I Figure 5-7: Wireless Propagation Problems Electromagnetic Interference (EMI) from Other stations Microwave 2. ovens, etc Attenuation: signal gets weaker with distance Blocking Object shadow Zone (Dead Spot)
5-11 Figure 5-7: Wireless Propagation Problems 2. Attenuation: signal gets weaker with distance 3. Shadow Zone (Dead Spot) 1. Electromagnetic Interference (EMI) from Other stations, Microwave ovens, etc. Blocking Object
I Figure 5-7: Wireless Propagation Problems Blocking Direct Signal Object Laptop 4. Multipath Interference Reflected Signal Direct and reflected signals may interfere 5-12
5-12 Figure 5-7: Wireless Propagation Problems Reflected Signal Laptop Direct Signal 4. Multipath Interference Direct and reflected signals may interfere Blocking Object
Inverse Square Law Attenuation Inverse square law attenuation To compare relative power at two distances Divide the longer distance by the shorter distance Square the result; this is the relative power ratio Examples 100 mW(milliwatts)at 10 meters At20 meters,100/(20/10)2=100mW/4=25mW At30 meters,100/(30/10)2=100mW/9=11mW Much faster attenuation than utP or fiber 5-13
5-13 Inverse Square Law Attenuation • Inverse square law attenuation – To compare relative power at two distances • Divide the longer distance by the shorter distance • Square the result; this is the relative power ratio – Examples • 100 mW (milliwatts) at 10 meters • At 20 meters, 100 / (20/10)2 = 100 mW / 4 = 25 mW • At 30 meters, 100 / (30/10)2 = 100 mW / 9 = 11 mW – Much faster attenuation than UTP or fiber
Frequently-Depended Propagation Problem Some Problems are Frequency-Dependent Higher-frequency signals attenuate faster Absorbed more rapidly by water in the air Higher-frequency signals blocked more by obstacles At lower frequencies, signal refract(bend) around obstacles like an ocean wave hitting a buoy At higher frequencies, signals do not refract; leave a complete shadow behind obstacles 5-14
5-14 Frequently-Depended Propagation Problem • Some Problems are Frequency-Dependent – Higher-frequency signals attenuate faster • Absorbed more rapidly by water in the air – Higher-frequency signals blocked more by obstacles • At lower frequencies, signal refract (bend) around obstacles like an ocean wave hitting a buoy • At higher frequencies, signals do not refract; leave a complete shadow behind obstacles
Figure 5-8: The Frequency Spectrum, Service Bands, and channels F requency Spectrum Signals in different channels do not interfere with one another (0 HZ to Infinity) 3. Channel 5. signal A Multiple Service Channel 4, Signal d Channels Band within a (FM Radio, Channel 3, Signal B Service Cellular Band: each Telephony, Channel 2, No signal Channel etc.) carries a Channel 1, signal e different signal 0 Hz 5-15
5-15 Figure 5-8: The Frequency Spectrum, Service Bands, and Channels Channel 5, Signal A Channel 1, Signal E Channel 2, No Signal Channel 3, Signal B Channel 4, Signal D 0 Hz 2. Service Band (FM Radio, Cellular Telephony, etc.) 1. Frequency Spectrum (0 Hz to Infinity) 3. Multiple Channels within a Service Band; each Channel carries a different signal 4. Signals in different channels do not interfere with one another