2
GHz
902-928 MHz
2.404-2.478 GHz
5.15 GHz and 17.1 GHz
2.402-2.480 GHz
Physical layer
DSSS/FHSS/IR
Frequency
hopping 162
hops/sec
FHSS 50 hops/sec
DFS (Dynamic
Frequency Selection)
with BPSK/ QPSK/
QAM
FHSS 1600
hops/sec
Channel access
CSMA/CA
TDMA
Hybrid (TDMA &
CSMA/CA)
TDMA/TDD
Master slave,
TDMA frequency
hopping
Raw data rate
2 Mbps & 11 Mbps/
6-54 Mbps
288
1and 2 Mbps
23.5 Mbps or 54 Mbps
1 Mbps
Range
150 feet
1000 feet
<150 feet
150feet
10 m to 100 m with
extended range
Power consumption
Not specified
Not specified
100 mW
Not specified
1 mW, 10 mW, 100
mW
Traffic
Data (DCF)
Data
Voice + Data
Data
Voice or Data
Error robustness
CRC/ARQ Type 2
CRC/ARQ type 1
1/2, 9/16, 3/4 rate FEC,
ARQ type 1
1/3 rate FEC, 2/3
rate FEC and ARQ
Type 1
Mobility support
Not specified
No
Yes
No
Yes
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Comparison between Different Architecture (2/2)
IEEE 802.11
Ricochet
HomeRF
HiperLAN
Bluetooth
Energy
conservation
Directory based
Yes
Yes
Yes
Guaranteed latency
Yes (uses PCF
(Point Coordination
Function))
<20 msec for voice
Yes (Supports
DiffServ
(Differentiated
Services)/ ATM/
RSVP (Resource
Reservation
Protocol ))
No device
Speech coding
Not specified
Not available
32 kbps with
ADPCM
OFDM
64 kbps with
CSVD/ logPCM
Security
40 bit RC4
RSARC-4
Blowfish
DES, 3-DES
Minimal (in PHY)
Communication
topology
Peer-peer, MS-BS
Peer-peer
Peer-peer, MS-BS
Peer-peer, MS-BS
Master-slave,
Master-multislave
Approx. price/point
$25
Variable
$18
Not specified
$10
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved