On Distributed Communications Series

VI. Mini-Cost Microwave

I. Introduction

In this Memorandum we consider something we have earlier referred to as "poor-boy" microwave. The "poor-boy" designation resulted from an imposed constraint on the design of an ensemble of microwave communications equipments--namely, that the designer should have to pay for the system out of his own pocket! Even so, a look at price tags for anything to do with any large electronic or communications system would appear to render the term "poor-boy" inappropriate. "Mini-cost," a contraction of "minimum-cost," now seems more fitting.

Mini-cost microwave, therefore, is a minimum-cost, line-of-sight microwave communications system designed to transmit digital information in as inexpensive a manner as possible. It is one way of building the links for the proposed Distributed Adaptive Message Block communications system with which this series of Memoranda is concerned.

The distributed system itself is designed around digital modulation, using redundant paths selected on an instant-by-instant basis. The communications links for such a system can be built in a different manner than their equivalents in today's systems, taking advantage of the system's less rigid distortion level and tandem reliability requirements. The fundamental objective for the system's links is that they permit formation of new routes cheaply (a necessary survivability criterion), yet allow transmission on the order of millions of bits per second (see ODC-I, -VII[1]); system reliability and a low raw error rate are secondary. And, since future networks conveying military traffic must be designed with the expectation of heavy damage, powerful digital error detection and error removal methods have been built into the system.

The low costs sought by the use of the mini-cost links are not based on the costs of today's microwave equipments. The proposed savings will be based, in part, upon several technical developments that have occurred during the past few years which promise lower costs and higher data rates in the future. These include:

  1. Development of a better understanding of digital transmission mechanisms and digital error removal techniques, such as automatic error detection and repeat transmission.
  2. Development of transistors able to generate watts of VHF power.
  3. Development of varactor diodes which permit harmonic multiplication in the SHF range.[2] (Power levels of 1/4 watt at 10 Gcs and 50 milliwatts at 13.3 Gcs are possible today.)
  4. Development of printed circuit "stripline" and "tri-plate" technology permitting economical mass production of microwave components.
  5. Development of inexpensive, lightweight foamed plastics able to maintain the structural stiffness necessary for microwave antennas.
  6. Development of a 50-watt, long-life, commercial thermoelectric generator using inexpensive fuel.
  7. The utilization of pure digital transmission which can tolerate lower signal-to-noise ratios than needed in traditional tandem analog signal modulation.
  8. The conceptual availability of a network configuration tolerant of random link failures without impairment of user-to-user network traffic.

[1] ODC is an abbreviation for the series title, On Distributed Communications. The numeral refers to the specific volume in the series. A list of all items in the series is found on p. 99.

[2] Super high frequency, 3-30 Gc.

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