ay spreads, sophisticated multi-tap equalizers must be applied. There is no time overlap between subsequent UFMC symbols. The symbol duration Nsub + LF - 1 with Nsub being the FFT size of the IFFT spreaders (the size of the subbands) and LF the length of the filter. Similar to FBMC, in UFMC typically the FFT window size is increased, resulting in a higher implementation complexity. Also in UFMC the insertion of a guard interval or CP is optional. Another feature of the unified frame structure is the usage of multiple signal layers. The users can be separated based on their interleavers as it is done in interleave division multiple access scheme. This will introduce an additional degree of freedom for the system, improve robustness against cross-talk, and help to exploit the capacity of the multiple access channel (uplink) [45]. The comparison of the PSDs of the OFDM and UFMC signals is shown in Fig. 3.22. In the processing of the UFDM signal, a Chebyshev filter with LF = 74 and side-lobe level attenu- ation of 40 dB has been used. Furthermore, we assume NFFT = 1024 and Ng = 0. It is shown that while the relative complexity of UFMC is more manageable than FBMC, the OOB components are significantly more suppressed compared to that of the OFDM signal. An alternative mathematical representation of the UFDM signal generation and processing can be given as follows: [(++ LF - 1),1] [N+LF - 1),1] [N,Nn] [N,1] where N, LF, NSB, and Nn denote the FFT size, the filter length, the number of subbands, and the number of complex QAM symbols, respectively; [n,k] represents the subband index and user number; Fn,k,Vn,k: and Sn,k denote a Toeplitz matrix comprising the filter impulse response, an IDFT matrix corresponding to the subband location, and a symbol matrix, respectively. The above mathematical model is illustrated in Fig. 3.23. Chapter 3 UFMC signal in the frequency domain OFDM signal in the frequency domain FFT bins Figure 3.22 Comparison of OFDM and UFMC signals in the frequency domain [38]. Transmit filter length IFFT 