【作者】 陈雷；

【导师】 余建国；

【作者基本信息】 北京邮电大学 ， 电子科学与技术， 2020， 博士

【摘要】 面对未来海量设备的接入,作为无线通信系统关键环节的多载波传输技术,需要支持小包数据通信、低延时通信、碎片化频谱接入等不同业务的需求。而第四代无线通信系统的核心技术之一正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM),由于存在同步要求严格、带外功率泄露严重、保护间隔造成频谱利用率降低等问题,已无法适应多样化业务的实施。从而,可提供更高频谱效率以及更低带外功率泄露的通用滤波多载波(Universal Filtered Multicarrier,UFMC)、滤波器组多载波(Filter Bank Multicarrier,FBMC)等载波传输技术受到了广泛关注。UFMC融合了 OFDM与FBMC系统的优势,可对载波进行连续分配而无需插入保护频带;允许对用户带宽的差异化配置,且载波间无需严格同步和正交,具有较大灵活性;其滤波器时延长度远小于FBMC系统,有利于实现低时延传输及提高频谱利用率;采用正交振幅调制(Quadrature Amplitude Modulation,QAM),与多输入多输出(Multi Input Multi Output,MIMO)技术兼容性高。然而,UFMC 由于滤波器的引入也为多载波传输带来新的问题:滤波器对带内载波的干扰、载波频率偏移(Carrier Frequency Offset,CFO)对滤波信号的影响、多径衰落的影响、多用户接入导致系统复杂度提高等。本文针对上述问题进行研究并提出解决方案,主要工作及创新性成果如下:1、针对UFMC滤波器过渡带信号衰减问题结合载波间干扰展开研究,提出基于载波加权调制的ICS-UFMC方案。该方案依据滤波器过渡带特性对用户子带采用分区差异化调制策略,通过成对载波加权调制来提高边带接收信号功率,接收端反向解析完成对边带衰减信号的补偿,同时通过抑制接收信号间的干扰因子实现载波间干扰的自消除。仿真实验表明,相同频谱效率下,ICS-UFMC对比标准UFMC和OFDM系统,载波干扰功率比(Carrier-to-Interference power Ratio,CIR)性能可提升8-12dB,误码性能可提升1-5倍。在CFO较小的情况下误码性能可提升近1个数量级。该方案已获得发明专利授权(专利名称:一种干扰抑制方法及装置,专利号:2016106209518)。2、针对ICS-UFMC重叠编码导致CFO引入相位误差高于标准UFMC系统的问题,本文提出抑制相位干扰的PICS-UFMC算法,核心思想是对滤波器过渡带载波对采用-π/2相位差的角度旋转加权方案,接收端采用反向角度加权来抑制CFO造成的相位干扰。经仿真实验验证,不同CFO条件下,PICS-UFMC方案误码性能均优于ICS-UFMC和标准UFMC方案,尤其对于较高CFO,该方案具有更为显著的性能优势,其误码性能可提高1倍以上。3、针对标准UFMC系统滤波时延扩展无法有效对抗多径衰落,特别是长时延信道传输时接收性能下降严重的问题,提出基于判决反馈均衡(Decision Feedback Equalization,DFE)和符号重构算法的 SCR-UFMC方案。该方案中DFE单元通过利用前一符号周期的判决反馈运算来消除符号间干扰;采用符号重构算法来完成缺失信息重构以避免载波间干扰的产生。在不同典型信道模型、不同QAM调制阶次以及非理想信道状态信息条件下进行仿真实验验证,方案可有效消除多径信道对UFMC传输信号的影响。在信噪比较大(>20dB)的情况下对比标准UFMC系统,短时延信道性能提升1倍以上,而长时延信道性能优势更加明显,误码性能可提升6-28倍。4、针对UFMC波形传输系统复杂度高于OFDM系统的情况,提出UFMC运算结构优化方案。对UFMC发射机提出频域滤波结构并提前完成用户信息抽取,这样既可以降低系统运算复杂度,又可提升系统传输效率,且接收机FFT运算规模也由2N点下降为N点。同时,针对用户信号多数“0”值填充特征并结合IFFT裁剪机制简化运算结构。对于接收机DFE单元,本文针对该过程仅需部分反馈信息进行运算的特点提出截短序列卷积方案,并将时域线性卷积改进为频域DFE快速运算结构,其运算复杂度在不同信道时延参数下均有较为显著的降低。更多还原

【Abstract】 To cope with the access of massive devices in the future,the multi-carrier transmission technology,which is a key link of the wireless communication system,needs to support the needs of different services such as small packet data communication,low-latency communication,and fragmented spectrum access.Orthogonal Frequency Division Multiplexing(OFDM),one of the core technologies of the fourth-generation wireless communication system,has problems such as strict synchronization requirements,severe out-of-band power leakage,and reduced spectrum utilization due to guard intervals.Unable to adapt to the implementation of diversified businesses.As a result,carrier transmission technologies such as Universal Filtered Multicarrier(UFMC)and Filter Bank Multicarrier(FBMC)that can provide higher spectral efficiency and lower out-of-band power leakage have received widespread attention.UFMC integrates the advantages of OFDM and FBMC systems,can continuously allocate carriers without inserting guard bands;allows differentiated configuration of user bandwidth,and does not require strict synchronization and orthogonality between carriers,which has greater flexibility;its filters The time extension is much smaller than that of the FBMC system,which is conducive to the low-delay transmission and improved spectrum utilization;Quadrature Amplitude Modulation(QAM)is adopted,which is compatible with Multi Input Multi Output(MIMO)technology high.However,the introduction of filters in UFMC also brings new problems for multi-carrier transmission:the interference of the filter to the in-band carrier,the influence of carrier frequency offset(CFO)on the filtered signal,and the influence of multipath fading,Multi-user access leads to increased system complexity,etc.This paper studies and proposes solutions to the above problems.The main work and innovative results are as follows:1.Aiming at the problem of signal attenuation in the transition band of UFMC filter combined with inter-carrier interference,the ICS-UFMC scheme based on carrier weighted modulation is proposed.According to the characteristics of the filter transition band,the solution adopts a differentiated modulation strategy for the user subbands.Paired carriers weighted modulation is used to increase the received signal power of the sideband.The receiving end performs reverse analysis to compensate for the sideband attenuated signal and suppress the interference factor between received signals to realize the self-cancellation of inter-carrier interference.Simulation experiments show that under the same spectrum efficiency,compared with the standard UFMC and OFDM systems,the carrier-to-interference power ratio(CIR)performance of ICS-UFMC can be increased by 8-12dB,and the bit error performance can be increased by 1-5 times.This solution has been granted an invention patent(Patent name:An interference suppression method and device,Patent No.2016106209518).2.Aiming at the problem that the ICS-UFMC overlapping coding causes the phase error introduced by the CFO to be higher than that of the standard UFMC system,this paper proposes the PICS-UFMC algorithm to suppress phase interference.The core idea is to use a-π/2 phase difference angle rotation weighting scheme for the filter transition band carrier pair,the receiving end uses reverse angle weighting to suppress the phase interference caused by CFO.Simulation experiments have verified that under different CFO conditions,the error performance of the PICS-UFMC scheme is better than that of the ICS-UFMC and standard UFMC schemes.Especially for higher CFOs,the scheme has more significant performance advantages and its bit error performance can be improved More than 1 times.3.Since the standard UFMC system filter delay extension cannot effectively combat multipath fading,especially the severe degradation of reception performance during long-delay channel transmission,an SCR-UFMC scheme based on Decision Feedback Equalization(DFE)and symbol reconstruction algorithm is proposed.In this solution,the DFE unit eliminates the inter-symbol interference by using the decision feedback operation of the previous symbol period;the symbol reconstruction algorithm is used to complete the missing information reconstruction to avoid the generation of inter-carrier interference.Simulation experiments are performed under different typical channel models,different QAM modulation orders,and non-ideal channel state information.The scheme can effectively eliminate the influence of multipath channels on UFMC transmission signals.When the signal-to-noise ratio is large(>20dB),compared with the standard UFMC system,the performance of the short-delay channel is more than doubled,while the performance advantage of the long-delay channel is more obvious,and the bit error performance can be increased by 6-28 times.4.Because the complexity of the UFMC waveform transmission system is higher than that of the OFDM system,an optimization scheme of the UFMC calculation structure is proposed.A frequency-domain filtering structure is proposed for the UFMC transmitter and user information extraction is completed ahead of time.This can reduce the complexity of the system,but also improve the transmission efficiency of the system,and the receiver FFT operation scale is also reduced from 2N points to N points.At the same time,the proposed scheme combines the most "0" value filling feature of the user signal and the IFFT clipping mechanism to simplify the calculation structure.For the receiver DFE unit,this paper proposes a truncated sequence convolution scheme based on the characteristic that the process requires only part of the feedback information for operation,and improves the time-domain linear convolution into a frequency-domain DFE fast operation structure.The computational complexity of the system is significantly reduced under different channel delay parameters.更多还原