  Recently, a new precoding technique called orthogonal time-frequency
signaling (OTFS) has been proposed for time- and frequency-selective
communication channels. OTFS precodes a data frame with a complete set of
spreading sequences and transmits the results via orthogonal frequency division
multiplexing (OFDM). OTFS uses two dimensional (2D) linear spreading sequences
in time and frequency which are the basis functions of a symplectic Fourier
transform. OTFS allows the utilization of time- and frequency-diversity but
requires maximum likelihood decoding to achieve full diversity. In this paper
we show performance results of a low-complexity equalizer using soft-symbol
feedback for interference cancellation after an initial minimum-mean square
error equalization step. Performance results for an implementation in the
delay-Doppler domain and in the time-frequency domain are compared. With our
equalizer, OTFS achieves a gain of 5dB compared to OFDM for a bit error rate of
$10^{-4}$ and a velocity of $200\,\text{km/h}$.
