208 
integrated in one only dome. 
the user's point of view it works as if there would be a GPS 
base station at a few kilometres distance, with direct radio 
connection to the rover. 
The organisation of the OMNISTAR system for one 
continent is graphically resumed by the figure 3. 
Fig. 3 - OMNISTAR system organisation: 
1) GPS satellites; 2) OMNISTAR permanent GPS stations 
network; 3) cable connection to Network Control Centre; 
4) Network Control Centre; 5) Geostationary 
communication satellite; 6) communication satellite 
coverage; 7) end user (precision navigation or survey) 
b) Cable-connected configuration. The GPS receiver is 
connected by a serial cable to an external OMNISTAR kit 
including antenna and receiver/decoder. Through the 
serial cable pass both the differential corrections in RTCM 
format (from OMNISTAR to GPS), and the GPS positions 
in NMEA format (from GPS to OMNISTAR); the latter are 
necessary, as told above, in order to compute the 
atmospheric correction at the user’s position. 
Figure 4 schematically resumes the layouts of the two 
options described above. 
GPS antenna OMNiSTAR™ antenna 
OMNISTAR™ receiver 
with integrated 
GPS receiver 
1 
DGPS position 
r 
Data logger 
2.3. System specifications 
The main technical data of the OMNISTAR system are A) Compact configuration 
briefly resumed as follows: 
• Coverage: almost world-wide, with "regional" networks 
for Northern and Southern America, Europe and North 
Africa, Central and Southern Africa, Asia and Australia 
• Connection from station network to NCC in a triple 
way: VSAT, leased lines and dial-up 
• Correction data message transmission frequency: 
1525 to 1559 MHz band 
• Differential correction format: RTCM SC-104 V.2 
(including range corrections and rate of change of 
corrections for all GPS satellites covering the 
continental area) 
• Sampling rate: 0.6 seconds (network stations); 2 to 3 
seconds (message upload) 
• Atmospheric biases evaluation effected at each base 
station 
2.4. User equipment 
As for the hardware, there are many possible options, but 
they can be resumed in two only equipment types: 
a) All-in-one configuration. GPS and OMNISTAR receivers 
are fully integrated. The two antennas can be also 
GPS antenna OMNISTAR™ antenna 
B) Cable-connected 
configuration 
Fig.4 - OMNISTAR user’s hardware configurations