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Carrier Modulation in Digital Communication Systems

Carrier Modulation in Digital Communication Systems . Xavier Fernando Ryerson Communications Lab (RCL). Why Carrier Modulation?. Until now we have been looking at baseband communications The information is sampled, quantized pulse coded and transmitted in baseband

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Carrier Modulation in Digital Communication Systems

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  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

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