With dish network satellite, a digital satellite system, different satellite installers, cheap satellite tv, free direct tv, and free satellite tv, it’s hard to keep on top of everything in the HDTV world. Everything is changing so rapidly, it’s a challenge to find the best dish network deals. Therefore, it’s important to understand where the US is headed on its own and with respect to the rest of the world.

In 1987, the FCC issued a ruling indicating that the HDTV standards to be issued would be compatible with existing NTSC service, and would be confined to the existing VHF and UHF frequency bands.

By the end of 1988, the FCC had received 23 different proposals for HDTV or EDTV standards. These were all analog (or mixed analog/digital systems like MUSE) and explored a variety of different options for resolution, interlace and bandwidth.

In 1990, the FCC announced that HDTV would be simultaneously broadcast (rather than augmented) and that its preference would be for a full HDTV standard (rather than the reduced resolution EDTV).

On May 31, 1990 General Instrument Corp. submitted the first proposal for an all digital HDTV system. By December 1990, ATRC announced its digital entry, followed quickly by Zenith and AT&T, then MIT. Thus there were four serious contenders for digital HDTV, as well as a modified "narrow" MUSE and an EDTV proposal. During the following year, these systems were tested.

In February 1993, the FCC made the key decision for an all digital technology -- but could not decide among the four contenders. Therefore, after some fuss, a recommendation was made to form a "Grand Alliance" composed of AT&T, GI, MIT, Philips, Sarnoff, Thomson and Zenith. This Grand Alliance would take the best features of the four systems and develop them into an HDTV standard. Most of the remainder of 1993 was devoted to establishing the features of this new standard.

During 1994, the system was constructed and 1995 is slated for testing. If all goes well, the FCC may be setting this standard by the end of 1995.

The Grand Alliance standard differs from all existing TV standards in three major ways. First, it is all digital standard -- to be broadcast with a packet transmission. Second, it supports multiple formats. Third, it is designed to be primarily compatible with computers rather than existing NTSC televisions.

The compression algorithms use both a motion compensated and discrete cosine transform (DCT) algorithm. The motion compensation exploits temporal redundancy. The DCT exploits spatial redundancy. MPEG-2 syntax will be used -- because it is already well established, will aid in world-wide acceptance, and will smooth the road to computer and multimedia compatibility. Audio will be supported by Dolby AC-3 digital audio compression. This will include full surround sound.

The core of the Grand Alliance concept is a switched packet system. Each packet contains a 4-byte header, and a 184 byte data word. Each packet contains either video, audio, or auxiliary information. For synchronization, the program clock reference in the transport stream contains a common time base. For lip sync between audio and video, the streams carry presentation time stamps that instruct the decoder when the information occurs relative to the program clock.

The terrestrial transmission system is a 8-level vestigial sideband (VSB) technique. The 8-level signal is derived from a 4-level AM VSB and then trellis coding is used to turn the 4-level signals into 8-level signals. Additionally, the input data is modified by a pseudo-random scrambling sequence which flattens the overall spectrum. Cable transmission is by a 16-level VSB technique without trellis coding.

Finally, a small pilot carrier is added (rather than the totally suppressed carrier as is usual in VSB). This pilot carrier is placed so as to minimize interference with existing NSTC service.

The Grand Alliance system is clearly designed with future computer and multimedia applications in mind. The use of MPEG-2 will permit HDTV to interact with computer multimedia applications directly. For example, HDTV could be recorded on a multimedia computer, and CD/ROM applications could be played on HDTV systems.