FMT/FBMC (Filtered multitone based filter bank multicarrier)

Filtered Multitone-Based Filter Bank Multicarrier (FMT/FBMC) is a type of multicarrier modulation technique that has gained significant attention in recent years due to its potential advantages over other multicarrier techniques such as Orthogonal Frequency Division Multiplexing (OFDM). In FMT/FBMC, the transmitted signal is divided into multiple subcarriers using a filter bank, and each subcarrier is modulated with a unique data signal. The subcarriers are then combined to form the final transmitted signal.

The primary advantage of FMT/FBMC over OFDM is its ability to reduce out-of-band radiation (OBR). OBR is a problem that arises in multicarrier techniques due to the overlap of the subcarrier spectra. In OFDM, the subcarriers are orthogonal to each other, which allows for simple demodulation but also causes high OBR. In contrast, FMT/FBMC uses a filter bank that employs overlapping filters to reduce the OBR. This technique allows for a better spectral efficiency since it reduces the amount of spectral guard bands required to prevent interference with adjacent channels.

The FMT/FBMC technique can be divided into two main parts: the filter bank and the modulation scheme. In the filter bank, the transmitted signal is divided into multiple subcarriers using a bank of filters. The filters used in the FMT/FBMC filter bank are typically designed to have a finite impulse response (FIR) and have overlapping spectra to reduce OBR. The number of filters in the filter bank and the bandwidth of each filter determines the number of subcarriers and the subcarrier spacing, respectively. The subcarriers are then modulated using a unique data signal.

In FMT/FBMC, the modulation scheme used is typically quadrature amplitude modulation (QAM) or phase shift keying (PSK). The modulation scheme used for each subcarrier can be different, which allows for adaptive modulation based on channel conditions. In FMT/FBMC, each subcarrier is modulated with a unique data signal. The data signals used for each subcarrier are typically derived from the original data signal using a technique called subcarrier mapping. Subcarrier mapping involves mapping a portion of the original data signal to each subcarrier. The mapping technique used in FMT/FBMC is typically designed to minimize interference between subcarriers and maximize spectral efficiency.

The demodulation process in FMT/FBMC is similar to that used in OFDM. The received signal is divided into subcarriers using a filter bank, and each subcarrier is demodulated using a unique demodulation scheme. In FMT/FBMC, the demodulation scheme used is typically either QAM or PSK. The demodulated data signals from each subcarrier are then combined to recover the original transmitted signal. The demodulation process in FMT/FBMC is typically more complicated than in OFDM due to the use of overlapping filters in the filter bank.

One of the main advantages of FMT/FBMC over OFDM is its ability to support non-contiguous spectrum allocation. In wireless communications, the available spectrum is typically divided into multiple non-contiguous frequency bands. OFDM cannot be used in such situations since it requires a contiguous frequency band. FMT/FBMC, on the other hand, can be used in non-contiguous spectrum allocation since it uses a filter bank that can be designed to support non-contiguous frequency bands.

Another advantage of FMT/FBMC over OFDM is its ability to support time-varying channels. In wireless communications, the channel conditions can vary rapidly due to changes in the environment. OFDM is sensitive to time-varying channels since it assumes a static channel. FMT/FBC, on the other hand, is designed to handle time-varying channels by using overlapping filters in the filter bank. The overlapping filters provide robustness against multipath fading and time-varying channels. This makes FMT/FBMC a suitable technique for use in mobile communications.

FMT/FBMC also has better energy efficiency compared to OFDM. In OFDM, the subcarriers are transmitted with equal power, which can lead to a high peak-to-average power ratio (PAPR). This requires the use of complex power amplifiers with high linearity, which are expensive and consume a lot of power. In FMT/FBMC, the subcarriers are transmitted with variable power, which reduces the PAPR and allows for the use of simpler power amplifiers.

There are different variants of FMT/FBMC, which differ in the design of the filter bank and the modulation scheme used. Some of the variants of FMT/FBMC include:

1. Offset QAM FMT/FBMC: This variant uses offset QAM as the modulation scheme and is designed to reduce OBR and improve spectral efficiency.
2. Filtered Multi-Input Multi-Output (F-MIMO) FMT/FBMC: This variant uses multiple antennas at the transmitter and receiver to increase the system capacity and improve the robustness against fading.
3. FBMC-OQAM: This variant uses offset QAM modulation and a filter bank with overlapping filters to reduce OBR and improve spectral efficiency.
4. Universal Filtered Multi-Carrier (UFMC): This variant uses a filter bank with non-overlapping filters and is designed to provide a smooth transition from 4G to 5G wireless systems.

In conclusion, FMT/FBMC is a multicarrier modulation technique that has gained significant attention in recent years due to its potential advantages over OFDM. FMT/FBMC reduces out-of-band radiation, supports non-contiguous spectrum allocation, and handles time-varying channels better than OFDM. FMT/FBMC is also more energy-efficient than OFDM and supports adaptive modulation. There are different variants of FMT/FBMC, which differ in the design of the filter bank and the modulation scheme used.