ap. Fig. 3.28 shows the ideal case by means of connecting the signal generator directly to a spec- trum analyzer. The idea is to demonstrate the impact of a nonlinear device on the highlighted advantage of 5G waveform candidates, where any nonlinearity will result in a spectral regrowth, and there is a risk that this spectral regrowth may undermine any optimization due to the waveform design. The improved spectral characteristics of the candidate waveforms are clearly visible in the top snapshot. In a second step, a nonlinear amplifier is introduced into the signal path. The top and bottom snapshots in Fig. 3.28 compare the LTE OFDM signal with FBMC, UFMC, and GFDM waveforms under two different conditions. A generic PA, which supports a frequency range of 50 MHz to 4 GHz, is used to demonstrate the effects of nonline- arity on the waveforms. The maximum input power for the PA is 0 dBm, and it has a typical Intermodulation products or spurs can develop within the analog and digital transmitters in combined systems using high-level injection. In some cases spurs can result in suboptimal signal quality or even cause stations to interfere with each other's signals. The term spectral regrowth is used to describe intermodulation products generated when a digital transmitter is added to an analog transmission system. Envelope tracking is an approach to RF amplifier design in which the power supply voltage applied to the RF power amplifier is continuously adjusted to ensure that the amplifier is operating at peak efficiency for power required at each instant of transmission. A conventional RF amplifier is designed with a fixed supply voltage and operates most efficiently only when operating in compression region. Amplifiers operating with a constant supply voltage become less efficient as the crest factor of the signal increases, because the ampli- fier spends more time operating below peak power and, therefore, spends more time operating below its maximum efficiency. New Radio Access Physical Layer Aspects (Part 1) 349 