  Orthogonal frequency division multiplexing (OFDM) has been widely adopted for
modern wireless standards and become a key enabling technology for cognitive
radios. However, one of its main drawbacks is significant spectral leakage due
to the accumulation of multiple sinc-shaped subcarriers. In this paper, we
present a novel pulse shaping scheme for efficient spectral leakage suppression
in OFDM based physical layer of IEEE 802.11af standard. With conventional pulse
shaping filters such as a raised-cosine filter, vestigial symmetry can be used
to reduce spectral leakage very effectively. However, these pulse shaping
filters require long guard interval, i.e., cyclic prefix in an OFDM system, to
avoid inter-symbol interference (ISI), resulting in a loss of spectral
efficiency. The proposed pulse shaping method based on asymmetric pulse shaping
achieves better spectral leakage suppression and decreases ISI caused by
filtering as compared to conventional pulse shaping filters.
