What signal modulation technique do cable operators use to transport digital television signals through the cable network?

What signal modulation technique do cable operators use to transport digital television signals through the cable network?

• A. QAM
• B. QPSK
• C. OFDM
• D. 8-VSB

Answer: (A)

Quadrature Amplitude Modulation (QAM) is used to carry digital television signals over cable. It works by varying both the amplitude and the phase of a carrier in two orthogonal components, allowing many bits to be packed into each transmitted symbol. This high spectral efficiency makes it possible to fit multiple digital channels, including HDTV, within the limited bandwidth of a single RF channel. QAM configurations like 256-QAM are common because they provide a good balance of throughput and robustness for cable networks. Other modulation schemes, such as QPSK, carry fewer bits per symbol and thus offer lower data rates; 8-VSB is used for over-the-air ATSC broadcasts, not typical cable transport, and OFDM is used in other contexts and newer architectures but is not the standard method for traditional cable TV transport.

Quadrature Amplitude Modulation (QAM) is used to carry digital television signals over cable. It works by varying both the amplitude and the phase of a carrier in two orthogonal components, allowing many bits to be packed into each transmitted symbol. This high spectral efficiency makes it possible to fit multiple digital channels, including HDTV, within the limited bandwidth of a single RF channel. QAM configurations like 256-QAM are common because they provide a good balance of throughput and robustness for cable networks. Other modulation schemes, such as QPSK, carry fewer bits per symbol and thus offer lower data rates; 8-VSB is used for over-the-air ATSC broadcasts, not typical cable transport, and OFDM is used in other contexts and newer architectures but is not the standard method for traditional cable TV transport.