 ing techniques, other types of precoding matrices often have undesirable complexity and compatibility issues. PAPR is one of the often-mentioned disadvantages of OFDM waveform. In practice, the crest factor reduction (CFR) techniques are applied to reduce the PAPR and digital predis- tortion algorithms will then correct for any distortion caused by the analog hardware used 348 Chapter 3 to amplify the signal. Both techniques will allow more efficient PA design and help mitigate major limitations of PAPR and spectral regrowth. Traditionally these techniques were only applied at the base station side, but currently, they are also used in mobile devices, mainly from the aspect of reducing power consumption. The use of envelope tracking 14 to reduce the static power consumption is an example of such techniques. Fig. 3.27 compares the PAPR performance of the prominent waveforms and shows that despite additional com- plexity and latency, the relative PAPR performance of multicarrier techniques remains about the same as OFDM and inferior to DFT-S-OFDM [47]. In the spectrum of rectangular pulse (i.e., a sinc function), besides the desired peak, there are some side-lobes that result in a theoretical infinite bandwidth of the rectangular pulse function, causing OOB emissions. Moreover, consecutive OFDM symbols are independent of each other; thus there is an inherent discontinuity in the time domain between them. In this way OFDM differs from single-carrier modulated signals after digital filtering. This dis- continuity translates into spectral spurs in the frequency domain. This typical characteristic can be improved by applying time-domain windowing that smooths out the transition from one symbol to another. However, this technique introduces an overlap between consecutive symbols that impacts signal quality and results in higher EVM. The transition time defines the duration of the overlap between two symbols. For a sampling rate of 30.72 MHz (20 MHz LTE signal), a transition time of 1 us translates into 30 samples overl