FMT (Filtered multitone)

Filtered Multitone (FMT) is a modulation technique that is used in digital communication systems to transmit data over a channel with high noise levels. It is a type of Orthogonal Frequency Division Multiplexing (OFDM) which uses a bank of filters to divide the available bandwidth into multiple subcarriers.

In this method, the data signal is first divided into several substreams, each of which is modulated onto a specific subcarrier frequency. These subcarriers are then combined to form a composite signal that can be transmitted over a channel.

The use of filters in FMT helps to overcome the issues of inter-symbol interference (ISI) and inter-carrier interference (ICI), which can be present in conventional OFDM systems. These issues arise due to the presence of frequency selective fading in the communication channel.

The basic idea behind FMT is to use a set of filters to divide the frequency band into several sub-bands or subcarriers, each of which is used to transmit a specific part of the data signal. The data is first divided into several substreams, each of which is modulated onto a specific subcarrier frequency. These subcarriers are then combined to form a composite signal that can be transmitted over a channel.

Each subcarrier is modulated using a simple amplitude and phase modulation technique, such as quadrature amplitude modulation (QAM) or phase shift keying (PSK). The modulation scheme used for each subcarrier can be different, and can be chosen based on the channel characteristics and the required data rate.

The filters used in FMT are designed to minimize the cross-talk between adjacent subcarriers, and to limit the frequency range of each subcarrier. This helps to reduce the effects of ICI and ISI. The filters are typically designed using a windowing function, such as the Kaiser window or the Blackman-Harris window.

One of the main advantages of FMT is its ability to adapt to varying channel conditions. FMT can adjust the number of subcarriers and the modulation scheme used for each subcarrier based on the channel characteristics. This allows it to maintain a high data rate even in channels with high noise levels or varying channel conditions.

Another advantage of FMT is its low computational complexity. The use of filters to divide the frequency band into subcarriers simplifies the signal processing required for modulation and demodulation. This reduces the computational complexity of the system and makes it more power efficient.

FMT has been used in a variety of communication systems, including digital audio broadcasting (DAB), digital video broadcasting (DVB), and digital subscriber line (DSL) systems. It has also been proposed for use in next-generation wireless communication systems, such as 5G and beyond.

In summary, FMT is a modulation technique that uses filters to divide the frequency band into subcarriers, which are used to transmit different parts of the data signal. This helps to overcome the issues of ISI and ICI in conventional OFDM systems, and allows for high data rates even in channels with high noise levels. FMT is a flexible and power-efficient modulation technique that has been used in a variety of communication systems.