摘 要
作为3G技术的演进技术，LTE以其更高的系统容量、传输可靠性及频谱利用率，已经成为全球各大主流运营商的共同选择，并且在全球商用过程中已经取得重大进展。MIMO技术毫无疑问是LTE的核心技术之一，但是由于MIMO系统中普遍存在的多个数据流及多个用户间的干扰问题以及各用户接收机的分布式处理，在接收端进行联合检测已然不实际，因此在发送端利用信道状态信息（CSI）调整发射策略的预编码技术应运而生，预编码技术有效地抑制MIMO系统中的多个数据流及多个用户间的干扰，在大幅降低接收机处理复杂度的前提下显著提升信道容量，因而有助于MIMO获得其特有的复用增益和分集增益。 本文对LTE中MIMO下行链路的预编码技术进行了研究。相对于线性预编码算法，如ZF（迫零）预编码和MMSE（最小均方误差）预编码算法，以THP（模代预编码）和VP（矢量扰动）等为代表的非线性预编码算法及它们的一些衍生算法能以可接受的复杂度为代价，获得相比于线性预编码更显著的性能增益。 然而，THP和VP预编码算法都需要引入取模操作，由于THP算法在发送和接受端都采用了取模操作，这将会会引入取模损耗、成形损耗及功率损耗。而VP在接收端也采用了取模损耗， 邵式平
也会引入取模损耗。这些损耗都会给THP和VP预编码的性能带来不小的负增益，严重影响非线性预编码下的MIMO系统的性能。针对以上问题，本文将提出改进后的THP和VP预编码的收发算法。文章主要工作如下：
简单回顾MIMO系统中预编码技术的原理及其作用，阐述ZF及MMSE等线性预编码算法和THP及VP等非线性预编码算法的设计原理，并利用MATLAB仿真，验证各种预编码算法的性能及它们各自的优缺点，得出相比于线性预编码北大投毒案算法，非线性预编码算法虽然在复杂度上有一定的提升，但是在BER性能上的确具有优越性，更加符合实际的LTE TDD系统的要求，初步确定THP和VP预编码的方案是可行的。只是考虑到复杂度的问题，我们还需要对现有的SE-VP预编码算法进行简化。(此段太口水话，罗嗦)
分析THP预编码算法因收发端均引入取模操作而带来的取模损耗、成形损耗及功率损耗等各种损耗，提出基于Turbo信道编码下的扩展星座图的软解调方案。另一方面，针对取模操作可能使得接收端的符号飘移到取模界限之外，我们提出扩展取模操作因子，但是扩展取模操作因子的系统在减小取模损耗的同时也会增加功率损耗，所以我们必须到折衷取模损耗和功率损耗的最优取模扩展因子，以使得加入取模扩展因子之后，系统的整体性能仍然能够有增益。生物医学工程学杂志（和下面完全重复，精简一下）
研究VP预编码的简化方案——LRA-VP预编码，并提出适用于带有AMC的链路和系统级仿真的基于LRA-VP的多用户不同调制方式下的预编码算法。分析LRA-VP预编码算法因接收端引入取模操作而带来的取模损耗，提出基于Turbo信道编码下的扩展星座图的软解调方案。同样，针对取模操作可能使得接收端的符号飘移到取模界限之外，我们提出扩展取模操作因子，但是扩展取模操作因子的系统在减小取模损耗的同时也会降低VP的预编码增益，所以我们必须到折衷取模损耗和预编码增益的最优取模扩展因子，以使得加入取模扩展因子之后，系统的整体性能仍能够有增益。
关键词：MIMO，THP，VP，非线性预编码，扩展星座软解调，取模扩展因子
ABSTRACT
As the evolution technology of the 3G technology, LTE (Long Term Evolution) has become the common choice of the world's major mainstream carriers and has made significant progress in the global commercial process because of its higher system capaci
ty, transmission reliability and spectrum efficiency. Undoubtedly, MIMO ((Multiple-Input Multiple-Output, MIMO) technology is undoubtedly one of the core technologies of LTE. However, due to the interference of multiple data streams in a MIMO system and a plurality of common between users and a distributed processing each user receiver, joint detection at the receiving end is already not practical, and therefore the precoding technologies that using the channel state information (CSI ) to adjust the transmission policy at the transmitting end have emerged, the precoding technique can effectively suppress interference between multiple data streams or a multiple users in MIMO system. It can significantly reduce the complexity of the receiver processing while significantly improve the channel capacity, thus helps MIMO obtain its unique multiplexing and diversity gain.李兴钢
In this paper, the precoding technique of MIMO in LTE downlink is studied. With respect to the linear pre-coding algorithm, such as ZF (Zero Forcing) precoding and MMSE (Minimum Mean Square Error) precoding algorithms., nonlinear precoding algorithms such as THP (Tomlinson Harashima Preeoding) and VP (Vector Perturbation) precoding c
921大地震
渝安集团an obtain significant performance gains at an acceptable expense of complexity.
However, THP and VP precoding algorithms both introduce modulo operation, because modulo operation is used at both sending and receiving end of the THP algorithms, which will introduces the modulo loss, shaping loss and power loss. At the same time, modulo operation is also used at the receiving end of VP which will introduce modulo loss. These losses will bring large negative gain to THP and VP witch seriously affects the performance of non-linear pre-coding in MIMO systems. To solve the above problems, this paper will present improved THP and VP precoding algorithms. The specific works of this dissertation include:
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