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TRANSCRIPT
2
Outlines
Wireless network components
Wireless technologies
Cellular Telephony (Wireless WANs)
Wireless WANs
Wireless MANs
Wireless LANs
Satellite Communication
Emerging Systems
WIRELESS NETWORK COMPONENTS
Basic Architecture consists of:
Radio Network components
Mobile Station (MS): Any Mobile Equipment
Base Station (BS): Responsible for relaying calls to and from mobile station.
Wire-line Transport Network
Mobile Switching Centre (MSC): A special switch configured for wireless
applications.
Databases
Home Location Register (HLR): A permanent record that contains entries of all
valid mobile stations
Visitor Location Register (VLR): A temporary record that is used to store and
retrieve information necessary to handle the calls of a visiting mobile user
3
Standardization of Wireless Networks
Wireless networks are standardized by IEEE.
Under 802 LAN MAN standards committee.
Application
Presentation
Session
Transport
Network
Data Link
Physical
ISO
OSI
7-layer
modelLogical Link Control
Medium Access (MAC)
Physical (PHY)
IEEE 802
standards
Message (Frame) Types in a Wireless Network
RTS
CTS
ACK
PS-Poll
CF-End & CF-End
ACK
• Data
• Data+CF-ACK
• Data+CF-Poll
• Data+CF-ACK+CF-
Poll
• Null Function
• CF-ACK (nodata)
• CF-Poll (nodata)
• CF-ACK+CF+Poll
• Beacon
• Probe Request & Response
• Authentication
• De-authentication
• Association Request &
Response
• Re-association Request &
Response
• Disassociation
• Announcement Traffic
Indication Message (ATIM)
CONTROL DATA MANAGEMENT
Hidden terminals
A sends to B, C cannot receive A
C wants to send to B, C senses a “free” medium (Carrier Sense fails)
collision at B, A cannot receive the collision (Collision Detection fails)
A is “hidden” for C
Exposed terminals
B sends to A, C wants to send to another terminal (not A or B)
C senses carrier, finds medium in use and has to wait
A is outside the radio range of C, therefore waiting is not necessary
C is “exposed” to B
Hidden and Exposed Terminals
BA C
Multiple Access with Collision Avoidance (MACA)
MACA uses signaling packets for collision avoidance
RTS (request to send)
sender request the right to send from a receiver with a short RTS packet before it sends a data packet
CTS (clear to send)
receiver grants the right to send as soon as it is ready to receive
Signaling packets contain sender address
receiver address
packet size
Variants of this method are used in IEEE 802.11
MACA avoids the problem of hidden terminals
A and C want to
send to B
A sends RTS first
C waits after receiving
CTS from B
MACA avoids the problem of exposed terminals
B wants to send to A, C
to another terminal
now C does not have
to wait, as it cannot
receive CTS from A
MACA Solutions
A B C
RTS
CTSCTS
A B CRTS
CTS
RTS
Overview of Current Wireless Technologies
Cellular Telephony (Wireless
WANs)
GSM, GPRS, EDGE
3G: CDMA2000, EDVO
3G: UMTS
LTE (Long Term Evolution)
Wireless WANs
802.16e
802.20
Wireless MANs
802.16/WiMAX
Wireless LANs
Wi-Fi
Satellite Communication
Emerging Systems
Ad hoc wireless networks
Sensor networks
Distributed control networks
Cooperative networks
Cognitive radio
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Wireless Networks
A Wireless revolution is set to transform the world telecommunications
Industry.
Wireless networks are a class of networks that use infrared or radio
channels as the transmission medium.
Classification of growth of wireless networks:
First generation analog voice wireless networks.
Second generation digital voice/data networks are under development.
Third generation networks are designed to carry multimedia traffic.
11Digital Media Lab - Sharif University of Technology
Wireless LANs (WLAN)
Wireless LANs connect local computers (100m)
Breaks data into packet
Channel access is shared (random access)
Backbone Internet provides best-effort service
Poor performance in some applications (e.g. video)
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Cellular Wireless
Single hop wireless connectivity to the wired world
Space divided into cells
A base station is responsible to communicate with hosts in its cell
Mobile hosts can change cells while communicating
Hand-off occurs when a mobile host starts communicating via a new base
station
Multi-Hop Wireless
May need to traverse multiple links to reach destination
Mobility causes route changes
3G Cellular
Data is bursty, whereas voice is continuous
Require different access and routing strategies
3G
384 Kbps to Mbps
Based on CDMA
Packet-based switching for both voice and data
4G starts to come up
Mostly based on OFDMA
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LTE-Beyond 3G
Evolutionary path beyond 3G
– Mobile class targets 100 Mbps with high mobility
– Local area class targets 1 Gbps with low mobility
3GPP is currently developing evolutionary/ revolutionary systems beyond 3G
– 3GPP Long Term Evolution (LTE)
IEEE 802.16-based WiMAX is also evolving towards 4G through 802.16m
LTE Enabling Technologies
Two main technologies
1. Orthogonal Frequency Division Multiplexing (OFDM)
2. Multiple-Input Multiple-Output (MIMO)
OFDM
Multi-carrier transmission offers various advantages over traditional single carrier approaches
Highly scalable
Simplified equalizer design in the frequency domain, also in cases of large delay spread
High spectrum density
Simplifies the usage of MIMO
Good granularity to control user data rates
Robustness against timing errors
Multiple-Input Multiple-Output (MIMO)
Future wireless services require high data rates and high signal quality
The wireless resources such as the bandwidth are scarce
Wireless channels have a lot of impairments such as fading, shadowing, and multiuser interference
One solution is the use of Diversity achieving schemes
Spatial diversity is of special interest!
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Evolution of LTE-Advanced
Asymmetric transmission bandwidth
Layered OFDMA
Advanced Multi-cell Transmission/Reception Techniques
Enhanced Multi-antenna Transmission Techniques
Support of Larger Bandwidth in LTE-Advanced
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0
32
64
9.6
128
144
384
1G 2G 3G
Voice
Text Messaging
Video Streaming
Still
ImagingAudio Streaming
Da
ta T
ran
sm
iss
ion
Sp
ee
d -
k b
ps
Electronic
Newspaper
Remote
Medical
Service
(Medical
image)
Video
Conference
(High quality)
Telephone
(Voice)
Voice
E-MailFax
Electronic
Publishing Karaoke
Video
Conference
(Lower quality)
JPEG
Still Photos
Mobile
Radio
Video Surveillance,
Video Mail, Travel
Image
Audio
Voice-driven Web Pages
Streaming Audio
Data
Weather, Traffic, News,
Sports, Stock updates
Mobile TV
E-Commerce
Video on
Demand:
Sports, News
Weather
WiMAX
WiMAX - Worldwide interoperability for Microwave
Access It is a forum of product certification for interoperability
Standard: IEEE 802.16-2004
Frequency Spectrum: 10 - 66 GHz (LOS)
2 – 11 GHz (NLOS) – both licensed and unlicensed
Last mile technology (MAN/WAN) Support point-to-point communication
Support Quality of Service (QoS)
Backhaul technology for wireless LANs (802.11)
Up to 30 miles of range with cell radius: 4-6 miles
Shared data rate up to 75 Mbps.
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Scalability
Channel bandwidths can be chosen by operator (e.g. for sectorization)
1.5 MHz to 20 MHz width channels. MAC designed for scalabilityindependent of channel bandwidth
MAC designed to support thousands of users.
Wide, fixed (20MHz) frequency channels
MAC designed to support 10’s of users
802.16802.11
Optimized for up to 50 Km
Designed to handle many users spread out over kilometres
Designed to tolerate greater multi-path delay spread (signal reflections) up to 10.0μ seconds
PHY and MAC designed with multi-mile range in mind
StandardMAC; Sectoring/MIMO/AMC for Rate/Range dynamic trade-off
Optimized for ~100 meters
No “near-far” compensation.
Designed to handle indoor multi-path(delay spread of 0.8μ seconds).
Optimization centersaround PHY and MAC layer for 100m range.
Range can be extended by cranking up the power – but MAC may be non-standard.
802.16802.11
Range
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Bit Rate: Relative Performance
802.16a ~5.0 bps/Hz
~2.7 bps/Hz54 Mbps20 MHz
63 Mbps10, 20 MHz;
1.75, 3.5, 7, 14 MHz;3, 6 MHz
802.11a
ChannelBandwidth
Maximumbps/Hz
MaximumData Rate
Optimized for outdoor NLOS performance
Standard supports mesh network topology
Standard supports advanced antenna techniques
Optimized for indoor performance
No mesh topology support within ratified standards
802.16802.11
Coverage
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Quality of Service (QoS)
Grant-request MAC
Designed to support Voice and Video from ground up
Supports differentiated service levels: e.g. T1 for business customers; best effort for residential.
TDD/FDD/HFDD – symmetric or asymmetric
Centrally-enforced QoS
Contention-based MAC (CSMA/CA) => no guaranteed QoS
Standard cannot currently guarantee latency for Voice, Video
Standard does not allow for differentiated levels of service on a per-user basis
TDD only – asymmetric
802.11e (proposed) QoS is prioritization only
802.16a802.11
Bluetooth
It is an always on, low power, short ranged radio link for communication
between mobile devices
Developed in 1994 by the Swedish company Ericsson to enable laptops
make calls over mobile phones
Also known as 802.15, it employs the 2.4 GHz unlicensed band, the same
as 802.11b wireless, but does not interfere with it
Provides data rates of up to 720 Kbps
Power output is around 1 milliwatt, compared to the average cell phone’s
500 milliwatt power output
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Bluetooth Applications
Major use in consumer electronics
Embedded in a whole slew of electronic products ranging from on PDAs,
cell phones and printers, to automobiles
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Ad-Hoc Networks
Setting up of fixed access points and backbone infrastructure is not always
viable
Infrastructure may not be present in a disaster area or war zone
Infrastructure may not be practical for short-range radios; Bluetooth (range ~
10m)
Ad hoc networks:
Do not need backbone infrastructure support
Are easy to deploy
Useful when infrastructure is absent, destroyed or impractical
Ad-Hoc Networks
Peer to peer communications
No backbone architecture
Dynamic topology
useful when infrastructure not available, impractical, or
expensive
military applications, rescue, home networking
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Ad-Hoc Networks
Each node generates independent data.
Source-destination pairs are chosen at random.
Routing can be multi-hop.
Topology is dynamic
Can allocate resources dynamically (rate, power, BW, routes,…)
Design Issues (Ad-Hoc Networks)
Transmission, access and routing strategies for ad hoc
networks are generally ad hoc
Ad hoc networks provide a flexible network infrastructure
for many emerging applications
The capacity is unknown
Energy constraints impose interesting design tradeoffs for
communication and networking
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Wireless Sensor Networks (WSN)
Wireless Sensor Networks are networks that consists of
sensors which are distributed in an ad hoc manner.
These sensors work with each other to sense some physical
phenomenon and then the information gathered is
processed to get relevant results.
Wireless sensor networks consists of protocols and
algorithms with self-organizing capabilities.
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Comparison (WSN) with Ad Hoc Networks
Wireless sensor networks mainly use broadcast
communication while ad hoc networks use point-to-point
communication.
Unlike ad hoc networks wireless sensor networks are
limited by sensors limited power, energy and
computational capability.
Sensor nodes may not have global ID because of the large
amount of overhead and large number of sensors.
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Distributed Control over Wireless Links
Packet loss and/or delay impacts controller performance
Controller design should be robust to network faults
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Cooperative Networks
Increase coverage area
Reduce number of blind spots
Reduce transmit power per node
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Challenges of Cooperation
Increase in transceiver complexity
More complex synchronization problems
More interference to be handled properly
Higher end-to-end delays
Real applications to justify the additional costs
45
Future of Wireless Technology
Mobile networks have already begun the migration to IP-based
networks
IP as the routing protocol
4G, New spectrum, and Emerging wireless air interfaces (very high
bandwidth 10 Mbps+)
It may entirely be IP-based and packet-switched
Increasing usage of wireless spectrum
On average, the number of channels has doubled every 30 months since
1985 (Cooper’s law)
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Design Challenges
Wireless Channels are a difficult and a capacity limited broadcast
communications medium
Two main problems in media
Fading
Interference
Traffic patterns , user locations and network conditions are constantly
changing
Energy and delay constraints
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MOBILITY MANAGEMENT
8C32810.131-Cimini-7/98
• Location Management – identification and authentication – home and visitor location data bases (cellular) – discovery and registration (Mobile IP)
• Routing – fixed data bases (connection-oriented) – Mobile IP (connectionless)
• Hand off – transmissions may be delayed or dropped
impacts higher layer protocols – multi-homing inefficient use of resources
overhead and delay impact throughput suboptimal routing delay inefficiency and higher congestion
QUALITY OF SERVICE (QoS)
• Traffic dependent performance metrics required for type of data
transmitted
– bandwidth – latency – likelihood of packet (message) loss
• Categories– guaranteed – predictive – best effort
• Implications for high speed wireless data
– QoS performance generally based on switched, fiber-optic,
wired networks
– wireless links have high loss probability and high latency due
to link layer retransmission and unpredictable link bandwidths
– QoS guarantees and predictions are difficult to
make for wireless networks it is not clear
that the best effort is good enough for most applications
• The desire for mobility coupled with the demand
for Internet and multimedia services indicate a
bright future for wireless data.
• Current products and services have unsatisfactory
performance for high-speed wireless data applications.
• The inherent limitations of the radio channel can be
significantly reduced using signal processing and
architectural techniques, at the expense of cost
and complexity.
• The network-level design must take into account
the physical layer limitations of the wireless channel,
as well as the impact of user mobility.
8C32810.65-Cimini-7/98
SUMMARY
References
T. Rappaport, “wireless Communications, Principles and Practice”, 2nd
Edition, Prentice Hall .
D. Tse, D. Vaswanath , “ Fundamentals of wireless communication”,
Cambridge university press, 2005.
A. Goldsmith, “wireless communications”, Cambridge university press,
2005.
51
Next Session
Wireless Multimedia Networking
Sharif University of Technology, Department of Computer Engineering, Multimedia Systems Course52
Ch2:54
WirelessNet
Tseng
802.11a: Specification enabling up to 54 Mb/s to be achieved in the 5 GHz
unlicensed radio band by utilizing OFDM
802.11b: Specification enabling up to 22 Mb/s to be achieved in the 2.4
GHz unlicensed radio band by utilizing DSSS
802.11c: Provides required information to ensure proper bridge operations, which is required when developing access points
802.11d: Covers additional regulatory domains, which is especially important for operation in the 5 GHz bands because the use of these
frequencies differ widely from one country to another
Task groups of 802.11
Ch2:55
WirelessNet
Tseng
802.11e: Covers issues of MAC enhancements for QoS, such as EDCF service differentiation and HCF
802.11f: Provides interoperability for users roaming from one access point to another of different vendor
802.11g: Specification enabling up to 54 Mb/s to be achieved in the 2.4 GHz unlicensed radio band
802.11h: Dynamic channel selection and transmission power control
802.11i: Specification for WLAN security to replace the weak Wired Equivalent Privacy (WEP)
802.11k: Radio resource measurement for 802.11 specifications so that a wireless network can be used more efficiently
Task groups of 802.11