D-STAR (Digital Smart Technologies for Amateur Radio) is a digital voice and data protocol specification for amateur radio. The system was developed in the late 1990s by the Japan Amateur Radio League and uses minimum-shift keying in its packet-based standard. There are other digital modes that have been adapted for use by amateurs, but D-STAR was the first that was designed specifically for amateur radio.
Several advantages of using digital voice modes are that it uses less bandwidth than older analog voice modes such as amplitude modulation and frequency modulation. The quality of the data received is also better than an analog signal at the same signal strength, as long as the signal is above a minimum threshold and as long as there is no multipath propagation.
D-STAR compatible radios are available for HF, 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, allowing streams of voice or packet data to be routed via amateur radio.
The system today is capable of linking repeaters together locally and through the Internet utilizing callsigns for routing of traffic. Servers are linked via TCP/IP utilizing proprietary "gateway" software, available from Icom. This allows amateur radio operators to talk to any other amateurs participating in a particular gateway "trust" environment. The current master gateway in the United States is operated by the K5TIT group in Texas, who were the first to install a D-STAR repeater system in the U.S.
D-STAR transfers both voice and data via digital encoding over the 2 m (VHF), 70 cm (UHF), and 23 cm (1.2 GHz) amateur radio bands. There is also an interlinking radio system for creating links between systems in a local area on 10 GHz, which is valuable to allow emergency communications oriented networks to continue to link in the event of internet access failure or overload.
Within the D-STAR Digital Voice protocol standards (DV), voice audio is encoded as a 3600 bit/s data stream using proprietary AMBE encoding, with 1200 bit/s FEC, leaving 1200 bit/s for an additional data "path" between radios utilizing DV mode. On air bit rates for DV mode are 4800 bit/s over the 2 m, 70 cm and 23 cm bands.
In addition to digital voice mode (DV), a Digital Data (DD) mode can be sent at 128 kbit/s only on the 23 cm band. A higher-rate data protocol, currently believed to be much like ATM, is used in the 10 GHz "link" radios for site-to-site links.
Radios providing DV data service within the low-speed voice protocol variant typically use an RS-232 or USB connection for low speed data (1200 bit/s), while the Icom ID-1 23 cm band radio offers a standard Ethernet connection for high speed (128 kbit/s) connections, to allow easy interfacing with computer equipment.
- Proprietary codec
Like other commercial digital modes (P25, TETRA, DMR, DPMR, NXDN, System Fusion), D-STAR uses a closed-source proprietary voice codec (AMBE) that's patented by Digital Voice Systems, Inc. (DVSI) because it was the highest quality and only codec available in silicon when the system was released. Unfortunately, amateur radio operators do not have access to the specification of this codec or the rights to implement it on their own without buying a licensed product. Amateurs have a long tradition of building, improving upon and experimenting with their own radio designs. The modern digital age equivalent of this would be designing and/or implementing codecs in software. Critics say the proprietary nature of AMBE and its availability only in hardware form (as ICs) discourages innovation. Even critics praise the openness of the rest of the D-STAR standard which can be implemented freely.
- Trademarked name
Despite many protestations from the Pro-D-STAR lobby that the standard was developed by the JARL and D-STAR is not only an Icom system, the mark 'D-STAR' is itself a registered trademark of Icom. According to the United States Patent and Trademark Office, a trademark is defined as "a word, phrase, symbol or design, or a combination of words, phrases, symbols or designs, that identifies and distinguishes the source of the goods of one party from those of others." Icom does hold a trademark for its stylized D-STAR logo. There is no indication Icom is charging other vendors to use any of the D-STAR branding.
- Usable range compared to FM
D-STAR, like any digital voice mode has comparable usable range to FM, but it degrades differently. While the quality of FM progressively degrades the further a user moves away from the source, digital voice maintains a constant voice quality up to a point, then essentially "falls off a cliff". This behavior is inherent in any digital data system, and it demonstrates the threshold at which the signal is no longer correctable, and when data loss is too great, audio artifacts can appear in the recovered audio.
- Emergency Communications Concerns
Many advanced D-STAR features rely on internet connections although simplex, repeated and crossband gateway voice and data communications do not. During widespread disasters that compromise commercial telecommunications infrastructure, D-STAR systems (as well as other modes that rely on the internet) may suffer outages or feature degradation that impacts operations. Without simulating such outages during drills, it is difficult to assess the impact of or establish D-STAR service recovery procedures in the event of such failures. As of the fall of 2011, there has been almost no discussion in the ham radio literature regarding actual drills where D-STAR systems were tested with completely failed or even intermittent telecommunications infrastructure. Comprehensive emergency communications plans used by ARES and other such organizations should address the possibility that such systems may not function as intended during major disasters.
The loss of Internet does not degrade the local operation of a D-STAR repeater system. Over the Internet linking and routing of traffic may be degraded. Some groups are using microwave based systems, such as HamWAN, to link repeaters.
In Icom's radio line, D-STAR does significantly add to the cost of a radio, which is a barrier to the adoption of the technology. In 2006 the cost of a D-STAR radio was compared to that of a standard analog radio, and the price difference was nearly double. This is due partly to the per-unit cost for the voice codec hardware and/or license and partly to manufacturer research and development costs that need to be amortized. As is the case with any product, as more units are sold, the R&D portion of the cost will decrease over time. The D-STAR capable radios also cost more than their equivalents from other brands, even before the D-STAR options boards are added (in the UK as of April 2011, Martin Lynch & Sons' website lists the Icom 2820 (without D-STAR) at £489, while the equivalent Yaesu, the FT8800, is listed at just £337).
FlexRadio Systems D-STAR implementation requires the use of a $129 add-on module to their FLEX-6000 Series Radios.
- Questionable legality
Many have argued[who?] that the proprietary codec constitutes a form of encryption, and encryption is prohibited by almost every country's amateur radio licence conditions. According to FCC rules, if the algorithm is publicly published or otherwise widely available enough that transmissions are not secret, it is considered encoding rather than encryption. Unfortunately D-STAR uses AMBE, a non public codec. However, French regulators, in April 2010, have issued a statement that rules D-STAR illegal in France, due to the ability to create a connection to the internet with it and the proprietary nature of the codec used. The French Amateur Radio society, DR@F - Digital Radioamateur France has an online petition against this ruling, calling for the government to allow the mode, as to ban it would deny them 'fundamental rights'.