Using GPS for monitoring air traffic separation standards in international airspace

When a GPS antenna is confined inside an aircraft looking out through a window as in a commercial airliner without an external antenna, it is beneficial to use multiple antennas in order to maximize the coverage. A bias in altitude has been observed between two receivers during a straight-and-level flight segment. The objective of this paper is to discuss the cause of the bias and present an algorithm that will compensate for the receiver-computed position without any hardware or software modification to the receiver when two antennas are connected, within the context of system safety and airspace monitoring. In this paper, we first discuss why two GPS antennas must be used. The performance degradation when two antennas are connected is quantified by using actual flight test data. A detailed algorithm as well as the associated performance enhancement is presented. Other technical issues involving dual-antenna operation are considered