Uplink coverage in cellular networks is constrained by the maximum UE transmit power, making peak-to-average power ratio (PAPR) reduction essential. While DFT-s-OFDM with frequency-domain spectral shaping (FDSS) achieves significantly lower PAPR than OFDM, especially with pi/2-BPSK, the PAPR remains too high for higher-rate transmission. Spectrum extension (SE) combined with FDSS (FDSS-SE) can further reduce the PAPR for higher-order QAM. This paper considers FDSS-SE with parametrized FDSS windows spanning a range of possible power ripples, as well as arbitrary circular shifts of the subcarrier coefficients. We optimize both the frequency shift and the SE size, and show that there exists an optimal SE size for reducing the PAPR and another one for increasing the rate. Analysis and simulations reveal that both optima largely depend on the window attenuation but are nearly invariant in proportion to the bandwidth. While the PAPR-optimal SE size is nearly invariant to the constellation order of regular QAM, the rate-optimal SE size depends also on the SNR. These insights provide practical guidelines for beyond-5G uplink coverage enhancement, highlighting that SE size should be individually configured according to the user's FDSS window and link quality.

翻译：蜂窝网络的上行链路覆盖受限于用户设备的最大发射功率，因此降低峰均比至关重要。虽然采用频域频谱成形的 DFT-s-OFDM（特别是结合 π/2-BPSK 调制）的峰均比显著低于 OFDM，但对于更高速率的传输，其峰均比仍然过高。频谱扩展与频域频谱成形相结合可以进一步降低高阶 QAM 调制的峰均比。本文研究了参数化频域频谱成形窗（覆盖一系列可能的功率波动）以及子载波系数的任意循环移位下的频域频谱成形-频谱扩展方案。我们同时优化了频移量和频谱扩展大小，并证明存在一个用于降低峰均比的最优频谱扩展大小和另一个用于提升速率的最优频谱扩展大小。分析与仿真表明，这两个最优值在很大程度上取决于频谱成形窗的衰减特性，但几乎与带宽成比例不变。虽然峰均比最优的频谱扩展大小对常规 QAM 的调制阶数几乎不变，但速率最优的频谱扩展大小还取决于信噪比。这些发现为 5G 之后的上行链路覆盖增强提供了实用指导，强调应根据用户的频域频谱成形窗和链路质量单独配置频谱扩展大小。