  In this study, we propose an approach to constructing on-off keying (OOK)
symbols for wake-up radios (WURs) by using sequences in the frequency domain.
The proposed method enables orthogonal multiplexing of wake-up signals (WUSs)
and orthogonal frequency division multiplexing (OFDM) waveforms. We optimize
the sequences with a tractable algorithm by considering the reliability of WUSs
in fading channels. The proposed algorithm relies on an alternating
minimization technique, i.e. cyclic algorithm-new (CAN), which was originally
proposed for obtaining a unimodular sequence with good aperiodic correlation
properties. In this study, we extend CAN to generate OOK waveforms with
Manchester coding. We demonstrate the performance of four optimized sequences
and compare with state-of-the-art approaches. We show that the proposed scheme
improves the wake-up radio receiver (WURx) performance by controlling the
energy distribution in frequency domain while removing the interference-floor
at the OFDM receiver.
