ximum likelihood estimator to estimate carrier frequency offset (CFO) and symbol timing. This is equivalent to long preamble in OFDM. Moreover, in [20], it is noted that the use of a short preamble, similar to that of OFDM, may be useful for coarse estima- tion of carrier, SO that fine-tuning of carrier and timing phase based on the long preamble can be established more robustly. Distributed pilots to track channel variations in payload part of FBMC packets have also been proposed [23, 24]. In the rest of this section, we review these methods in some detail. 5.5.1 Preamble Design Figure 5.8 presents the packet format that has been proposed in [20-22, 25, 26]. The short preamble consists of a few tones with wider separation than the subcarrier spacing, to allow detection of large CFO values. It is used to obtain a coarse estimate of the CFO, SO that the residual CFO (after removal of the estimated CFO) will be within the range of half symbol spacing. The long preamble, then, may be used for fine-tuning the carrier. The works presented in [21, 25, 26] do not mention the short preamble, but they make assumption that CFO is within the range of half symbol spacing. Naturally, to satisfy this assumption a mechanism similar to short preamble may be necessary. There is also some difference in the long preamble proposed in [21, 25, 26] and the one proposed in [20, 22]. In the context of SMT waveform, the long preamble proposed in [21, 25, 26] is constructed based on a set of complex-valued pilot symbols that occupy all subcarriers. The long preamble proposed in [20, 22], on the other hand, is real-valued and only occupies the alternate subcarriers; the other subcarriers are left empty. This modification/simplification of the long preamble, as demonstrated through numerical results in [22], improves the accuracy of the CFO estimates significantly. Here, to make suggestions to further improve the preamble design, we first note that the preamble is a packet component that constitutes a loss in the bandwidth efficiency of Sho