Radiobeacon DGNSS coverage-planning a national case study

Abstract

300 kHz marine radiobeacon transmitters are used in some 40 countries for broadcasting Differential Global Navigation Satellite System corrections (radiobeacon DGNSS). In Europe, their widespread adoption led to unforeseen difficulties: significant loss of coverage of many beacons due to interference. This situation has resulted in a reorganisation of radiobeacon frequencies throughout the European Maritime Area, with the objective, of minimising mutual interference. In this paper we present a case study of one country: Norway. The extent of Norwegian radiobeacon coverage before, and after, the re-assignment of frequencies is computed using the Bangor coverage prediction model. This software package takes into account the effects of beacon power, location, frequency, ground conductivity, fading due to a beacon's own skywave signal, atmospheric noise and also interference received via both groundwave and skywave propagation. It plots the regions within which the resulting signals meet IMO standards. Where overlapping beacon coverage is available, a key concern is ensuring that the receiver always selects the beacon that provides the best navigation performance. A new beacon selection strategy has been proposed in which the best station is the nearest one that can satisfy the minimum requirements of signal strength, signal-to-atmospheric-noise ratio and signal-to-interference ratio. A modified version of the coverage prediction software is used to identify the best beacon according to this strategy throughout Norwegian coastal waters. The choice of alternate beacon to be employed in the case of failure of the preferred station is also discussed.