Reduction and optimization of almanac transmission for GNSS satellites

Almanacs are satellite position and clock data of reduced precision, which are transmitted by navigation satellites to fasten signal acquisition. Currently, each satellite is transmitting the almanacs of all satellites independent of the receiver-satellite geometry. This means that the transmission of the complete almanacs takes 12 minutes for GPS. This paper suggests an optimized almanac transmission scheme, which takes the receiver-satellite geometry into account and thereby reduces the number of almanac transmissions for each satellite. The optimization of the subsets of satellites and of the order of transmissions within each subset reduces the number of almanac transmissions from 27 to 8 for Galileo. Moreover, the optimization of the almanacs also enables an approximately two times faster signal acquisition.