Towards practical channel reciprocity exploitation: Relative calibration in the presence of frequency offset

Relative calibration has been proposed as a simple way to practically exploit the reciprocity of the wireless channel. It is based on a simple convolutional model for the relationship between the channel impulse responses in both directions, and accounts for the discrepancies between transmit and receive radiofrequency components, without the need for specific calibration hardware. However, the relative calibration methods developed so far have been shown to lack robustness with respect to frequency offset between the devices on both sides of the considered channel. In this article, we introduce a relative calibration algorithm that properly deals with the presence of frequency offset. We verify its robustness and assess its performance through simulations, and validate experimentally the proposed model on measured channels.