GPS Differential Corrections from Space-time Remote Reference Receivers by 
Michael H. Reilly and Malkiat Singh 
 
It is well known that code pseudorange increments relative to the known free 
space ranges to GPS satellites at reference GPS receivers can be applied as 
differential corrections to corresponding code pseudoranges for roaming GPS 
receivers, in order to improve the free space model determination of their 
positions.  The success of this approach is virtually assured, except for 
possible multipath and urban canyon effects, and has been verified for small 
space and time latency of the differential corrections, i.e., small space 
separation between reference and roaming receivers and timeliness of the 
differential corrections.  The question remains about how useful reference 
receiver data is for differential corrections associated with larger space-time 
latency.  We investigate this relative to Internet data from the Continuously 
Operating Reference System (CORS) receiver network, where we use atmospheric 
compensation models, updated by data from the CORS receivers and weather stati 
 ons, to correct space-time latency relative to atmospheric contributions.  
Ground truth data for differential corrections, provided by a differential GPS 
receiver that is equipped to receive real time differential corrections from a 
US Coast Guard reference receiver in Annapolis, is available for comparisons.  
To the extent that the space-time latency issue for differential corrections can 
be overcome, it would be possible to relax space-time density requirements for a 
reference receiver network.