In this paper, bias and Cramer-Rao bound (CRB) analyses for both proposed line of sight (LoS)-based and conventional received signal strength (RSS)-based ranging methods are provided. A minimum bias of LoS-based ranging is derived, which is based on the asymptotic variance (AsV) of the estimator. Mean square error lower bound (MSEB), which is the summation of CRB and the square of minimum bias, is employed to compare with existing RSS-based methods. The existing RSS-based ranging methods are categorized, and corresponding biases are analyzed. The multipath fading effect to the final range estimation has been modeled into the MSEB. The proposed LoS-based ranging method minimizes the effect of non-LoS (NLoS) component (i.e., the multipath fading) in the received signal. The derived model was validated by simulation. Both the analytic model and simulation results show that the performance of the proposed LoS method is superior to that of the conventional RSS-based methods.