GPS-Squitter Interference Analysis

This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. 6. Abstract GPS-Squitter is a system concept that merges the capabilities of Automatic Dependent Surveillance (ADS) and the Mode S beacon radar. The result is an integrated concept for seamless surveillance and data link that permits equipped aircraft to participate in ADS andlor beacon ground environments, offering many possibilities for transition from a beacon to an ADS-based environment. Since GPS-Squitter and its associated data ,link share the 1030/1090-MHz beacon frequencies with other users (e.g., ground beacon radars and TCAS), th ere is some level of interaction between the operation of these various systems. One form of interaction is the effect on GPS-Squitter operation caused by the activities of other users. This effect, plus the effect of self-interference of GPS-Squitter operation, determines the operational capacity of GPS-Squitter. The complementary process is the effect of the GPS-Squitter operation on the other users of the beacon frequencies. This report provides an analysis of the interference to other users of the 1030/1090-MHz beacon frequencies caused by GPS-Squitter operation. The principal interference effect is channel occupancy on the beacon frequencies that prevents the reception of a desired signal by a receiver. The basis for the analysis is to estimate the channel occupancy on the beacon frequencies and its effect on the operation of victim receivers on those frequencies. The analysis is performed separately for the two frequencies. The analysis of 1030-MHz interference estimates the effect of the 1030-MHz data link activity that may be associated with GPS-Squitter (such as differential correction broadcast and two-way data link) on the operation of a transponder receiver. The 1090-MHz analysis estimates similar interference effects on (1) a terminal or en route sensor receiver and (2) a TCAS receiver. The results indicate that the operation of GPS-Squitter and its assoeiated data link will have a negligible effect on the other users of these frequencies.