SYSTEM TRANSMISSION PARAMETERS DESIGN FOR THRESHOLD PERFORMANCE

Abstract

The paper is an extension of two previous works published in the ITC 1974 and 1976 proceedings by the same author. It is the intent of this publication to summarize the two previous papers; to include corrections; to expand the explanations; and to add new material. This information has been accumulated from many system designs based on the described procedures. It deals with a variety of transmission systems and combinations of multiplexing schemes. A number of tables and constants are provided as standards to be used in telemetry system design thereby reducing calculating time. System engineers are given a basic step by step procedure and format for the design of any type of transmissions system. Also a computer program is now available to automatically calculate all of the parameters necessary for the system design. The last presentation of the system design procedure dealt with the information accumulated over several years, and established the parameters from which the design equations for PCM and PAM were updated. Since that time a concentrated effort was initiated to verify the correct bandwidth equation which would be optimum for FM/FM Multi-tone Systems. Again cognizant scientists and engineers were contacted and interviewed. From past history and successes, it was well known that the bandwidth equation known as “Carson’s Rule” provided an adequate bandwidth to guarantee the system accuracies. However, it was also known that systems were in use, operating with smaller bandwidth than specified by Carson’s Rule, and also providing acceptable data accuracies. From the best information available, these systems were designed empirically with painstaking testing effort to insure their accuracy. The investigation lead to another bandwidth equation which appears to be the correct approach for providing the optimum bandwidth for Multi-Tone Systems. There is no doubt that this is not the first application of this bandwidth equation, but this author could not find any documented information as to its use or validity when applied to multi-tone systems. This presentation has designated the new bandwidth equation as the “Multi-Tone Bandwith Equation” or “M/T Bc”. The actual equation and its verification are provided later in this presentation. A second corrective update was made in the design of the PAM/FM/FM Channel where the subcarrier design equations are established based on the same parameters as PCM. Since PCM and PAM are both pulse modulation, their design theories are similar for a subcarrier channel. In the final PAM/FM/FM analysis, a lower frequency SCO will be used as compared to that which was previously specified. Again, the validity and verification of this update in the procedure is described later. Finally, a third and significant addition to this presentation has been provided by Mr. Matthew Egler, of Microcom Corporation, who has written four (4) computer programs based on this procedure. Not only does this program provide the system design effort, but also provides a program for the mixing networks required for systems with PCM or PAM baseband, modulation together with a higher frequency SCO Multiplex system on the same baseband PCM/PAM/FM + FM/FM. Without this network, the baseband pulse adulation is rendered useless when coupled with an SCO Multiplex system. A third program available on the same floppy disc, is the computation of the SCO Voltages and mixer amplifier gain necessary for modulating a transmitter with a specified modulation sensitivity in accordance with the channel deviations as computed by the System Design program. The final program is the margin calculation based on the equations and procedure specified in Attachment E of this presentation. Hopefully this presentation will represent the final procedures and equations. However, if any new information is accumulated based on analysis, experimentation, or field use, which has an impact on the result of this paper, a further update will be submitted to keep the methods described herein current and state-of-the-art. It is the author’s contention that the capability to accurate system design lies in the use of the noise equations, and the procedures developed around those equations.