5G-Advanced and likely 6G will support a new low-power wake-up signal (LP-WUS) enabling low-power devices, equipped with a complementary ultra low-power receiver to monitor wireless traffic, to completely switch off their main radio. This orthogonal frequency-division multiplexed (OFDM) signal will emulate an on-off keying (OOK) modulation to enable very low-energy envelope detection at the receiver. Higher rate LP-WUS, containing multiple OOK symbols within single OFDM symbol, will be generated using the time-domain pulse multiplexing of discrete Fourier transform spread (DFT-s-) OFDM. In this context, this paper presents a general signal design framework for DFT-s-OFDM-based OOK generation. General properties of subcarrier coefficients are derived demonstrating that only DFT of the bits needs to be computed online and repeated over the band before applying appropriate frequency-domain processing. The conventional approach of generating rectangular-like OOK waveforms is then addressed by a combination of pre-DFT bit-spreading and post-DFT processing; and the least-squares (LS) method from Mazloum and Edfors, proposed for 5G LP-WUS and also Ambient-IoT, is shown to be implementable as such. Even though aesthetically pleasing and of independent interest, rectangular-like OOK waveforms are not optimal for 5G LP-WUS scenarios due to their limited robustness to channel frequency-selectivity and timing offset, and so shaping methods for spreading the OOK spectrum and concentrating the OOK symbol energy are described and shown to improve the bit error rate performance under practical conditions.

翻译：5G-Advanced及未来的6G预计将支持一种新型低功耗唤醒信号（LP-WUS），使得配备有辅助超低功耗接收器的低功耗设备能够完全关闭其主无线电，同时监测无线流量。这种正交频分复用（OFDM）信号将模拟启闭键控（OOK）调制，以实现接收端极低能量的包络检测。通过在单个OFDM符号内包含多个OOK符号来生成更高数据率的LP-WUS，将利用离散傅里叶变换扩频（DFT-s-）OFDM的时域脉冲复用技术实现。在此背景下，本文提出了一种基于DFT-s-OFDM的OOK信号生成的通用设计框架。推导了子载波系数的一般性质，证明仅需在线计算比特的DFT并在频带内重复，再施加适当的频域处理即可。针对生成类矩形OOK波形的传统方法，本文通过结合DFT前比特扩展与DFT后处理的方式予以解决；同时表明，Mazloum与Edfors提出的最小二乘（LS）方法（为5G LP-WUS及环境物联网所提出）可按此方式实现。尽管类矩形OOK波形在美学上令人满意且具有独立研究价值，但由于其对信道频率选择性和定时偏移的鲁棒性有限，在5G LP-WUS场景中并非最优。因此，本文描述了用于扩展OOK频谱并集中OOK符号能量的整形方法，并证明其在实用条件下可改善误码率性能。