her f-ISI or b-ISI. All curves of the figure are generated from the analytical results. 2.4 Numerical Results 2 RBs 5 RBs 10 RBs 20 RBs 50 RBs Number of CRs Figure 2.5 Average effective interference power with respect to subcarriers VS. number of CRs with N = 1024, Ncr = 0, Np = Na = 512, ap = 0.6, aq = 0.65; the solid black dots indicate the number of CRs equal to the width of the filter main lobe of the corresponding subband. All curves of the figure are generated from the analytical results. f-OFDM (1 RB) f-OFDM (2 RBs) f-OFDM (5 RBs) f-OFDM (10 RBs) f-OFDM (20 RBs) f-OFDM (50 RBs) EbNo (dB) EbNo (dB) Figure 2.6 Error performance for f-OFDM systems under AWGN channel with QPSK modulation. (a) Ncp = = = Moreover, error floors also tend to develop for all subbands. Another interesting observation is that the performance degradation in narrower subbands is higher than that in the wider subbands, again suggesting that narrower subbands suffer more in-band interference. In Figure 2.6b, the BER performance is significantly improved due to the use of the CR. There is still a gap of approximately 2-5 dB, subject to how wide the subband of interest is, which implies that there is still space to improve, especially for narrow subbands. 2 Filtered OFDM: An Insight into Intrinsic In-Band Interference Figure 2.7 Error performance comparison with and without implementation of BwPIC for f-OFDM systems under AWGN channels with QPSK modulation. one-tap equ. (0 CR) ZF(0 CR) MMSE(0 CR) BwPIC (0 CR, 1 Iter) BwPIC (0 CR, 2 Iters) one-tap equ. (24 CR) ZF(24 CR) MMSE(24 CR) BwPIC (24 CRs, 1 Iter) BwPIC (24 CRs, 2 Iters) EbNo (dB) The effect of different approaches to interference suppression is shown in terms of BER performance enhancement in Figure 2.7 with two different CR length setting, Ncr = 0 and Ncr = 24 in a subband of 12 subcarriers. It can be seen that ZF and MMSE have almost the same BER performance in both CR settings. However, the BER performance with the implementation of BwPIC improves significantly compared to the sy