the subcarriers are shifted by half a subcarrier such that the DC spur falls between two subcarriers and thus can be easily cancelled at the receiver without affecting the data associated with the adjacent subcar- riers. In LTE, this shift does not exist, and the DC spur falls on a subcarrier that does not carry data. This shift results in a small asymmetry, and together with the variable SU, results in a variable minimum guard band as shown in the last set of rows. This one is defined using the half subcarrier shift on the lowest valid SCS, and higher SCSs are 12.3 5G Standalone Performance Aspects in Frequency Range 1 Table 12.3 Maximum power reduction (MPR) for power class 2 and 3. Edge RB allocations Outer RB Inner RB Modulation (PC2 only) allocations allocations PI/2 BPSK 16-QAM 64-QAM 256-QAM 16-QAM 64-QAM 256-QAM aligned such that the first subcarrier of all RBs is aligned within all the valid SCSs. This alignment is needed to ensure that multiple signals using different SCSs can be received within the same FFT process. 12.3.2 Impact of Large Channel Bandwidths on PA Efficiency Enhancement Techniques In LTE, a number of power amplifier efficiency enhancement techniques have been developed to increase the phone battery life. There are mainly two techniques that are implemented which both use a DC/DC converter to provide the supply to the power amplifier: The DC/DC converter voltage follows the power level requested at the power ampli- fier output. This technique is called adaptive power tracking (APT). The DC/DC con- verter only needs to dynamically follow the Transmit Power Control (TPC) requests and thus use relatively low switching frequencies and achieve efficiencies >90%. The power amplifier still relies on its intrinsic linearity, but its supply is adjusted to the minimum voltage needed. The DC/DC converter output voltage follows the envelope of the RF signal fed at the power amplifier output. This technique is called envelope tracking (ET). In this case, the DC/DC converter needs to support a bandwid