A Novel Uplink Scheduling Algorithm for the Galileo System

This paper describes a novel uplink scheduling (ULSC) algorithm for the Galileo system. The algorithm is designed to meet the stringent dissemination requirements that are currently foreseen for the provision of the Galileo Commercial Service (CS). In particular, these include "link availability" (LA) requirements that call for a minimum percentage of time ("availability") when a minimum number of satellites ("space vehicles," SVs), connected with an uplink station antenna, shall be in view with a generic user at a minimum elevation angle. LA requirements for CS were not fully considered in the design phase of the ULSC algorithm, which is currently implemented at the Mission and Uplink Control Facility (MUCF) of the Galileo Ground Segment. Similarly, this type of requirements is not considered in the ULSC algorithms available in the scientific literature. In particular, current solutions take into account only specifications about 1) the maximum "gap" duration between two subsequent contacts and 2) the minimum contact duration (MCD). In the new ULSC algorithm, LA specifications are effectively dealt with by a proper selection of the subset of the SVs to be allocated. In particular, the proposed selection scheme takes into account the specifications about both maximum gap duration and MCD while maximizing the "spatial diversity" of the solution. Such a diversity is defined as the union of the coverage areas of the allocated satellites. The performance of the new ULSC algorithm is evaluated based on the final deployment stage (full operational capability) of the Galileo system. The performance is also compared with that of the ULSC algorithm currently implemented at the Galileo MUCF ("reference" algorithm). Numerical results show that, compared to the reference algorithm, the average disconnection duration is reduced by more than 50%. In addition, the availability of the links needed for the provision of CS is significantly improved (up to 7%). As a result, preliminary LA requirements for CS are met using the new ULSC algorithm, while the reference algorithm has limitations to meet the new stringent LA requirements.