In OFDM, what is the length of the cyclic suffix that is added before windowing?
You, as the designer of an OFDM system, define the length of the CP based on your requirements.

The main requirements are:


Long enough to "swallow" the duration of the longest expected channel impulse response to inhibit ISI / make the linear convolution channel effect look like a circular convolution
Not longer than necessary, since it "wastes" transmit time, and thus reduces data rate
(optional, depending) in a length that allows for efficient synchronization (e.g. via Schmidl&amp;Cox)


So, there's no single answer to this. The answer is:


  It depends, and when you've fully understood the reason why we use CP in OFDM systems, this will become very much more intuitive.