Digital kommunikation ger fler repeaterkanaler

D-STAR, a standard published in 2001, is the result of three years of research funded by the Japanese government and administered by the JARL to investigate digital technologies for amateur radio. The research involved Japanese radio manufacturers and other observers. Icom provided the equipment used for development and testing. D-STAR radios and repeaters have been tested extensively and are now ready for public use.

D-STAR is an open protocol – although it is published by JARL, it is available to be implemented by anyone. (For definitions and explanations of terms, there is a glossary on page 6.) While Icom is the only company to date that manufactures D-STAR-compatible radios, any equipment or software that supports the D-STAR protocol will work with a D-STAR system. D-STAR systems can be built using both commercial and homebrew equipment and software.

In a D-STAR system, the air link portion of the protocol applies to signals travelling between radios or between a radio and a repeater. D-STAR radios can talk directly to each other without any intermediate equipment or through a repeater using D-STAR voice or data transceivers. The gateway portion of the protocol applies to the digital interface between D-STAR repeaters (see figure 1). D-STAR also specifies how a voice signal is converted to and from streams of digital data, a function called a codec. The D-STAR codec is known as AMBE® (Advanced Multi-Band Excitation) and the voice signal is transmitted in the D-STAR system at 3600 bits/second (3.6 kbps).

The D-STAR system supports two types of digital data streams. The Digital Voice (DV) stream used on 144 and 440 MHz contains both digitized voice (3600 bps including error correction) and digital data (1200 bps). Using a DV radio is like having both a packet link and FM voice operating simultaneously. The Digital Data (DD) stream, used only on 1.2 GHz, is entirely data with a bit rate of 128k bps. The data connection to a radio that uses DV is via an RS-232 interface or USB 1.0. An Ethernet connection is used for high-speed DD D-STAR data. Ordinary terminal emulation software (DV) or a Web browser (DD) will do just fine for exchanging data (see figure 2).

Handheld and mobile radios

For voice conversations, D-STAR repeaters act just like familiar analog repeaters – everyone listening can hear your transmissions. Because your call sign is incorporated into every transmission, the D-STAR repeater “registers” your call sign and shares it around the D-STAR system. If you travel into a new D-STAR repeater’s coverage area, register with a short transmission and your location will be quickly updated around the D-STAR network. This allows you to call someone registered with any other D-STAR repeater, no matter where that may be. If you call someone registered elsewhere, your voice will be routed to the appropriate repeater in digital form, where it is then heard just as you would expect if you were both using the same repeater!

Many data communications needs don’t require high-speeds, particularly for emergency communications. Status reports, damage assessment, shift changes, resource requests – all they take are a few keystrokes. D-STAR combines voice and low-speed data into a single channel simultaneously. There’s no need for a separate TNC and radio. Just connect your laptop or PDA and go.

A high-speed D-STAR connection looks just like an Ethernet connection to your laptop or other network device. Why run cables for a temporary or portable installation when mobile rigs will do the job? Connect across miles instead of meters! If a D-STAR repeater offers a broadband Internet connection, you have worldwide connectivity through your radio.

Emergency communications managers can put D-STAR’s high-speed data capabilities to work building systems that support their “served agency” with IT tools they understand and expect; email, file transfer, and Web browsing. Spreadsheets, graphics, maps, lists, Web pages – all flow easily through the D-STAR system (see figure 3).

If a picture is worth a thousand words, why not use D-STAR to paint the image? Weather and traffic information from the Internet are available via a D-STAR repeater’s broadband connection. Add a digital camera to a laptop and your D-STAR radio becomes a Web cam. Emergency management is greatly enhanced when images are available. The next time your group helps out on race day, D-STAR can make it possible to send photos at the finish line, on the course – anywhere your operators are.

Repeaters and repeater systems

D-STAR gateway protocols and software support linking repeater systems over a few miles or around the world. A regional group of repeaters create a D-STAR zone, shown in figure 4, working together and addressable in the D-STAR system as a unit. Whether you live in the wide-open spaces or a densely populated area, D-STAR repeaters can be tied together to make up the repeater system you want using either Internet or microwave links.

Repeaters linked with D-STAR can also share information using the same D-STAR link. This information includes repeater operating information and statistics. System designers can add entirely new functions, sharing weather and control information, for example. Another possibility is “smart systems” that track interference or user location.

If you’ve tried to coordinate a repeater channel on 2-meters or 440 MHz in any metropolitan area, you know how crowded the bands are! The D-STAR voice and low-speed data signal offers a significant improvement in spectrum efficiency, requiring only a 6 kHz channel instead of the 20, 25, or even 30 kHz of analog wide-band FM. As shown in figure 5, D-STAR repeaters can be interleaved between existing channels or multiple repeaters deployed in the spectrum of only one analog FM repeater.

As authorized users make their initial transmission to a D-STAR system, the call sign information attached to the digitized voice packets is recorded by the repeater controller. The controller then shares the information with other D-STAR systems through the D-STAR gateway registry. The registry is maintained on gateway servers located around the world as shown in figure 6 -- currently Japan, the United States, and the UK. When an authorized D-STAR user makes a call to a call sign not currently registered on that repeater system, the registry allows the repeater controller to route the call to the repeater on which the targeted user was last registered.

New services and system examples

Imagine arriving in town as a visitor or on business. Connect a laptop or PDA to your D-STAR handheld, key in a few simple characters, and request a “what’s happening” report from a local D-STAR kiosk server. In seconds, you’re viewing text listing meetings, clubs, electronics stores, and events. Need a weather check? A few more characters and the screen fills with the current report.

The low-speed data ports of D-STAR handheld radios are compatible with the GPS NMEA data interface. With GPS data integrated into the D-STAR digital data stream, your location data is forwarded to the D-PRS server where gateway software connects you to the APRS® reporting system. The interface is built-in to D-STAR radios – no separate TNC and transceiver required!

It’s only natural that D-STAR’s digital voice capabilities will be linked up with the most popular repeater sharing applications, EchoLink® and IRLP. Since your voice is already digitized within the D-STAR system, third party bridges and converters to and from other digital voice systems an obvious and expected future addition.

Since D-STAR’s data looks just like any other Internet data to a browser or Web application, why not use D-STAR’s high-speed data to build a link to your club’s HF station? Want to control your electronics at home? Either high-speed or low-speed D-STAR data can do the job. D-STAR is built to support 21st century tools - the Web, networking, Ethernet, TCP/IP - so free your imagination!

The open D-STAR protocol provides a rich, exciting set of tools with which hams can experiment and build. Icom supports developers with the D-STAR forums at www.icomamerica.com/amateur/dstar – please join this growing community. In addition, Icom is preparing technical support documentation for the developer, such as protocols and interface descriptions.

Air Link: The portion of data transmission that takes place as a radio signal. The D-STAR air link includes both modulation methods and data packet construction.

Area: The geographical region served by one D-STAR repeater.

Authorization: Adding a user to the D-STAR registry.

Bridge: A connection between just two devices, such as between two ID-1 transceivers.

Client: A program that requests data (programs, Web pages, documents, etc.) from servers.

Codec: Code/Decode, a circuit or program that translates an analog signal to and from digital form, usually refers to an audio signal, such as voice or music. Different codecs, such as AMBE or MP3, have different rules for the translation between analog and digital.

Controller: The part of a D-STAR repeater that handles and routes the voice and data streams either between modules or between modules and the gateway.

DD (Digital Data): The D-STAR high-speed digital data signal.

DV (Digital Voice): The D-STAR digital voice + low-speed data signal.

EchoLink®: (www.echolink.org) and IRLP (Internet Relay Linking Project - www.irlp.net), systems that allow repeaters to share digitized voice signals using Voice-Over-Internet Protocol (VOIP) technology.

Encapsulate: To incorporate data packets from one protocol inside the data packets of another.

Ethernet: The set of protocols that control local area network (LAN) connections, described by the IEEE 802.3 standard.

FEC: Forward Error Correction, the process of adding information to data so that the receiver can correct errors caused by the transmission process.

Gateway: The part of a D-STAR repeater that connects the controller to other gateways via the Internet.

IP: Internet Protocol, the protocol that controls how data packets are exchanged on the Internet.

Module: A D-STAR module is the part of a D-STAR repeater that implements voice or data communication over the air.

Register: Capture the call sign of a received signal and post it to the system registry for other D-STAR repeaters to use for the purposes of routing calls.

Registry: A shared data base of authorized user call signs and gateways.

Route: To direct data packets to specific destinations.

Server: A computer that supplies data (programs, Web pages, documents, etc.) to clients when requested.

Zone: A group of D-STAR repeaters linked together and connected to other D-STAR systems by a single gateway.