Fast and reliable coordinate determination with GNSS in real time is the main objective of continuous operating reference system (CORS) network users. To provide services for coordinate determination, Network-based Real Time Kinematic (NRTK) system called “LatPos” has been established and operated in Latvia since 2006. One of the factors, affecting the performance of LatPos system services, is activity of ionosphere. Ionosphere is a region of the earth's atmosphere, from about 60 kilometers up to 1000 km above the earth's surface, in which there is a high concentration of free electrons, spatially variated, affected by space weather, seasonal and solar cycle changes. Ionospheric activity conditions depending on mentioned factors can be analyzed by LatPos system data. Some data processing strategies has been developed and LatPos RTK network performance results obtained, during different ionospheric activity conditions. This paper focused on both segments: the NRTK performance and the rover receiver coordinate determination possibilities in field when high ionospheric activity occurs.