Effect of channel variability on pilot design for joint communications and positioning in OFDM

The accuracy of the estimation of time-delay and channel coefficients in Orthogonal frequency division multiplexing (OFDM) communication systems can be improved by reducing the variability of channel coefficients, i.e. reducing channel covariance and increasing channel mean for a given power. First, we prove that the effect of channel variability between different OFDM symbols cannot be directly captured by extending expected Cramer Rao bound (ECRB) for one OFDM symbol to M OFDM symbols. Then, the effect of channel variations between different OFDM symbols is modeled as the variations of channel covariance and channel mean for one OFDM symbol and a given channel power. A pilot design approach based on per-symbol signal to noise and interference ratio (SINR) for a given time-delay estimation accuracy is investigated. The results show that reducing channel covariance and improving channel mean for a given channel power leads to more accurate estimation of time-delay and channel coefficients. Furthermore, one can save the total power for a given estimation accuracy and channel capacity.