# OFDM vs FBMC-Similarity and difference between OFDM and FBMC modulation

This page on OFDM vs FBMC describes similarity between OFDM and FBMC as well as difference between OFDM and FBMC modulation types. The merits and demerits of FBMC modulation is also covered. Both are multicarrier modulation techniques used to provide high data rates.

## OFDM Modulation

OFDM is a multicarrier modulation scheme known as Orthogonal Frequency Division Multiplexing. In this densely packed low frequency subcarriers are assigned with some complex data symbols before RF up conversion. Each subcarriers carry data. In this OFDM modulation, each subcarried is demodulated successfully in the absense of ISI and ICI. This is achieved with the concept of cyclic prefix(CP).

The addition of CP results into reduction of spectral efficiency and hence it is not favourable for multicarrier uplink as well as cognitive radio system.

## FBMC Modulation

In this FBMC modulation type, set of synthesis & analysis filters are designed and introduced in the chain. Hence desired bandwidth efficiency along with spectral efficiency can be achieved.

In FBMC modulation, filters(usually low pass) are uniformly spaced and are higher in selectivity to achieve minimum crosstalk. After this modulation is applied using several subcarrier center frequencies to generate synthesis and analysis filters. Subcarriers are arranged either odd or even stacked. There is no center frequency used.

## Difference between OFDM and FBMC

FBMC modulation based systems are complex in comparison to OFDM. This is due to exchange of FFT/IFFT modules by the filter banks.

Major comparion factor in these two techniques is number of multiplications(real) per symbol(complex).

In OFDM implementation, Split radix algorithm will have,
CFFT/IFFT = M (log(M) - 3 ) + 4

In FBMC, no. of real mltiplications per complex symbol is calculated as follows:
CSFB = log2(M/2) - 3 + 4*K
CAFB = 2 (log2(M) - 3 ) + 4*K
Where, SFB is synthesis filter bank and AFB is analysis filter bank

OFDM suffers from poor spectral selectivity compare to FMBC. The same is shown in the figure.

• Provide spectrum efficient and more selective system
• CP(Cyclic Prefix) is not needed
• Provide robust narrowband jammers

## FBMC Demerits/Challanges

• The development of MIMO based FBMC is very limited and is non-trivial.
• to design wider BW and higher dynamic range system will have more challenges in achieving RF performance
• More complex as compared to OFDM. It introduces overhead in overlapping symbols in the filter bank(in time domain).

## Applications of FBMC

• Cognitive Radio Communications
• Multiple Access Networks