Wireless LANs and PANs
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Transcript of Wireless LANs and PANs
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Wireless LANs and PANs
Chapter 14
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
IEEE 802.11
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
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
Figure 14.1 Peer-to-peer wireless mode
Server with wireless card
Laptop with wireless card
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Wireless LAN access point
Figure 14.2 Client/Server wireless configuration
Wireless card
Wired Network
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Wireless Distributed Network
Station
Access point
Wired network
Access point
Distributed system
Access point
Station
StationStation
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
IEEE 802.11
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
Data rate
Power consumptionComplexity
802.15.4
802.15.IBluetooth
802.11aHiperLAN
802.11g*
802.11
WPAN
802.11b
WLAN
* Standard in progress
Scope of Various WLAN and WPAN Standards
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Ricochet
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
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
Network interconnection facilityMicrocell radios onstreet lights, utility poles
Wireless access point
Name server
Router
Gateway
Gateway to Internet, Intranets, LANS, Compuserve, AOL and other on-line servicesComputer device
Modem radio
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The Ricochet Wireless Modem
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
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
V.34, 28,800 bps access. Good Availability Unlimited access. Flexible pricing.
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HomeRF
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)
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
Mobility Flexibility: Simultaneous internet access while sharing
a single internet connection with other PCs. Simple: Installation time is small. Economical: Less than $100 for each networked PC. Secure 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
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
D4
U4
D4
U4
D3
U3
D2
U2
D1
U1B D3
U3
Hop
Service slot
Connection period CSMA/CA access
mechanism
D4
U4
D3
U3
D2
U2
D1
U1B D3
U3
Hop
Voice slot transmission
Forward (downlink) slots
Reverse (uplink) slots
CFP1
Control point beacon (CPB)
CFP2
Superframe 20 msRetransmission node Connection node #1
Structure of MAC Frame HomeRF
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Home RF Network
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
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..
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
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
Fixed Network
AP
AP AP
AP
MSMS
Figure 14.8 A simple HiperLAN system
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Hiper LAN/2 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
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 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
BluetoothCellular Link
Figure 14.9 Use of Bluetooth to connect notebook
Base Station
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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
Fixed Line
Figure 14.11 Bluetooth providing a universal bridge to existing data networks
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Figure 14.12 Bluetooth: A mechanism to form ad hoc networks of connected devices away from fixed network infrastructures
Bluetooth
Personal Ad hoc Network
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Bluetooth
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
Fast frequency hopping to reduce interference. Adaptive output power to minimize interference. Short data packets to maximize capacity. Fast acks allowing for low coding overhead for links. Flexible packet types that support a wide application range. CVSD (Continuous Variable Slope Delta Modulation)
voice coding that can withstand high bit error rates. 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
Piconet 1
Piconet 4
Piconet 3
Piconet 2
M2
M1
M3
M4
S2,1
S2,2
S2,3
S3,1 S3,2
S3,3
S2,4 /S3,4
S1,2 /S2,5
S 1,3 /S 4,4
S1,1
S1,4
S1,5
S4,1
S4,2S4,3
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
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) 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)
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
Upper Layer
Baseband
SDP
LMP Audio
Bluetooth Core Protocol
L2CAPE
Low Radio Layer
SDP – Service Discovery ProtocolL2CAP – Logical Link Control and Adaptation Layer Protocol
LMP – Link Manager Protocol
Bluetooth Core Protocol
Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved
Protocols
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 Yes No Yes No
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