Indoor Positioning Based on LTE Carrier Phase Measurements and an Inertial Measurement Unit

A tightly-coupled inertial navigation system (INS) with cellular long-term evolution (LTE) signal aiding for indoor positioning is developed. The navigation approach is based on a carrier phase-based software-defined receiver (SDR), which tracks LTE signals and provides aiding corrections to an inertial measurement unit (IMU) in a tightly-coupled fashion via an extended Kalman filter (EKF). The indoor positioning framework employs an outdoor receiver, referred to as the base, which estimates the unknown clock biases of LTE eNodeBs and shares these estimates with the indoor navigating receiver. The availability and strength of received LTE signals indoors is evaluated in different conditions: different floor levels and in rooms with and without windows. It is demonstrated that the received carrier-to-noise ratio C/N-0 in all such conditions is 48-80 dB-Hz. The performance of the developed system is evaluated in an indoor environment over a trajectory of 109 m using a tactical-grade IMU. The two-dimensional position root mean- squared error (RMSE) for the proposed LTE-IMU system is demonstrated to be 3.52 m with a standard deviation of 3.85 m and a maximum error of 8.1 m. In contrast, the IMU-only system provided an RMSE of 9.91 m with a standard deviation of 9.67 m and a maximum error of 22.53 m.