Research On Non-orthogonal Waveform Modulation And Non-orthogonal Multiple Access Techniques

The flourish of the fifth generation(5G)of mobile communications is driven to transmit the data with higher transmission rates,more densely connected devices,and lower transmission delays,and the application scenarios will become more diverse.In order to meet the needs of 5G for diverse application scenarios,academia and industry have studied and adopted more advanced technical methods to further improve the system capacity and the spectrum efficiency.Waveform modulation and multiple access technologies are key technologies at the physical layer.On one hand,although OFDM technology is widely used in many existing communication systems,its inherent high out-of-band emission(OOBE)and its sensitivity to time-frequency offsets have limited its further improvement of spectral efficiency.On the other hand,when the orthogonal multiple access method is still employed in the massive machine-type-communications(m MTC)scenario,since the number of users that the system can connect to at the same time will be strictly limited by the number of allocated orthogonal channels,then the competitive transmission of large,sporadic small data packet services on limited time-frequency resources will cause a “signaling storm” problem and an increase in transmission delay caused by a large number of data retransmissions due to a sharp increase in the collision probability of users,which will significantly reduce the system transmission efficiency.Therefore,it is of great significance to study filtering or windowing-based non-orthogonal waveform modulation(NOWM)techniques and non-orthogonal multiple access(NOMA)techniques.This thesis will focus on 5G-oriented waveform modulation and multiple access technologies,and carry out related researches on multiple access schemes based on orthogonal or non-orthogonal waveform modulation and their low-complexity transceiver design.In order to take advantage of NOMA and NOWM schemes simultaneously,the problem of non-orthogonal multiple access based on NOWM modulation is studied.Specifically,an uplink transmission scheme for pattern-division multiple access(PDMA)based on discrete Fourier transform spread generalized multi-carrier(DFT-S-GMC)modulation,DFT-S-GMC-PDMA for short,is studied.Firstly,implementation schemes of the proposed DFT-S-GMC-PDMA in the time domain and frequency domain are presented,respectively.Secondly,the equivalent channel response matrix and noise formulas of both implementation schemes are derived.Furthermore,simulation results are given to show that the DFT-S-GMC-PDMA can achieve a comparable performance to PDMA based on discrete Fourier transform spread OFDM(DFT-S-OFDM-PDMA),while the improvement of complexity is less than 3%.System performance under different equalizers and different PDMA patterns are also evaluated where neglectable performance loss is observed.Thanks to the robustness against CFO,the multiple-access interference performance of the DFT-S-GMC-PDMA scheme is about 0.5 d B superior to that of the corresponding the DFT-S-OFDM-PDMA scheme.It indicates by simulation that the proposed DFT-S-GMC-PDMA is robust to CFO at the cost of neglectable performance loss,and thus it is a more attractive candidate for the uplink transmission of m MTC.In order to deal with the problem of flexible multiple access in 5G heterogeneous networks,a unified multiple-access transmission structure based on filter bank multi-carrier(FBMC)modulation that can support multiple multiple-access schemes is studied.By using the filter bank transceiver's efficient implementation structure and scalable matrix transformation module,this paper presents a unified multiple-access structure called FBMC-SMT based on filter bank multi-carrier and scalable matrix transform,which can realize the flexible transmission of 3G and 4G to improve the system performance.As a special case of FBMC-SMT,the performance evaluation of FBMC-CDMA is conducted by extensive simulations.It is verified that FBMC-CDMA with 16 subbands allocated outperforms the traditional single carrier wideband code division multiple access when the number of code channels assigned is larger than 5.Moreover,the signal-to-interference-plus noise ratio(SINR)analysis of FBMC-SMT is also given and matches the simulation results very well.Hence,the proposed FBMC-SMT can serve as a unified architecture to flexibly integrate multi-RATs,thus to meet variable application requirements in 5G and beyond heterogeneous wireless networks.In order to tackle the issue of high receiver complexity of multi-user uplink transmission based on non-orthogonal modulation,an uplink low-complexity reception algorithm for multi-user oversampling filter block transmission is studied.Through application of discrete Fourier transform(DFT),the special banded structure and circular properties of the modulation matrix in the frequency domain of each user are derived.By exploiting the newly derived properties,a simplified zero-forcing(ZF)receiver is proposed for multi-user cyclic block over-sampling filter bank(CB-OSFB)uplink systems in the multipath channels.In the proposed receiver,the matrix inversion operation of the large dimension multi-user equivalent channel matrix is transformed into DFTs and smaller size matrix inversion operations.Simulation is given to show that the proposed ZF receiver can dramatically reduce the computational complexity while with almost the same symbol error rate as that of the traditional ZF receiver.