**Effective HF Communications: Synergy of Good Engineering Practice,
Optimum System Resources, and Timely Space Weather Information with an
Emphasis on Polar Problems**

John M. Goodman

John W, Ballard

Radio Propagation Services Inc.

April 26, 2007

The paper will specify the specific needs for global aviation
communication and will include our Dynacast[^1] technology and the need
for careful engineering of the infrastructure, and the management of all
resources, including frequencies and stations, to do the job properly.
It will include Space-Weather information, good propagation analysis,
and system engineering of the entire network. The paper will indicate
the utility of various assets, including: magnetic indices, ionosonde
and riometer data and the application of these and related data types.
Data assimilation methods are mentioned and the importance of short-term
forecasting is emphasized in practical approaches.

The segment of the paper is devoted to a description of the current
status of Dynacast, an HF system performance system, developed by RPSI.
A top level description is provided. The ingredients include: a
propagation model, an adjustable ionospheric sub-model, a scheme for
incorporation of space-weather data, a data base of parameters for all
radio systems within the network, and an agreed-upon tailored output for
the specific customer targeted.

There are a number of flavors of the Dynacast system. A typical scheme
involves the insertion of update information from an RPSI client into a
Dynacast server using the Internet. The Dynacast server is the engine of
the system and all computations are executed by this unit. Some basic
data exploited by the RPSI client to produce the update information is
derived from public sources such as NOAA-SEC as well as some internal
sources. In one particular application of the methods, we maintain a
current data base of system and operational parameters within the
Dynacast server, including: antenna properties, receiver and transmitter
characteristics, specified flight plans, and aircraft reporting points.
The Dynacast engine (i.e., server) delivers ranked frequency- station
pairs in terms of communication reliability for every specified
reporting point on the flight plan, taking into account the latest
available propagation information obtained from the RPSI client. The
location of the Dynacast server depends upon the requirements of the
customer. The system we describe has undergone some recent testing under
real-life conditions.

A test of the RPSI Dynacast® system was conducted for a series of
Continental Airlines flights from CONUS to Hong Kong and return via
Hawaii and Guam. The trials were performed during August of 2006, a
period of low sunspot activity and modest magnetic activity, providing a
fair trial of the system under typical conditions. The Dynacast system
provided listings of best frequencies and stations organized in
descending order of reliability. Information was provided to the ground
stations and to the aircraft radio operator. The system performed as
expected and provided useful information to enable rapid and reliable
communication whenever network structure was adequate. As a bonus, the
system provided information that could assist in the evaluation of
sub-optimal system configurations and provided guidance for network
improvements. Finally we conclude that ATS would benefit from the
insights provided by the techniques which are incorporated within the
Dynacast system.

There are special issues vis-à-vis the polar environment. For HF
communications, the transauroral and polar cap regions provide
strikingly different aspects of communication than those associated with
the midlatitude and equatorial regions. This is well-known and there is
considerable literature on the subject. RPSI analyzed over-the pole
routes in a study sanctioned by organizations such as NavCanada and
ARINC. We have also examined the communication problems associated with
Antarctica for NSF and the U.S. Navy. We concluded from the NavCanada
study that the burden for communication effectiveness is borne by the
system topology (i.e., station locations), system assets (i.e.,
transmitters, antennas and frequencies), and quasi-real-time frequency
management. However, the best frequency management system in the world
will not trump the deficiencies of an inadequate population of
communication stations or a paucity of propagating frequencies. The
reverse is also true. As time permits, we will describe a few sample
scenarios of polar propagation and remedial actions.

Dynacast methodologies are currently used to guide frequency management
decisions within the ARINC GLOBALink/HF communication system, and the
Gannet communication services to aircraft in the polar regions from a
station in Iceland.

[^1]: Dynacast is an RPSI tradename. Dynacast forecasting technology is
    covered by US patent 5943629 issued in 1999; and a separate patent
    application for aviation services described herein has been
    submitted.