Carrier Modulation in Digital Communication Systems

1
Carrier Modulation in Digital Communication
Systems

• Xavier Fernando
• Ryerson Communications Lab (RCL)

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
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
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
Up Conversion

• Carrier modulation up converts the signal to a
  suitable band
• Baseband ? Bandpass
• Also note the bandwidth doubles

6
Frequency Division Multiplexing (FDM)

• Carrier Modulation enables sharing a common
  channel by number of users/services