Orthogonal frequency-division multiplexing (OFDM) has been selected as the basis for the fifth-generation new radio (5G NR) waveform developments. However, effective signal processing tools are needed for enhancing the OFDM spectrum in various advanced transmission scenarios. In earlier work, we have shown that fast-convolution (FC) processing is a very flexible and efficient tool for filtered-OFDM signal generation and receiver-side subband filtering, e.g., for the mixed-numerology scenarios of the 5G NR. FC filtering approximates linear convolution through effective fast Fourier transform (FFT)-based circular convolutions using partly overlapping processing blocks. However, with the continuous overlap-and-save and overlap-and-add processing models with fixed block-size and fixed overlap, the FC-processing blocks cannot be aligned with all OFDM symbols of a transmission frame. Furthermore, 5G NR numerology does not allow to use transform lengths shorter than 128 because this would lead to non-integer cyclic prefix (CP) lengths. In this article, we present new FC-processing schemes which solve or avoid the mentioned limitations. These schemes are based on dynamically adjusting the overlap periods and extrapolating the CP samples, which make it possible to align the FC blocks with each OFDM symbol, even in case of variable CP lengths. This reduces complexity and latency, e.g., in mini-slot transmissions and, as an example, allows to use 16-point transforms in case of a 12-subcarrier-wide subband allocation, greatly reducing the implementation complexity. On the receiver side, the proposed scheme makes it possible to effectively combine cascaded inverse and forward FFT units in FC-filtered OFDM processing. Transform decomposition is used to simplify these computations, leading to significantly reduced implementation complexity in various transmission scenarios. A very extensive set of numerical results is also provided, in terms of the radio-link performance and associated processing complexity.

中文翻译：

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5G 新无线电中频谱增强 CP-OFDM 波形的频域信号处理


正交频分复用 (OFDM) 已被选为第五代新型无线电 (5G NR) 波形开发的基础。然而，需要有效的信号处理工具来增强各种先进传输场景中的 OFDM 频谱。在早期的工作中，我们已经证明，快速卷积 (FC) 处理是一种非常灵活且高效的工具，可用于滤波 OFDM 信号生成和接收器侧子带滤波，例如，对于 5G NR 的混合数字参数场景。 FC 滤波通过使用部分重叠处理块的基于有效快速傅里叶变换 (FFT) 的循环卷积来近似线性卷积。然而，利用具有固定块大小和固定重叠的连续重叠保存和重叠相加处理模型，FC处理块不能与传输帧的所有OFDM符号对齐。此外，5G NR 数字学不允许使用短于 128 的变换长度，因为这会导致非整数循环前缀 (CP) 长度。在本文中，我们提出了新的 FC 处理方案，可以解决或避免上述限制。这些方案基于动态调整重叠周期和外推 CP 样本，这使得即使在 CP 长度可变的情况下也可以将 FC 块与每个 OFDM 符号对齐。这降低了复杂性和等待时间，例如在迷你时隙传输中，并且作为示例，允许在12子载波宽子带分配的情况下使用16点变换，从而大大降低了实现复杂性。在接收器侧，所提出的方案使得在 FC 滤波 OFDM 处理中有效地组合级联逆向和正向 FFT 单元成为可能。 变换分解用于简化这些计算，从而显着降低各种传输场景的实现复杂度。就无线电链路性能和相关处理复杂性而言，还提供了一组非常广泛的数值结果。