  To optimize the use of the spectrum, it is expected that the next generation
of wireless networks (5G) will enable coexistence of newly introduced services
with legacy cellular networks. These new services, like Device-To-Device (D2D)
communication, should require limited synchronization with the legacy cell to
limit the amount of signaling overhead in the network. However, it is known
that Cyclic Prefix-Orthogonal Frequency Division Multiplexing (CP-OFDM) used in
Long Term Evolution-Advanced (LTE-A) is not fit for asynchronous environments.
This has motivated the search for a new waveform, able to enhance coexistence
with CP-OFDM. Namely, it has been widely suggested that new devices could use
OFDM/Offset-Quadrature Amplitude Modulation (OFDM/OQAM) to reduce the
interference they inject to legacy cellular users. However, values of
interference are usually measured at the input antenna of the receiver, based
on the PSD of the interfering signal. We showed in previous works that this
measurement is not representative of the actual interference that is seen after
the demodulation operations. Building on this finding, we provide in this paper
the first exact closed forms of cross-interference between OFDM/OQAM and
CP-OFDM users. Our results prove that using OFDM/OQAM only marginally reduces
interference to legacy users, in contradiction with many results in the
literature.
