The objective is to propose FBMC (Filter Bank Multi Carrier) physical layer for future radio systems that is more efficient than the present OFDM (Orthogonal Frequency Division Multiplexing) physical layer and better suited to the new concepts of DASM (Dynamic Access Spectrum Management) and cognitive radio.
The difference in frequency responses between FBMC and OFDM has a considerable impact on the performance of wireless systems and their operational flexibility. The FBMC approach has the following features
- no guard time, or cyclic prefix, is needed,
- full capacity of the transmission bandwidth is achieved using OQAM (Offset Quadrature Amplitude Modulation),
- mask constraints for the transmitted signals are easily satisfied,
- sub-channels can be grouped into independent blocks, which is crucial for scalability and dynamic access, for example,
- with the absence of leakage in the frequency domain, high resolution spectral analysis is achieved,
- the same device can be used in cognitive radio for spectrum sensing and reception, even simultaneously, which guaranties perfect coherence between the two functions.
In short, the difference can be expressed as follows:
- with OFDM, sub-carriers are spread across the transmission channel bandwidth.
- with FBMC, the transmission channel is divided into sub-channels.
When considering block diagrams, the PPN block in the filter bank replaces the device for prefix insertion/suppression used in OFDM. The FFT is common to both OFDM and FBMC, which is an important aspect for the compatibility issues.
