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Stephen Giles 990 53849 75/116 [email protected]
Kanagaratnam Sathananthan 990 53266 75/1105
Textbook Wireless Communications and Networks
by William Stallings, Prentice-Hall
Topics to be covered
Week 1 Wireless Introduction and Applications
Week 2 Radio Communications Principles
Week 3 Access Technologies
Week 4 Cellular Networks
Week 5 Cellular Networks ctd...
Week 6 IEEE802.11 Introduction
Week 7 IEEE802.11 ctd...
Week 8 Bluetooth Technology
Week 9 Network_Management_Issues
Week 10 Wireless_Security
Week 11 VPN
Week 12 Selected_Topics_in_Wireless
Week 13 Revision
Assessment:
Exam 2 hour 50%
Assignment 1 Research Essay 25%
Laboratory Work 25%
10 lab sessions each worth 2.5% of final
APPLICATION
PRESENTATION
SESSION
TRANSPORT
NETWORK
DATA LINK
PHYSICAL
WLANs Operate at this portion of the OSI model
Infra-RedInfrared (IR) systems use very high frequencies, just below visible light in the electromagnetic spectrum, to carry data.
Like light, IR cannot penetrate opaque objects; it is either directed (line-of-sight) or diffuse technology.
http://www.wlana.org/learn/educate2.htm#tech
Inexpensive directed systems provide very limited range (3 ft) and typically are used for PANs but occasionally are used in specific WLAN applications.
High performance directed IR is impractical for mobile users and is therefore used only to implement fixed subnetworks.
http://www.wlana.org/learn/educate2.htm#tech
Diffuse (or reflective) IR WLAN systems do not require line-of-sight, but cells are limited to individual rooms.
http://www.wlana.org/learn/educate2.htm#tech
Bluetooth
Bluetooth technology is a relatively new wireless personal area networking (WPAN) technology that has gained significant industry support and will coexist with most wireless LAN solutions.
http://www.wlana.org/learn/educate2.htm#tech
The Bluetooth specification is for a 1 Mbps, small form-factor, low-cost radio solution that can provide links between mobile phones, mobile computers and other portable handheld devices and connectivity to the internet.
http://www.wlana.org/learn/educate2.htm#tech
This technology, embedded in a wide range of devices to enable simple, spontaneous wireless connectivity is a complement to wireless LANs — which are designed to provide continuous connectivity via standard wired LAN features and functionality.
http://www.wlana.org/learn/educate2.htm#tech
Radio LANs
Current Radio LANs use a transmission technique called Spread Spectrum. Instead of using the one narrow frequency range for transmitting data, in Spread Spectrum transmissions are over a range of frequencies at a time.
Direct Sequence Systems - Direct sequence is perhaps one of the most widely known and utilized spread spectrum systems and it is relatively simple to implement.
A narrow band carrier is modulated by a code sequence. The carrier phase of the transmitted signal is abruptly changed in accordance with this code sequence.
http://www.tapr.org/ss/
The code sequence is generated by a pseudorandom generator that has a fixed length. After a given number of bits the code repeats itself exactly.
The speed of the code sequence is called the chipping rate, measured in chips per second (cps). For direct sequence, the amount of spreading is dependent upon the ratio of chips per bit of information.
http://www.tapr.org/ss/
At the receiver, the information is recovered by multiplying the signal with a locally generated replica of the code sequence.
http://www.tapr.org/ss/
Frequency Hopping Systems - In frequency hopping systems, the carrier frequency of the transmitter abruptly changes (or hops) in accordance with a pseudo random code sequence. The order of frequencies selected by the transmitter is dictated by the code sequence. The receiver tracks these changes and produces a constant signal.
http://www.tapr.org/ss/
Access Point (AP)Network connection point for wireless devices
Access point
Laptop computer
Hand held computer
IEEE802.11Wireless LANs operating at data rates of 1 or 2 Mbps and operating in the 2.4GHz band were defined in the original IEEE802.11 specification ratified in 1997.The specification was for a cable-free LAN at the Datalink and Physical layers of the OSI model.
IEEE802.11bIn September 1999, an amendment to the original standard added 5.5 Mbps and 11 Mbps. IEEE802.11b was named Wi-Fi (TM of Wireless Ethernet Compatibility Alliance WECA).
Physical Layer Convergence Procedure PLCP
MAC
Physical Medium Dependent PMD
Reformats data into form suited to PMD sub-layer and monitors medium for traffic Controls transmission and reception of data through wireless medium
PHY
IEEE802.11b uses the Ethernet-like multiple-access with collision-avoidance (CSMA/CA) method
Ethernet proper is based on CSMA/CD, where CD stands for "collision-detection." Wireless LANs can't always detect a collision between two transmitting devices, so instead, it tries for collision-avoidance
IEEE802.11a
Released in 1999
Operates in the 5 GHz frequency range and offers the possibility of 6 to 54 Mbps
HiperLAN2 (European) has similar
capabilities.
IEEE802.11g
Operates in the 2.4 GHz frequency range and offers the possibility of up to 54 Mbps
Is interoperable with IEEE802.11b Access Points and NICs
Applications of the Technology
Examples:
Retail,Hospitality,Education and Corporate trainingManufacturing,Government,Flexible office and public space environments http://www.symbol.com/products/wireless/wireless_products_lit.html
Retail Promotional and training videos On-line music sampling Portable, graphic-rich gift registries Customer service initiatives such as self-checkout
http://www.symbol.com/products/wireless/wireless_products_lit.html
Hospitality
Real-time connections to enable curbside or remote check-in for hotel guests avoiding lines at the front desk
http://www.symbol.com/products/wireless/wireless_products_lit.html
High-speed Internet access for hotel guests
Convention center networking for trade shows and conferences
Support of multimedia presentations and video streaming for guest meeting and information services
http://www.symbol.com/products/wireless/wireless_products_lit.html
Education and Corporate Training
Temporary networks for mobile training programs
Streaming multimedia to support on-line lectures
Wireless Internet and e-mail access
Security initiatives
http://www.symbol.com/products/wireless/wireless_products_lit.html
Manufacturing
Real-time transfer of mechanical, flow and other graphic-rich files
Security initiatives
Manufacturing workstations where production line layouts are frequently changed
http://www.symbol.com/products/wireless/wireless_products_lit.html
Government
Temporary networks for disaster area and refugee center support, including transferring photos and other vital information
Crime and accident scene support
Security initiatives via wireless monitoring systems and remotely accessed cameras
http://www.symbol.com/products/wireless/wireless_products_lit.html
More Flexible Office and Public Space Environments
Temporary project team and ad-hoc networking
CAD/CAM file transfer for collaborative product development teams
Wireless e-mail, document and PowerPoint® transfer
http://www.symbol.com/products/wireless/wireless_products_lit.html
Cable-less video conferencing
Flexible customer visit center configuration
Wireless local area networking where wiring isn't possible, such as landmark buildings or sites with asbestos considerations
http://www.symbol.com/products/wireless/wireless_products_lit.html
Kiosks in malls, airports, museums and other spaces where interactive programs depend on high-speed remote data retrieval
http://www.symbol.com/products/wireless/wireless_products_lit.html
Interference Problems
Most of the wireless LAN systems at the moment operate in the 2.4GHz band.
This is also used by Bluetooth and DECT systems. Thus interaction between radio transmissions of the various technologies may result.
Also, other radio equipment may interfere with the reception of signals.
Security/Privacy Issues
Many of the wireless LANs in use today potentially suffer from one major difference with wired LANs –the data is freely accessible due it radio transmission
Two issues arise – data privacy and authentication
WEP – Wired Equivalent Privacy deals with both issues
Data is encrypted to prevent its use following inappropriate capture
Use of authentication servers (e.g. RADIUS) is promoted
Unfortunately, WEP is flawed…..
WPA – WiFi Protected AccessTemporary alternative to WEP providing better security
IEEE802.11i – new standard providing high levels of security (due soon)