Research On The Multi-carrier Modulation Techniques Based On The Gabor Transform

Because of the high spectrum efficiency and the strong anti-multipath ability, Orthogonal Frequency Division multiplex (OFDM) becomes one of the key technologies of the fourth generation mobile communication system.Along with the continuous demand of people in high quality broadband services, OFDM technology will be applied more and more widely in communication.OFDM technology use each sub-data stream to modulate different carriers by dividing high-speed data streams into many parallel sub-data streams.Due to the lower speed of each sub-data stream,OFDM technology can effectively eliminate intersymbol interference (ISI) that multipath time delay creates.But inserting the CP makes the data symbol period larger and makes OFDM system more sensitive to the spread of signal frequency spectrum that carrier frequency offset and doppler effect create,and effects the performance of the system.Because the demand of mobile users in multi-media communication grows, How to effectively eliminate ICI that frequency diapersive channels create is particularly important.To solve the above-mentioned problem,the thesis has gived a lot of research and analyze to MCM technology based on the Gabor Transform. The main content are:by analyzing the performance of windowed OFDM system, the conclusion is drew that this windowing technology can only reduce out-of-band energy radiation of OFDM symbols,but can not effectively eliminate ICI that the carrier frequency offset causes.Therefore the paper proposes using OFDM system based on the Gabor Transform(G-OFDM)to solve carrier frequency offset, and the simulation results show that compared with windowed OFDM system, G-OFDM system has improved considerably in performance and is not affected by pulse roll-off factor. Even if the roll-off factor is 1, G-OFDM system is still better able to suppress ICI.For G-OFDM system that exist multi-path expansion and doppler expansion,the paper proposes a new optimum pulse shaping method to resist channel interference by matching Gaussian pulse shaping filter with doubly dispersive channels. The simulation results show that this optimal G-OFDM systerm can obtain better SIR performance than rectangle pulse shaping OFDM system,and while it reduces ISI,it provides better protection against ICI caused by frequency dispersive channel.Moreover,the bigger the frequency dispersive the better the performance of ICI cancellation.