4096 IFFT 120 kHz 512 IFFT 1024 IFFT 2048 IFFT 4096 IFFT Table 4.3. FFT length according to the 5G bandwidth and SCS 4.1.4. NR frame structure in the time domain The downlink and uplink transmissions are organized into frames of 10 ms duration, each divided into 10 1 ms subframes. Each frame is also divided into two half-frames of size equal to five subframes: - half-frame 0 is made up of subframes 0-4; - half-frame 1 is made up of subframes 5-9. For the LTE interface, the subframe is made up of two time slots. For the NR interface, the number of time slots (slots) constituting the subframe depends on the spacing between the subcarriers (Table 4.4). For the LTE interface, the value of the Interval Transmission Time (ITT) corresponds to the duration of the subframe and has a fixed value of 1 ms. For the NR interface, the slot duration has a value that depends on the frequency spacing between the subcarriers (Table 4.4). Subcarrier Number of slots Number of slots subspacing per subframe per frame 15 kHz 30 kHz 0.5 ms 60 kHz 0.25 ms 120 kHz 0.125 ms 240 kHz 0.0625 ms Table 4.4. Structure of the NR frame in the time domain 5G-NR Radio Interface - The Physical Layer One Frame = 10 ms One sub-frame = 1 ms One slot = 1 ms, SCS= 15 kHz One slot = 0.5 ms, SCS= 30 kHz One slot = 0.25 ms, SCS= 60 kHz One slot = 0.125 ms, SCS= 120 kHz One slot = 14 symbols Figure 4.3. Time structure of the 5G-NR frame To avoid interference between two symbols, the OFDM modulator inserts a symbol replica at the start of each symbol. This replica constitutes the Cyclic Prefix (CP) and occupies a fixed percentage in each time slot. For the 5G-NR access interface, there are two types of prefix (Table 4.5): - the normal cyclic prefix, which applies to all numerologies; - the extended cyclic prefix, which only applies for the numerology = 2. The extended cyclic prefix improves the robustness of communication in a time dispersive channel, but reduces spectral efficiency. For the LTE interface, a slot lasts 0.5 ms and includes seven OFDM symbols for