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Publications:

ARRL 13th DCC Proceedings 1994

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This proceeding is available on CD-ROM


Location:
Bloomington, Minnesota

Coordinator:

Hosted by:
TwinsLAN ARC

Abstracts:
13th Digital Communications Conference
August 20, 1994

A Proposal for a Standard Digital Radio Interface
by Jeffrey Austen, K9JA
Introduction: Just about everyone who has ever used packet radio has had to deal with what should be a simple task: that of properly connecting radios and terminal node controllers (TNCs) together. Unfortunately, many people have learned that it is not very simple. Not only do the proper signal connections need to be determined between each radio and TNC but the correct audio levels must be set in order for the system to work well. This problem is compounded for persons with multiple TNCs or multiple radios. Every time a radio or TNC is changed, the system must be readjusted for proper receive and transmit audio levels, as well as proper delay times to accommodate the key-up time of the transmitter. These problems are exacerbated by the existence of differing connectors for different models of radios and TNCs. All of this can be attributed to the fact that the interface between the equipment uses analog signals despite the fact that packet radio is a mode of digital communications. For operation at speeds greater than 1200 bits per second (b/s) most radios do not even provide a connector for the appropriate signals. Operators of digipeaters or remote sites are burdened with the task of hauling around extra test equipment and adjusting radios on-site instead of performing these adjustments in a convenient location such as a laboratory or home station. Emergency operation is difficult because it is almost impossible to properly connect various equipment quickly in the field unless the exact configuration is known beforehand.

In this article a proposal for a digital radio (DR) interface is developed. This interface is designed to support all current packet modulation methods and speeds and any which can be reasonably anticipated for future use. It provides "plug and play" operation between any digital radio and TNC.

Proceedings Paper



Automatic Packet Reporting System (APRS)
by Bob Bruninga,WB4APR
Introduction: The Automatic Packet Reporting System (APRS) is a multi-purpose program for the PC which makes use of data from the amateur packet network to provide a number of interesting and valuable functions. APRS embodies WB4APR's expedence over the last 13 years using packet radio for real-time communications in public service events. It also incorporates the capability for operating over non-local distances without use of the existing packet network. APRS accomplishes the real-time display of operational traffic via packetbroadcasts and map displays.

Proceedings Paper



Broadcast, UI and un-connected protocols-the future of Amateur Packet Radio?
by Paul Evans, W4/G4BKI
Abstract: An overview of the user applications of packet radio is presented and the relevance of connected protocols in each scenario is examined. Suggested formats for unconnected systems are made and conclusions drawn.

Proceedings Paper



Packet, GPS, APRS and the Future
by Paul Evans, W4/G4BKI
Abstract: The Global Positioning System produces wider ranging applications every day. The relatively easy hookup to amateur radio devices makes it the ideal experimenter's "toy" and tool. The benefits it can provide the world of amateur radio are numerous, not least of which is the way in which it brings that element of experimentation back into the hobby AND impresses the "authorities" whenever it is demonstrated or used in disaster situations.

Proceedings Paper



Computer Networks in Africa: From Utopian Discourse to Working Reality
by Iain Cook
Abstract: The task of this paper is to explore the less-utopian discourses surrounding computer networks in the developing world, and contrast these discourses with the everyday practice of computer networks. In particular, this project will look at how one computer network, RINAF, is set up in Africa. The information for this investigation has been culled from various sources across the Internet. The bulk of the information has been provided by men and women working in the-field.

Proceedings Paper



A Low Cost DSP Modem for HF Digital Experimentation
by Johan Forrer, KC7WW
Introduction: This article describes an HF modulator-demodulator (modem) that is based on Digital Signal Processing (DSP) principles. A practical approach is shown, rather than the usual terse mathematics that usually accompanies this kind of discussion. This article is intended for those interested in experimenting with HF digital communications using DSP software. A low cost DSP platform is also described for implementing some of the ideas presented in this article including complete source code for a high performance HF digital modem.

Proceedings Paper



G-TOR: The Protocol
by Mike Huslig, Phil Anderson, Karl Medcalf and Glenn Prescott
Abstract: The purpose of this document is to present a detailed description of the G-TOR protocol. It is assumed that the reader is familiar with ARQ systems such as AMTOR, Pactor, and Packet; terms such as MASTER, SLAVE, ISS, IRS as they pertain to protocols; and binary, HEX and C-language number notations. Operation, performance objectives, and performance results of systems using this protocol are not discussed; these aspects of G-TOR have been covered widely in trade publications. The description is organized in sections as follows: a general overview, including term definitions and initialization of parameters; timing; definition and usage of data, control, BK, and connect and disconnect frames; data formats; speed change procedures; the Huffman table; and Golay coding and data interleaving. Appendices containing flow charts, a Huffman decoding tree, and a C language routine for Golay encoding/decoding follow the protocol description.

Proceedings Paper



GMON-a G-TOR Monitoring Program for PC Compatibles
by Richard Huslig and Phil Anderson, W0XI
Abstract: The G-TOR data communications protocol is an innovation of the technical staff of Kantronics Co., Inc. It was introduced in March 1994 as an inexpensive means of improving point-to-point digital communications in the HF radio bands. It has been implemented in the KAM Plus and KAM-E and is now offered for licensing to other manufacturers. Monitoring of G-TOR frames is difficult since a variety of frame formats exist as shown in Figure 1. Although a data frame is always 1.92 seconds in duration, it might be sent at 100, 200, or 300 baud; it might contain real data or Golay parity bits in ASCII or Huffman encoded form; and it may be received in Lower or Upper Side Band. Each data frame must be deinterleaved at the receiver...

Proceedings Paper



A Theoretical Evaluation of the G-TOR Hybrid ARQ Protocol
by Glenn E. Prescott, WB0SKX and Phil Anderson, W0XI
Abstract: The recently-introduced G-TOR protocol for HF data communications employs several features which maintain the throughput of Ihis system in the presence of noise and interference. In this paper we take a closer look at the most important of these features - the hybrid ARQ protocol - in order to provide G-TOR users with a better understanding of the technical details of the protocol and an appreciation of the role of the Golay forward error correcting code in improving the overall system performance. We will demonstrate the advantages of using a hybnd ARQ protocol by presenting a theoretical evaluation of the throughput of the G-TOR hybrid ARQ protocol in the presence of Gaussian noise. Graphs of throughput versus channel bit error rate will show that the combined use of error detection and Golay forward error correction is a powerful approach to extending the throughput of a conventional stop-and-wait ARQ system on the HF bands.

Proceedings Paper



On Fractal Compression of Images for Narrowband Channels and Storage
by W. Kinsner, VE4WK
Abstract: Fast transmission of digital images and fast video over packet radio can only be possible by compression of the original uncompressed source material that contains many bits. This paper provides several comments on a new class of compression techniques based on fractals. This approach may exceed by far the compression limit of the JPEG technique.

Proceedings Paper



Fast CELP Algorithm and Implementation for Speech Compression
by A. Langi, VE4ARM, W. Grieder, VE4WSG, and W. Kinsner, VE4WK
Abstract: This paper describes a fast algorithm and implementation of code excited linear predictive (CELP) speech coding. It presents principles of the algorithm, including (i) fast conversion of line spectrum pair parameters to linear predictive coding parameters, and (ii) fast searches of the pararneters of adaptive and stochastic codebooks. The algorithm can be readily used for speech compression applications, such as on (i) high quality low-bit rate speech transmission in pointto-point or store-and-forward (network based) mode, and (ii) efficient speech storage in speech recording or multimedia databases. The implementation performs in real-time and near real-time on various platforms, including an IBM-PC AT equipped with a TMS320C30 module, an IBM PC 486, a SUN Sparcstation 2, a SUN Sparcstation 5, and an IBM Power PC (Power 590).

Proceedings Paper



Wavelet Compression for Image Transmission Through Bandlimited Channels
by A. Langi, VE4ARM, and W. Kinsner, VE4WK
Abstract: This paper studies an image compression scheme using wavelets for image transmission through bandlimited channels. During encoding, the scheme first transforms the image to a wavelet domain and then compresses the wavelet representation into an image code. Conversely, during decoding, the scheme first decompresses the image code into wavelet representation and then transforms it back to the original domain. The wavelet transform is explained from a perspective of signal representation in L2(R) space. The transform is further computed using a pyramidal algorithm. The compression is possible because (i) the wavelet representation has many small values that can be coded using fewer bits, and (ii) the wavelet basis functions are localized in space and frequency domains such that an error in the wavelet representation only locally affects the image in those domains. An experiment has been performed to compress two 256x256 greyscale images on such a scheme through (i) a transformation using a simple wavelet called DAUB4, (ii) redundancy removal by truncation the small-valued wavelet representation, and (iii) a ZIP compression (based on Shannon-Fano and Lempel-Ziv-Welch techniques). The results show that highly truncated wavelet representation (2 90%) still provides good image quality (PSNR > 30dB) at less than 2 bits per pixel (bpp). Severe truncation still preserves general features of the image.

Proceedings Paper



ROSE X.25 Packet Switch Status Update
by Thomas A. Moulton, W2VY
Abstract: The past year has been very busy for both the development and the network expansion. Highlights include support for 64k EPROM, reformatted applications, X.29 Invitation to Clear and enhancements for IP users. These changes and others that are planned continue to expand the richness of the ROSE X.25 Packet Switch as a network backbone tool. It can pass data transparently with no changes being made to the applications that people are using.

Proceedings Paper



A Primer on Reliability as Applied to Amateur Radio Packet Networks
by T.C. McDermott, N5EG
Scope: Many messages have been sent regarding linking of large number of packet radio switches, nodes, digipeaters, etc. And some have commented on the desirability of very long packet networks. This monograph will describe how to calculate the availability of such a system, given knowledge of the performance of the equipment.

Proceedings Paper



FSK Modem with Scaleable Baud Rate
by Wolf-Henning Rech, N1EOW, and Gunter Jost, KD7WJ
Introduction: Binary FSK modulation of the RF carrier is a well known and widely used transmission scheme for digital information. Old RTTY modems are the first example in amateur radio; nowadays packet radio is the most prominent FSK application. The advantage of FSK is compatibility with existing FM voice radios and simple implementation, including robustness against misalignment, bad transmission characteristics of the radios, or frequency drift. More sophisticated RF modulation schemes are rarely used until now. Combined with coding techniques they could provide more efficient use of the RF bandwidth at low SNR but need very careful construction of both modem and transceiver. Subcarrier modulation techniques, like APSK or AQPSK, are disadvantegous in respect to RF bandwidth and SNR.

Well-known amateur radio FSK modem concepts are those of K9NG and G3RUH which both use an additional scrambler with the polynomial l+x12+xl7. Their implementations are different in detail but basically compatible at the air interface. G3RUHs filtering is more sophisticated with an EPROM hard-coded FIR filter in the transmitter to achieve best spectral purity without alignment.

Both are designed for 9.6 kbaud, need an RF bandwidth of about 20 kHz and work fine with IF filters down to 15 kHz. They can be modified to other baud rates by changing a large number of parts in the analog filters and using another clock frequency. This can be useful to double the speed to 19.2 kbaud with slightly modified radios with 30 kHz IF bandwidth, or even more with broader IFs, like broadcast type WBFM circuits.

We have improved the G3RUH modem keeping in mind the idea of simple baud rate scalability through the clock frequency [1,2]. This task can be solved by replacing the analog filters through switched-capacitor circuits combined with a completely digital DCD circuit. To care for birdies, broadband noise and other 'alias' effects of time discrete filter circuits some analog anti-aliasing filters are added which restrict the scalability to a range of 1:8 in baud rate, e.g. from 9k6 to 76k8.

Proceedings Paper



MacAPRS: Mac Automatic Packet Reporting System-A Macintosh Version of APRS
by Keith Sproul, WU2Z, and Mark Sproul, KB2ICI
Abstract: MacAPRS is a Macintosh version of the popular APRS, Automatic Packet Reporting System, by Bob Bruninga, WB4APR, [1]. Bob introduced his APRS program at the ARRL CNC in 1992. APRS is a system that uses Packet Radio to track objects, using maps on computer screens. His version runs on Intel-based computers running DOS.

Since the introduction in 1992, this program has gained widespread popularity and has had many uses. The most obvious of these uses has been in public service events such as bike-a-thons and other public events covering large areas. It has also been used for such things as tracking amateur balloon launches and tracking the space shuttle.

This paper discusses both the improvements/enhancements to the APRS system and also the introduction of the Macintosh version. It also discusses many of the real-world applications of this system and future possibilities.

Proceedings Paper



Formation of the TAPR Bulletin Board System Special Interest Group
by David A. Wolf, WO5H
Abstract: Recognizing that future improvements to BBS operation were being hindered by a lack of central resource which people could consultfor help and the exchange of ideas, the Board of Directors of Tucson Amateur Packet Radio, Incorporatedl created a special interest group to study methods to address this issue. This paper describes the formation of the TAPR BBS SIG, its purpose and its progress to date.

Proceedings Paper



How Amateur Radio Operators Can Emulate an HF ALE Radio
by David R. Wortendyke, N0WGC
Abstract: Automatic Link Establishment (ALE) techniques became popular for Government HF radios four years ago with the adoption of Federal Standard 1045, and a Government effort to test all candidate HF ALE radios for interoperability and performance before major procurement actions could occur. Testing ALE radios in 1990 was a cumbersome process. As a spin-off the Institute for Telecommunication Sciences (ITS) in Boulder, Colorado investigated new techniques to simplify the method of testing. Last year ITS produced an audio compact disc (CD) with over 50 tracks of computer generated ALE modem tones. These ALE tones exercise almost all of the primary functions and addressing combinations required by the HF ALE Radio Federal Standard. All that is required to simulate an ALE radio is the CD, a CD player, and an HF transceiver with a microphone VOX input. As part of the development effort to produce the ALE modem tones, a computer program was written which makes PC "wave" files, or the digital audio (DA) files for the CD. The wave files may be played using a good quality PC sound card. This software uses ASCII text protocol files to produce the sound files, and the complete software package is now available free of charge on the Internet as of July 1, 1994. This paper describes the software use, and some of the future potential, for emulating an ALE radio using only typical amateur equipment.

Proceedings Paper



A Preview of HF Packet Radio Modem Protocol Performance
by Teresa Young, Stephen Rieman and David Wortendyke, N0WGC
Abstract: Many tests have been conducted over-the-air using various modem protocols designed specifically for HF radio links. It is impractical to compare the over-the-air performance of the protocols, primarily because the atmospheric propagation path conditions are always dynamically changing (non-stationary statistics). Engineers at the Institute for Telecommunication Sciences (ITS) developed a Windows program on a desktop PC to conduct controlled laboratory testing of modem protocols. Using this automated test program, we subjected the modems to a repeatable set of simulated propagation paths for a wide range of signalto-noise (S/N) ratios. The six protocols tested were: AX.25, AMTOR, PACTOR, SlTOR, CLOVER II, and Baudot. The ionospheric propagation conditions were simulated by two narrow-band, Watterson model, HF propagation channel simulators. Clear channel paths through the simulators and three degraded conditions were used: Gaussian noise, CCIR Good paths, and CCIR Poor paths. Over 3000 data file transfers were performed in a randomized manner at various S/N ratios for each of the six protocols. Both ARQ and broadcast mode were used when appropriate. All files received with an error were preserved so an extended computer analysis could be performed. Two metrics were chosen to evaluate the performance of the protocols: 1. throughput, a measure of the data transfer rate, and 2. errors, an indicator of the effectiveness of the protocol. The two metric parameters are compared for each protocol, various channel conditions, and signal strengths. A short preview of the data is provided by this paper.

Proceedings Paper



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