【作者】 王杰令；

【导师】 杨宏； 易克初；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2009， 博士

【摘要】 随着近年来无线通信中的移动电话、数据、图像、多媒体、互联网应用等业务的不断发展,要求无线通信系统能在复杂环境下提供更高的传输速率,并具有更高的可靠性,因此抗多径衰落技术一直是经久不衰的研究热点。本文以块传输系统为研究对象,围绕其频带效率与其在多径衰落信道中的传输性能进行了深入研究,主要贡献概括为以下几个方面:1.提出了一种块传输系统的多数据块联合调制算法。通过深入分析准正交时分复用(QOTDM)系统的频谱结构之后,提出了一种改进的QOTDM系统方案,并提出了一种适于该系统的高性能盲均衡算法。在此基础上,针对如何减小单载波块传输与正交频分复用系统中循环前缀占用系统开销的问题,提出了一种基于QOTDM的多数据块联合调制算法;利用多个数据块共用一个循环前缀,有效降低了系统冗余,提高了系统的频带效率,而且联合调制的数据块在接收机分解后,相互之间不产生干扰。块调制算法不仅可用于单载波块传输与正交频分复用系统,也可应用于采用这两者传输技术的超宽带以及MIMO等系统。理论分析以及仿真结果证明,该算法在慢衰落信道条件下与已有算法相比性能完全没有损失,而频带效率明显提高。2.提出一种新颖的适于二径衰落信道应用的双向裁决判决反馈均衡器。这种均衡算法通过对带有判决反馈结构的时间正向、逆向无限冲激响应(IIR)均衡器的输出判决量进行最大比合并而获得分集增益,使误码特性改善。该合并过程采用线性复杂度的处理,而不是像已有的双向裁决判决反馈均衡器那样的高复杂度,因为后者需要在最终裁决过程中逐个符号采用加窗最大似然序列估计算法。仿真结果表明,所提算法无论是最小还是非最小相位系统信道条件下都能超过已有的双向判决反馈IIR均衡器的性能。3.针对单载波块传输系统的时、频域均衡器在不采用信道编码的情况下无法获得多径分集增益的缺点,提出了一种可应用于非扩频的单载波块传输系统的RAKE接收算法。这种RAKE接收机是通过均衡器重构各个多径信号分量,再结合多级干扰抵消获得多径分集增益的,能明显改善误码性能。理论分析和仿真结果表明,所提出的算法能够与常规单载波均衡器相结合明显改善检测性能,而且可推广到与其它多种常见均衡算法相结合使用。4.提出多天线非扩频通信系统的干扰抵消与空时二维RAKE接收机方案。探讨了二发一收MIMO系统中单载波频域均衡算法的原理,针对目前对该算法的研究仅限于两个发射天线的情况,将它推广应用到具有四个发射天线的系统。提出了该系统的干扰抵消检测方案,与单载波传输系统类似,该MIMO系统中的干扰抵消技术也能改善初始均衡器的检测性能。然后进一步提出该系统的空时二维RAKE分集接收方案,将接收信号中的各条多径分量分解后分别进行空时分组码的空时合并,然后再进行多径分集合并,在获得空时分组码提供的空间分集增益基础上,进一步取得多径的分集增益。此外,在非扩频的多用户MIMO通信系统中实现了空时二维RAKE接收;当各用户信息从接收信号中分解后,分别独立进行空时二维分集合并,获得空间与多径的分集增益。仿真结果表明,所提出的几种算法都可以良好工作。更多还原

【Abstract】 With the increasing development of various services via wireless communications such as mobile voice, data, image, multimedia and internet applications in the recent years, the wireless communication is required to provide higher transmission rate with higher reliability, so that anti-multipath-fading techniques have been a hot point in this research area.This dissertation researches on block transmission system, paying great attention to the frequency band efficiency as well as the transmission performance in the multipath fading channels. The main contributions of the dissertation are as follows.A multiple blocks joint modulation technique is proposed. Through analyzing the spectral property of quasi-orthogonal time division multiplexing (QOTDM) system, a modified QOTDM system scheme and a blind equalizer for the system are proposed. Then, aiming at the problem of how to reduce the redundancy of the cyclic prefix (CP) in single carrier block transmission (SCBT) and orthogonal frequency division multiplexing (OFDM) systems, a QOTDM based block modulation (BM) algorithm is proposed, where multiple blocks are jointly modulated together to share a CP, which remarkably increases its band efficiency. When the BM frame is decomposed at the receiver, the multiple blocks can be obtained from the received signal without inter-block interference (IBI). The BM algorithm can be applied not only to SCBT and OFDM systems, but also to multi-input multi-output (MIMO) or MIMO-OFDM systems. Theoretical analysis and simulations show that the proposed system scheme for slow-fading channels has much higher band efficiency without performance degradation compared with the existing algorithms.A novel bidirectional arbitrated decision feedback (BAD) equalizer is presented for two-path fading channels, which can effectively improve the bit-error performance by acquiring diversity gains from combining the output of the forward and reversal infinite impulse response (IIR) equalizers with decision feedback architectures using maximal ratio combining (MRC) rule. The combining procedure needs only linear complexity rather than so high complexity of the local maximal likelihood sequence estimation (MLSE) as employed in the existing BAD equalizers. Simulations show that the proposed BAD algorithm obviously over-performs the existing bidirectional IIR equalizer with decision feedback in both channel conditions of minimum and non-minimum phase systems. Aiming at the defect of losing diversity gain in SCBT systems with time domain or frequency domain equalization, a RAKE receiver scheme for non-spectrum-spreading SCBT system is proposed, which can improve the bit-error performance by taking advantage of the multipath diversity gains. The RAKE receiver is realized by means of reconstruction of the multipath signals and multi-stage interference cancellation equalizer. Theoretic analysis and simulation results show that the proposed algorithms can effectively improve the performance of the single-carrier equalizer; moreover, it can also be combined with other equalizers since its initial solution can be obtained by using various commonly used equalizers.A scheme of space-time two dimensional (2D-) RAKE receiver is proposed for non-spectrum-spreading MIMO systems. Firstly, the single carrier frequency domain equalization combined with space-time block codes (STBC-SC-FDE) is investigated, and the scheme applied to the MIMO system with four transmit antennas is deduced. Then, similar to the interference cancellation (IC) technique in single antenna systems, the space time IC technique is employed to improve the performance of STBC-SC-FDE. Further, the 2D-RAKE receiver is accomplished in the system by decomposing the received signal and combining the multipath components based on STBC combination and multipath combination rules. Finally, the proposed 2D-RAKE is introduced into the multiuser MIMO systems to achieve both the spatial and multipath diversity gains for each user. Simulation results show that the proposed algorithms behave well.更多还原