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FBMC (Filter Bank Multicarrier)

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Filter Bank Multicarrier (FBMC) is a digital modulation technique that is becoming increasingly popular for use in high-speed communication systems. It is a type of multicarrier modulation technique that uses a bank of filters to transmit information across multiple subcarriers. In this article, we will discuss the working principles, advantages, and disadvantages of FBMC.

Background and History

The development of FBMC technology can be traced back to the early 1980s when it was first proposed as an alternative to the popular multicarrier modulation techniques such as Orthogonal Frequency Division Multiplexing (OFDM) and its variations. Unlike OFDM, which uses orthogonal subcarriers, FBMC employs a bank of overlapping filters that can be designed to be more selective than the orthogonal subcarriers. This allows FBMC to achieve higher spectral efficiency and better performance in frequency selective channels.

Working Principles of FBMC

The basic idea behind FBMC is to use a bank of filters at the transmitter to divide the input signal into multiple subcarriers. Each subcarrier carries a portion of the signal that is modulated using some form of digital modulation technique, such as Quadrature Amplitude Modulation (QAM). At the receiver, a bank of matched filters is used to recover the original signal from the subcarriers.

The filters used in FBMC are designed to have a narrow bandwidth and high selectivity, which means that they can eliminate interference from adjacent subcarriers. In addition, FBMC can be designed to have very low out-of-band emissions, which makes it a good choice for use in crowded frequency bands.

FBMC can be implemented using two different approaches: the Frequency Domain Equalization (FDE) approach and the Time Domain Equalization (TDE) approach.

Frequency Domain Equalization (FDE) Approach

In the FDE approach, the input signal is first divided into multiple subcarriers using a bank of filters. The subcarriers are then modulated using some form of digital modulation technique, such as QAM. At the receiver, a bank of matched filters is used to recover the original signal from the subcarriers. However, since the filters used in FBMC are not orthogonal, there is some inter-carrier interference (ICI) between the subcarriers.

To mitigate the effects of ICI, FDE uses frequency domain equalization to correct for the interference. This involves estimating the channel response in the frequency domain and then using this estimate to compensate for the ICI. This can be done using a variety of techniques, such as zero-forcing or minimum mean square error (MMSE) equalization.

Time Domain Equalization (TDE) Approach

The TDE approach is similar to the FDE approach, but instead of using frequency domain equalization, it uses time domain equalization. In the TDE approach, the input signal is first filtered using a bank of overlapping filters. The filtered signal is then modulated using some form of digital modulation technique, such as QAM.

At the receiver, a bank of matched filters is used to recover the original signal from the subcarriers. However, since the filters used in FBMC are not orthogonal, there is some inter-symbol interference (ISI) between the symbols. To mitigate the effects of ISI, TDE uses time domain equalization to correct for the interference. This involves estimating the channel response in the time domain and then using this estimate to compensate for the ISI.

Advantages of FBMC

FBMC has several advantages over other multicarrier modulation techniques, such as OFDM. These advantages include:

  1. Better spectral efficiency: FBMC can achieve higher spectral efficiency than OFDM due to its ability to use overlapping subcarriers. This means that FBMC can transmit more data in the same amount of bandwidth than OFDM.
  2. Robustness in frequency selective channels: FBMC is more robust than OFDM in frequency selective channels, as the use of overlapping subcarriers allows it to better handle multipath fading and other types of channel distortions.
  3. Low out-of-band emissions: FBMC can be designed to have very low out-of-band emissions, which makes it a good choice for use in crowded frequency bands.
  4. Low latency: FBMC has lower latency than OFDM, as the use of overlapping subcarriers allows it to transmit and receive data in a shorter amount of time.

Disadvantages of FBMC

FBMC also has some disadvantages that need to be considered when designing communication systems. These disadvantages include:

  1. Complexity: FBMC is more complex to implement than OFDM, as it requires the use of a bank of filters and more complex equalization techniques.
  2. Sensitivity to phase noise: FBMC is more sensitive to phase noise than OFDM, as the use of overlapping subcarriers can cause interference between adjacent subcarriers.
  3. High computational requirements: FBMC requires more computational power than OFDM, as the use of a bank of filters and more complex equalization techniques requires more processing power.

Applications of FBMC

FBMC has a wide range of applications in communication systems, including:

  1. Mobile communications: FBMC can be used in mobile communication systems, such as 4G and 5G, to achieve higher spectral efficiency and better performance in frequency selective channels.
  2. Digital Broadcasting: FBMC can be used in digital broadcasting systems, such as DAB and DAB+, to provide high-quality audio and data services.
  3. Wireless LANs: FBMC can be used in wireless LANs to provide high-speed data transmission and better performance in frequency selective channels.

Conclusion

Filter Bank Multicarrier (FBMC) is a digital modulation technique that uses a bank of filters to divide the input signal into multiple subcarriers. FBMC has several advantages over other multicarrier modulation techniques, such as Orthogonal Frequency Division Multiplexing (OFDM), including better spectral efficiency, robustness in frequency selective channels, low out-of-band emissions, and low latency. However, FBMC also has some disadvantages, such as complexity, sensitivity to phase noise, and high computational requirements. FBMC has a wide range of applications in communication systems, including mobile communications, digital broadcasting, and wireless LANs.