| Orthogonal frequency division multiplexing(OFDM)is a widely adopted solution of the fourth generation mobile communication system(4G)because of its advantages aginst multipath channel and implementation by the fast Fourier algorithm.However,in the future mobile communication system,it will face more diverse application scenarios.OFDM is unable to meet the requirements of the future mobile communication systems because of its sensitivity to frequency offset and high peak-to-average ratio.The generalized frequency division multiplexing(GFDM),which is extended by OFDM,with its flexibility and out-ofband spectrum characteristics,has become a most popular multi-carrier modulation solution.The combination with multi-antenna technology is also the trend of future communication development.This thesis focuses on the MIMO-GFDM that combines multi-antenna technology with GFDM.The main research contents are the problem of BER performance improvement and out-of-band radiation reduction in MIMO-GFDM system.The main work is as follows:1.In the traditional MIMO-GFDM system,since the subcarriers are in non-orthogonal states,mutual interference between subcarriers is caused.When zero-forcing is used,noise amplification phenomenon may occur,which affects the BER performance of the system.To solve this problem,this thesis proposes a TR-STC-Org-GFDM system based on GFDM with orthogonal sub-carriers(Org-GFDM).This system not only solves the interference problem between subcarriers fundamentally,casused by the non-orthogonality,in traditional TR-STC-GFDM system,but also overcomes the noise amplification when using ZF receiver.2.In order to improve the BER performance of the improved system,this thesis proposes a WHT-STC-Org-GFDM system combining the improved system with the Walsh-Hadamard transformation,whose BER performance is even better.Simulations show that the BER performance is significantly improved when the roll-off factor takes different values comparing with the traditional MIMO-GFDM system.3.With the continuous increase in the number of wireless devices and users,the scarcity of spectrum resources has become increasingly prominent.In order to make it possible to transmit signals in the white space of the TV frequency,it is necessary to further reduce the out-of-band radiation of the GFDM in the MIMO-GFDM system.At present,there are mainly two kinds of out-of-band spectrum reduction schemes,namely time domain windowing(TW)and interfering carrier insertion(CCs).However,their suppression effects at the edge of the adjacent signal and the edge far from the signal are poor.To solve this problem,this thesis proposes a serial processing method(CCs+TW)combining TW and CCs.Simulations show that compared with the existing methods,the CCs+TW method improves the problem that the suppression effect of the TW method at the edge subcarriers of the adjacent signal is not good,and also avoids the spectral burst of the CCs method at the outof-band position.However,there is still room for improvement as the approach cannot achieve enough synergy of CC insertion and TW.4.For the problem that the suppression effect of TW and CCs method cannot be perfectly superposed,this thesis proposes an interference avoidance transmission by partitioned frequenwy-and time-domain processing(IA-PFT).The signal subcarriers are divided into two parts: time domain processing subcarriers and frequency domain processing subcarriers.TW and the CCs method are used for out-of-band radiation suppression,and the two signals are finally combined.The simulation result shows that the IA-PFT method not only solves the deficiencies of TW and CCs,but also solves the problem that CCs+TW cannot be perfectly combined,and possesses ideal suppression performance. |
