Analysis on TOA and TDOA Location Estimation Performances in a Cellular System

In a computer simulation result on the location estimation for a cellular system, we found that a Time Difference Of Arrival (TDOA) method outperforms a Time Of Arrival (TOA) method when Non-Line-Of-Sight (NLOS) channels are dominant, whereas the TOA method outperforms the TDOA method when LOS channels are dominant. We could not easily accept the result, because TDOA method loses one degree of freedom in the number of usable range estimates when selecting a range estimate as a reference and doubles the variance of range error when subtracting the reference range estimate. In this paper, we try to theoretically prove the interesting result by the computer simulation. We divide the root mean square location estimation error into two factors, such as the error variance contributed from range sampling error and the error bias contributed from positive NLOS range error. For the error variance, we evaluate it by the Cramer-Rao lower bound, whereas for the error bias, we analyze it by perturbation method.