【作者】 李俊；

【导师】 江涛；

【作者基本信息】 华中科技大学 ， 信息与通信工程， 2019， 博士

【摘要】 相比于正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM),基于交错正交幅度调制的滤波器组多载波(Offset Quadrature Amplitude Modulation based Filter Bank Multicarrier,OQAM/FBMC)采用了设计良好的原型滤波器,可以获得更低的旁瓣性能。并且,OQAM/FBMC不需要使用循环前缀(Cyclic Prefix,CP),具有更高的谱效。因此,OQAM/FBMC技术成为了未来无线通信系统的物理层备选技术之一。此外,多输入多输出(Multiple-Input Multiple-Output,MIMO)技术可以极大改善通信系统性能,一直是工业界和学术界的研究热点。因此,OQAM/FBMC与MIMO技术的结合将在未来无线通信系统中扮演非常重要的角色。本论文主要研究MIMOOQAM/FBMC系统发射分集技术,包括Alamouti发射分集和延迟分集技术,具体研究内容包括:1、提出了OQAM/FBMC系统发射端块状Alamouti编码方案。在OQAM/FBMC系统中,虚部干扰受到周围数据的影响并具有随机性。通过对虚部干扰系数进行分析,证明了虚部干扰系数存在特殊的反演对称性。基于这一发现,提出了块状Alamouti分集方案。该方案利用反演对称性对OQAM/FBMC发送数据进行合理的分组编码,使得加上虚部干扰后形成的复数数据能够满足正交形式,从而可以在接收端成功译码,获取分集增益。在块状Alamouti分集方案基础上,进一步去掉了保护间隔,并对引入的干扰进行了分析和均衡。2、针对OQAM/FBMC系统Alamouti发射分集方案在高频率选择性信道下存在性能损失的问题,提出了基于频率扩展的Alamouti接收机方案。CP的引入简化了OFDM系统在高频率选择性信道下的接收端均衡处理。而OQAM/FBMC没有使用CP,只能依靠原型滤波器对抗多径衰落信道,在高频率选择性信道下使用简单的均衡处理已经无法满足需求。为了改善OQAM/FBMC在高频率选择性信道下的性能,提出了一种基于频率扩展的Alamouti接收机方案,将Alamouti译码模块移动到频率解扩模块之前。与传统的基于子载波的Alamouti译码方案不同,提出的Alamouti译码方案可以在更细粒度的频率点上进行,从而能够更好地对抗频率选择性衰落。此外,通过在Alamouti译码模块之前引入相位因子,可以在每个频率点上实现满分集增益。仿真结果表明,在高频率选择性衰落信道下,传统分集方案在高阶调制下误码性能存在很高的平台,几乎无法有效工作。而本方案可以突破这一瓶颈,并且在低信噪比时相比传统方案仍有4dB的性能提升。3、研究了OQAM/FBMC系统延迟分集方案。提出了两种基于频率扩展快速实现架构的OQAM/FBMC循环延迟分集方案。所提方案均是在频率解扩前的频点上进行等效信道均衡处理。但第一种方案在发射端是直接对每个符号进行循环延迟处理,在延迟量比较大时会引入较大的干扰。为了解决这一问题,第二种方案通过采用循环卷积替代线性卷积的方式,对OQAM/FBMC发射数据进行了分块处理,每个数据块都添加了CP。之后再对每个数据块进行循环延迟处理时,循环延迟量不再有限制。由于CP是对每个数据块进行添加,引入的开销比OFDM系统小。仿真结果表明,第一种基于线性卷积的方案比较适合平坦衰落信道。第二种基于循环卷积的方案在频率选择性衰落信道下仍然能够获取较高的分集增益。综上所述,本文研究了OQAM/FBMC系统下的Alamouti发射分集和延迟分集方案。所提方案在平坦衰落及频率选择性衰落信道下都能获取较高的分集增益,保障了通信可靠性。更多还原

【Abstract】 Compared with orthogonal frequency division multiplexing(OFDM),offset quadrature amplitude modulation based filter bank multicarrier(OQAM/FBMC)has lower spectral sidelobes due to the well-designed prototype filter.Moreover,OQAM/FBMC systems have higher spectral efficiency since they do not require cyclic prefix(CP).The above advantages have made OQAM/FBMC a promising candidate for future wireless communications systems.On the other hand,multiple-input multiple-output(MIMO)has attracted significant attention due to its great potential in boosting the performance of wireless communication systems.Hence,the integration of MIMO with OQAM/FBMC is expected to play a significant role in future wireless communication systems.This thesis mainly focuses on the transmit diversity techniques in MIMO-OQAM/FBMC systems,including Alamouti transmit diversity and delay diversity schemes.The main research contents are as follows:1.A block-wise Alamouti transmit diversity scheme is proposed for the OQAM/FBMC system.In OQAM/FBMC systems,the imaginary interference is random and influenced by the surrounding data.Through the analysis of the imaginary interference coefficients,we prove that the imaginary interference coefficients have special symmetry property.Based on this discovery,a block-wise Alamouti diversity scheme is proposed,which makes use of the symmetry property to reasonably group and encode the transmitted data.It is proved that the combined complex data after adding the imaginary part interference satisfy the orthogonal condition.Hence,the transmitted data can be successfully decoded at the receiver and the diversity gain is achieved.Moreover,the guard interval in the block wise scheme is further removed,and a simple equalization scheme is proposed to equalize the introduced interference.2.Alamouti coded OQAM/FBMC systems suffer from severe performance degradation in highly frequency selective channels.To address this problem,a novel receiver for the Alamouti coded OQAM/FBMC system based on frequency spreading is proposed.The introduction of CP simplifies the equalization of OFDM systems in highly frequency selective channels.However,OQAM/FBMC does not employ CP,which could only rely on the prototype filter to combat multipath fading.In the case of a highly frequency selective channel,the simple equalization processing is not enough.To improve the performance of OQAM/FBMC system in highly frequency selective channels,a novel receiver based on frequency spreading is proposed for the Alamouti scheme,where the Alamouti decoding module is moved to the front of the frequency despreading module.Unlike the traditional subcarrier-based Alamouti decoding scheme,the Alamouti decoding in the proposed receiver could be performed on each frequency point to better combat the frequency selectivity.Moreover,the full diversity is achieved on each frequency point by introducing a phase factor before Alamouti decoding.Simulation results show that the traditional Alamouti receiver has poor error performance under high order modulation in highly frequency selective channels,which can hardly work.The proposed scheme still has 4dB performance improvement compared with the traditional scheme under low SNR.3.The delay diversity scheme in the OQAM/FBMC system is studied.So far,research on delay diversity in the OQAM/FBMC system is still very scarce.To address this problem,two cyclic delay diversity schemes based on frequency spreading OQAM/FBMC are proposed.The equalization of the proposed schemes are performed on frequency frequency points before frequency despreading.However,the first scheme directly carries out cyclic delay processing for each symbol in the transmitter,which introduces interference at a large cyclic delay.To solve this problem,the second scheme is proposed.In the second scheme,the transmitted data of OQAM/FBMC systems are block-based by replacing linear convolution with circular convolution,and CP is inserted prior to each block.Then,the cyclic delay scheme is carried out on each data block,and the length of the cyclic delay is no longer limited.Since CP is inserted to each data block,the introduced overhead is smaller than that of the OFDM system.Simulation results show that the first scheme based on linear convolution is suitable for the flat fading channel.The second scheme based on cyclic convolution can still obtain diversity gain in frequency selective channels.In summary,the Alamouti transmit diversity scheme and delay diversity scheme in OQAM/FBMC systems are investigated.The proposed schemes can obtain high diversity gain in both flat fading and frequency selective fading channels,which guarantees the communication reliability.更多还原