Your question is not clear, you want to determine the RTK status in Rover? If true, the Rover side needs to send $ GPGGA at the NMEA output, then you can use Ublox-Center to determine the RTK status.
NMEA-0183 message: GGA
Time, position, and fix related data
An example of the GBS message string is:
Note – The data string exceeds the NMEA standard length.
GGA message fields
||Message ID $GPGGA
||UTC of position fix
||Direction of latitude:
|5|Direction of longitude:
|6|GPS Quality indicator:
0: Fix not valid
1: GPS fix
2: Differential GPS fix, OmniSTAR VBS
4: Real-Time Kinematic, fixed integers
5: Real-Time Kinematic, float integers, OmniSTAR XP/HP or Location RTK|
|7|Number of SVs in use, range from 00 through to 24+|
|9|Orthometric height (MSL reference)|
|10|M: unit of measure for orthometric height is meters|
|12|M: geoid separation measured in meters|
|13|Age of differential GPS data record, Type 1 or Type 9. Null field when DGPS is not used.|
|15|The checksum data, always begins with *|
Note – If a user-defined geoid model, or an inclined plane is loaded into the receiver, then the height output in the NMEA GGA string is always the orthometric height (height above a geoid). The orthometric height is output even if no user-defined geoid is loaded (there is a simplified default geoid in the receiver), or if a user-defined geoid is loaded, or if an inclined plane is used.