Cubic metric reduction for repetitive CAZAC sequences in frequency domain

To meet the requirements of Occupied Channel Bandwidth (OCB) of unlicensed spectrum, in NR-based Access to Unlicensed Spectrum (NR-U) of 5G New Radio (NR) system, the channels of PRACH and PUCCH have to employ some frequency domain sequence repetition schemes. These repetition schemes cause serious Cubic Metric (CM) problems for these channels, although these two types of channels are composed of Constant Amplitude Zero Auto-correlation (CAZAC) sequences. Considering the properties of CAZAC sequences, which are used for PRACH and PUCCH (refer to PUCCH format 0 and format 1) in 5G NR system, in this paper, we propose some new schemes of CM reduction for these two channels taking into account the design principles to ensure the sequence performance of the autocorrelation and cross-correlation. Then the recommended CM reduction schemes are evaluated and the optimized parameters are further provided considering both CM performance and the complexity.