Filter Bank Multicarrier (FBMC) systems are a subclass of multicarrier (MC) systems. While its basic principle, dividing frequency spectrum into many narrow subchannels, may not be new, MC systems have seen wide adoption in recent years (LTE, WLAN).

Cyclic Prefix based Orthogonal Frequency Division Multiplexing (CP-OFDM) is certainly the most researched and popular type of MC. Channel estimation and equalization become trivial tasks thanks to the high-performance digital signal processors (DSPs) available on the market. With the insertion of some redundancy (Cyclic Prefix, or CP), the frequency selective propagation channel becomes a frequency flat subchannel. The disadvantage of CP-OFDM when compared to other MC modulation schemes is a loss in spectral efficiency due to CP insertion,  higher out-of-band radiating (since the subcarriers have sync-like frequency behavior), and a higher sensitivity to narrowband interferers.

FBMC methods have their roots in the pioneering works of Chang

[1] and Saltzberg [2] who introduced multicarrier techniques over two decades before the introduction and application of OFDM to wireless communication systems. A general overview of the FBMC system model is shown in Figure 2. FBMC modulation can be considered as an evolved OFDM. The filter banks address the main disadvantages of OFDM mentioned above. First, their subchannels can be optimally designed in the frequency domain to have desired spectral containment. Second, FBMC systems do not require redundant CP and thus are more spectral efficient.

 Figure 1: OFDM transmitter

Figure 1: OFDM transmitter

Figure 2: Filter Bank based Multicarrier (FBMC) transmitter

Figure 2: Filter Bank based Multicarrier (FBMC) transmitter

With high enough out-of-band attenuation of the sub-band filters, the filter bank itself can provide sufficient frequency isolation to implement the needed reception and selectivity. This enables you to move all signal processing functions after the filter bank to the low sampling rate.

In the multiuser context, the subchannels or groups of subchannels allocated to the users are spectrally separated as soon as an empty subchannel is present in-between. Therefore, users do not need to be synchronized before they gain access to the transmission system. This is a very important factor for uplink in traditional base station-centric networks or in future dynamic spectrum access systems. In cognitive radio, FBMC offers the possibility to simultaneously carry out spectrum sensing and transmission functions with the same device .

As a multicarrier scheme, FBMC can benefit from multi-antenna systems. MIMO techniques can also be applied. Further research is still required in this area, however.

One example of a research project that studies FBMC in 5G applications is 5GNow [3]. Another one, already finished, was Physical Layer for Dynamic Spectrum Access and Cognitive Radio (PHYDAS) [4] [5], which explored FBMC as a new concept for dynamic access spectrum management and cognitive radio applications.

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References:

[1] R. Chang, “High-speed multichannel data transmission with bandlimited orthogonal signals,” Bell Sys. Tech. J., vol. 45, pp. 1775–1796, Dec. 1966.[2] B. Saltzberg, “Performance of an efficient parallel data transmission system,” IEEE Transactions on Communication Technology, vol. 15, no. 6, pp. 805–811, 1967.[3] 5GNow project: http://www.5gnow.eu/[4] FBMC physical layer : a primer, http://www.ict-phydyas.org/[5] FBMC physical layer – principle, Maurice Bellanger, http://www.ict-phydyas.org[6] Tobias Hidalgo Stitz, “Filter Bank Techniques for the Physical Layer in Wireless Communications”, Tampere University of Technology, 2010