Simultaneous Localization and Communications under Imperfect Timing-frequency Synchronization

Simultaneous localization and communications (SLAC) is an emerging localization technique. The basic idea is to extract the position and velocity information of mobile stations from estimated channel state information (CSI). In related work, base stations (BS) and mobile devices are generally assumed to be time-frequency synchronized, and high accuracy SLAC could be expected. However, on the one hand, perfect synchronization is impossible. This assumption results in over-optimistic performance bounds and significant positioning errors in practice. On the other hand, to search for the starting point and central frequency of received signals, timing-frequency synchronization is required for communications instead. In this paper, we will propose a more realistic and reliable SLAC framework based on existing orthogonal frequency division multiplexing (OFDM) protocols. In channel modeling, phase shifts over subcarriers and time slots are proportional to residual synchronization offsets (RSOs) rather than propagation delays and Doppler shifts. Combining the initial synchronization results and RSOs, time-difference-of-arrivals (TDoAs) and frequency-difference-of-arrivals (FDoAs) can be obtained. We also design a TDoA/FDoA-based algorithm for the joint position and velocity estimation. Finally, numerical evaluations are conducted, and the results verify the reliability of our proposed SLAC framework. In our SLAC framework, sub-meter-level positioning accuracy can be expected.