f channel, the CFR is well approximated by a constant over the neighbourhood Sm,n [26]. Typically, due to the associated sharp pulse-shaping filters in FBMC, the interference mainly arises from the first-order neighbourhood Sum,n n +1), (m 1, n)}. Upon using the above inherent properties of FBMC systems, the intrinsic interference in P. Singh and E. Sharma (3.23) is well approximated as (3.24) (m,n)Esum, which also implies that R{jIm,n} 2 0. Employing the above result in (3.18), the received symbol , at the FT index (m, ) can be recast as (3.25) Here the term bm,n ==dm,n = + j1m,n is known as virtual symbol, which is the summation of the desired symbol dm,n and the corresponding interference component Im,n. The model in (3.25) is widely popular with the name interference approximation model (IAM) [26], because it utilizes the property that each FBMC symbol interferes with the symbols in its small FT neighbourhood, over which the CFR can be approximated to a constant. With zero mean i.i.d. OQAM symbols, each of power Pd, Im,n has a mean zero and power E[|Im,/2] 2 Pd [27]. Furthermore, the OQAM symbol dm,n and the interference term Im,n are zero mean independent. The virtual symbol bm,n thus has mean zero and power (3.26) Following Fig. 3.2b, one can obtain a reliable estimate of OQAM symbols using the model in (3.25) as follows: (3.27) The function -1 (dm,n) in Fig. 3.2b at the mth subcarrier, by combining the estimated OQAM symbols dm,2n and dm,2n+1, obtains the estimate cm,n of complex- valued QAM symbol as follows m even (3.28) The SISO-FBMC system model discussed above can be easily extended to MIMO with N transmit and Nr receive antennas. Similar to (3.7), the FBMC baseband signal s'[k] at the th transmit antenna is expressed as (3.29) m=0nEZ 3 FBMC: A Waveform Candidate for Beyond 5G where 1 < t < Nt, and d'm,n is an OQAM symbol transmitted by th antenna at the frequency-time point (m,n). The signal at the rth antenna of FBMC receiver is expressed as <r < Nr. (3.30) The scaler hr,[k] above symbolises an Lh-t