ACM & Multiple Access
- FBMC
As cellular IoT has been one of key driving forces
to 5G, spectrally efficient support for heterogeneous
services that have quite different requirements
is becoming ever so important. Accordingly, several
enabling methods such as multi-RAT coexistence
and flexible spectrum sharing have been actively
investigated.
Recently, FBMC has drawn much attention as an
enabling technology for enhancing the fundamental
spectral efficiency, though its theory has a long history
similar to that of Orthogonal Frequency Division
Multiplexing (OFDM).
Because of the well-localized time/frequency traits
adopted from a pulse shaping filter per subcarrier,
the FBMC system can reduce the overhead
of guard band required to fit in the given spectrum
bandwidth, while meeting the spectrum mask requirement.
Furthermore, the effectively increased symbol duration
is suitable for handling the multi-path fading
channels even without Cyclic Prefix (CP) overhead.
Consequently, the FBMC system can reduce the inherent
overheads such as CP and guard-bands in
CP-OFDM. FBMC is also attractive in specific asynchronous
scenarios, including Coordinated Multi-
Point Transmission and Reception (CoMP) and
Dynamic Spectrum Access (DSA) in a fragmented
spectrum.
However, to maintain the transmission symbol rate,
the conventional FBMC system generally doubles
the lattice density either in time or in frequency compared
with OFDM while adopting Offset Quadrature
Amplitude Modulation (OQAM). In OQAM, inphase
and quadrature-phase modulation symbols
are mapped separately with half symbol duration
offset. Thus, so-called OQAM-FBMC or Staggered
Multi-Tone (SMT) causes intrinsic interference that
makes it difficult to apply conventional pilot designs
and corresponding channel estimation algorithms
as well as MIMO schemes as in CP-OFDM systems
[22].
With a base-filter that takes the spectrum confinement
and the orthogonality among adjacent subcarriers
into consideration, the QAM-FBMC system
performs comparable to the CP-OFDM system
even without the CP overhead, while the guard-
band overhead reduction is also available from the
well-confined spectrum. Sophisticated receiver algorithms
including channel estimation and equalization
can further mitigate the multi-path fading
channel impact without the CP.