Bandpass Signals

• The baseband signals described above cannot be used in radio communications.
• (Near) DC frequencies do not propagate through the air.
• Hence, signals containing higher frequencies must be used.
• Example: The antipodal signal set below contains frequencies near $f_0=\frac{5}{T}$.
• The technical term for signals containing frequencies (much) larger than 0 Hz is passband signals.
• The frequency of the sinusoid used in generating the passband signals is called the carrier frequency.
• Usually, the carrier frequency is much larger than the the bit rate $\frac {1}{T}$.
• Frequency Division Multiple Access (FDMA) system can be constructed using passband signals with different carrier frequencies.

  

Figure 2.26: Passband BPSK signal set.