Availability correlation distances for HF communications in a global network

In an operational HF communications network, connectivity must be maintained for the times during which traffic is to be circulated or directed through the network. For both voice and data service the notion of real-time channel evaluation has been found to provide necessary and sometimes critical information for evaluating the potential for communication over one or many circuits. While this information may not be sufficient in cases of pathological ionospheric behavior, it is needed for link establishment and maintenance as well as similar functions at the network level. A global resource management concept, Dynacast(R), involving station and frequency selectivity, has been developed using a constellation of FMCW swept-frequency chirp sounder systems, and a developmental test of the method has been undertaken. Based upon data collected during a comprehensive experiment between 1993-1996, TCI/BSR engineers have evaluated the spatial and temporal variation of frequencies in selected aeronautical-mobile and maritime-mobile bands for a number of paths. We have also monitored other information derivable from oblique-incidence ionograms, including the maximum observable frequency and the appearance of E_s ionization. We have used this information to deduce guidelines for our resource management subsystem. Issues include: ground station separation, sampling rate, accuracy versus “age” of forecast, etc. We have measured the cross-correlation of signal availability for a large number of paths and for variety of control point separations. Our paper outlines the system concept and the extent to which our analyses have assisted in the development of the operational system