Application Research About Filtered Multi-Tone Technology In Cognitive Radio

Wireless spectrum is a precious natural resource, the current wireless communication systems based on static spectrum allocation result in the lack of spectrum resources. The study found that some spectrum bands in the vast period of time are not occupied. In order to improve spectral efficiency, people began to consider allowing cognitive users using the free permits allocated band, without producing any interference to the authorized users, the purpose is to improve the spectrum utilization. This cognitive spectrum of wireless communications technology is called cognitive radio. Now the technology has become new research directions in the future of wireless communications.Nowadays IEEE 802.22standards is responsible for the development of cognitive radio, which suggests using OFDM modulation in uplink and downlink in the draft. OFDM requires spectrum overlap with each other, with a high spectral efficiency. But it is based on this, the system frequency synchronization is very sensitive to one small offset, which will causes strong interference between cognitive users and authorized users. In order to reduce interference between sub-carriers, OFDM uses virtual sub-carriers, which inevitably reduces the spectrum efficiency, contrary to cognitive radio improving the purposes of spectrum efficiency. Because of the shortcoming which OFDM causes in cognitive radio applications, the paper proposes an alternative multi-carrier: filtered multi-tone modulation (FMT) as one kind of cognitive radio physical layer technology. All sub-carriers are not mutually superposed, but side by side with each other. This arrangement of sub-carriers greatly reduces the carriers'interference. Even if some frequency offset, inter-carrier interference is very small, thus reducing the interference perception of the cognitive radio users and authorized users. And FMT does not require virtual sub-carriers, greatly improving the spectral efficiency.There is a little application research about FMT of the cognitive radio in literature currently. Thesis analyses the interference between authorized users and cognitive users in the carrier frequency offset and Doppler frequency offset channel with FMT, and under the same conditions compared with OFDM. The simulation found that, FMT can more reduce the interference between users than OFDM, while FMT without virtual sub-carriers and cyclic prefix, which greatly increases spectrum efficiency. Therefore, FMT is more suitable as a cognitive radio physical layer technology.