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Iuwne10 S01 L02


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Iuwne10 S01 L02

  1. 1. Wireless Fundamentals Introducing WLAN RF Principles
  2. 2. Wireless Spectrum <ul><ul><li>Wireless networks use RF signals. </li></ul></ul><ul><ul><li>Radio frequencies are electromagnetic waves. </li></ul></ul><ul><ul><li>Spectrum defines wave sizes, grouped by categories. </li></ul></ul><ul><ul><li>Wireless network radio range is in the microwave segment. </li></ul></ul>
  3. 3. Frequency <ul><ul><li>The frequency determines how often a signal is seen. </li></ul></ul><ul><ul><li>One cycle per second equals 1 Hz. </li></ul></ul><ul><ul><li>Low frequencies travel farther in the air than high frequencies. </li></ul></ul>
  4. 4. <ul><ul><li>The signal generated in the transmitter is sent to the antenna. </li></ul></ul><ul><ul><li>The movement of the electrons g enerates an electric field, which is the electromagnetic wave. </li></ul></ul><ul><ul><li>The size of the cycle pattern is called the wavelength. </li></ul></ul>Wavelength
  5. 5. <ul><ul><li>Amplitude is the vertical distance, or height, between crests. </li></ul></ul><ul><ul><li>For the same wavelength and frequency, different amplitude s can exist. </li></ul></ul><ul><ul><li>Amplitude represents the quantity of energy injected in the signal. </li></ul></ul><ul><ul><li>The value of the amplitude is usually regulated because it can affect the receivers. </li></ul></ul>Amplitude
  6. 6. Free Path Loss <ul><ul><li>As the wave spreads away from the emitter, it gets weaker. </li></ul></ul><ul><ul><ul><li>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. </li></ul></ul></ul><ul><ul><li>Determining a range is determining the energy loss depending on the distance. </li></ul></ul>
  7. 7. Absorption <ul><ul><li>Absorption takes energy from the wave. </li></ul></ul><ul><ul><li>This energy is dissipated as heat in the obstacle. </li></ul></ul><ul><ul><li>When 100% of the energy is taken, the wave stops. </li></ul></ul><ul><ul><li>The effect of absorption is to reduce amplitude. </li></ul></ul><ul><ul><li>The signal is therefore less powerful, but the same wavelength and frequency are maintained. </li></ul></ul>
  8. 8. Reflection <ul><ul><li>Part of the energy is reflected . </li></ul></ul><ul><ul><li>Part of the energy may be transmitted . </li></ul></ul><ul><ul><li>The angle of reflection is the same as the initial angle . </li></ul></ul><ul><ul><li>Reflection depends on the roughness of the material relative to the wavelength and the angle . </li></ul></ul><ul><ul><li>Amplitude has no impact . </li></ul></ul>
  9. 9. Multipath <ul><ul><li>O ccurs when a signal reflects from surfaces and signals arrive at the receiver at different times </li></ul></ul><ul><ul><li>Delayed multiple copies of the same signal hit the receiver </li></ul></ul><ul><ul><li>D epends on the wavelength and the position of the receiver </li></ul></ul>
  10. 10. Multipath: Phase <ul><ul><li>Two signals are in phase when the crests of their cycles coincide. </li></ul></ul><ul><ul><li>Being out of phase weakens both signals or cancels them if amplitude and wavelength are the same. </li></ul></ul>
  11. 11. <ul><ul><li>Scattering o ccurs when microparticles deviate the wave in multiple directions . </li></ul></ul><ul><ul><li>It a ffects shorter wavelengths more than longer ones . </li></ul></ul><ul><ul><li>It c an weaken the signal or block it . </li></ul></ul>Scattering
  12. 12. Refraction <ul><ul><li>Refraction o ccurs when a wave passes from one medium to another , causing the wave to change direction. </li></ul></ul><ul><ul><li>Refraction has a m inor effect on indoor networks . </li></ul></ul><ul><ul><li>It c an have a big impact on outdoor long - range links . </li></ul></ul>
  13. 13. <ul><ul><li>Line of sight is necessary for good signal transmission. </li></ul></ul><ul><ul><li>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). </li></ul></ul><ul><ul><li>Visual obstacles may or may not prevent radio line of sight. </li></ul></ul>Line of Sight
  14. 14. Fresnel Zone <ul><ul><li>Determines an area around radio line of sight where reflections have most negative impact on the signal </li></ul></ul><ul><ul><li>Should be at least 60% free from obstacles </li></ul></ul>
  15. 15. RSSI and SNR <ul><ul><li>RSSI is the signal strength indicator. </li></ul></ul><ul><ul><li>The dBm value is obtained from a signal grading coefficient, which is determined by the vendor. </li></ul></ul><ul><ul><li>RSSI usually a negative value, the closer to 0 the better. </li></ul></ul><ul><ul><li>SNR is signal strength relative to noise level. </li></ul></ul><ul><ul><li>The higher the SNR, the better. </li></ul></ul>
  16. 16. Summary <ul><ul><li>The wireless spectrum expresses the range of radio waves . </li></ul></ul><ul><ul><li>Frequency is how often the same cycle repeats per second . </li></ul></ul><ul><ul><li>Wavelength is the distance of the same points in a signal cycle . </li></ul></ul><ul><ul><li>Amplitude is how strong the signal is and how high the wave . </li></ul></ul><ul><ul><li>Once radiated, some energy will be lost as the signal spreads, incurring f ree p ath l oss . </li></ul></ul><ul><ul><li>As the signal goes through obstacles, absorption weakens it . </li></ul></ul><ul><ul><li>The signal can also bounce on objects, which is reflection . </li></ul></ul>
  17. 17. Summary (Cont.) <ul><ul><li>When reflection occurs and several signals arrive at the receiver, a multipath issue occurs. </li></ul></ul><ul><ul><li>Scattering occurs when the signal is reflected in many directions by small obstacles. </li></ul></ul><ul><ul><li>Refraction occurs when the signal goes from one medium to another and changes direction. </li></ul></ul><ul><ul><li>For a signal to be transmitted in good condition, radio line of sight should exist between endpoints. </li></ul></ul><ul><ul><li>Around the line of sight, a zone, the first Fresnel zone, should be mostly free from obstacles. </li></ul></ul><ul><ul><li>RSSI determines received signal strength and SNR determines the signal-to-noise ratio at the receiver. </li></ul></ul>