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CDMA system concept

 

     

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WCDMA

MAT

GSM

 

     

CDMA system concepts

  • CDMA protocols ??????????????????????? SSMA (spread-spectrum multiple access)protocols ?????????? spread-spectrum modulation ?????????????????? radar ??????? communication ?????? ???????????????????????????? ?????????????????????????????
  • ????????? spread-spectrum modulation ???????????????????? 2 ?????????????????????????????

1.transmission bandwidth ?????????? information bandwidth ????

2. bandwidth ?? radio frequency ?????????? function ????? ??????????? information ????? (?????? bandwidth ???????????????? information signal)

  • ??????????? spread-spectrum modulation ????????? information signal ???? transmission signal ????? bandwidth ???????? ????????????????????????????? information signal ???? code signal ??????????????? data ????? spectral width ??????? data signal ???, power ?? original signal ????????????? transmission bandwidth ???????????????????????? power density ??? , ??????? transmitted bandwidth ??? information bandwidth ?????????? processing gain ,Gp ?????? spread-spectrum,

Gp = Bt / Bi

??? Bt ??? transmitted bandwidth ??? Bi ??? information bandwidth

  • ????????????????????????????????????????? code ???? ????????????? original information ????? ?????????????????????????????????? code ?????? modulate ??? data ??????????? coding ????????????????????? bandwidth ???????????????? ?????? SS ???????????????????????????????? narrow band, ??????? communication ????????? ??????????????????????????????????

1.?????????????? multiple access
???????????????????????? spread-spectrum ?????????????? ????????????????????????????????????????????????? unique code ???????? cross-correction ???????????????? code ?????, ?????????????????????????????? code ??????????? despread ????????????? spread-spectrum ???????????????? ???????????? spread-spectrum ????? ????????????????? bandwidth ???????????????? ??????????? bandwidth ??????????????? power ??????????????????????????????????? power ???????? interfering ???? ?????????????????????????????????????????????????????????????

2.???????????? multipath interference
?? radio channel ????????????????????????????????????? ????????????????????????????? (reflections) ?????????????????????????????????????????? ???????????????????????????????????????????????????????????????????? amplitudes ??? phases ?????????, ????????????????????????????????????????????????????????????????????????????????????????????????????????????, ?? time domain ??????????????????????????????? , ????????? spread-spectrum modulation ????????????????? multipath interference

3.code ??? code ??? ??????????????? ( Privacy )
?????????????????????????????????????????? code ???????????????? ????????

4.Interference rejection
cross-correlating ???????? code ????????? narrowband ???????? power ??????????? ????????????????????? power ???????? interference ?? information bandwidth

5.Anti-jamming capability
???????? narrowband jamming , ????????????????????????????????? narrowband ????????

6.Low probability of interception (LPI)
??????????????????? ?????????????????? power ??? ,?????? spread-spectrum ?????????? detect

 


 

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