On the minimization of different sources of error for an RTT-based indoor localization system without any calibration stage

Prior to the trilateration process, different sources of error disturb the range estimates in any localization system, especially in dense cluttered environments where the non-line-of-sight (NLOS) between the mobile user (MU) and the access points (AP) becomes the main problem. Common error mitigation approaches are based on linear or Gaussian assumptions that are not fulfilled in this kind of scenarios, such as indoor or dense urban outdoor areas. This paper points out the better performance of a round-trip time (RTT)-based localization system when combining a prior NLOS measurements correction (PNMC) method with particle RTT-only tracking, since hard decisions are only made in the last stage of the positioning process, and neither linear nor Gaussian models are assumed. The final performance leads to a reduction of more than 57% of the error obtained without any mitigation technique, keeping the requirement of no calibration stage.