carrier frequency offset (CFO) and Doppler * Corresponding Author: Miaowen Wen; teemwwen@scut.edu.cn Radio Access Network Slicing and Virtualization for 5G Vertical Industries, First Edition. Edited by Lei Zhang, Arman Farhang, Gang Feng, and Oluwakayode Onireti. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. 1 ICI Cancellation Techniques Based on Data Repetition for OFDM Systems 1.2 OFDM Principle Consider an OFDM system of bandwidth B. The entire frequency band is divided into N sub- bands, each of bandwidth BN = B/N. Given the channel coherence bandwidth BC satisfying BN << BC < B, which usually holds for a sufficiently large value of N, the frequency-selective fading channel is converted into multiple-frequency flat fading subchannels (or say subcar- riers). This can be also explained in the time domain as follows. The symbol duration of the modulated signal on each subcarrier is given by TN 22 1/BN. When BN << BC, the sym- bol duration TN is much larger than the channel delay spread Tmax max 22 1/Bc, which indicates that each subcarrier experiences flat fading. Therefore, as long as all subcarriers are orthog- onal to each other, high data-rate interference-free parallel transmission can be achieved. How to ensure subcarrier orthogonality and perform the discrete implementation of OFDM will be discussed in detail in this section. 1.2.1 Subcarrier Orthogonality In an OFDM system, the substream on the k-th subcarrier Xk is linearly modulated relative to the subcarrier frequency fk, and the modulated signals associated with all the subcarriers are summed together to form the transmitted signal as (1.1) where kAf with Af representing the subcarrier interval, and fc denot- ing the basic carrier frequency. To ensure orthogonality among all subcarriers, the frequency tones {f, must satisfy the following condition: given any two subcarriers k and p, (1.2) where 0 k, p N - 1. The solution to Eq. (1.2) turns out to be Af = n/Tn, where n is a nonzero integer. The choice of n = 1 is preferred as 