Scan scheduling of multi-function phased array radars using heuristic techniques

Abstract

This paper describes a scan scheduler based on heuristic principles for MPRF airborne fire control radar. The design of the heuristic scheduler is based around a set of simple rules which work in conjunction with a priority framework to provide the required outputs to the system, in this case the next beam azimuth and elevation. A new heuristic scheduling algorithm has been produced that incorporates the elements of the best published algorithms. The heuristic rule set incorporates a hierarchy of function priorities and an overload strategy that provides graceful degradation of surveillance tasks to service target tracking. Simulations were designed and executed to stress the full capabilities of the scheduler. Superior performance was demonstrated in all but the most extreme of overload conditions. In common with all priority-based systems the scheduler surveillance performance degraded under heavy load conditions. This scheduler mitigated this degradation by altering the surveillance volume under load. A novel approach to prioritising beam position updates in heavy loading conditions was implemented such that the beam scanned from the boresight position first. This approach optimises search time by ensuring that the areas with high beam dilation compensation factors were updated at a lower rate. Realistic parameters were used, based on an existing fighter radar system (AN/APG-63) and showed improvements when compared with that radar's existing mechanical system. The chosen PRFs and dwell times gave initial acceptable performance but the adaptability of the MFR allowed the variation of dwell time and data rate to show further performance gains. The set of heuristics used in the scheduler showed emergent behaviour that took account of track loading and the search time available in an overload situation to cope automatically with loading and shedding of tasks. This non-programmed behaviour resulted in graceful degradation of system performance under overload conditions. Although the graceful degradation is emergent behaviour, it can be deduced by formal reasoning and shown to be implied by the heuristic rules.