  Enabling bistatic radar sensing within the context of integrated sensing and
communication (ISAC) for future sixth generation mobile networks demands strict
synchronization accuracy, which is particularly challenging to be achieved with
over-the-air synchronization. Existing algorithms handle time and frequency
offsets adequately, but provide insufficiently accurate sampling frequency
offset (SFO) estimates that result in degradation of obtained radar images in
the form of signal-to-noise ratio loss and migration of range and Doppler
shift. This article introduces an SFO estimation algorithm named tilt inference
of time offset (TITO) for orthogonal frequency-division multiplexing
(OFDM)-based ISAC. Using available pilot subcarriers, TITO obtains channel
impulse response estimates and extracts information on the SFO-induced delay
migration to a dominant reference path with constant range, Doppler shift, and
angle between transmit and receive ISAC nodes. TITO then adaptively selects the
delay estimates that are only negligibly impaired by SFO-induced intersymbol
interference, ultimately employing them to estimate the SFO. Assuming a
scenario without a direct line-of-sight (LoS) between the aforementioned
transmitting and receiving ISAC nodes, a system concept with a relay reflective
intelligent surface (RIS) is used to create the aforementioned reference path
is proposed. Besides a mathematical derivation of accuracy bounds, simulation
and measurements at 26.2 GHz are presented to demonstrate TITO's superiority
over existing methods in terms of SFO estimation accuracy and robustness.
