Filters used in FBMC On page 137, chapter 5 in the book titled 5G Physical Layer: Principles, Models and Technology, the author says:

An important attribute of the FBMC waveforms is that they typically do
not employ any CP or GI, unlike the OFDM-based waveforms. The
prototype filters in the FBMC waveforms have long decaying tails which
can make them robust to the ISI caused by frequency-selective channels

Question: Why would filter long decaying tails make a signal robust to ISI caused by frequency selectivity?
long decaying tails which can make them robust

Why would filter long decaying tails make a signal robust

can make them robust, not makes them robust!
You need a long filter length for narrow bandwidth and steep transition width.
So, with a long filter, you can make very narrow subcarrier channels.
Those being narrow, they don't &quot;see&quot; multipath, they only see a flat channel.