Issue of Data, Clock (IODC) Value Selection Process and IS-GPS-200H Compliance
Written by CGSIC   
Wednesday, 20 December 2017

The Air Force has released a memorandum which informs the GPS community of an IS-GPS-200H compliant change to the Issue of Data, Clock (IODC) value selection process in the GPS control segment software. The IODC values will now be any numbers in the range 0 to 1023 to support requirements in IS-GPS-200H paragraph 20.3.4.4. Historically, the IODC values were typically chosen from the range 0 to 255. This IS-GPS-200H compliant change to the IODC selection process will be reinstalled in a later update to the GPS software no earlier than 01 Mar 2018. The full memo has been posted to the U.S. Coast Guard Navigation Center website at https://www.navcen.uscg.gov/pdf/gps/IODC_Change_Letter_SIGNED_v2_20171220.pdf