f subcarriers N = 128 is considered over a type A Rayleigh fading channel for vehicular scenarios that has Lh = 6 taps, with the delay profile (in ns) 0, 310, 710, 1090, 1730, 2510 and power profile (in dB) 0.0, - -1.0, -9.0, - 10.0, - 15.0, -20.0 between the (t,r)th 3 FBMC: A Waveform Candidate for Beyond 5G N = 6 Perf W Imperf W SNR, dB SNR, dB Fig. 3.4 (a) MSE gain of the semi-blind (SB) CSI estimator (perfect Wm) over the pilot-aided LS CSI estimator with N = 128, Z. = 3 and M = N = 2 and (b) MSE comparison of the SB (perfect and imperfect Wm) and LS CSI estimators with Nr = 4, M = N = 2 and Nd = 320 transmit-receive antenna pair. The isotropic orthogonal transform algorithm (IOTA) prototype pulse [15] of duration 4T is used for pulse shaping in FBMC system. Pilot and data symbols are drawn from the real and imaginary parts of 4-QAM symbols. The SNR on each subcarrier is calculated as 2Pd/o2. It can be seen from Fig. 3.4a that the semi-blind CSI estimation technique for 2 X 4 and 2 X 6 MIMO-FBMC systems can be observed to provide MSE gain of 6 dB and 7.78 dB over the pilot only LS CSI estimator, respectively. This happens because the MSE per parameter for the latter does not change with Nr, whereas it decreases with N for the former. This NMSE trend validates the CRLB analysis presented in Section 3.4.3. It is also seen that both SB and LS techniques achieve their respective CRLBs. Figure 3.4b shows the NMSE as a function SNR for the SB and LS CSI estimators. The graphs in the presence of perfect and imperfect knowledge of whitening matrix are marked as Perf Wm and Imperf Wm, respectively. For the Perf Wm case, Wm = Sm m, where SmImQH is obtained using the SVD of the CSI matrix Hm. For the Imperf Wm case, Wm is estimated using the second- order statistical characteristics of Nd = 320 OQAM data symbols. The SB CSI estimator in the presence of imperfect Wm can be seen to perform close to its perfect Wm counterpart. It can also be seen that the NMSE of both the LS and SB techniques with Z = 1 floors at high SNR.