subcarriers and N time symbols. We assume M and N to be powers of two SO that fast Fourier transform (FFT) and its inverse (IFFT) can be deployed for the DFT and IDFT operations, respectively. Table 6.1 summarizes the computational complexity of different modulator/demodulator structures in terms of the number of complex multiplications (CMs). Conventional OFDM-based OTFS modulator/demodulator in [4] includes the fol- lowing operations; SFFT-1/SFFT to take the data from delay-Doppler domain to the time-frequency domain and vice versa, 2D time-frequency windowing, and M-point IFFT/FFT operations for OFDM modulation/demodulation. Based on discussions in Section 6.5, transmit windowing is not considered. Thus, for a fair comparison, only receiver windowing is considered in the complexity analysis here. Implementation of SFFT-1/SFFT block requires M number of N-point IFFT and N number of M-point FFT operations. OFDM modulation/demodulation demands N number of M-point IFFT/FFT operations. Usually, channel-independent window functions are real valued and thus windowing demands number of CMs. Based on the results of Section 6.5, OTFS modulator and demodulator can be efficiently implemented by combining SFFT-¹ and SFFT operations with OFDM modulator and demodulator blocks, respectively. Following this approach, Figure 6.2 shows that imple- mentation of OTFS modulator requires only M number of N-point IFFT operations. Being the dual of the modulator, implementation of OTFS demodulator demands M number of N-point FFT operations with an additional windowing operation over the received OFDM time symbols; see Figure 6.3. To give a more quantitative impression about our complexity analysis and comparisons above, let M = 2048 and N = 8, which are roughly in line with the parameters in the 3GPP LTE systems. In this case, the modem structure that was presented in Section 6.5 is around eight times simpler than the conventional one in [4] while being around 3.5 times simpler than OFDM. Compared with the conventional demodulator in 