The Software Decommutation Model (SDM)

Abstract

It is well known that current PCM telemetry formats are outstripping the capability of commercial off-the-shelf (COTS) Telemetry Systems to implement the corresponding data conversions required to process them. Two complementary approaches are needed for solving this problem: one is to put end users into direct touch with the information stored in telemetry streams; and the other is to convert telemetry applications into this new way of doing things. It is less known that a single technology, software decommutation, provides a practical foundation for both approaches. This document explains why this is so. While developing this software decommutation theme, a very sharp line must be drawn between a software decommutation approach and the COTS telemetry systems solution so that the label "software decommutation" will not be used in misleading ways. The key to drawing this line is SDM's (Software Decommutation Model) ability to: * Extract bits from the raw telemetry stream into 64-bit parameter "containers" in a platform independent ("big endian" or "little endian") manner. * Process algorithms in an algorithm chain on telemetry parameter data to support the desired formatting (i.e. engineering unit conversion). * Easily integrate "special" processing of non-IRIG 106 telemetry data as required (i.e. multiple embedded streams, mode changes, embedded packetized data, etc.). * Independently interface to user-developed data displays locally or via a network connection. *Note: The SDM cannot process a PCM stream directly; to do its job, a databridge is required that provides telemetry data as frame aligned IP packets via a network port.