  This paper aims at the problem of time-of-flight (ToF) estimation using
channel state information (CSI) obtainable from commercialized MIMO-OFDM WLAN
receivers. It was often claimed that the CSI phase is contaminated with errors
of known and unknown natures rendering ToF-based positioning difficult. To
search for an answer, we take a bottom-up approach by first understanding CSI,
its constituent building blocks, and the sources of error that contaminate it.
We then model these effects mathematically. The correctness of these models is
corroborated based on the CSI collected in extensive measurement campaign
including radiated, conducted and chamber tests. Knowing the nature of
contamination in CSI phase and amplitude, we proceed with introducing
pre-processing methods to clean CSI from those errors and make it usable for
range estimation. To check the validity of proposed algorithms, the MUSIC
super-resolution algorithm is applied to post-processed CSI to perform range
estimates. Results substantiate that median accuracy of 0.6m, 0.8m, and 0.9m is
achievable in highly multipath line-of-sight environment where transmitter and
receiver are 5m, 10m, and 15m apart.
