Table 6. RMS values of the second test integrated system 
  
  
  
  
  
  
RMS (m) 
KE E N U 
EKF 67.214 30.703 43.888 
EKF-NHC 36.088 16.557 37.725 
AKF 14.169 16.019 28.464 
AKF+NHC 11.222 10.963 22.721 
  
  
  
  
  
  
4.4 Analysis 
The first test integrated system implements AKF with NHC can 
achieve 25% in horizontal position error and 25% in vertical 
position error in comparison with AKF based algorithm. The 
second test integrated system implements AKF with NHC can 
achieve 26% in horizontal position error and 20% in vertical 
position error from AKF based algorithm. 
Comparing to the results of the first test integrated system 
(geodetic GPS receiver) and the second test integrated system 
(low-cost GPS receiver), similar improvement ration can be 
obtained. In the case of EKF based INS/GPS tightly-coupled 
integration with non-holonomic constraints, all the results in 
this field scenario have 40% up improvement in horizontal 
position error and 30% averaged improvement in 3D position 
error from EKF to EKF with non-holonomic constraints. In the 
other case of AKF based INS/GPS tightly-coupled integration 
with non-holonomic constraints; the results show the 25% 
averaged improvement in 3D position error. 
From the results of EKF, EKF with NHC, AKF and AKF with 
NHC applied in the integrated systems, the non-holonomic 
constraints can improve the EKF and AKF based integration 
algorithms. Therefore, the aid of non-holonomic constraints to 
the Kalman filters applied in land vehicles can be reveal here, 
especially during no GPS signals. 
5. CONCLUSION 
The objective of this study 1s to implement EKF and AKF based 
tightly-coupled INS/GPS integrated system with non-holonomic 
constraints for land vehicles. 17-state EKF and 17-state AKF 
with non-holonomic constraints can raise the position accuracy 
especially during GPS signal obstructions for land vehicles. 
The case of the 17-state EKF based tightly-coupled INS/GPS 
integrated system can reach 30% averaged improvement in 3D 
position error with non-holonomic constraints. The other case 
of 17-state AKF based tightly-coupled INS/GPS integrated 
system can reach 25% averaged improvement in 3D position 
error with non-holonomic constraints. Especially, the non- 
holonomic constraints can be the aid for the stand-alone INS to 
decrease the position drift during the GPS obstructions over 1 
minute in those two cases of the INS integrated with the 
geodetic GPS receiver and the low-cost GPS receiver. Therefore, 
the AKF based INS/GPS tightly-coupled integrated algorithm 
with non-holonomic constraints can provide more stable 
navigation solutions than EKF and AKF based integration 
algorithms applied in a hostile environment. 
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