on 5.3 suggest that linear phase SR-Nyquist filters that have been widely used for single carrier data transmission are the most trivial choice for prototype filter in FBMC systems. This indeed remains an accurate statement as long as the underly- ing channel is time invariant or varies slowly. However, in cases where the channel is fast varying, a more general class of SR-Nyquist filters that satisfy the Nyquist condition along both the time and frequency axis should be adopted. Taking note of this, here we discuss prototype filter designs for time-invariant and time-varying channels separately. 5.4.1 Prototype Filters for Time-Invariant Channels The classical prototype filter for FBMC systems that was suggested in [3, 4] was the square-root raised-cosine (SRRC) filter. More specifically, both [3, 4] suggested using an SRRC filter with the roll-off factor a = 1. In practice, where FBMC systems are imple- mented in discrete time, SRRC response should be sampled and truncated. The truncation of the SRRC response may result in a filter with poor frequency response, thus making SRRC a poor choice. Advancements in digital filters design have led to very effective methods for designing SR-Nyquist filters for any specified finite length. These designs, two of which are presented here, aim at balancing the stop-band attenuation and the Nyquist property of the designs. Martin [13] has proposed a design method whose goal is to satisfy the Nyquist criterion approximately, while achieving good attenuation in the stopband. A nice property of this method is that when the number of samples per symbol interval is N and the filter length is BN + 1, where B is an integer greater than 1, there are only parameters that need to be found for the optimization of the design. More specifically, the prototype filter is constructed as (5.17) otherwise where the coefficients ko through kB-1 are to be optimized. The optimum choices of the coefficients ko through KB-1' for different values of B, are tabulated in [13] and, also in [14]. More 