 i.e. 2, 4, 8, and 16, allows an effective multimode base transceiver station (BTS) implementation with LTE. If the subcarrier spacing (15 kHz) and symbol duration used in LTE are unchanged, and only the number of subcarriers is increased, a very large FFT size in the receiver and transmitter side would be the result, which is not desirable either. Further, with higher frequencies, the phase noise would cause the subcarriers to be non-orthogonal, and thus the system performance would be degraded, or not pos- sible at all with higher frequency bands. Also, a shorter symbol duration would not be achieved with the 15 kHz subcarrier spacing. Another approach for enabling shorter latency is the introduction of the mini-slot, which means using allocations as low as 2, 4, or 7 symbols. Besides the latency, the use of the mini-slot will also make dealing with the hybrid beamforming easier, as is explained later in this chapter. The use of higher bands also has impacts from the increased phase noise. The higher the carrier frequency, the more phase noise is generated, as shown in the example depicted in Figure 6.3. Thus, increasing the subcarrier spacing is also a must for the use of OFDM with higher frequencies. In particular, the use of higher-order modulation would be difficult otherwise as the system design would limit the maximum signal-to- noise ratio (SNR) that can be achieved. The CMOS oscillator shown in Figure 6.3, for example, will exhibit seriously degraded performance with 15 kHz subcarrier spacing when going to the 10-30 GHz frequency range. For this, 5G deployments with sub-6 GHz bands will use 15 or 30 kHz subcarrier spacing, while the bands above 24 GHz will use 120 kHz subcarrier spacing. The 240 kHz subcarrier spacing is only for L1 control information, as covered later in this chapter. All this will naturally drive the use of higher subcarrier spacing with shorter symbol duration with 5G radio design. Due to the large range of spectrum to be covered with 5G, a single numerology cannot serve all the cas