  The underlying waveform has always been a shaping factor for each generation
of the cellular networks, such as orthogonal frequency division multiplexing
(OFDM) for the 4th generation cellular networks (4G). To meet the diversified
and pronounced expectations upon the upcoming 5G cellular networks, here we
present an enabler for flexible waveform configuration, named as filtered-OFDM
(f-OFDM). With the conventional OFDM, a unified numerology is applied across
the bandwidth provided, balancing among the channel characteristics and the
service requirements, and the spectrum efficiency is limited by the compromise
we made. In contrast, with f-OFDM, the assigned bandwidth is split up into
several subbands, and different types of services are accommodated in different
subbands with the most suitable waveform and numerology, leading to an improved
spectrum utilization. After outlining the general framework of f-OFDM, several
important design aspects are also discussed, including filter design and guard
tone arrangement. In addition, an extensive comparison among the existing 5G
waveform candidates is also included to illustrate the advantages of f-OFDM.
Our simulations indicate that, in a specific scenario with four distinct types
of services, f-OFDM provides up to 46% of throughput gains over the
conventional OFDM scheme.
