  The next generation of wireless networks will face different challenges from
new scenarios. The main contribution of this paper is to show that Generalized
Frequency Division Multiplexing (GFDM), as a baseline of flexible circular
filtered multicarrier systems, can be used as a framework to virtualize the PHY
service for the upper layers of 5G networks. This framework opens the
possibility to apply software-defined network principles to produce
software-defined waveforms capable of addressing the requirements of future
mobile networks. Hence, a block oriented concept will be used to provide the
modulation service, emulating different flavors of waveforms designed to go
beyond the well-established Orthogonal Frequency Division Multiplexing (OFDM)
principles, in scenarios where they perform best. The virtual physical layer
(PHY) service opens the opportunity to have a fast and dynamic evolution of the
infrastructure, as applications change over time. The presented unified
modulation concept contributes with future research directions to address burst
and continuous transmissions, referencing basic approaches for synchronization
and advanced receiver design that can be exploited in future for the whole
frame structure design and channel estimation strategies.
