Research On Multicarrier Modulation With Nonuniform Carrier Spaces

Multicarrier modulation is a form of parallel data transmission, which is efficient to reduce the detrimental effects of multipath fading. It can improve the data rate in the wireless band-limited channel. As the main technique of multicarrier modulation, the conventional orthogonal frequency division multiplexing (OFDM) technique use subcarriers with uniform spaces. The channel gains of the subcarriers are the uniform samples of the channel frequency response. This method may not be efficient when the channel has variable gains in different subcarriers.In this thesis, we present a multicarrier modulation scheme with pseudo nonuniform subcarrier spaces. Based on generalized discrete fourier transform(GDFT), this method can adjust the spaces of the subcarriers. When the channel information is available at the transmitter, we can enlarge the subcarrier space in part of bandwidth where the channel gains are"bad"and reduce it where the channel gains are"good"in order to improve the bit error rate of system. The new methord is based on the channel state information so it is necessary to know the characteristic of wireless channel. Wireless channel is time-varing, which has two characteristics: large-scale fading and small-scale fading. Indoor channel model is adopted in simulation. Warpped discrete fourier transform(WDFT), which is used for signal processing, adjust the sample location via a all-pass warpping function. In this thesis, WDFT is introduced into communication. Base on this concept, we propose the method of adjusting the subcarriers spaces and the modulation/demodulation using GDFT. Finally the simulation and results are presented.