RESULTS OF DGPS EXPERIMENTS WITH DIFFERENT RTCM RADIO SOURCES IN THE CEI AREA 
R. Cefalo *, R. Pagurut *, J. Plasil °, T. Sluga * 
* Department of Civil Engineering, University of Trieste, Italy 
° Faculty of Electrical Engineering, Czech Technical University, Praha 
cefalo@dic.univ.trieste.it 
Commission VI, Working Group 3 
KEY WORDS: DGPS, RTCM, LW transmission, FM transmission. 
ABSTRACT 
Several radio sources generating RTCM corrections are available in the CEI area, even without a full coverage. Some of them are 
simultaneously present in some areas, thus allowing static and kinematic analyses of accuracy and continuity. Our intent was to test 
some different RTCM correction sources received in one place, in order to compare the different accuracy of the systems. All this, in 
view of detecting one or more RTCM correction systems able to give satisfatorily accurate results with a full coverage on the CEI 
area. The considered DGPS radiodiffusion methods are two Low Frequency transmitted signals, i.e. ALF, and LF signal from 
Podebrady (Prague), and one FM transmitted signal: DARC. 
This paper reports the adopted techniques and the detailed results of some experiments performed together by different components 
of the CEI Working Group on Satellite Navigation Systems. 
1. EXISTING METHODS 
At least the following DGPS radiodiffusion methods are 
available in the CEI area, some on a large area, others only 
locally, giving different positioning accuracy greatly due to the 
distance from the correction source: 
TERRESTRIAL ANTENNAS: 
- LOW FREQUENCY: 
ALF (Accurate Positioning by Low Frequency) 
operated by Bundesamt fuer Cartographie und Geodesie (BKG) 
in Frankfurt am Main; 
LF transmitter in Podebrady, a small town 50 km east 
of Prague, which transmits DGPS corrections generated in the 
Czech Technical University (CTU) Reference Station, in 
Prague; 
MARINE RADIOBEACON: Some years ago, an 
experimental emission from Venice, Punta Maestra by Italian 
Navy and Codevintec Italiana, Milan, was successfully 
experimented with a car trajectory from the top of the Apennine 
Highway to Trieste; 
-HIGH FREQUENCY (VHF,UHF): 
RDS (Radio Data System): It should be soon available 
for experiments in the Italian eastern highways; 
DARC (Data Radio Channel)/Swift (System for 
Wireless Infotainment Forwarding and Télédistribution) - the 
RTCM and RTK emission is a service by ORF (Österreichische 
Rundfunk) on the FM band; 
DAB (Digital Audio Broadcasting), about 250 MHz: 
Bavaria, province of Bozen (RAI and RAS); 
MOBILE TELEPHONES: Experiments were done 
with TACS, showing difficulties in maintaining the connection. 
These systems are very useful for research since there is no 
need of transmission licence, but the number of users is limited. 
TELECOM UNICATION SATELLITE EMISSIONS: 
RACAL: several experiments on the highways 
showed the feasibility of the method on open areas. The method 
is less feasible in urban areas, due to building covering; 
OMNISTAR: Same as RACAL; and 
EGNOS (European Geostationary Overlay Service): 
Same as RACAL. 
2. THE CZECH TECHNICAL UNIVERSITY (CTU) 
REFERENCE STATION 
The Czech Technical University (CTU) Reference Station is 
based on three GPS receivers: 
1. Leica MX9400R receiver 
2. Trimble GPS Pathfinder Community Base Station 
3. Novatel GPSCard 951R in 486 PC computer 
The Leica receiver is the core of the reference station and gives 
corrections which are disseminated wireless. The Trimble 
receiver generates corrections for postprocessing. It also backs 
up Leica. The Novatel Card is the first - and by now rather 
obsolete - receiver that backs up both receivers mentioned 
above. 
Corrections are broadcast with one-second step in real time by 
1) VHFR(B)DS channel 
2) LF channel 
Correction Dissemination by VHF RDS Channel cover Prague 
and its near surroundings. 
The data of pseudorange measurements made by Leica receiver 
modulate an LF transmitter in Podebrady (Fig. 1) - a small town 
50 km east of Prague. The transmitter works on 111.8 kHz 
frequency, with a 500 bps bit rate. The transmitter output power 
is 80 kW. It is backed up by a 5 kW standby transmitter. 
Corrections are placed into 60 bit frames. FEC is provided by 
CRC code (60,41). 
The CTU designed and manufactured receivers for both LF and 
VHF channels. They receive signals, prove message parity, and 
ignore frames with detected errors. At receiver output, there are 
corrections in RTCM 104 format. 
LF signal coverage is shown in Fig. 2. It covers a large share of 
Central Europe. Flags mark the places where corrections were 
tested, even if by different GPS receivers. 
It was noticed that the accuracy of position determination first 
and foremost depends on the quality of the GPS receiver. 
2D accuracy (95%) - approximately 0.76 m - was obtained in 
Prague and its surroundings. 
Deutsche Telecomm did experiments on the Baltic coast, and 
reported that accuracy was about 6 meters.