Wireless LAN technology

Presentation Reference from
Wireless Communications & Networks
Book by William Stallings

1. UNIT III
Wireless LAN Technology
Infrared LANs
Spread spectrum LANs
Narrow bank microwave LANs
IEEE 802 protocol Architecture
IEEE802 architecture and services
802.11 medium access control
802.11 physical layer

2. Wireless Local Area Network (WLAN)
•A wireless local area network (WLAN) is a wireless computer
network that links two or more devices using wireless
communication within a limited area such as a home, school,
computer laboratory, or office building .
•This gives users the ability to move around within a local coverage
area and yet still be connected to the network.
•Through a gateway, a WLAN can also provide a connection to the
wider Internet.
•Most modern WLANs are based on IEEE 802.11 standards and
are marketed under the Wi-Fi brand name.

3. Wireless LAN Applications
Four application areas for Wireless LAN’s:
•LAN extension
•Cross Building interconnect
•Nomadic access
•Ad hoc networks

4. LAN extension
Wireless LAN linked to a Wired LAN on same premises
ØWired LAN
–Backbone
–Supports servers and Stationary Workstations
ØWireless LAN
–Stations in large areas such as offices, warehouses etc.
–Historical buildings
–Small offices

5. Single-Cell Wireless LAN Configuration

6. Multi-Cell Wireless LAN Configuration

7. Cross-Building Interconnect
ØConnecting LANs in nearby buildings
–Wired LAN or Wireless LAN
ØPoint-to-point wireless link is used
ØDevices connected are typically Bridges or Routers
ØSignal point-to-point link is not a LAN

8. Nomadic access
ØWireless link between LAN hub and mobile data terminal
equipped with an antenna
–Laptop or Notepad
ØUses:
–Transfer of data from portable computer to office
server
–Extended environments such as acces

9. Ad hoc networking
ØTemporary peer-to-peer network set-up for immediate
network access without any use of centralized
server
Eg: Connecting laptops temporarily to a network for
a limited amount of time

10. Infrastructure Wireless LAN Configuration

11. Ad hoc LAN Configuration

12. Requirements of Wireless LANs
•Throughput
•Number of Nodes
•Connection to the backbone LAN
•Service Area (100 to 300m)
•Battery power consumption
•Transmission robustness and Security
•Collocated Network Operation
•License free operation
•Handoff/ Roaming (MAC protocol)
•Dynamic Configuration

13. Did you know what they do???
Know these terms
•SSID
•DNS
•DHCP
•Hub
•Switch
•Bridge
•Router

14. üList and briefly define four application areas for wireless
LANs.
üList and briefly define key requirements for wireless LANs.
üWhat is the difference between a single-cell and a multiple-
cell wireless LAN?
Questions

15. WIRELESS LAN TECHNOLOGY
Wireless LAN Technology
Wireless LANs are generally categorized according to the
transmission technique that is used
Categories are
•Infrared (IR) LANs
•Spread Spectrum LANs
•Narrowband Microwave

16. WIRELESS LAN TECHNOLOGY
Infrared (IR) LANs
•An individual cell of an IR LAN is limited to a single room,
because infrared light does not penetrate opaque walls.
Spread spectrum LANs
•This type of LAN makes use of spread spectrum transmission
technology.
•In most cases, these LANs operate in the ISM (Industrial,
Scientific, and Medical) bands so that no FCC licensing is
required for their use in the United States.

17. WIRELESS LAN TECHNOLOGY
Narrowband microwave
These LANs operate at microwave frequencies but do not
use spread spectrum. Few frequencies require licensing
from the FCC.

18. Infrared light
•Infrared radiation is electromagnetic radiation (EMR) with
longer wavelengths than those of visible light, and is
therefore invisible to the human eye. It is sometimes
called infrared light.
•It extends from the nominal red edge of the visible
spectrum at 700 nanometers (frequency 430 THz), to
1 millimeter (300 GHz)
•Most of the thermal radiation emitted by objects near
room temperature is infrared. (example TV remote)

19. EM Spectrum Visible Light Zone
A typical human eye will respond to wavelengths from about
380 to 740 nanometers. In terms of frequency, this corresponds to
a band in the vicinity of 430–770 THz. Electromagnetic radiation
in this range of wavelengths is called visible light or simply light.
Figure: Comparison of wavelength, frequency and energy for the electromagnetic
spectrum.
(Credit: NASA's Imagine the Universe)

21. WIRELESS LAN TECHNOLOGY
Infrared LANs and Advantages
•The spectrum for infrared is virtually unlimited, which
presents the possibility of achieving extremely high data
rates.
•Infrared shares some properties of visible light that make it
attractive for certain types of LAN configurations.
•Infrared light is diffusely reflected by light-coloured objects;
thus it is possible to use ceiling reflection to achieve
coverage of an entire room.
•Infrared light does not penetrate walls or other opaque
objects.

22. WIRELESS LAN TECHNOLOGY
Advantages:
•Infrared communication can be more easily secured
against eavesdropping than microwave communication.
•Separate infrared installation can be operated in every
room in a building without interference, enabling the
construction of very large infrared LANs.
•The equipment is relatively inexpensive and simple.
•Uses Intensity Modulation

23. WIRELESS LAN TECHNOLOGY
Drawbacks
•Many indoor environments experience rather intense
infrared background radiation, from sunlight and
indoor lighting.
•This ambient radiation appears as noise in an
infrared receiver, requiring the use of transmitters of
higher power.

24. WIRELESS LAN TECHNOLOGY
Transmission techniques for IR data transmission:
Directed Beam Infrared:
•Directed beam IR can be used to create point-to point
links.
•In this mode, the range depends on the emitted power
and on the degree of focusing.
•A focused IR data link can have a range of kilometres.

25. WIRELESS LAN TECHNOLOGY
Indoor Point-to-point IR Links

26. WIRELESS LAN TECHNOLOGY
•One indoor use of point-to-point IR links is to set up a
token ring LAN.
•A set of IR transceivers can be positioned so that data
circulate around them in a ring configuration.
•Each transceiver supports a workstation or a hub of
stations.

27. WIRELESS LAN TECHNOLOGY
Omnidirectional
•An omnidirectional configuration involves a single base
station that is within line of sight of all other stations
on the LAN.
•Station is mounted on the ceiling.
•The base station acts as a multiport repeater.
•The ceiling transmitter broadcasts an omnidirectional
signal that can be received by all of the other IR
transceivers in the area.

28. WIRELESS LAN TECHNOLOGY
Diffused
•In this configuration, all of the IR transmitters are
focused and aimed at a point on a diffusely reflecting
ceiling.
•IR radiation striking the ceiling is reradiated
omnidirectionally and picked up by all of the receivers in
the area.

29. WIRELESS LAN TECHNOLOGY
Configuration for Omnidirectional IR LANs

30. Network of Portable & Stationary Wireless Stations using IR

31. Spread Spectrum LANs
•Multiple cell arrangement
•Most popular type of wireless LAN
•Two configurations:
–Hub topology: infrastructure mode
–Peer-to-peer topology: multi-hop ad hoc network

32. Spread Spectrum LAN configurations
•Hub topology:
–Mounted on the ceiling and connected to backbone
–Need MAC protocol
–May act as multiport repeater
–Automatic handoff of mobile stations
–Stations in cell either:
•Transmit to / receive from hub only
•Broadcast using omnidirectional antenna
•Peer-to-peer mode:
–No hub
–Need a distributed MAC protocol

33. Spread Spectrum LANs Transmission Issues
•Licensing regulations differ from one country to another
•USA FCC authorized two unlicensed applications within the ISM band:
–Spread spectrum - up to 1 watt
–Very low power systems- up to 0.5 watts
–902 - 928 MHz (915 MHz band)
–2.4 - 2.4835 GHz (2.4 GHz band)
–5.725 - 5.825 GHz (5.8 GHz band)
–2.4 GHz also in Europe and Japan
–Higher frequency means higher potential bandwidth
Interference:
–Devices at around 900 MHz, including cordless telephones, wireless microphones,
and amateur radio
–Fewer devices at 2.4 GHz; microwave oven
–Little competition at 5.8 GHz
•Higher frequency band, more expensive equipment

34. Narrowband Microwave LANs
•Use of a microwave radio frequency band for
signal transmission.
•Relatively narrow bandwidth.
•Just wide enough to accommodate signal.
•Licensed & unlicensed.

35. Licensed Narrowband RF
•Microwave frequencies usable for voice, data, and
video licensed within specific geographic areas to
avoid interference.
•In United States:
–Radium 28 km.
–Can contain five licenses.
–Each covering two frequencies.
–Motorola holds 600 licenses (1200 frequencies) in the
18-GHz range.
–Cover all metropolitan areas with populations of
30,000 or more in USA.

36. Licensed Narrowband RF
•Use of multiple-cell configuration.
•Adjacent cells use non overlapping frequency bands.
•Motorola controls frequency bands:
–Can assure nearby independent LANs do not interfere
•All transmissions are encrypted.
•Licensed narrowband LAN guarantees interference-free
communication.
•License holder has legal right to interference-free data
channel.

37. Unlicensed Narrowband RF
•1995, Radio LAN introduced narrowband wireless
LAN using unlicensed ISM spectrum
–Used for narrowband transmission at low power
•0.5 watts or less
–Operates at 10 Mbps in 5.8 GHz band
–50 m in semi-open office and 100 m in open office
•Makes use of peer-to-peer configuration.

38. Unlicensed Narrowband RF
•Elects one node as dynamic master
–Based on location, interference, and signal strength.
•Master can change automatically as conditions
change.
•Includes dynamic relay function.
•Stations can act as repeater to move data between
stations that are out of range of each other.

39. Comparison of WLAN Technologies