The WAAS/L5 Signal for Robust Time Transfer: Adaptive Beamsteering Antennas for Satellite Time Synchronization

Abstract

Geostationary satellites of the Wide Area Augmentation System (WAAS) offer a novel, robust, and cost-effective means of synchronizing time at widely-separated ground facilities, to levels of ~50ns, without the need for dedicated long-distance wired communication networks. However, reliance on satellite-based signals for time synchronization in high-reliability applications is problematic without explicit hardening against radio frequency interference (RFI). The primary innovations to be discussed in this paper are: (1) adaptive electronicallysteered multi-element antenna arrays and signal processing strategies for RFI mitigation, (2) live signal, synthetic interference, and hardware-in-the-loop testing of jammer cancellation algorithms, and (3) preparations for over-the-air interference tests which will probe the effects of front-end saturation on digital beamsteering performance. We describe a hardware system assembled from readily-available commercial building blocks (data acquisition system, antennas, etc.), and a critical goal of this research is to realize significant GPS anti-jam performance in an open-architecture (or non-defenserelated) platform. Therefore, the central innovations in this research enable adaptive electronic beamsteering with high-dynamic-range signals (14-bit I/Q digitization), employing commercial off-the-shelf (COTS) hardware and computer systems, and targeted for a civilian highreliability, high-volume (many hundreds of deployed systems) GPS timing application.