【作者】 程鹏；

【导师】 张文军；

【作者基本信息】 上海交通大学 ， 通信与信息系统， 2012， 博士

【摘要】 在“移动通信宽带化”和“宽带接入移动化”的趋势下,以LTE和LTE-Advanced为代表的新一代无线通信技术使得系统接入速率相比3G技术产生了质的飞跃,而预编码正是LTE/LTE-Advanced中的核心技术之一。为了有效简化系统接收机的设计和明显改善系统的误码率性能,通过对发射信号预先进行某种预处理来对抗无线通信环境下的各种不良影响的技术被称为预编码。随着LTE/LTE-Advanced的不断发展,预编码技术在不同的应用场景下呈现出不同的作用形态。本论文正是围绕着预编码技术领域中的核心问题,从LTE/LTE-Advanced涉及到的主要场景出发,对其中的单天线预编码技术、单用户MIMO系统中有限反馈预编码反馈压缩策略、多用户MIMO优化的预编码设计和基于预编码的双向中继系统中的信道估计等问题进行了创新性研究。这些研究力求在平衡系统性能和计算复杂度的同时,能够积极探索和发掘系统性能潜力,最大程度降低无线信道传播带来的衰减。全文主要研究内容归纳如下首先,本文讨论了单天线传输下的预编码技术。从预编码的观点出发,分析了LTE/LTE-Advanced下行OFDM传输技术对抗频率选择性衰落的能力,分析了LTE/LTE-Advanced上行DFT-SOFDM传输技术低峰值平均功率比的特性。矢量OFDM作为单载波和多载波OFDM传输的桥梁,在系统设计上具有很大的灵活性。但是,目前对于矢量OFDM在频率选择性衰落信道下完整的性能刻画尚属空白。本文正是从这一问题出发,详细分析了矢量OFDM在频率选择性衰落信道下的性能,研究了矢量OFDM中预编码技术所带来的信号空间分集增益,并对矢量OFDM中每个矢量块均进行了细致的研究。这些研究成果对实际系统应用矢量OFDM时提供了重要的理论依据,这也是本文第一个主要的创新点。然后,本文讨论了单用户MIMO下的预编码技术。尽管完美信道对于发射端设计预编码矩阵至关重要,但是接收机对于信道信息的直接量化反馈却给系统性能带来了明显的制约。本文正是在这一背景下,对更加有效的基于码本(codebook)的有限反馈技术进行了深入研究。由于实际系统下OFDM的引入使得预编码的反馈数据量随着载波或子带(subband)数目线性增加,所以本文提出了一种有限反馈量压缩技术。该技术能够使得系统在反馈开销和吞吐率性能上取得一个较好的折中。以上内容是本文第二个主要的创新点。随着系统对总吞吐量和小区用户密度的要求不断提高,从点对点的单用户模型向点对多点的多用户模型进行过渡成为了主要的研究方向。相比单用户MIMO,多用户MIMO预编码需要在解决用户内的数据流串扰同时,还需解决用户间的数据流串扰问题。本文以此为背景讨论了多用户MIMO下的线性预编码技术,具体介绍了块对角化(BD)预编码和最大信漏噪比(SLNR)预编码技术的基本原理。本文在原始SLNR技术上进一步发掘潜力,通过理论推导两个矩阵同时对角化的一种特殊形式,提出一种SLNR最大化松弛预编码方案。在多数据流传输情况下,提出的新预编码方案相对原始SLNR方案能够有效平衡多数据流间的信道增益,从而具有更好的系统误码性能。此外,提出的方法能保持几乎相同的系统归一化和速率。这部分内容是本文第三个主要的创新点。最后,本文关注了协同通信中的预编码技术,总结了多小区预编码设计上的主要思路。本文针对双向中继系统提出了一种基于压缩感知理论信道估计的方法。由于在双向中继系统中,等效信道并不稀疏,这会直接限制压缩感知理论的应用。本文从这一问题着手,利用预编码技术并结合双向中继特殊的结构解决了这一难题,使得系统能效得到显著优化,这也是预编码技术一种新的作用。以上内容是本文第四个主要的创新点。本文对于新一代无线通信系统中的预编码技术的总结、研究和创新丰富了预编码技术的理论研究成果,对实际系统中的预编码技术的应用也具有重要的指导意义。更多还原

【Abstract】 On the behalf of the new-generation wireless communications, the LTE and LTE-Advanced techniques allow the system access speed to be signiifcantly enhanced, com?pared to previous3G technologies. Precoding is one of the key technologies in the LTEand LTE-Advanced. In a narrow sense, precoding makes some kind of pre-disturbanceto the transmitted signals so that it could combat with the adverse effects, and thus ef?fectively improves system performance as well as simpliifes the design of the receiver.With the continuous development of the LTE and LTE-Advanced, the precoding tech?niques begin to show a different forms of role.In this dissertation, several hotspots in the precoding research ifeld are investi?gated from signal transmission aspect of physical layer, including the precoding tech?niques in single-antenna systems, feedback data compression strategy of SU-MIMOprecoding systems, optimal precoding design of MU-MIMO systems, and precodingtechniques in two-way relay systems. These researches strive to explore the essence ofsignal transmission, and release the potential of system performance. In view of thepractical feasibility, the proper tradeoff between performance and complexity is alsounder consideration. The main contents are summarized as follows.First, this paper discusses the precoding techniques in a single antenna transmis?sion scenario. From the precoding view, we analyze the downlink OFDM transmis?sion technology in LTE/LTE-Advanced with the capabilities of combating with thefrequency-selective fading channel. Then we investigate the precoding effect in up?link DFT-SOFDM transmission and demonstrate its low PAPR characteristic. Finally,we carry out a comprehensive and rigorous theoretical analysis towards vector OFDMand further reveal its signal space diversity gain. As the bridge of the single carrier and multicarrier transmission, vector OFDM provides the great flexibility in system design. However, the complete analysis of the performance of the vector OFDM in frequency selective fading channel is still absent. This paper gives a detailed analysis of the vector performance of OFDM in frequency selective fading channels. We indicate the benefits of precoding techniques in vector OFDM and the performance of each vector block is also carefully analyzed. The results of these studies provide an important theoretical basis for the practical system. These results are the first innovative point.This paper discusses the single-user MIMO precoding scheme. Despite the knowl-edge of the perfect channel information at the transmitter is crucial to the design of pre-coding matrix, the quantization of the channel information introduces many constraints with the system design. Based on this issue, the more effective codebook based lim-ited feedback is taken into account. Since the introduction of OFDM in the practical system increases the feedback overhead, this paper proposes a feedback compression technology. The proposed method allows the system to strike a good balance of the feedback overhead and throughput performance. The proposed scheme is the second innovative point.With the requirement of the system total throughput, the shift from single-user model (point-to-point) to the multi-user model (point to multipoint) becomes a ma-jor research direction. Compared to single-user MIMO, multi-user MIMO precoding needs to solve inter-stream interference and inter-user interference simultaneously. We will discuss the linear multi-user MIMO precoding scheme, including the block di-agonalization (BD) scheme and the SLNR scheme. By deviating a new form of two matrices simultaneous diagonalization, we propose an SLNR maximize relaxation pre-coding scheme. In the case of multiple streams transmission, the proposed scheme can balance the effective gains among the data streams, which offers a better BER perfor-mance. In addition, the proposed method can keep almost the same sum rate with the original one. The proposed scheme is the third innovative point.Finally, the paper focuses on the precoding schemes in cooperative communica-tion systems, and summarizes the main ideas on the precoding design in collaborative multicells. Further, we propose a novel channel estimation method for two-way relay-ing system, which is largely based on compressed sensing theory. Since the equivalent channel in two-way relaying systems is not sparse, we exploit the precoding method to solve this problem. The proposed scheme significantly optimized the energy efficiency. Above contents are the fourth innovative point.The summary, research and innovation of the precoding scheme in the new gener-ation of wireless communication systems enrich the theoretical results of the precoding techniques, providing insights to the practical system design.更多还原