Improving the precision of the software receiver GLONASS L1

March 23, 2012

Some time ago I became interested in improving the precision of GLONASS Scilab receiver. The difference between mean value and max/min values of coordinates up to 35 m for stationary receiver is too big.

PVT solution of GLONASS L1 Scilab receiver
Figure 1 PVT solution of GLONASS L1 Scilab receiver

After improving several weak parts of the code the difference between mean value and max/min values of coordinates lowered to 6 m, i.e. almost in 6 times. Results from the updated version of the receiver is on the figure 1. The same signal record as in the post GLONASS - frist experiments was used.
After analysis of the original GNSS-SDR source code several weak places were found. Their improvement could increase receiver's precision. Here is the list of these weak places:
1. High variance of DLL-discriminator data;
2. Pseudorange calculations are based on round-off measurements;
After reducing correlator's arms spacing from 0.5 to 0.05 chips and after lowering DLL loop filter bandwidth from 2.0 to 0.5 Hz with additional adding assistance from PLL-assisted-FLL variation of DLL discriminator data was lowered. This fact with additional refuse from round-off during pseudorange calculations allowed to receive results that are shown on figure 1.
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