Global Mobile Satellite Communications Applications by Stojče Dimov Ilčev

Author:Stojče Dimov Ilčev
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

4.3.2.1 UHF 406 MHz LEOSAR System

The 406 MHz LEOSAR system uses the same PEO satellites as the 121.5 MHz system and operates with the same basic constraints, which result from the non-continuous coverage provided by LEOSAR satellites, although with significantly improved performance. The use of LEO satellites provides for a strong Doppler effect in the uplink signal, which allows the use of Doppler positioning techniques. The 406 MHz LEOSAR system operates in two coverage modes for the detection and location of beacons: the local and the global coverage modes. In the local mode, a LUT tracking a satellite receives and processes signals from transmitting beacons in the field of view of the satellite. In the global mode, LUT receives and processes data from the 406 MHz beacons transmitting from anywhere in the world.1. 406 MHz Local Mode—When the satellite receives 406 MHz signals, the onboard SAR Processor (SARP) recovers the digital data from the beacon signal, and measures the Doppler shift and time tags the information. The result of this processing is formatted as digital data and transferred to the repeater downlink for transmission to any LUT in view. The data are also simultaneously stored on the spacecraft for later transmission and ground processing in the global coverage mode. In addition to the 406 MHz local mode provided by the 406 MHz SARP instruments, a 406 MHz repeater, on Sarsat satellites only, can also provide a 406 MHz local coverage mode of operation, similar to the 121.5 MHz local mode.

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