(3.13) can be simplified (3.16) m=0nEZ where (3.17) symbolises channel frequency response (CFR) for the mth subcarrier. The channel h[k] is considered to be quasi-static throughout the chapter. Separating the desired and undesired terms in (3.16), one obtains (3.18) (m,n) Interference 3.3.1 Data Detection To begin with, let the transmission channel be ideal, i.e. h[k] = 8[k]. Thus, the CFR Hm = 1, and it follows from (3.18) that (3.19) (m,n)#(m,n) 3 FBMC: A Waveform Candidate for Beyond 5G It follows from (3.10) that the quantity (m,n)(m,n) dm,n(5)m.n is real in nature. Consequently, OQAM symbol dm,n at the receiver can be estimated as (3.20) In practice, channel h[k] is not ideal. Therefore, as shown in Fig. 3.2b, equalization operation is performed before detecting OQAM symbols. By performing the ZF equalization in (3.18), the estimate of OQAM symbol at the subcarrier m and symbol instant n is (3.21) where the quantity (3.22) (m,n) is called the intrinsic interference in FBMC systems. Since the quantity Hm is complex, n{jlm,n} # 0. The term n{jlm,n} characterises the ISI and inter-carrier- interference (ICI) between the transmitted OQAM symbols. This is unlike OFDM systems wherein the former is suppressed using the CP and the latter is mitigated using the orthogonality among the subcarriers. It sounds difficult to obtain a reliable estimate of the OQAM symbol dm,n at this stage. However, introduction of few approximations by exploiting the inherent properties of FBMC systems leads to a reliable estimate of OQAM symbols as follows. The interference evaluation in (3.22) can be recast as (3.23) where the symbol Sum,n symbolises the neighbourhood of the desired symbol at subcarrier-symbol time index (m, n) by excluding the index (m, ). Since prototype filter p[k] in FBMC is well localized both in frequency and time, the interfer- ence due to the FT points (m,n outside the neighbourhood Sum,n is negligible since mm0[26] Furthermoe since the subcarrier bandwidth is significantly smaller than the coherence bandwidth o