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networkingchpt 8


wireless spectrum continum of the electromagnetic waves used for data and voice communication
wireless spectrum spans frequencies between 9khz and 300ghz
wireless spectrum arranges by lowest to highest frequencies
itu sets standards for international wireless service,including frequency allocations,signaling,and protocols used by wireless devices;wireless equipment,satellite orbits
radiation pattern describes the relative strength over a three dimensional area of all the electromagnetic energy the antenna sends or receives
frequency how many times it repeats in a given interval
frequency measured in hertz
most wireless networks use frequencies between 2.4ghz or 5ghz
gigahertz one billion
megahertz one million
hertz 1 to 100
fcc determines our frequencies and what ranges can be used for what purposes
airwaves collectionof frequencies available for communications
similiarities with wired transmission layer 3 and higher protocols
similiarities with wired transmission signal originationi,from electrical current,travel along conductor
wired signals originate from electrical current traveling along a conductor
lack of a fixed path requires wireless signals to be transmitted,received,controlled
wireless transmission tuned to the same frequency
wired transmission across cables
tuned to the same frequency tuned to the same channel
directional antenna issues wireless signals along a single direction
omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions
range reachable geographical area
reflection the wave encounters an obstacle and bounces it back toward its source
diffraction signal splits into secondary waves when it encounters an o
scattering reflection or multiple different directions of signal
reflection bounce
radiation strength in the three dimensions
three dimension horizontal vertical backwards and forwards,depth
directional antenna point to point link
omnidirectional many different receivers must pick up the signal,tv and radio stations
range geographical area that an antenna or wireless sytem can reach
line of sight uses the least amount of energy and results in the reception of the clearest amount of energy
line of sight signals travel in a straight line,directly from transmitter to the receiver
three phenomenas of signal propagation reflection diffraction scattering
multipath signals wireless signals follow a number of different paths to their destination
scattering occurs when a wireless signal encounters an object that has small dimensions compared with a signals wavelength
downside to multipath signaling travel different distances between their transmitter and receiver
significant cause of fading multipath signaling
fading variation in signal strength as a result of electromagnetic energy
multipath signal advantage better chance of reaching destination
multipath signal disadvantage signal delay
wireless signals susceptible to noise,no wireless shielding
noise emi
the extent of interference that a wireless signal experiences depends partly on the density of signals in a geographical area
signal degradation fading attenuation noise
attenuation farther signal moves from the transmission antenna the weaker it gets
narrowband a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies
amplifier boots or strengthens an analog signal,wave signal
amplify a signal with noise on it makes the signal stronger and the noise stronger amplified
2.4 ghz band older frequency range of 2.4 - 2.4835 ghz
2.4 ghz band older 11 communication channels that anyone can use
unlicensed frequency one for which the fcc does not require users to register their service
width of a band how wide that specific frequency is,range,
5ghz band ,newer 5 billion
5ghz band 24 unlicensed bands each 20 mhz wide
5ghz used by weather,military radar communications
four frequency bands 5.1 5.3 5.4 5.8
broadband relatively wide wireless spectrum band
narrowband transmitter concentrates signal energy at a single frequency
spread spectrum the use of multiple frequencies to transmit a signal
spread spectrum a signal never stays continuously within one frequency range during its transmission
fhss frequency hopping spread spectrum
fhss transmission a signal jumps between several different frequencies within a band in a synchronization pattern known only to the channels receiver and transmitter
broadband higher throughputs than narrowband
spread spectrum multiple frequencies used to transmit signal,offers security
fhss synchronization pattern known only to channels receiver,transmitter
fhss signal jumps between several different frequencies within a band
dsss direct sequence spread spectrum
dsss a signals bits are distributed over an entire frequency band at once
dsss each bit is coded so that the receiver can reassemble the original signal upon receiving the bits
fhss devices in the is split the 2.4-2.4835 band into 79 distinct frequencies
wireless communication categories fixed mobile
fixed wireless systems the location of the transmitter and receiver do not move
advantage of fixed receivers location is predicatable so no wasted energy
fixed transmitter,receiver locations do not move
fixed transmitting antenna focuses energy directly toward receiving antenna
fixed point to point link results
mobile receiver can be located anywhere within the transmitters range
ad hoc wlan trnsmit directly to each other via wireless nics without an intervening connectivity device
wireless nodes stations
wlan architecture adhoc wap
ad hoc wlan wireless nodes transmit directly to each other
adhoc wlan use wireless nics,no intervenig connectivity device
adhoc wlan poor performance
wireless access points wap
wap accepts wireless signals from multiple nodes
wap retransmits signals to network
access points base stations
Created by: cgeaski