IMPROVED SYSTEM RELIABILITY THROUGH MASTER INDEPENDENT OPERATION

R. W. B. Janes

Peer Reviewed

Abstract:	Positional information in Loran-C systems has traditionally been derived from two time differences measured between signals from a fixed triad of a master and two secondaries. In this limited mode of operation a station outage of the master means loss of all positional information. Loss of a secondary may require acquisition of a new secondary or, at least, suffering a shift in position resulting from a change in geometry and land paths. The introduction of master independence to a Loran-C receiver eliminates the problem of master outage on all but the chains that have only three stations. A two chain Loran-C receiver that computes position from various combinations of stations is basically immune to a single station outage in areas where two Loran-C chains are receivable. In a master independent receiver that is tracking two chains with four stations each, there are 12 time differences being measured. Loss of any one station on either chain, even a master, reduces this number to 9. In fact, so long as any 4 stations are operational out of the eight positional information is available though accuracy may be diminished as the choice of geometry has been lost. A ranging capability provides a backup when only two stations are available. In order to avoid a shift in calculated position when forced to give up a prime station due to outage, positional information from the various pairs of stations is compared and reconciled continuously. When a single station is lost it does not change the calculated position because this possibility has been allowed for in the position calculations.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 30, Number 3
Pages:	227 - 233
Cite this article:	Janes, R. W. B., "IMPROVED SYSTEM RELIABILITY THROUGH MASTER INDEPENDENT OPERATION", NAVIGATION: Journal of The Institute of Navigation, Vol. 30, No. 3, Fall 1983, pp. 227-233.
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