Veripos Standard HF service is a GPS augmentation service that based upon the delivery of differential GPS corrections via High Frequency (HF) radio. The power of Veripos HF resides in the fact that it is not dependent upon line-of-sight to the stations. Obstructions may attenuate the signal, but reception is still possible when the receiving antenna is masked - a characteristic that can be a major advantage when operating in the close vicinity of offshore structures.
Description
Veripos Standard HF is capable of providing a wide area of coverage using relatively low transmitter power levels. Although transmission frequency bandwidth is limited when utilising HF radio for DGPS transmission, the Veripos Standard HF service has been designed to ensure superior system availability and performance. This is achieved through the use of an efficient proprietary transmission format and dual broadcast frequency bands.
The proprietary transmission data format allows slow transmission rates (50 baud) which provides a high level of integrity and reliability in the data link plus better performance at long range. With an update rate typically 3-5 seconds, a full set of correction data has a subsequent age less than 6 seconds.
During the hours of dawn and dusk, and during times of ionospheric activity, HF transmissions can fade and become intermittent at longer ranges. To minimise the impact of this phenomenon, Veripos HF stations transmit correction data on two independent and widely-spaced frequencies (nominally 1.6MHz and 3.5MHz).
Correction Message Format
Differential corrections are broadcast from the Veripos HF stations in a proprietary transmission format which provides a high level of data integrity and reliability. The message data format comprises ten 30-bit words, each comprising a pseudorange correction for a GPS satellite, with two of the words containing service information data.
