UE in order to ensure uplink frame synchronization where NTA-offset depends on the frequency band of operation [18]. It can be seen that for the 15-kHz subcarrier spacing, Chapter 3 Cell size Latency 15 kHz 15 kHz 30 kHz 30 kHz 15 kHz 30 kHz 120/240 30 kHz 60 kHz 60 kHz 60 kHz Medium Very high Frequency Figure 3.43 Relationship of numerology, carrier frequency, latency, and cell size [53]. Downlink frame Uplink frame TTA = (N TA + N TA-offset 3GPP 38.133 Table 7.1.2-2 Frequency range of uplink transmission NTA-offset (XT) Timing advance from FR1 FDD band without LTE-NR coexistence case or FR 1 25,600 MAC CE or RAR TDD band without LTE-NR coexistence case message FR1 FDD band with LTE-NR coexistence case FR1 TDD band with LTE-NR coexistence case 39,936 or 25,600 13,792 NTA 16.64T /2" TA=0, 1,..., 3846 (From RAR message) T = 509 ns NTA-new = NTA-old + (T -31)16.64/2 T=0, 1,..., 63 (From MAC CE) Figure 3.44 Illustration of uplink timing calculation in NR [ [12,39]. New Radio Access Physical Layer Aspects (Part 1) 387 an NR slot has the same structure as the LTE subframe, which is important for supporting LTE/NR coexistence scenarios. In the case of co-located deployment, slot and frame structures may be aligned to simplify cell search and inter-frequency measurements [9,16,17,19]. Coordination of control signals and channels in time domain will also be possible to avoid inter- ference between LTE and NR. Given that a slot is defined as a fixed number of OFDM sym- bols, a larger subcarrier spacing results in a shorter slot duration, which can be used to support low-latency applications. 3GPP NR further supports a more efficient approach to low-latency transmissions by allow- ing scheduling shorter slot sizes known as mini-slots (see Fig. 3.42). The mini-slot-based transmissions can also preempt an already ongoing slot-based transmission to another device, allowing immediate transmission of application data requiring very low latency. Mini-slots can be used for low-latency applications such as URLLC and operation in u