While the cyclic prefix creates a guard period in time domain to preserve orthogonality, an
OFDM symbol rarely begins with the same amplitude and phase exhibited at the end of the
prior OFDM symbol causing spectral regrowth and therefore, spreading of signal bandwidth
due to intermodulation distortion. To limit this spectral regrowth, it is desired to
create a smooth transition between the last sample of a symbol and the first sample of
the next symbol. This can be done by using a cyclic suffix and raised cosine
windowing.

To create the cyclic suffix, the first *N*_{WIN} samples
of a given symbol are appended to the end of that symbol. However, in order to comply
with the 802.11g standard, for example, the length of a symbol cannot be arbitrarily
lengthened. Instead, the cyclic suffix must overlap in time and is effectively summed
with the cyclic prefix of the following symbol. This overlapped segment is where
windowing is applied. Two windows are applied, one of which is the mathematical inverse
of the other. The first raised cosine window is applied to the cyclic suffix of symbol
*k* and decreases from 1 to 0 over its duration. The second raised
cosine window is applied to the cyclic prefix of symbol *k*+1 and
increases from 0 to 1 over its duration. This process provides a smooth transition from
one symbol to the next.

The raised cosine window, *w*(*t*), in the time domain can
be expressed as:

where:

Adjust the length of the cyclic suffix via the window length setting property, with suffix lengths set between 1 and the minimum cyclic prefix length. While windowing improves spectral regrowth, it does so at the expense of multipath fading immunity. This occurs because redundancy in the guard band is reduced because the guard band sample values are compromised by the smoothing.

The following figures display the application of raised cosine windowing.