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QAM is used in a variety of communications systems such as Dial-up modems and WiFi. In cable systems, a QAM tuner is linked to the cable in a manner that is equivalent to an ATSC tuner which is required to receive over-the-air (OTA) digital channels broadcast by local television stations when attached to an antenna. Most new HDTV digital ...
Any converter box converts the digital signal for the current digital sub-channel to an analog signal (at the reduced screen resolution of the analog standard), outputs that signal onto analog channel 3 or 4 (set by the user to avoid any conflict with local over-the-air channels) and sends that signal to the analog tuner on the TV.
A signal sent by an ideal transmitter or received by a receiver would have all constellation points precisely at the ideal locations, however various imperfections in the implementation (such as noise, low image rejection ratio, phase noise, carrier suppression, distortion, etc.) or signal path cause the actual constellation points to deviate ...
Analog QAM is used in: NTSC and PAL analog color television systems, where the I- and Q-signals carry the components of chroma (colour) information. The QAM carrier phase is recovered from a special colorburst transmitted at the beginning of each scan line. C-QUAM ("Compatible QAM") is used in AM stereo radio to carry the stereo difference ...
A separate tuner is required to receive HD satellite broadcasts. Cable television companies in the U.S. generally prefer to use 256-QAM to transmit HDTV. Many of the newer HDTVs with integrated digital tuners include support for decoding 256-QAM in addition to 8VSB for OTA digital. Cable television companies started carrying HDTV in 2003.
ATSC and DVB-T specify the modulation used for over-the-air digital television; by comparison, QAM is the modulation method used for cable. The specifications for a cable-ready television, then, might state that it supports 8VSB (for broadcast TV) and QAM (for cable TV). 8VSB is an 8-level vestigial sideband modulation.
ATSC 2.0 was a planned major new revision of the standard which would have been backward compatible with ATSC 1.0. The standard was to have allowed interactive and hybrid television technologies by connecting the TV with the Internet services and allowing interactive elements into the broadcast stream.
QAM Mapper: the bit sequence is mapped into a base-band digital sequence of complex symbols. There are 5 allowed modulation modes: 16- QAM , 32-QAM, 64-QAM, 128-QAM, 256-QAM. Base-band shaping: the QAM signal is filtered with a raised-cosine shaped filter, in order to remove mutual signal interference at the receiving side.