Abstract: The relation betweenGDOP (geometry dilution ofposition) and BS (base station) number at the center of a polygon was derived with and without the correlativity between TDOA ( time difference of arrival) measurements considered. A GDOP method for computing TDOA and TDOA/ AOA (angle of arrival) under NLOS (non-line-of-sight) environment was presented. Theoretical analysis and simulation results show that the correlativity between TDOA measurements increases GDOP, and location performances are improved andGDOP is decreased byTDOA/AOAmethod if the standard error ofAOA measurement is less than 5°.