wireless networks (1).ppt

8/14/2019 Wireless Networks (1).ppt

1/33

Wireless Networks


2/33

Wireless LAN Applications

LAN Extension,

Cross Building Interconnect.

Nomadic Access, Ad Hoc Networks


3/33

Wireless LAN Requiretnents

Throughput: The medium access control protocolshould make as efficient use as possible of the wirelessmedium to maximize capacity.

Number of nodes: Wireless LANs may need to support

hundreds of nodes across multiple cells. Connection to backbone LAN: In most cases,

interconnection with stations on a wired backbone LANis required. For infrastructure wireless LANs, this iseasily accomplished through the use of control modulesthat connect to both types of LANs. There may also needto be accommodation for mobile users and ad hocwireless networks.


4/33

Service area:A typical coverage area for awireless LAN has a diameter of 100 to 300 m.

Battery power consumption: Mobile workersuse battery-powered workstations that need to

have a long battery life when used with wirelessadapters. This suggests that a MAC protocolthat requires mobile nodes to monitor accesspoints constantly or engage in frequenthandshakes with a base station is inappropriate.Typical wireless LAN implementations havefeatures to reduce power consumption while notusing the network, such as a sleep mode.


5/33

Transmission robustness and security: Unlessproperly designed, a wireless LAN may be interferenceprone and easily eavesdropped. The design of awireless LAN must permit reliable transmission even in a

noisy environment and should provide some level ofsecurity from eavesdropping.

Collocated network operation:As wireless LANsbecome more popular, it is quite likely for two or morewireless LANs to operate in the same area or in some

area here interference between the LANs is possible.Such interference may thwart the normal operation of aMAC algorithm and may allow unauthorized access to aparticular LAN.


6/33

License-free operation: Users would prefer tobuy and operate wireless LAN products withouthaving to secure a license for the frequencyband used by the LAN.

Hand-off / roaming: The MAC protocol used inthe wireless LAN should enable mobile stationsto move from one cell to another.

Dynamic configuration: The MAC addressing

and network management aspects of the LANshould permit dynamic and automated addition,deletion, and relocation of end systems withoutdisruption to other users.


7/33

Wireless LAN Technology

Infrared (lR) LANs:An individual cell of an IR LAN islimited to a single room, because infrared light does notpenetrate opaque walls.

Spread spectrum LANs: This type of LAN makes use

of spread spectrum transmission technology. In mostcases, these LANs operate in the ISM (Industrial,Scientific, and Medical) bands so that no licensing isrequired for their use.

Narrowband microwave: These LANs operate at

microwave frequencies but do not use spread spectrum.Some of these products operate at frequencies thatrequire licensing, while others use one of the unlicensedISM bands.


8/33

Strengths and Weaknesses of

infrared

unlimited spectrum possible to achieveextremely high data rates.

The infrared spectrum is unregulated

worldwide, which is not true of someportions of the microwave spectrum.

Infrared light is diffusely reflected by light-

colored objects; thus possible to useceiling reflection to achieve coverage of anentire room.


9/33

Infrared light does not penetrate walls or other

opaque objects.

First, infrared communications can be more easily

secured against eavesdropping than microwave; Second, a separate infrared installation can be

operated in every room in a building without

interference, enabling the construction of very large

infrared LANs. equipment is relatively inexpensive and simple.


10/33

Drawbacks

Many indoor environments experience ratherintense infrared background radiation, fromsunlight and indoor lighting.

Ambient radiation appears as noise in aninfrared receiver, thus requiring the use oftransmitters of higher power than wouldotherwise be required.

Increases in transmitter power are limited byconcerns of eye safety and excessive powerconsumption.


11/33

Transmission Techniques

Directed Beam Infrared point-to-point links

cross-building interconnect

Ominidirectional Single base station in LOS of all other stations.

Ceiling mounted.

Diffused

IR transmitters are focused and aimed at a point on adiffusely reflecting ceiling.

IR radiation striking the ceiling is reradiated.


12/33


13/33


14/33


15/33


16/33


17/33


18/33


19/33


20/33


21/33


22/33


23/33


24/33


25/33


26/33


27/33


28/33


29/33


30/33


31/33


32/33


33/33

wireless networks (1).ppt

Documents