Parente, C., and C. Meneghini. “Advantages of Multi GNSS Constellation: GDOP Analysis for GPS, GLONASS and Galileo Combinations”. International Journal of Engineering and Technology Innovation, Vol. 7, no. 1, Jan. 2017, pp. 1-10, http://ojs.imeti.org/index.php/IJETI/article/view/367.