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非线性预编码中的星座扩展及解调方法研究

发布时间:2018-12-27 19:31
【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操作,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,总结对比它们各自的优缺点。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,考虑基于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,本文考虑扩展取模间隔方案,但是扩展取模间隔的系统在减小取模损耗的同时也会增加功率损耗,因此本文提出找到折衷取模损耗和功率损耗的最优取模扩展因子,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。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,考虑基于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,本文考虑扩展取模间隔方案,但是扩展取模间隔的系统在减小取模损耗的同时也会降低VP的预编码增益,所以本文提出找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,系统的整体性能仍可以得到提升。
[Abstract]:As the evolution technology of 3G technology, LTE has become the common choice of major operators in the world because of its higher system capacity, transmission reliability and spectrum efficiency. And has made significant progress in global commercial processes. MIMO technology is undoubtedly one of the core technologies of LTE. However, due to the common problems of multiple data streams and interference between multiple users in MIMO system and the distributed processing of each user receiver, it is no longer practical to carry out joint detection at the receiving end. Therefore, a precoding technique using channel state information (CSI) to adjust the transmission strategy is proposed at the transmitter. The precoding technique can effectively suppress the interference between multiple data streams and users in MIMO system. While greatly reducing the processing complexity of the receiver, the channel capacity is significantly increased, which is helpful for MIMO to obtain its unique multiplexing gain and diversity gain. In this paper, the precoding technology of MIMO downlink in LTE is studied. Compared with linear precoding algorithms, such as ZF (zero forcing) precoding and MMSE (least mean square error) precoding, Nonlinear precoding algorithms, such as THP (Modular precoding) and VP (Vector perturbation), and some of their derivation algorithms can obtain more significant performance gains than linear precoding at the cost of acceptable complexity. However, both the THP and VP precoding algorithms need to introduce the mold extraction operation. Because the THP algorithm uses the mold extraction operation at both the sending and receiving end, this will introduce the die extraction loss, the shaping loss and the power loss. The VP also uses the mode-taking operation at the receiving end, which will also introduce the loss of the mode-fetching. These losses will bring negative gain to the performance of THP and VP precoding, which will seriously affect the performance of MIMO systems under nonlinear precoding. In order to solve the above problems, this paper proposes an improved transceiver algorithm for THP and VP precoding. The main work of this paper is as follows: briefly review the principle and function of precoding technology in MIMO system, expound the design principle of linear precoding algorithm such as ZF and MMSE and nonlinear precoding algorithm such as THP and VP, and make use of MATLAB simulation. Verify the performance of various pre-coding algorithms and compare their advantages and disadvantages. This paper analyzes the loss of THP precoding algorithm which is caused by the introduction of mode-taking operation into the transceiver, and considers the soft demodulation scheme of extended constellation diagram based on Turbo channel coding, such as the loss of mode-fetching, the loss of shaping and the loss of power. On the other hand, in view of the fact that the mode-taking operation may cause the symbol of the receiver to drift beyond the mode-taking limit, this paper considers the extended mode-taking interval scheme, but the system with the extended mode-taking interval will increase the power loss while reducing the mode-taking loss. In this paper, we propose to find out the optimal modulus extraction expansion factor between the mode extraction loss and the power loss, so that the overall performance of the system can still have gain after the addition of the mode extraction expansion factor. In this paper, the simplified scheme of VP precoding, LRA-VP precoding, is studied, and a precoding algorithm based on multi-user modulation schemes based on LRA-VP is proposed for link and system-level simulation with AMC. This paper analyzes the loss of LRA-VP precoding algorithm caused by the introduction of mode-removal operation at the receiver, and considers the soft demodulation scheme based on the extended constellation diagram based on Turbo channel coding. Similarly, in view of the fact that the mode-taking operation may cause the symbol of the receiver to drift beyond the threshold of the mode-taking, this paper considers the extended mode-taking interval scheme, but the system with the extended mode-taking interval can reduce the loss of the mode-fetching and the precoding gain of the VP at the same time. In this paper, we propose to find the optimal modulus extraction expansion factor between the loss and the precoding gain, so that the overall performance of the system can be improved after the addition of the modulus extraction expansion factor.
【学位授予单位】:电子科技大学
【学位级别】:硕士
【学位授予年份】:2015
【分类号】:TN929.5

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