Stopband Energy Suppression Of OQAM/FBMC Signals

Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation(OQAM/FBMC)is considered as the most attractive candidate modulation scheme to replace Orthogonal Frequency Division Multiplexing(OFDM)for the future mobile communication systems due to its superiority in spectrum efficiency.OQAM/FBMC eliminates the effects of multipath interference without the requirement of a Cyclic Prefix(CP),and thus improves the data rate and the spectrum efficiency.A key challenge in realizing future mobile communication systems is to reduce serious out-of-band emission(OOBE)which results in strong user interference.However,the performance of the OQAM/FBMC system in time and frequency is mutually exclusive when the signal is shaped by the prototype filter.To address this,our thesis proposes a novel method to minimize the normalized stopband energy of the transmit signal in the OQAM/FBMC system.The key of our proposal is to design the distribution of input symbols.First,the power spectral density(PSD)of the OQAM/FBMC signal is derived in general case without any assumption on the statistical properties of input OQAM symbols.The derived PSD is more representative compared to the traditional PSD where the input OQAM symbols are assumed to be independent and identically distributed.According to the above derivation,it is observed that the PSD not only depends on the prototype filter but also depends on the statistical properties of data symbols.Then,in order to determine how input symbols affect the sidelobes of the signal,we use a fixed-parameter filter and formulate an optimization problem about signal sidelobes by designing the distribution of input symbols.Traditional solutions usually reduce the signal stopband energy by optimizing the filter coefficients,which will inevitably increase the sidelobes of the signal's stopband boundary.The proposed scheme differs from the conventional scheme in that the non-primary sidelobes of the optimized signal maintain the same magnitude of decline as the original OQAM/FBMC signal.Simulation results show that the proposed scheme can significantly reduce the energy of the OQAM/FBMC signal stopband without raising the edge of the signal stopband.Finally,a joint symbol distribution and prototype filter optimization problem is formulated to minimize the stopband energy of the signal.The nonlinear optimization problem is solved by the quadratic programming method to obtain the optimal symbol distribution and filter coefficients.The signal power spectral density and Out-of-Band leakage after joint optimization,filter optimization and symbol distribution optimization are simulated respectively in the dissertation.Simulation results show that joint optimization achieves better performance compared to traditional optimization schemes.