What is in this article?:
- A tutorial on modulation technologies, from ASTC, OFDM, QAM to DVB
- Modulation schemes have different characteristics for different media
- New technologies on the horizon
The distribution of content involves the need to adapt digital information to its means of carriage — what we typically call transmission — and to understand that fully, we need to understand the process of digital modulation.
Content distribution and transmission are implemented differently on wireless, wired and physical media, where each one uses modulation schemes tailored to carry content most efficiently and robustly. Wireless transmission includes terrestrial, satellite and wireless LAN channels, with VSB and OFDM serving the first, phase shift keying (PSK) for the second and OFDM again for the third. Wired transmission to the home is mostly by coaxial cable, using quadrature amplitude modulation (QAM), or by twisted pair, using OFDM over DSL. Physical media, i.e., DVD or Blu-ray, use an optical channel coding called eight-to-fourteen modulation (EFM).