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the NB-IoT transmission scheme is the same as that of 4G Long-Term Evolution (LTE), which uses OFDMA for the downlink (DL) signal. Figure shows the NB-IoT DL signal frame structure, in which one radio frame consists of 10 subframes with a duration of 1 ms and each subframe consists of 14 OFDM symbols. For each OFDM symbol, 12 subcarriers spaced by 15 kHz can carry either a Zadoff–Chu synchronization signal (NPSS/NSSS) or a system/user information data channel (NPBCH/NPDCCH/NPDSCH) in QPSK modulation. Hence, the nominal DL signal bandwidth is 180 kHz, which coincides with that of the LTE resource block, and the baseband sampling rate of the generated I/Q signal samples is Fs = 1.92 Msps. In order to conform to the real application scenario, this paper will follow the 3GPP specification to generate the above gNB signals/channel for this research.
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IEEE/ICACT20230155 Slide.06
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