  This paper presents unitary-precoded single-carrier (USC) modulation as a
family of waveforms based on multiplexing the information symbols on time
domain unitary basis functions. The common property of these basis functions is
that they span the entire time and frequency plane. The recently proposed
orthogonal time frequency space (OTFS) and orthogonal time sequency
multiplexing (OTSM) based on discrete Fourier transform (DFT) and Walsh
Hadamard transform (WHT), respectively, fall in the general framework of USC
waveforms. In this work, we present channel estimation and detection methods
that work for any USC waveform and numerically show that any choice of unitary
precoding results in the same error performance. Lastly, we implement some USC
systems and compare their performance with OFDM in a real-time indoor setting
using an SDR platform.
