【作者】 王欣；

【导师】 罗汉文；

【作者基本信息】 上海交通大学 ， 通信与信息系统， 2008， 硕士

【摘要】 随着无线多媒体业务、无线网络和移动计算设备的迅猛发展,近年来能支持高速数据传输速率的宽带移动通信系统成为研究热点。一些新兴的无线传输、无线接入技术正在不断兴起,吸引了世界上众多的参与者。在众多的无线技术当中,正交频分复用(OFDM, Orthogonal Frequency Division Multiplexing)技术以其独特的魅力成为最大的一个亮点。OFDM在技术上存在相当大的优势,除频谱利用率高和较强的带宽扩展性外,其在抗多径衰落性能方面的优势也非常明显,同时,OFDM还具有灵活分配频谱资源的性能。OFDM凭借其突出的技术优势成为了宽带无线通信系统一种高效的技术方案,从WLAN到WiMAX、Flash-OFDM,从LTE到B3G,再到超宽带无线通信技术UWB,OFDM几乎成了新一代无线通信技术的标志。因此,开展OFDM及其相关技术的研究具有重要的理论意义和实际应用价值。本文首先介绍了宽带OFDM移动通信系统的基本原理和结构;讨论了空时处理技术、同步、信道估计和自适应技术等。本文针对发送端优化设计的两个方面进行了系统和深入的研究,尤其是发送端资源最优化分配和基于有限反馈的发送端预编码优化设计。发送端资源最优化分配属于链路自适应技术的一种,根据信道条件调整资源分配的参数,能够有效的提高OFDMA系统的无线资源利用率。与传统的静态资源分配方案相比较,自适应资源分配采用了最优化处理方式,极大了提高了系统性能。在此基础上本文提出了一种基于分组的自适应子载波和功率分配算法。利用相邻OFDM符号之间较大的时间相关性,将子载波分组,再进行子载波组和功率的优化分配。计算机仿真结果表明,该算法不仅有效提高了系统容量,而且降低了算法的计算复杂度,并能很好的满足用户间的比例性。在MIMO空分复用系统中,发送端线性预编码对系统性能的提高起着重要的作用。在系统发送端对信号使用某些处理方法,使得信号能够适应信道的特征,从而使系统性能得到提高。预编码优化设计必须依据信道状态信息CSI,考虑到发送端在实际情况下并不能获得准确完全的信道状态信息,因此本论文着重研究发送端已知部分信道状态信息的情况,采用基于有限比特反馈的方式优化设计发送端预编码。本论文首先提出了发送端预编码优化设计的问题模型,然后介绍了基于有限比特反馈的预编码优化设计方法,接下来根据有限反馈模型,提出了一种总功率受限条件下基于MMSE准则的预编码联合优化算法,这种算法按照发送端最佳预编码矩阵的结构,将复用预编码和功率控制结合考虑,基于MMSE准则进行发送端预编码优化设计。计算机仿真结果表明,该算法与已有的等功率预编码优化设计方案相比,在没有增加反馈开销的前提下改善了系统BER性能。在此基础上,鉴于不同的优化设计目标,本文又提出了一种Qos限定条件下基于容量准则的预编码联合优化算法。该算法联合考虑复用预编码和功率控制,基于容量准则进行发送端预编码优化设计。计算机仿真结果表明,该算法在没有增加反馈开销的前提下提高了系统容量,同时满足了系统Qos要求。有限反馈预编码采用设计码本选择码字的方式进行优化设计,码本设计和码字选择是其中最重要的两个步骤,考虑到有多种码字选择准则,本文提出了另一种基于性能准则的码字选择方法,分别基于MMSE准则和BER准则选择最佳码字。基于性能选择码字是最直接的准则,计算机仿真结果表明,与已有的码字选择准则,例如最大化最小特征值;最小化系统MSE矩阵的迹;最小化系统MSE矩阵的行列式等相比,该方式进一步改善了有限比特反馈预编码方案的性能,而且基于Qos准则的码字选择方式适用于任何码本,也适用与任何有限反馈预编码设计方式,具有通用性。论文根据3GPP-LTE提案所关注的技术,对宽带OFDM系统发送端优化设计技术做了深入研究,取得了一些研究成果。对于移动通信技术的发展和实际系统的应用需求,如何优化有限反馈预编码设计等相关技术还有待进一步深入研究。更多还原

【Abstract】 With the development of wireless multimedia, wireless network and mobile computing equipment, recently the wideband mobile communication systems become the hot research technique. Several new techniques on wireless communication and wireless access field are brought forward, which absorb many researchers all over the world. During all these wireless techniques, Orthogonal Frequency Division Multiplexing (OFDM) is the most outstanding technique. OFDM technique has big advantage over other techniques both in its high availability of frequency and in its ability for mitigating the effects of delay spread, moreover, OFDM technique also can allocate the system resource dynamically. OFDM has became an effective technique with its outstanding advantages. From WLAN to WiMAX and Flash-OFDM, From LTE to B3G and even to UWB technique, OFDM is the symbol in the new generation of wireless communication.Firstly, the paper introduces the principle and architecture of wideband OFDM mobile systems. Moreover, this paper presents the key techniques which include space-time coding, synchronization, channel estimation and adaptive technique, etc.Considering that optimal design in transmitter is the key technique of wideband OFDM mobile communication systems, this paper does some research on the two aspects in optimal design in transmitter part, one is the optimal resource allocation in transmitter part, the other is the optimal precoder design with limited feedback.The technique of optimal resource allocation in transmitter part belongs to the adaptive techniques in link level. In this technique we can adjust the parameter of resource allocation according to channel state information (CSI) in order to raise the availability of wireless resource in OFDMA system. Adaptive resource allocation adopts the optimization method and improves the system performance compared to the static resource allocation method. An improved sub-carrier and power allocation algorithm for multi-user is introduced in this paper which uses the concept of grouped sub-carrier. After grouping the subcarrier according to the relativity of adjacent OFDM symbols, we do the optimal allocation among grouped sub-carriers and power. Simulation results show the improved algorithm has a lower computational complexity and a higher capacity compared to the previous ones, and meets the constraints of proportionality at the same time.In MIMO spatial multiplexing system, the precoder in transmitter part is very important to system performance. The signal can adapt to the channel state after pretreatment by which can enhance system performance. The design of optimal precoder depends on CSI, however, we could not get the fully exact CSI in practice, this paper focus on the research on the situation of partial CSI at transmitter. We designs the precoder based on limited feedback. This paper firstly introduces the problem module of optimal precoder design in the transmitter part. Then this paper brings forward the method of precoder design with limited feedback. Following that, this paper proposes a joint optimal precoding algorithm for MIMO system with limited feedback. Based on optimize theory, we propose the optimal transmitter structure which combines power control with precoding, and we also bring forward a novel MMSE criteria based codebook construction algorithm. Simulation results show that the proposed structure and codebook design algorithm outperform the precious equal power allocation based codebook. Based on this new algorithm, this paper also proposes a combined precoder design algorithm based on capacity with Qos constrain.Simulation results show that the proposed algorithm improves the system capacity with the same feedback spending and achieves the Qos demand at the same time. In the scheme of optimal precoder design with limited feedback the codebook design and codeword selection parts are the most crucial. Considering different principles in codeword selection step, this paper proposes a Qos based codeword selection scheme in optimal precoder design with limited feedback which selects the best codeword in order to optimize system performance of MSE and BER. The simulation results show that the proposed scheme is more direct and outperform the precious codeword selection method. And the most important thing is that this Qos based scheme is applicable to any codebook and any precoder design method with limited feedback.The paper does deep research about the design of optimal transmitter in wideband OFDM system according to the important techniques in 3GPP LTE conference, and forms some papers and patents. We need do more research about the techniques of mobile communication and application in real life, especially on the technique of precoder design with limited feedback.更多还原