D-STAR (Digital Smart Technologies for Amateur Radio) is an FDMA and GMSK digital voice and data protocol specification developed in the late 1990s as the result of research by the Japan Amateur Radio League to investigate digital technologies for amateur radio. While there are many other newer digital on-air technologies being used by amateurs that have come from other services, D-STAR is one of the first on-air and packet-based standards to be widely deployed and sold by a major radio manufacturer that is designed specifically for amateur service use.
Other non-digital voice modes such as amplitude modulation, frequency modulation, and single sideband have been widely used since the first half of the 20th century. By comparison, digital voice signals offer clearer signals and use less bandwidth than their analogue counterparts. As long as the signal strength is above a minimum threshold, and no multi-path is occurring, the quality of the data received is better than an analog signal at the same strength.
D-STAR compatible radios are available on VHF, UHF, and microwave amateur radio bands. In addition to the over-the-air protocol, D-STAR also provides specifications for network connectivity, enabling D-STAR radios to be connected to the Internet or other networks and provisions for routing data streams of voice or packet data via amateur radio callsigns.
The only manufacturer to offer D-STAR compatible radios is Icom. As of February 1, 2013, no other amateur radio equipment manufacturer has chosen to include D-STAR technology in their radios. The technology requires the use of a proprietary AMBE Codec that is owned by Digital Voice Systems, Inc.
Information Courtesy of Wikipedia