e the subcarrier filtering is performed in the time domain by modifying the rectangular pulse shape of CP-OFDM to have smoother transitions in time at both ends. In an alternative approach known as subband filtering, the PSD of the entire subband is made well-localized without changing the CP-OFDM symbol's rectangular pulse. For this purpose, the subband CP-OFDM signal is passed through a frequency-localized filter whose bandwidth is close to the size of the subband. As a result, only a few subcarriers close to edges of the subband in frequency domain are affected by the filter, as the filter suppresses their out-of-subband side-lobes. This leads to F-OFDM signal generation. A key property of this approach is that the filter length can exceed the CP length, which allows better frequency localization than the subcarrier-based approach without causing any ISI. Although the subcarrier-based approach provides a lower complexity, it cannot achieve the frequency localization Subband 1 IFFT with Spectrum input subcarrier CP 1 insertion shaping filter symbols spacing 1 h1(n) hi(n) Subband 2 IFFT 2 with Spectrum input subcarrier CP 2 insertion shaping filter Spectrum FFT k with Subband k symbols spacing 2 h2(n) shaping filter CP k removal subcarrier hk(n) spacing k detection Subband N IFFT N with Spectrum input subcarrier insertion shaping filter symbols spacing N hn(n) Transmitter Receiver Figure 3.18 Illustration of transmit/receive processing for frequency-localized OFDM-based waveforms 49]. New Radio Access Physical Layer Aspects (Part 1) 337 performance of the subband-based approach, and further causes ISI in multipath channels with large delay spread. A combination of the two approaches can provide a tradeoff between complexity and frequency localization. In particular, in the latter approach, the CP- OFDM signal of each subband is first subcarrier-filtered with an excess window length smaller than that of the original subcarrier-based approach. Then, the windowed signal is subband filtered with a filter length smal