Differentail Global Postioning System

i m working in vintron convergys on Differentail Global Postioning System. it is installed in dumpers & excavators. in control base also
problem:base have no gps receiver to recieve the data from satallite in this case this found ok. but when we put gps receiver the system get restarted and data is not in correct form. this system is ok when we remove the gps receiver from control base system .
but theory say “there may be a referance from where control system calaculate the distance, postion, and other data of the dumpers & excavators”