onos pheric　electron　content　and　hardware　delay analysis 　based　on　different　constraints

based　on　different 　constraintsdouble－fre quency　measurement　data 　from　11gps　stations 　inthe　vicinit y　of 　china　and　230global 　gps　stations　were　used 　to 　calculate 　vertical 　ionos phere　electroncontentvtec the　dcb　of　gps　satellitesand　corresponding　receivers 　based　on　the 　spherical 　harmonic　function　model．the　results 　show　that 　the　vtec　and　the 　combination　dcb　of　gps　satellite 　andreceiver　were　not　affected　by　constraints．the　dcb　precision　of 　the 　combination　obtained 　is 　less 　than　2ns 　comparing　with　codeand　the 　correction　rate 　of　vtec　relative 　to　code　can 　reach　up　to 　９0percent we　also 　predict 　spherical 　harmonic　coefficients　using　the　ar　modelthe 　correction　rate 　ofvtec　based　on　the　prediction 　coefficients 　can 　reach 　to 　80percentthus 　fixin g　the 　sum　of 　the 　satellitedcbs　is 　better 　than 　fixin g　a　sin gle 　satellite　dcb．