Page 202 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes Optimization of MBC links to satisfy required performance parameters requires weighing and
trading-off system design factors, such as operating frequency, antenna gain, transmitter power
and receiver threshold levels. In the 1980s MBC systems provided an average throughput in the
area of 75 to 100 words per minute (wpm), but careful system design using much more powerful
microprocessors now available should produce orders of magnitude increases to that average
performance level.

Performance requirements for MBC systems usually are stated relative to wait times (for message
transmission) and information throughput time (user information transfer rate). Both of these are
based on the arrival frequency and usable lifetime of trails. Thus, performance must be stated in
terms of averages and it is customary to use daily average. Also, the performance requirement
is identified relative to the type of telecommunications service to be provided. MBC has great
flexibility in usable applications. Point-Multipoint and Multi-Single Point or Mesh-network
configurations all are feasible services available from MBC systems.

A further significant characteristic of MBC systems, relative to their flexibility, is the connectivity
range, covering both line-of-sight (LOS) and beyond LOS (BLOS). Unlike other BLOS systems,
such as those using high frequency (HF) radio waves, the same VHF configuration used to
communicate BLOS using meteor trails has the capability to provide connectivity to terminals
within LOS range. This allows continuous geographic coverage, with some realignment of
configuration, to almost 1,200 miles.

12.2.3 Meteor Burst Communication Basics

Meteor meteor burst radio communications relies on the fact that meteors continually enter the
Earth’s atmosphere. As they do so they burn up leaving a trail of ionisation behind them. These
trails which typically occur at altitudes between about 85 and 120 km can be used to “reflect”
radio signals. In view of the fact that the ionisation trails left by the meteors are small, only
minute amounts of the signal are reflected and this means that high powers coupled with
sensitive receivers are often necessary.

Meteor scatter propagation uses the fact that vast numbers of meteors enter the Earth’s
atmosphere. It is estimated that around 10^12 meteors enter the atmosphere each day and these
have a total weight of around 10^6 grams.
Fortunately for everyone living below, the vast majority of these meteors are small, and are
typically only the size of a grain of sand. It is found that the number of meteors entering the
atmosphere is inversely proportional to their size. For a tenfold reduction in size, there is a
tenfold increase in the number entering the atmosphere over a given period of time. From this
it can be seen that very few large ones enter the atmosphere. Although most are burnt up in
the upper atmosphere, there are a very few that are sufficiently large to survive entering the
atmosphere and reach the earth.

12.2.4 Meteor Burst Communication Network Applications

A meteor burst communications system (MBCS) uses ionized meteor trails as a means of radio
signal propagation. These trails exist in the 80 to 120 km region of the earth’s atmosphere, and
reflect the RF energy between two stations. The height of the trails allows over-the-horizon
communication at distances up to 2000 km. However, because the ionized trails exist for only
short periods of time (usually from a few milliseconds to a few seconds) communication is
intermittent, and high-speed digital transmission techniques must be used to convey the
information. The system is particularly well suited for long-range, low data rate applications for
both messaging and data acquisition.
Meteor Burst communications has been a viable communications medium since the 1950s. It was
quickly recognized as an alternative to Satellite. In addition, since no equipment has to be placed
in orbit, it is not susceptible to conventional or nuclear war side-effects.

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