Ionospheric Scintillation Monitoring Using Commercial Single Frequency C/A Code Receivers

Abstract

The earth’s ionosphere can cause serious problems for many radio applications: DOD C31 and navigation sys- tems and commercial applications such as communica- tions, radio astronomy and navigation. They can all be seriously affected by ionospheric disturbances. Distur- bance effects such as amplitude fading and phase scintil- lation limit the ability to coherently integrate weak sig- nals. One solution, which reduces the effective data capacity of the channel, is the use of time-interleaved modulation schemes in which data is sent repeatedly to ensure its error-free reception. Another solution is to use alternate resources during the times of predicted signal outages due to scintillation fading. However, these pre- dictions are generally based on monthly climatology and are poor for a specific time in a particular region due to the variability and dynamics ‘of the earth’s ionosphere. A more real-time and local solution is required. GPS signals provide an excellent means for measuring scintillation effects on a disperse global basis because they are continuously available and can be measured through many points of the ionosphere simultaneously. GPS signals are themselves affected, but because of the spread spectrum properties of the signal, tracking through disturbances with a GPS receiver is usually pos- sible with reasonably wide bandwidth tracking loops, and scintillation parameters can be extracted. There are GPS applications, however, such as surveying where inte- grated carrier phase measurements are used, in which scintillation can easily disrupt operational activities [ 11. This paper presents the result of a Small Business Inno- vative Research (SBlR) Phase I study and testing of a software-modified commercial C/A code receiver to per- form this function. The result is a design of a low-cost, portable Ionospheric Scintillation Monitor (ISM) being developed on a follow-on SBlR Phase II project.