1. Wireless Fundamentals Introducing WLAN RF Principles

2. Wireless Spectrum

• Wireless networks use RF signals.

• Radio frequencies are electromagnetic waves.

• Spectrum defines wave sizes, grouped by categories.

• Wireless network radio range is in the microwave segment.

3. Frequency

• The frequency determines how often a signal is seen.

• One cycle per second equals 1 Hz.

• Low frequencies travel farther in the air than high frequencies.

4.

• The signal generated in the transmitter is sent to the antenna.

• Themovement of theelectronsg enerates an electric field, which isthe electromagneticwave.

• The size of the cycle pattern is called the wavelength.

Wavelength 5.

• Amplitude is the vertical distance, or height, between crests.

• For the same wavelength and frequency, different amplitude scan exist.

• Amplitude represents the quantity of energy injected in the signal.

• The value of the amplitude is usually regulated because it can affect the receivers.

Amplitude 6. Free Path Loss

• As the wave spreads away from the emitter, it gets weaker.

• • The quantity of energy declines as the distance increases; the quantity of energy available on each point of the circle is less as the circle is larger, and the receiver catches only part of this energy.

• Determining a range is determining the energy loss depending on the distance.

7. Absorption

• Absorption takes energy from the wave.

• This energy is dissipated as heat in the obstacle.

• When 100% of the energy is taken, the wave stops.

• The effectof absorption is to reduce amplitude.

• The signal is therefore less powerful, but the same wavelength and frequencyare maintained.

8. Reflection

• Part of the energy is reflected .

• Partof the energymay be transmitted .

• The angle of reflection is the same as the initial angle .

• Reflection depends on theroughness of thematerial relative to the wavelength and the angle .

• Amplitude has no impact .

9. Multipath

• O ccurs whenasignal reflectsfromsurfaces andsignalsarriveatthe receiver at different times

• Delayed multiple copies of the same signal hit the receiver

• D epends on the wavelength and the position of the receiver

10. Multipath: Phase

• Two signals are in phase when the crests of their cycles coincide.

• Being out of phase weakens both signals or cancels them if amplitude and wavelength are the same.

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• Scattering o ccurs when microparticles deviate the wave in multiple directions .

• It a ffects shorter wavelengths more than longer ones .

• It c an weaken the signal or block it .

Scattering 12. Refraction

• Refraction o ccurs whenawave passes from one medium to another , causing the wave to change direction.

• Refraction has a m inor effect on indoor networks .

• It c an havea bigimpact on outdoor long - range links .

13.

• Line of sight is necessary for good signal transmission.

• Earth curvature plays a role in the quality of outdoor links, even with a distance of a few miles (depending on the elevation of the transmitter and receiver).

• Visual obstacles may or may not prevent radio line of sight.

Line of Sight 14. Fresnel Zone

• Determines an area around radio line of sight where reflections have most negative impact on the signal

• Should be at least 60% free from obstacles

15. RSSI and SNR

• RSSI is the signal strength indicator.

• The dBm value is obtained from a signal grading coefficient, which is determined by the vendor.

• RSSI usually a negative value, the closer to 0 the better.

• SNR is signal strength relative to noise level.

• The higher the SNR, the better.

16. Summary

• The wireless spectrum expresses the range of radio waves .

• Frequency is how often the same cycle repeats per second .

• Wavelength is the distance of the same points in a signal cycle .

• Amplitude is how strong the signal is and how high the wave .

• Once radiated, some energy will be lostasthe signal spreads, incurringf reep athl oss .

• As the signal goes through obstacles, absorption weakens it .

• The signalcan also bounce on objects, which is reflection .

17. Summary (Cont.)

• When reflection occurs and several signals arrive at the receiver, a multipath issue occurs.

• Scattering occurs when the signal is reflected in many directions by small obstacles.

• Refraction occurs when the signal goes from one medium to another and changes direction.

• For a signal to be transmitted in good condition, radio line of sight should exist between endpoints.

• Around the line of sight, a zone, the first Fresnel zone, should be mostly free from obstacles.

• RSSI determines received signal strength and SNR determines the signal-to-noise ratio at the receiver.

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