2K. NR numerology The subcarrier spacing is scalable to the power of 2 of 15 kHz in NR. This is called numerology and it is represented with u. The subcarrier spacing is fixed at 15 kHz only in LTE. The reason to choose the subcarrier spacing as multiples of 15 kHz is to allow for better coexistence between LTE and NR. It would be much more difficult if a different carrier spacing was selected. Having different subcarrier spacings allows support for services with different International Mobile Telecommunications (IMT) 2020 requirements, from high-reliability use cases to low-latency use cases. 3GPP Release 15 supports the following numerologies for NR. 5G Air Interface and Physical Layer Procedures - Part 1 Af = 2H '15[kHz] Cyclic prefix Normal Normal Normal, Extended Normal Normal Figure 4.13 - Supported transmission numerologies for NR Release 15 supports subcarrier spacings of 15, 30, 60, 120, and 240 kHz with the numerologies 0, 1, 2, 3, and 4 respectively. The phase noise at high-frequency bands such as Millimeter Wave (mmWave) is bigger than the typical phase noise that lower frequencies experience. One of the main ways to mitigate this increased phase noise is to use larger subcarrier spacing. As a result, 15 and 30 kHz will be used for synchronization broadcast transmissions below 6 GHz, whereas 15, 30, and 60 kHz will be used for data transmissions below 6 GHz. Note that 60 kHz subcarrier spacing for below 6 GHz is optional for devices. For frequency bands above 6 GHz, 120 and 240 kHz will be used for synchronization and broadcast, and above 60 kHz and 120 kHz for data transmission. A single cyclic prefix length is supported in all cases. However, normal and extended cyclic prefix lengths can be included for 60 kHz subcarrier spacing. In the future, specifications will include the data transmission at 240 and 480 kHz for forward- compatibility purposes. We might also see 3.75 kHz subcarrier spacing in the future as new cases are introduced. Illustration of numerologies The following figure shows an examp