????(Communications System) ??????

1
???????

• ?2? ?????

2
??????
3
????(Communications System)??????
4
???? ?????

• ???????
• ?????????????
• ??(Analog)
• ??(Digital)
• ?????
• ??(Bandwidth)???????(Data Rate)

5
????(Analog Signal)?????(Digital Signal)
6
????????
7
??(phase)???
8
?????????????
9
??????????
10
????????????
11
?????(radio spectrum)
12
????????(transmission impairment)

• ??(attenuation)?????(attenuation distortion) ?
• ????(delay distortion) ?
• ??(noise) ?

13
??????????????
14
?????(channel capacity)

• Nyquist Bandwidth
• ????(Shannon Capacity)??

15
????????????

• ??????????(radio channel impairments)
• ??????????
• ????????(large-scale propagation model)
• ????????(small-scale propagation model?fading
  model)

16
???????? ????????

• ????(path loss)
• ??????????(free space propagation model)
• ??????????(propagation mechanism)

17
??????????
18
?????????? ???(multipath)???
19
Fresnel zones???
20
???????

• ????(extra large zone)
• ???(extra large zone)
• ???????(middle zone)
• ???(small zone?microzone)

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???????(Outdoor propagation models)

• Longley-Rice model
• Durkins model
• Okumura model
• Hata model
• Walfisch and Bertoni model
• Wideband PCS microcell model

22
???????? ????????

• ????????,????(multipath)????(Doppler)??
• ?????????(statistical distribution of received
  envelope)
• ???????(duration of fading)
• ?????

23
?????????????

• ??????????????????????
• ????????????????????(Doppler shifts),???????????(r
  andom frequency modulation)
• ?????????(multipath propagation
  dalay)???????(time dispersion) ?

24
?????????

• ??????(multipath propagation)
• ????????
• ?????????
• ???????

25
?????(Doppler effect)
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???????(mobile radio channel)?????

• ??(bandwidth)?????????(received power)?????
• ???????????

27
??????????(mobile multipath radio channel)???

• ????(impulse response)
• ????(coherence bandwidth)????????????
• ????(coherence time)

28
????????
29
VSWR (voltage standing wave ratio)???
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AP??????
31
??(decibel)