Filtered Multitone Modulation Systems, Adaptive Technology Research

Up to now, 3G has been launched into business in many countries, and researches are focused on the next generation communication system, called 4G, which is expected to provide ubiquitous, high-quality, and high-rate mobile multimedia transmission. The next generation communication system has to support the transmission of high rate data and multimedia applications in the radio spectrum, which is already extremely scarce. As one of the effective transmission technologies, Multi-carrier modulation (MCM) transmits the data information parallel with several sub-carriers, and it makes symbol duration of each sub-channel much longer than the delay spread of the multipath channel. Therefore, MCM can provide high data rate and efficiently avoiding intersymbol inference (ISI) arosing by multipath propagation.As one of the multicarrier techniques, Orthogonal Frequency Division Multiplexing (OFDM) can make the best use of radio spectrum and efficiently reduce the multipath fading. OFDM has been adopted in several standards, such as IEEE802.11a, HIPERLAN/2. However, there are some disadvantages in OFDM system such as sensitivity to frequency offset, symbol synchronization and so on. We investigate a new multi-carrier modulation technique: Filtered Multitone (FMT) modulation. It divides the whole channel into several sub-channels with filter bank, so the spectrum of each subchannel has a high level of spectral containment in FMT system. And Inter-channel Interference (ICI) is effectively reduced, so FMT overcomes the weakness of being sensitive to frequency offset in OFDM system. However, the using of filter banks brings ISI to the system. Therefore, subchannel equalization is necessary to reduce the remaining ISI introduced by the filter banks.Adaptive technology is one of the crucial techniques for the mobile broadband systems. Its basic idea is that the transmitted power level, symbol transmission rate, constellation size, coding rate/scheme or any combination of these parameters can be adaptively adjusted by the current channel state information (CSI). By this way, adaptive technology can make the best use of the current channel environment.