trackwhilescan

Track While Scan, often abbreviated as TWS, is a mode used in GNSS receivers that enables continuous tracking of satellites currently being tracked while simultaneously scanning for additional satellites. The goal is to maintain navigation continuity and reduce time-to-first-fix in environments where signals are weak or rapidly changing.

In practice, trackwhilescan implementations use either parallel processing channels or time-multiplexed processing. Tracking loops for already acquired satellites run alongside search loops that probe the sky for new signals and gather ephemeris and almanac data. The receiver’s scheduler prioritizes keeping existing tracked satellites locked while intermittently performing scans to update satellite visibility, Doppler estimates, and potential acquisitions. Information gathered from scans informs acquisition strategies and helps the receiver quickly reacquire satellites after brief signal interruptions.

Benefits of trackwhilescan include faster reacquisition of satellites, shorter time to first fix, and improved robustness in challenging conditions such as urban canyons or multipath environments. Trade-offs can include higher power consumption and greater processing requirements, as not all implementations optimize for power. Some devices may limit scan activity to conserve energy.

Applications of trackwhilescan span modern GNSS devices, including smartphones, wearables, automotive navigation systems, and aviation equipment. The exact behavior and efficiency of a TWS implementation vary by chipset and firmware, but the general principle remains consistent: maintain current signal tracking while continually looking for new satellites to enhance positioning performance.