Categories Of Radio Systems

Radio Communication and broadcasting systems may be either controlled by the ionosphere, as in HF skywave systems, or simply influenced by it, as in transionospheric radio communication and navigation systems (see Section 1.1). In the former case, the ionosphere is actually an inexorable part of the system; while in the latter case, the ionosphere is fundamentally a nuisance. In both instances an account of the ionosphere is at least beneficial to system design and operation. In the case of HF skywave systems, the accounting may be a critical factor in system performance. What is not well understood is that radio communication systems that are affected by the ionospheric personality are not necessarily inferior to systems that are little influenced by the ionosphere. Intelligent use of space weather information may lead to significant improvements in performance of adaptive HF systems. In fact, under some conditions, HF digital communication can be just as reliable as satellite communication. This may be surprising to some communication specialists, and it indicates the power of adaptive system design as powered by space weather data. It is noteworthy that our emphasis is on intelligent exploitation of space weather data as part of an adaptive HF system incorporating sufficient levels of time, path and frequency diversity. We must be clear on that point.

The influence of the ionosphere on radio systems falls into two general categories. Category 1 involves those systems that depend upon the ionosphere (i.e., involve the ionosphere as part of the system); and Category 2 involves those systems for which the ionosphere is simply a nuisance. In addition to these categories, we may organize the various systems into three disciplines: communication navigation, and surveillance. This issue is covered more fully in Chapter 4. From Table 1-2, we see that all three disciplines may be found in listings of category 1 and 2 systems.

Table 1-2. Categories of Radio Systems in terms of Ionospheric Dependence

Category 1

Category 2

VLF-LF Communication and


MF Communication

HF Communication

HF Broadcasting ("shortwave"


OTH Radar Surveillance HFDF and HF SIGINT

Satellite Communication

Satellite Navigation (e.g., GPS & GLONASS) Space-based Radar & Imaging Terrestrial Radar Surveillance & Tracking

Meteor Burst Communications

Any other system for which the ionosphere is not necessary for conveyance ___

In this chapter, we have not offered any new technical data regarding particular space weather observables and communication system impairments, as the literature is already replete with such associations. Rather, the author's goal is to offer some observations based upon many years of R&D experience within government and industry. The basis for these observations derives from early work at the Naval Research Laboratory supporting civilian and DoD communication and surveillance activities. Within the same time frame, we incorporated various methodologies for assessment and prediction of communication performance, including the ionospheric measurements using sounder systems and solar measurements using satellite platforms. Indeed, Navy specialists were the first to develop an approach for application of space weather data in a near-real-time computer platform, PROPHET, which was a quasi-operational system [Rothmuller, 1978].

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