# Review of Channel Estimation for Candidate Waveforms of Next Generation Networks
## 3 Fundamentals of Channel Estimation
### Channel Estimation for Filter Bank GFDM  
Channel estimation for filter bank GFDM is a new research area waiting to be exploited, especially in filter bank GFDM-OQAM. Very little research has been carried out in this area in terms of developing algorithms for estimating the channel fading. In fact, to the best of the authors' knowledge, no CE algorithm has been proposed in the literature for filter bank GFDM-OQAM. As such, more work can be done in this research area in order to effectively estimate the channel distortion, in particular, adopting the semi-blind and blind based CE techniques. Nevertheless, we classify the techniques adopted to estimate the channel distortion in filter bank GFDM in Figure 14. The classification is based on the general knowledge of CE techniques. Moreover, we summarise some of the CE technique adopted in filter bank GFDM in Table 4.  
Figure 14: CE schemes for conventional GFDM. \begin{table}
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**Reference** & **Aim of Research** & **CE Schemes Applied** & **Applicable Technique or Waveform** & **Approach** & **Obtained Results** \\ \hline \multirow{9}{*}{[51]} & Modification of GFDM systems for CE using orthogonal pilot insertion method for interference free CE & Interference free pilot insertion (IPT) based CE & Pilot-assisted CE for GPDM transceivers & Insertion of pilot subsymbols such that received symbol frequency domain at pilot frequencies have no influence from the data subsymbols for IFPI CE & \multirow{9}{*}{**Approach**} & \multirow{9}{*}{**Obtained Results**} \\ \cline{1-1} \cline{5-5}  & Reduced complexity CE for BFDM-OQAM transceivers in dispersive time-varying channels & Training-based CE for BFDM-OQAM & ML based CE for BFDM-OQAM based transceivers & ML CE based on use of correlation matrix & Proposed estimator offers significant robustness against Doppler spread \\ \hline \multirow{9}{*}{[113]} & CE for IFMC based transceivers using FIR pre-compensation and SW approach & Pilot-aided CE for UFMC systems & LS and LMMSE based approach for UFMC systems & Training-based CE by FIR filter pre-compensation at transmitter performing of obtained raw channel estimate using SW approach & UFMC achieves the same or slightly better SER performance under AWCN and frequency/flat fading vehicular-A channels in comparison to CF  
\begin{table}
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In [126], two novel pilot based CE methods (pilot interference cancellation (Pilot-IC) and transmitter interference cancellation (Tx-IC) are proposed for estimating the fading channel coefficients for GFDM based transceivers with QAM modulation (GFDM-QAM). In Pilot-IC, interference is only pre-cancelled at pilot symbols while interference is simultaneously pre-cancelled at both pilot and data symbols for Tx-IC. These estimation algorithms are realised with scattered pilots over time and frequency grid, thereby ensuring a reduction in overhead. Thus, this makes it possible to estimate the channel fading over frequency selective and time-varying channels. The performances of the two proposed CE schemes are analysed in terms of MSE and un-coded BER for time-invariant frequency selective pedestrian B (PB) channels, where pilot symbols are scattered over the sub-carriers of one GFDM symbol with interpolation performed in the frequency domain. Moreover, in [126], the CE performances of the two proposed algorithms are compared with the CE performance of conventional OFDM. The initial results obtained show that the two proposed algorithms demonstrate the same MSE performance and comparable performance with OFDM. The performances of both CE techniques are analysed for matched filtering (MF) and zero forcing (ZF) receivers using the same PB channel. It is observed from the un-coded BER performances that both pilot-IC and Tx-IC have the same BER performance, which is also comparable to OFDM systems.