Performance evaluation of single and dual frequency Carrier Smoothing techniques for LAAS

The state-of-art Local Area Augmentation System (LAAS) system for 21st century is being developed by USA, to provide aircraft precision approach and landing. In India, LAAS is still in conceptual stage. Prominent error sources namely ionosphere, troposphere, multipath and receiver noise affect LAAS performance. LAAS employs Single Frequency Carrier Smoothing (SFCS) to mitigate spatially uncorrelated errors like multipath and thermal noise. Temporal and spatial gradients of ionosphere affect the performance of SFCS. As India comes under low latitude regions, Indian ionosphere is characterized by large ionosphere gradients. To mitigate ionospheric effects, dual frequency GPS data for smoothing is employed. This paper presented the effect of temporal gradients on SFCS and assessed the performance of Dual Frequency Smoothing (DFS) techniques. The results due to the developed algorithms are encouraging and are agreeing with the results published elsewhere.