Methods, systems and devices for wireless communication are described. One example method includes performing a first mapping in which information bits are mapped to transmission resources in a first portion of a two-dimensional delay-Doppler grid. Herein, the two-dimensional delay-Doppler grid comprises N Doppler elements and M delay elements, where N and M are positive integers. The method further includes performing a second mapping in which a reference signal is mapped to transmission resources in a second portion of the two-dimensional delay-Doppler grid, and generating a transmission waveform from a signal combination of an output of the first mapping and an output of the second mapping. The transmission waveform corresponds to an output of an orthogonal time frequency space (OTFS) waveform of the signal combination, and at least the output of the second mapping undergoes a time domain spreading.