d are shown in Figure 2.4, where the ISI represents f-ISI or b-ISI as both have the same power distribution indicated in Figure 2.3. These results provide a direct comparison among subbands with varying width from 1 to 50 RBs. It can be seen that the maximum normalized power remains constant as the width of subband grows. How- ever, this is not the case with the minimum and average normalized power, where both decrease as the subband width increases. This implies that narrower subbands are more prone to in-band interference compared to wider subbands. These features apply to both the ICI and ISIs. Figure 2.5 presents the average effective interference power of six subbands of variable width versus the number of CRs, where Ncp = Ncs = Ncr/2. The effective interference here refers to the sum of the ICI, f- and b-ISI. The effect of CR length for alleviating in-band interference is observed from all these curves. The power of the average effective interfer- ence decreases as the length of CR increases, and it drops under 25 dB for all six subbands when the number of CRs equals the length of the corresponding filter main lobe due to the fact that most of the filter energy is contained in the main lobe. The BER performance of f-OFDM under the AWGN channel is evaluated and plotted in Figure 2.6. The results are presented in two cases, NC cr = 0 in Figure 2.6a and Ncr = 72 Figure 2.6b, each having six curves corresponding to a different subband width and a curve representing the BER of legacy OFDM for a benchmark comparison. Taking into consid- eration the computational complexity at the receiver side, one-tap equalization method is adopted. When the in-band interference is not handled by introducing CR, the performance of f-OFDM, as shown in Figure 2.6a, degrades dramatically compared with OFDM systems. Subband width (RBs) Figure 2.4 Max, min, and average normalized power of ICI/ISI with respect to subcarriers against subbands of different width with N = 1024, Ncr = 0, Np = Na = 512, ap = 0.6, = 0.65; ISI represents eit