09:40
RENJIN BOSE R.K
I thought this chapter was probably the most important as a fundamental target to knowing how wireless interacts with its environment, what may affect a radio wave and how it may perform.
Understand what a radio wave is including the electromahnetic spectrum and radiation types such as radio, light, x-ray etc
To produce a radio wave an ac current (alternating current passes through an antenna producing a signal. ac current has a typically sinusoidal waveform as oposed to dc current which is linear at a fixed amplitude.
The signal generated by the antenna is dependent on the changes in the ac current properties.
Properties of the ac current that may vary are wavelength, frequency, amplitude, phase and polarity.
Electromagnetic waves can travel through objects.
In a vaccuum RF travels a the speed of light which is approximately 300,000 km per second or 186,000 miles per second.
When a wave is generated it moves away from the antenna, it is said to propogate.
When a wave propogates and comes into contact with objects it can change, these changes are propogation behaviours, these include absorption, reflection, refraction, scattering, diffraction, loss, free space path loss and multipath,
Understand RF characteristics and the relationship between wavelength and frequency. There is an inverse relationship between wavelength and frequency.
where λ=wavelenth, ƒ=frequency, c=speed of light
Simple transposition of the above formula can prove the following
The higher the frequency the shorter the wavelength.
The longer the wavelength the lower the frequency.
Typical wavelengths in the 802.11 RF spectrum are
A wave will attenuate or lose signal strength as it apsses through a medium, a signal with a higher wavelength and therefore a higher frequency will attenuate more for a given medium. An RF wave may attanuate to such a degree that it is below the receive sensitivity of the receiving radio and cannot be demodulated successfully and has become unuseable.
Theoretically a radio wave will travel forever in a vaccuuum.
Coverage distance of a radio wave is dependent on attenuation, brick, glass, water and even air will attanuate an RF signal.
Attenuation in air is called free space path loss.
2.4 GHz radio waves will propogate better than 5.0 GHz radio waves.
Frequenccy is the number of times an event occurs in specified time, in RF it is measured in Hertz which is cycles per second. 2.4GHz is 2.4 billion cycles per second.
Amplitude can be seen as the power or strength of a wave and when you look at an oscilloscope you would see the height of the wave vary with a change in amplitude.
Phase is the reltionship between two or more waves that share the same frequency. Phase can be measured in distance, time or more usually degrees. If two waves are in alignment they are said to be in phase. Phase is imprtant as signal amplitude may increase or decrease dependent on the phase relationship and is known as multipath
Understand what a radio wave is including the electromahnetic spectrum and radiation types such as radio, light, x-ray etc
To produce a radio wave an ac current (alternating current passes through an antenna producing a signal. ac current has a typically sinusoidal waveform as oposed to dc current which is linear at a fixed amplitude.
The signal generated by the antenna is dependent on the changes in the ac current properties.
Properties of the ac current that may vary are wavelength, frequency, amplitude, phase and polarity.
Electromagnetic waves can travel through objects.
In a vaccuum RF travels a the speed of light which is approximately 300,000 km per second or 186,000 miles per second.
When a wave is generated it moves away from the antenna, it is said to propogate.
When a wave propogates and comes into contact with objects it can change, these changes are propogation behaviours, these include absorption, reflection, refraction, scattering, diffraction, loss, free space path loss and multipath,
Understand RF characteristics and the relationship between wavelength and frequency. There is an inverse relationship between wavelength and frequency.
λ=c/f
where λ=wavelenth, ƒ=frequency, c=speed of light
Simple transposition of the above formula can prove the following
The higher the frequency the shorter the wavelength.
The longer the wavelength the lower the frequency.
Typical wavelengths in the 802.11 RF spectrum are
2.4 GHz = 12.5cm or 4.8"
5.0 GHz = 6.25 cm or 2.46"
A wave will attenuate or lose signal strength as it apsses through a medium, a signal with a higher wavelength and therefore a higher frequency will attenuate more for a given medium. An RF wave may attanuate to such a degree that it is below the receive sensitivity of the receiving radio and cannot be demodulated successfully and has become unuseable.
Theoretically a radio wave will travel forever in a vaccuuum.
Coverage distance of a radio wave is dependent on attenuation, brick, glass, water and even air will attanuate an RF signal.
Attenuation in air is called free space path loss.
2.4 GHz radio waves will propogate better than 5.0 GHz radio waves.
Frequenccy is the number of times an event occurs in specified time, in RF it is measured in Hertz which is cycles per second. 2.4GHz is 2.4 billion cycles per second.
Amplitude can be seen as the power or strength of a wave and when you look at an oscilloscope you would see the height of the wave vary with a change in amplitude.
Phase is the reltionship between two or more waves that share the same frequency. Phase can be measured in distance, time or more usually degrees. If two waves are in alignment they are said to be in phase. Phase is imprtant as signal amplitude may increase or decrease dependent on the phase relationship and is known as multipath
Those of who love wireless will no doubt be aware of the CWNP or Bust competition which offered a great opportunity to win some great resources to complete the CWNA or CWSP certification tracks.
The competition was hosted by George Stefanick of my80211 and sposored by the kind people of CWNP.
The winners were announced a few days ago and are posted here on my80211.
I just want to say congratulations to the guys and wish them luck on their exciting journey.
I have got to know two of them reasonably well trough forums and will be following their exploits religiously. They each have to blog their activities weekly and I know they are keen as mustard to get started.
Congratulations to John Bogard, Rick Todd and Darby Weaver. Their blogs can be followed via these links.
The competition was hosted by George Stefanick of my80211 and sposored by the kind people of CWNP.
The winners were announced a few days ago and are posted here on my80211.
I just want to say congratulations to the guys and wish them luck on their exciting journey.
I have got to know two of them reasonably well trough forums and will be following their exploits religiously. They each have to blog their activities weekly and I know they are keen as mustard to get started.
Congratulations to John Bogard, Rick Todd and Darby Weaver. Their blogs can be followed via these links.
CWNA Objectives
Here is a link to the CWNA exam objectives.
I have also put together a spreadsheet that is a copy of the objectives to help guide your study and assess your knowledge.
In order to get the best out of the spreadsheet grade your competency in the rating column honestly as its only you that you will be cheating, for example "1" is I haven't got a clue what that means and a "5" will be I am very comfortable with that subject area.
Saturday, 24 April 2010
CWNA Study Guide Chapter 1 Communications Fundamentals Key Learning Points
These are what I feel are the key learning points from chapter 1 of the CWNA Study Guide, knowing and understanding these will help pass the CWNA exam
Standards Bodies
IEEE - Institute of Electrical and Electronics Engineers
FCC - Federal Communications Commission
ITU-R - International telecommunication Union - Radiocommunication Sector
TELEC - Telecom Engineering Center
ETSI - European Telecommunications Standards Institute
WECA - renamed to Wi-Fi Alliance in 2000
WFA - Wi-Fi Alliance
ISO - International Standards Organisation
Wi Fi Alliance Programs
802.11 a/b/g/n
WPA2 - based on 802.11i
WMM - based on 802.11e
WMM-PS - WMM Power Save
WiFi Protected Setup - easy setup for home wifi networks using PIN, push button, usb etc
CWG-RF (Converged Wireless Group - RF Profile) - defines performance metrics for wi-fi ad cellular radios in converged handsets ensuring both technologies perform well in the presence of each other
Voice Personal - for SOHO environments supprting upto 4 calls
Future Wi Fi Alliance Programs
Voice Enterprise - due in 2010
RF Fundamentals
Carrier wave is a signal that is modified (modulated) to convey data
Each of the following can be modulated to convey information
Frequency
Amplitude
Phase
Keying Methods
Know the difference between current state and state transition.
Keying methods are also know as modulation techniques.b
ASK - Amplitude Shift Keying
Varies amplitude and uses current state
Susceptible to interference
FSK - Frequency Shift Keying
Varies frequency and uses current state
Found in some legacy 802.11 systems
PSK - Phase Shift Keying
Varies the phase and uses state transition
If phase changes per symbol period "1"
If no phase change per symbol period "0"
Advanced versions of PSK can encode multiple bits per symbol period.
Standards Bodies
IEEE - Institute of Electrical and Electronics Engineers
FCC - Federal Communications Commission
ITU-R - International telecommunication Union - Radiocommunication Sector
TELEC - Telecom Engineering Center
ETSI - European Telecommunications Standards Institute
WECA - renamed to Wi-Fi Alliance in 2000
WFA - Wi-Fi Alliance
ISO - International Standards Organisation
Wi Fi Alliance Programs
802.11 a/b/g/n
WPA2 - based on 802.11i
WMM - based on 802.11e
WMM-PS - WMM Power Save
WiFi Protected Setup - easy setup for home wifi networks using PIN, push button, usb etc
CWG-RF (Converged Wireless Group - RF Profile) - defines performance metrics for wi-fi ad cellular radios in converged handsets ensuring both technologies perform well in the presence of each other
Voice Personal - for SOHO environments supprting upto 4 calls
Future Wi Fi Alliance Programs
Voice Enterprise - due in 2010
RF Fundamentals
Carrier wave is a signal that is modified (modulated) to convey data
Each of the following can be modulated to convey information
Frequency
Amplitude
Phase
Keying Methods
Know the difference between current state and state transition.
Keying methods are also know as modulation techniques.b
ASK - Amplitude Shift Keying
Varies amplitude and uses current state
Susceptible to interference
FSK - Frequency Shift Keying
Varies frequency and uses current state
Found in some legacy 802.11 systems
PSK - Phase Shift Keying
Varies the phase and uses state transition
If phase changes per symbol period "1"
If no phase change per symbol period "0"
Advanced versions of PSK can encode multiple bits per symbol period.
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