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Carrier modulation

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Carrier modulation

  1. 1. Carrier Modulation inDigital Communication SystemsXavier FernandoRyerson Communications Lab (RCL)
  2. 2. Why Carrier Modulation? Until now we have been looking at baseband communications The information is sampled, quantized pulse coded and transmitted in baseband However, baseband transmission is not suitable in many situations Carrier modulation is needed in these cases Fe examples are listed in the next few slides
  3. 3. Wireless Communications Examples: FM Radio: 88 – 108 MHz WLAN – 2.4 or 5 GHz Cellular Radio: 806-890 MHz GPS: 1215 – 1240 MHz The air-interface is shared by many different users & services Each service has a certain allocated frequency Carrier modulation is needed to occupy only the given spectrum
  4. 4. Digital Telephony/Cable Modem Many of you may have Rogers Digital Phone & Cable Modem The voice and internet data is modulated on a carrier frequency (not overlapping with TV Bands) and transmitted via cable in addition TV Channels using QPSK or 16QAM modulation TV Bands: 60-88 MHz, 180 – 216 MHz and 476-890 MHz
  5. 5. Up ConversionCarrier modulation up converts the signal to a suitable bandBaseband  BandpassAlso note the bandwidth doubles
  6. 6. Frequency DivisionMultiplexing (FDM) Carrier Modulation enables sharing a common channel by number of users/services

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