|Short delay multipath is common in some challenging environments, such as urban canyons and indoor positioning, where high accuracy requirements are not easy to satisfy due to lack of effective methods of short multipath mitigation. Short Multipath Insensitive Code Loop Discriminator (SMICLD), first proposed by Jardak & Samama  based on modification of the code loop discriminator, is insensitive to short delay multipath. Its discriminator curve (S-curve), however, is asymmetrical, and it always outputs zero when the code tracking error is negative. As a result, large code tracking bias may be induced by noises or signal code phase jumps. So the stability of SMICLD is a problem. This paper constructs a modified code tracking loop aided by SMICLD. Although the modified DLL (delay lock loop) has a zero-crossing point bias in multipath environments, it can function well in adjusting the local replica code phase to the correct direction when the code tracking error is negative. The modified DLL aided by SMICLD uses SMICLD when the code tracking error is positive; and switches to the modified DLL when the code tracking error is negative. A zero-crossing point searching strategy is proposed to distinguish the cases of zero tracking error and negative tracking error. The code tracking loop proposed in this paper lets the modified DLL and SMICLD complement each other. The modified DLL aided by SMICLD has been implemented in the software GPS receiver developed by our group in Beihang University. Its performance against short delay multipath is tested and compared with SMICLD, MEDLL and narrow correlation technique by using a digital IF (intermediate frequency) GPS signal simulator. Test results show that the algorithm proposed in this paper can not only mitigate short delay multipath, but also overcome the instability of SMICLD.
Proceedings of the 2017 International Technical Meeting of The Institute of Navigation
January 30 - 2, 2017
Hyatt Regency Monterey
|1316 - 1329
|Cite this article:
Weng, Xu, Kou, Yanhong, "Modified Code Tracking Loop Aided by Short Multipath Insensitive Code Loop Discriminator," Proceedings of the 2017 International Technical Meeting of The Institute of Navigation, Monterey, California, January 2017, pp. 1316-1329.
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