a bits in parallel QAM- modulated subcarriers using frequency division multiplexing. The carrier spacing is care- fully selected SO that each subcarrier is located on other subcarriers' zero-crossing points in the frequency domain. Although there are spectral overlaps among subcarriers, they do not interfere with each other, if they are sampled at the subcarrier frequencies. In other words, they maintain spectral orthogonality. The OFDM signal in frequency domain is generated through aggregation of NFFT parallel QAM-modulated subcarriers where adjacent subcar- riers are separated by subcarrier spacing 1/Tu. Since an OFDM signal consists of many par- allel QAM subcarriers, the mathematical expression of the signal in time domain can be expressed as follows: (NFFT-1)/2 Siei2nk(t-tg)/Tw k=-(NFFT-1)/2 where x(t) denotes the OFDM signal in time domain, Sk is the complex-valued data that is QAM-modulated and transmitted over subcarrier k, NFFT is the number of subcarriers in frequency domain, Wc is the RF carrier frequency, and Tg is the guard interval or the CP length. For a large number of subcarriers, direct generation and demodulation of the OFDM signal would require arrays of coherent sinusoidal generators which can become excessively complex and expensive. However, one can notice that the OFDM signal is actually the real part of the inverse discrete Fourier transform (IDFT) of the original complex-valued data symbols {sk|k = - (NFFT 1)/2, (NFFT 1)/2}. It can be observed that there are N < NFFT subcarriers each carrying the corresponding data Ak. The inverse of the subcarrier spacing Af = 1/Tu is defined as the OFDM useful symbol dura- tion , which is NFFT times longer than that of the original input data symbol duration. 3.2.1.1 Cyclic Prefix The inclusion of CP in OFDM makes it robust to timing synchronization errors. Robustness to synchronization errors is relevant when synchronization is hard to achieve such as over New Radio Access Physical Layer Aspects (Part 1) 317 the sidelink. It can also be relevant if a