Cubic Metric Reduction for Repetitive CAZAC Sequences in frequency domain in 5G System
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To meet the increasing requirements for wireless communications, unlicensed access is being accepted as one of the most significant solutions to improve resource availability and system scalability in 5G NR, which is called NR-based Access to Unlicensed Spectrum (NR-U). As an OFDM system, 5G will face the problem of high Cubic Metric (CM). To satisfy the usage rules of Occupied Channel Bandwidth (OCB) of unlicensed spectrum, NR-U's PRACH and PUCCH, which are composed of CAZAC sequences, have to use some sequence repetition mechanisms in frequency domain, which brings more serious CM problems. Based on the characteristics of Constant Amplitude Zero Auto-correlation (CAZAC) sequences, which are used for PRACH and PUCCH (refer to PUCCH format 1 and format) in 5G, this paper proposes new mechanisms of CM reduction for PRACH and PUCCH with the repeated sequence in frequency domain considering the design principles to ensure the sequence performance of the auto-correlation and cross-correlation for CAZAC sequence-based PRACH and PUCCH. Then the proposed CM schemes are evaluated and the optimized parameters for the proposed CM schemes are further provided considering CM performance and the complexity.
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